numerical analysis of the effects inside human body during
TRANSCRIPT
NUMERICAL ANALYSIS OF THE EFFECTS
INSIDE HUMAN BODY DURING EXPOSURE TO
NON-IONIZING ELECTROMAGNETIC WAVES
(HIGH AND EXTREMELY LOW FREQUENCIES)
BY
MR. APICHART SIRIWITPREECHA
A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR
OF PHILOSOPHY IN ENGINEERING
FACULTY OF ENGINEERING
THAMMASAT UNIVERSITY
ACADEMIC YEAR 2017
COPYRIGHT OF THAMMASAT UNIVERSITY
Ref. code: 25595410300163SME
NUMERICAL ANALYSIS OF THE EFFECTS
INSIDE HUMAN BODY DURING EXPOSURE TO
NON-IONIZING ELECTROMAGNETIC WAVES
(HIGH AND EXTREMELY LOW FREQUENCIES)
BY
MR. APICHART SIRIWITPREECHA
A DISSERTATION SUBMITTED IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR
OF PHILOSOPHY IN ENGINEERING
FACULTY OF ENGINEERING
THAMMASAT UNIVERSITY
ACADEMIC YEAR 2017
COPYRIGHT OF THAMMASAT UNIVERSITY
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Dissertation Title NUMERICAL ANALYSIS OF THE
EFFECTS INSIDE HUMAN BODY
DURING EXPOSURE TO NON-IONIZING
ELECTROMAGNETIC WAVES
(HIGH AND EXTREMELY LOW
FREQUENCIES)
Author Mr. Apichart Siriwitpreecha
Degree Doctor of Philosophy in Engineering
Department/Faculty/University Mechanical Engineering, Engineering,
Thammasat University
Dissertation Advisor Professor Phadungsak Rattanadecho, Ph.D.
Academic Year 2017
ABSTRACT
Recently, the utilizations of electromagnetic wave are rapid widespread use
for the usual life of population all of countries in the world, especially the
electromagnetic wave in range of non-ionizing radiation. The electromagnetic radiation
environments have become very complex because there are a lot of electromagnetic
radiation source devices. These devices have created the increasing number of
electromagnetic radiation interference problems. The electromagnetic wave interacts
with the living tissues of the population and may lead to detrimental effects on human
health from high intensity radiation or exposed for a long time. There is concern about
the possible biological effects induced by these electromagnetic radiations in the
biological tissues. The interaction mechanisms of electromagnetic radiation in
biological tissues are very important for more understanding of the biological effects.
For ethical consideration, it is difficult to measure these distributions directly to the
alive human body. This study presents the numerical analysis of the biological effects
on several organs inside human trunk exposed to non-ionizing radiation. It can be
separated in two major categories; high frequency (microwave), and extremely low
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frequency (high voltage transmission lines). The specific absorption rate (SAR) and
induced current density are calculated on several organs inside human body model
exposed to high frequency and extremely low frequency, respectively. In this study, the
effects of physical parameters such as operating frequency, power density, exposure
time, mode of polarization, are systematically investigated on distributions of specific
absorption rate and temperature profiles within each organ inside human body model
using the finite element method (FEM). The obtained results of incident
electromagnetic fields on human body and biological effects on each organ inside
human body will be compared to the limitations which set by ICNIRP. The numerical
simulated results give us for better understanding in the realistic situation of the
interaction between non-ionizing radiations and human tissues, and their biological
effects due to these waves.
Keywords: Biological effects, Human body, Electromagnetic wave, High frequency,
Extremely low frequency
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ACKNOWLEDGMENTS
I would like to express my gratitude to my advisor, Pro. Dr. Phadungsak
Rattanadecho, department of Mechanical Engineering, Thammasat University, for his
invaluable guidance and giving me the opportunity to the graduate study.
I am grateful to the members of my graduate committee, Asst. Pro. Dr. Watit
Pakdee, Asst. Prof. Dr. Isares Dhuchakallaya, Asst. Prof. Dr. Nopbhorn Leeprechanon,
and Asst. Prof. Dr. Teerapot Wessapan. Their comments are helpful for my graduate
work.
I would like to express my deep appreciation to my parents and my family. I
am grateful to members of the Center of Excellence in Electromagnetic Energy
Utilization in Engineering (CEEE), my friends, and Khun Shotima Chanon for the
encouragement to me throughout in the period of my graduate study.
Apichart Siriwitpreecha
2017
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TABLE OF CONTENTS
Page
ABSTRACT (1)
ACKNOWLEDGMENTS (3)
TABLE OF CONTENTS (4)
LIST OF TABLES (9)
LIST OF FIGURES (10)
LIST OF ABBREVIATIONS (15)
CHAPTER 1 INTRODUCTION
1.1 Electromagnetic wave 1
1.1.1 High frequency (Microwave) 8
1.1.2 Extremely low frequency (High voltage transmission
lines)
10
1.2 Literature surveys 13
1.2.1 High frequency 13
1.2.2 Extremely low frequency 17
1.3 Research objectives 25
1.4 Scope of research 25
1.5 Expected benefits 26
1.6 Research procedure 26
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CHAPTER 2 THE RELATED THEORY
2.1 Electromagnetic wave propagation 29
2.1.1 Uniform plane wave propagation 34
2.1.2 Reflection and transmission of uniform plane wave 36
2.1.2.1 Normal incident 36
2.1.2.2 Oblique incident 39
2.1.2.2.1 TE Polarization 40
2.1.2.2.2 TM Polarization 43
2.1.3 Standing wave 45
2.2 Electromagnetic wave propagation of overhead
transmission lines
46
2.3 The propagation of electromagnetic wave in biological
tissues
48
2.4 Interactions of electromagnetic wave with biological tissues 51
2.4.1 High frequency of electromagnetic wave 51
2.4.2 Extremely low frequency of electromagnetic wave 54
CHAPTER 3 THE EFFECTS INSIDE HUMAN BODY MODEL
EXPOSED TO HIGH FREQUENCIES OF NON-
IONIZING ELECTROMANETIC WAVE
3.1 Introduction 56
3.2 Numerical simulation 58
3.2.1 Human model 59
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3.2.2 Equation of electromagnetic wave propagation
analysis
60
3.2.3 Governing equations for electromagnetic wave
propagation
61
3.2.4 Boundary conditions for electromagnetic wave
propagation
61
3.2.5 Equation of heat transfer in human body 63
3.2.6 Governing equations for human body model 63
3.2.7 Boundary conditions for human body model 64
3.2.8 Interaction of electromagnetic wave and human
organs
64
3.2.9 Initial condition for heat transfer 65
3.2.10 Penetration depth 65
3.3 Simulation procedure 66
3.4 Results and discussions 67
3.4.1 Verification of the model 67
3.4.2 Influence of exposure time of electromagnetic wave 69
3.4.3 Influence of power of electromagnetic wave 73
3.4.4 SAR distribution in the human body 76
3.4.5 Temperature distribution in the human body 78
3.4.6 The maximum SAR and temperature on organs in the
human body
80
3.5 Conclusions 83
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CHAPTER 4 THE EFFECTS INSIDE HUMAN BODY MODEL
EXPOSED TO EXTREMELY LOW FREQUENCY
OF NON-IONIZING ELECTROMANETIC WAVE
4.1 Introduction 85
4.2 Formulation of the problem 87
4.3 Methods and models 88
4.4 Governing equations 90
4.4.1 Electromagnetic field distribution 90
4.4.2 Electric field and current density distributions inside
human body
92
4.5 Boundary conditions 92
4.6 Calculation procedure 93
4.7 Results and discussions 94
4.7.1 Verification of the models 94
4.7.2 Electromagnetic field distribution 96
4.7.3 Electric field distribution inside human body 99
4.7.4 Current density distribution inside human body 101
4.7.5 Comparison distribution patterns between electric
field and current density on several organs inside
human body
102
4.8 Conclusions 106
CHAPTER 5 OVERALL CONCLUSIONS 108
CHAPTER 6 RECOMMENDATIONS FOR FUTURE WORK 111
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REFERENCES 112
PUBLICATIONS 118
BIOGRAPHY 120
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LIST OF TABLES
Table Page
3.1 Thermal property of tissues 60
3.2 Dielectric properties of tissues 60
3.3 Comparison of the results obtained in the present work with
those of Nishizawa and Hashimoto
69
3.4 The organ in human body which has the maximum SAR and
temperature in TE mode
82
3.5 The organ in human body which has the maximum SAR and
temperature in TM mode
82
4.1 Dielectric property of tissues 89
4.2 Average and maximum electric fields under overhead
transmission lines at each height above ground both of single-
circuit and double-circuit
100
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LIST OF FIGURES
Figure Page
1.1 Electromagnetic wave propagation 2
1.2 Electromagnetic wave spectrum 4
1.3 The utilizations of electromagnetic radiations 7
1.4 The utilizations of high frequency in range of non-ionizing
radiation
9
1.5 The extremely low frequency electromagnetic wave in the
environment from overhead transmission lines
12
1.6 The 2-D human body model 15
1.7 The SAR distributions inside human body model;
(a) 915 MHz (b) 2450 MHz
15
1.8 The temperature distributions at frequencies 915 MHz and
2450 MHz with times;
(a) 1 minute (b) 10 minute (c) constant time
16
1.9 The 2-D human body model 20
1.10 The electric field distribution due to 380 kV transmission lines 20
1.11 The model of human body standing under overhead
transmission lines
22
1.12 The contour of electric field under overhead transmission lines
with the absence and presence of human body
22
1.13 Configuration of four-bundled, double-circuit, 500 kV
transmission lines
23
1.14 The simulation of (a) electric field and (b) magnetic field
distribution due to high-voltage transmission line
23
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1.15 The configuration of single-circuit overhead transmission
lines
24
1.16 The magnetic field distributions;
(a) single-circuit (b) double-circuit
24
1.17 Research procedure 28
2.1 The sinusoidal wave 31
2.2 The polar plot of phasor 31
2.3 The uniform plane wave propagation 35
2.4 The plane wave incident from medium 1 to medium 2 results
in a reflected wave and transmitted wave
37
2.5 The oblique incident electromagnetic field from medium 1 to
medium 2
39
2.6 The TE polarization 40
2.7 A pair of axis (𝑥′ and 𝑧′) superimposed on coordinate system
to find equivalence 𝑧′ and -�̂�′
41
2.8 The TM polarization 43
2.9 The standing wave pattern of uniform plane wave in a lossless
medium
45
2.10 Loss tangent of electromagnetic propagation in dielectric 49
2.11 A schematic view for the variation of the relative permittivity
and conductivity of biological tissue for a wide frequency
range of electromagnetic wave
50
2.12 The blood circulatory system of human body 52
2.13 Idealized biological tissue systems 53
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3.1 The leakage electromagnetic wave from the industrial
microwave
59
3.2 Cross sectional model of human body 59
3.3 Boundary conditions for electromagnetic wave propagation
and heat transfer
62
3.4 An initial two-dimensional finite element mesh of human
cross section model
66
3.5 Geometry of the validation model obtained from the paper 68
3.6 Comparison of the calculated SAR distribution to the SAR
distribution from the paper
68
3.7 The maximum temperature increase on organs in human body
due to electromagnetic wave at frequencies of 300 MHz, 915
MHz, 1300 MHz and 2450 MHz in various exposure time
71
3.8 SAR distribution on organs in human body exposed to
electromagnetic wave which are propagated at power 100 W
and exposure time 20 minutes in various frequencies in;
(a) TE mode (b) TM mode
72
3.9 The maximum SAR on organs of each electromagnetic wave
power of heating source which are propagated in;
(a) TE mode (b) TM mode
74
3.10 The maximum temperature increase on organs of each power
of heating source which are propagated in;
(a) TE mode (b) TM mode
75
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3.11 SAR distribution of human body exposed to electromagnetic
wave at frequencies of 300 MHz, 915 MHz, 1300 MHz and
2450 MHz which are propagated at power 100 W and
exposure time 20 minutes in;
(a) TE mode (b) TM mode
77
3.12 Temperature distribution of human body exposed to
electromagnetic wave at frequencies of 300 MHz, 915 MHz,
1300 MHz and 2450 MHz which are propagated at power 100
W and exposure time 20 minutes in;
(a) TE mode (b) TM mode
79
3.13 Temperature distribution on tissues in human body exposed to
electromagnetic wave at frequencies of 300 MHz, 915 MHz,
1300 MHz and 2450 MHz which are propagated at power 100
W and exposure time 20 minutes in;
(a) TE mode (b) TM mode
81
4.1 The 2-D cross section diagrammatically the single-circuit of
500 kV overhead transmission lines
87
4.2 The 2-D cross section diagrammatically the single-circuit of
500 kV overhead transmission lines
88
4.3 The 2-D human body model 89
4.4 Boundary conditions 93
4.5 The convergence test of the maximum electric field at the high
1 m above ground
94
4.6 The pattern of electric field distribution of reference and
present simulated results;
(a) Reference simulated result, (b) Present simulated result
95
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4.7 The comparison of the reference and present simulated
electric field distributions at 1 m above ground under high
voltage overhead transmission lines
96
4.8 The electric field distributions due to overhead transmission
lines
97
4.9 Electric field distributions under high-voltage overhead
transmission lines
98
4.10 Electric field distributions under high-voltage overhead
transmission lines
100
4.11 Current density inside human body 101
4.12 The extrusion lines at 4 levels inside human body 102
4.13 The distribution patterns inside human body at the height 0.92
m above ground
104
4.14 The distribution patterns inside human body at the height 1.10
m above ground
104
4.15 The distribution patterns inside human body at the height 1.38
m above ground
105
4.16 The distribution patterns inside human body at the height 1.52
m above ground
105
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ABBREVIATIONS
Nomenclature
𝑐𝑝 specific heat capacity (J/kgK)
𝐸 electric field intensity (V/m)
𝐻 magnetic field intensity (A/m)
𝑓 frequency of microwave (Hz)
𝑘 thermal conductivity (W/mK)
𝑄 heat (W/m3)
𝑡 time (s)
𝑇 temperature (C)
𝑣 velocity of propagation (m/s)
tan dielectric loss coefficient
Greek letters
permittivity (F/m)
permeability (H/m)
density (kg/m3)
electric conductivity (S/m)
Wavelength of electromagnetic wave (m)
angular frequency (rad/s)
reflection coefficient
transmission coefficient
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Subscripts
𝑏 blood
𝑒𝑥𝑡 external
𝑖 subdomain
𝑚𝑒𝑡 metabolic
p penetration
𝑟 relative
o Free space, initial condition
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CHAPTER 1
INTRODUCTION
In recent years, the utilizations of non-ionizing electromagnetic wave are
common used in every day for population all countries around the world. Most activities
in everyday life of population need to use energy from electricity such as transportation,
electronic appliance, telecommunication including the increasing of cellular telephones
which are widespread to use. Moreover, the industries need to use electricity in very
large scale. Thus, the electrical power demand increases very rapidly. For the last few
decades, the concern about the human risk from non-ionizing electromagnetic fields has
been interested in a topic to epidemiologists and scientists. These electromagnetic fields
interact with the human body and may lead to detrimental effect on human health from
high intensity radiation. However, the resulting thermo-physiologic response of the
human body is not well understood. In order to gain insight into the phenomena
occurring within the human body with biological effects due to non-ionizing
electromagnetic fields, a detailed knowledge of interactions between biological tissues
and electromagnetic fields in various frequencies are necessary. This is because the
behaviors of biological tissues in various frequencies of non-ionizing electromagnetic
field are different.
1.1 Electromagnetic wave
Electromagnetic wave is a phenomenon that takes the form of self-
propagating waves in a vacuum or in matter which emits from a source. The propagation
of electromagnetic wave can be carried the electromagnetic radiant energy from source
to any space. The component of electromagnetic wave consists of electric field and
magnetic field. The electric field and magnetic field oscillate in phase perpendicular to
each other and perpendicular to the direction of energy propagation as shown in figure
1.1.
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(http://micro.magnet.fsu.edu/primer/java/electromagnetic)
Figure 1.1 Electromagnetic wave propagation
The mathematical conceptualization of electromagnetic radiation was first
introduced by James Clerk Maxwell, the Scottish mathematical physicists. Maxwell
derived a wave form of the electric and magnetic equations, revealing the wave-like
nature of electric and magnetic fields, and their symmetry. Maxwell’s equations are the
mathematical equations. It can be described how electric and magnetic fields are created
by electric charges and electric currents and in addition they give relationship between
these fields. It is a set of four vector-differential equations that govern all of
electromagnetic radiations as shown in equation (1.1) - (1.4). The first two sets of
Maxwell’s equations are Gauss’ law for electric and magnetism, respectively. In Gauss'
law, is the volume electric charge density, �⃗⃗� is electric flux density, �⃗� is the magnetic
flux density, is the permittivity and is the permeability of matter. They can be
described the electric field �⃗� and the magnetic field �⃗� in vacuum and matter, together
with their sources (charge density and current density). The last two sets of Maxwell’s
equations are Faraday’s law and Ampere’s law, respectively. They are responsible for
electromagnetic radiation. The curl operator represents the spatial variation of the fields,
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which are coupled to the time variation. For the electromagnetic wave propagation, the
electric field is altered in space, which gives rise to a time-varying magnetic field. A
time-varying magnetic field then varies as a function of location (space), which gives
rise to a time varying electric field. These equations wrap around each other in a sense,
and give rise to a wave equation. These equations can be predicted electromagnetic
radiation. In Ampere’s law, �⃗⃗� is the magnetic field, 𝐽 is the electric current density (in
Amps/meter-squared). Maxwell’s equations provide a complete description of
electromagnetic radiation and underpin all the technology utilizations of
electromagnetic radiation.
∇ ∙ �⃗⃗� = 𝜌 (1.1)
∇ ∙ �⃗� = 0 (1.2)
∇ × �⃗� = −𝜕�⃗⃗⃗�
𝜕𝑡 (1.3)
∇ × �⃗⃗� = 𝜕�⃗⃗⃗�
𝜕𝑡 + 𝐽 (1.4)
The electromagnetic wave has the specific characteristic depends on its
frequency or wavelength. It can be classified into several types according to the
frequency of its wave. Figure 1.2 shows the types of electromagnetic wave, gamma
rays, X-rays, ultraviolet radiation, visible light, infrared radiation, microwaves, radio
waves, order of decreasing frequency and increasing wavelength.
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In the quantum theory, electromagnetic radiation consists of photons,
elementary particles responsible for all electromagnetic interaction. The energy of an
individual photon is quantized. It depends on frequency of electromagnetic radiation,
given by Planck’s equation,
𝐸 = ℎ. (1.5)
Where is frequency of electromagnetic radiation, and h is Planck’s constant,
6.625 10-34 Js. The energy of photon of high frequency is greater than that of low
frequency, inversely for wavelength. Figure 1.2 shows that the electromagnetic
radiation in range of gamma rays has the maximum energy, and long radio wave has
the minimum energy of electromagnetic radiation.
The electromagnetic radiation can be classified into two important types upon
the effect in medium of the propagated electromagnetic radiation, non-ionizing
radiation and ionizing radiation. For the low frequencies of electromagnetic radiation
in range of radio wave, microwave, infrared, and visible light, have low energy. The
photons of these electromagnetic radiations do not individual have enough energy to
ionize atoms or molecules of medium. The electromagnetic radiation which cannot
ionize atoms of medium is called non-ionizing radiation. The effects of these radiations
on living tissues are caused primarily by heating effects from the combined energy
transfer of many photons. For the high frequencies of electromagnetic radiation in range
of ultra violet, X-rays, and gamma rays, have high energy. The photons of these
electromagnetic radiations have enough energy to ionize atoms or molecules of
medium. The electromagnetic radiation which can ionize atoms of medium is called
ionizing radiation. These radiations have the ability to cause damage living cells, and
can be affected to a health hazard.
In everyday life, there are a lot of utilizations from electromagnetic radiation
because of the difference specific characteristic in various frequencies of
electromagnetic field. Figure 1.3 shows the utilizations of electromagnetic radiation in
each range of frequency. The electromagnetic radiations are not only huge benefit for
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human but also harmful to human who exposed to these electromagnetic radiations
exceeded the limitation.
Recently, the utilizations of electromagnetic wave are rapid widespread use
for the usual life of population all of countries around the world, especially the
electromagnetic wave in range of non-ionizing radiation. The electromagnetic radiation
environments have become very complex because there are a lot of electromagnetic
radiation source devices. These devices have created the increasing number of
electromagnetic radiation interference problems. There is concern about the possible
biological effects induced by these electromagnetic radiations in the biological tissues.
The interaction mechanisms of electromagnetic radiation in biological tissues are very
important for more understanding of the biological effects. The electromagnetic
radiations can be penetrated into the biological tissues. Thereafter, the biological tissues
will be absorbed energy of electromagnetic radiation. This absorbed energy maybe
affect to the biological tissues exposed to the electromagnetic radiation if the exposure
exceeded the limitations. The absorbed energy of biological tissues is not depend only
on the external power density of electromagnetic radiation source, but also on the
properties of the biological tissues such as dielectric property of tissues. Moreover, the
other factors, such as time duration of exposure, intensity of electromagnetic radiation,
water content of biological tissue and frequency of electromagnetic radiation, are very
important to absorbed energy of biological tissues. The biological effects inside
biological tissues exposed to different types of electromagnetic radiation in range of
non-ionizing radiation will be different because of the behaviors of biological tissues in
various frequencies of electromagnetic radiation are different. The research of
biological effects inside biological tissues exposed to non-ionizing electromagnetic
radiation can be separated in two major categories; High frequency (Microwave), and
Extremely low frequency (High voltage transmission lines).
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1.1.1 High frequency (Microwave)
Microwave is one type of the electromagnetic wave which has high frequency
in range of non-ionizing electromagnetic radiation, 300 MHz – 300 GHz. The
utilizations of microwave have been used in many industrial and household applications
such as heating process, drying process, telecommunications. Figure 1.4 shows the
example of the utilizations of high frequency in range of non-ionization electromagnetic
radiation such as radar, industry microwave, microwave oven, wireless, mobile phone,
etc. These utilizations are rapidly increasing in worldwide because of the several
advantages of microwave. Moreover, the microwave for heating source has the
advantages more than other heat sources such as high speed start up, selective energy
absorption, instantaneous electric control, no pollution, high energy efficiency and high
product quality. For other sources of heating method, the rising temperature of materials
is started on the surface and then proceeds to the inner of materials. But microwave can
be penetrated into the materials. The absorbed energy is converted into thermal energy
within the material, the rising temperature is started inside of materials.
The rapid development of microwave applications for the utilizations of
humankind causes an increase in public concern about health risks from microwave
energy emitted from various sources (Spiegel et al., 1984, Wang et al., 1999, Harita
et al., 2004, Yang et al., 2007,). The absorbed energy of microwave induces temperature
increase on organs in the human body exposed to microwave. The criteria which use to
obtain gain further understanding of the biological tissues absorption characteristic of
the human body is the specific absorption rate, SAR, (Kanai et al., 2007). The SAR can
be converted to thermal energy, temperature will be increased. The temperature increase
of several organs inside human body is one of the main tasks in the evaluation of the
human risk related to the exposure of microwave to the human body.
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1.1.2 Extremely low frequency (High-voltage transmission lines)
During the last few decades, the economy and the enlarging of city in many
countries in the world are very growing from year by year. Most activities in everyday
life of population need to use energy from electricity such as transportation and
electronic appliance. Moreover, the industries need to use electricity in very large scale.
In Thailand, the electrical power demand increases very rapidly in order to fulfill the
vast need of electrical power in the big city. The high-voltage overhead transmission
line transportations have been constructed to carry electricity from station to station or
from station to substation. The Electricity Generating Authority of Thailand (EGAT)
constructed the enlarge transmission capacity by installing 500 kV extra high-voltage
power transmission lines with frequency of 50 Hz. In the AC system, the extra high-
voltage power transmission lines have more than 2200 circuit-kilometer in Thailand,
which have four-bundled of single-circuit and double-circuit configurations. The
electromagnetic wave can be emitted from the high-voltage overhead transmission lines
to the environment around the conductor lines with frequency of 50 Hz, the same as the
frequency of AC electricity in the transmission lines. The magnitude of electromagnetic
field depends on the voltage and current of transmission lines. There is concern about
the problem of these extra high-voltage overhead transmission lines because some parts
of the high-voltage overhead transmission lines pass or near the communities. Figure
1.5 shows the extremely low frequency electromagnetic wave in the environment from
overhead transmission lines. For the improving of living standard, the consciousness of
environment protection and health for people who live near the passing transmission
lines area and the worker who climb on the high-voltage post to maintain the
transmission lines needs to be increasing. The power frequency (50/60 Hz)
electromagnetic field still draws the attention of many researchers worldwide to
investigate its harmful effects on living bodies especially on human. The AC electric
and magnetic fields induce surface charges on biological human bodies and weak
currents in these bodies. Recently, it has been suggested that if there is any harmful
effect to health, induced currents may cause this effect. The brain and heart are
considered critical target organs because of their functional dependence upon neural
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cell function. The lower limit of current density is estimated from the field strength
required to induce currents equal to those generated by electrical processes in the heart
and in the brain. Naturally, the occurring current densities in these organs are estimated
to be in the range of 1 mA/m2 to 100 mA/m2. A number of national and international
organizations have formulated guidelines for limitation of occupational and general
public exposures to electric and magnetic fields. There are clear hazards posed by
induced current densities sufficient to produce disturbance in rhythmic cardiac function,
such as extra systole and ventricular fibrillation. These effects are estimates to occur at
current densities above 1000 mA/m2. The amount of the current, even if a human is
directly beneath a transmission line, is extremely small. The maximum body current
induced by electric field is much greater than the body current induced by magnetic
field. Thus, the current induced from electric fields are important more than the current
induced by magnetic fields. In extremely low frequency, the penetration depth in
medium is high. The absorbed energy of electromagnetic field is not significant because
it is very low in extremely low frequency. The induced current density distribution on
some organs inside human body standing under the extra high-voltage overhead
transmission line needs to be investigated. These profiles of induced current density are
compared to the universal standards limitations such as IEEE standard C95.6, ICNIRP
guidelines ACGIH threshold Limit Values and to NRPB.
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1.2 Literature surveys
1.2.1 High frequency
The utilizations of microwave have been used in usual for the people. There
is concern about the human risks from the environment electromagnetic radiation from
the devices of microwave. The biological tissues will be absorbed the energy of
microwave and converted to thermal energy. The specific absorption rate (SAR) is one
of the criteria to consider the risk of biological effects. The experimental data on the
correlation of SAR levels to the temperature increase on biological tissues in the human
body are still sparse. The distributions of SAR cannot be measured directly to the alive
biological tissues of human body because of ethical consideration. The computational
analysis has been used to study the distributions of SAR and temperature in biological
tissues inside human body. The earlier studies of heat transfer in human tissues used the
general bioheat equation to investigate, (Pennes, 1984). Thereafter, coupled model of
Maxwell’s equation and bioheat equation were used to model human tissues exposed to
electromagnetic wave. It can be explained the electromagnetic wave propagation and
heat transfer in tissues in the human body. There are some research have been studied
temperature distribution over the surface and various biological tissues exposed to
electromagnetic wave. Some of these researches which were studied the effects in
biological tissues inside human body due to high frequency of electromagnetic radiation
are shown as,
Shinichiro Nishizawa and Osamu Hashimoto, 1999, used the method of
moments to analyze the shielding effects of lossy dielectric materials. The shielding is
located in front of the human body model. They calculated the SAR in a three-layered
elliptical tissues, skin, fat, and muscle, inside human body model exposed to
electromagnetic field in range of 200-800 MHz. It was shown that the whole average
SAR inside human body model can be increased because of the multiple reflections
between the human body and shielding.
Om P. Gandhi et al., 2001, calculated SAR and temperature distributions
inside human head model exposed to electromagnetic field due to cellular telephones at
frequencies of 835 and 1900 MHz. The SAR distributions were solved by the bioheat
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equation. It was shown that the temperature in brain can be up to 0.5C with the SAR
of 10 W/kg for any 10 g of brain tissue.
V. L. Dragun et al., 2005, proposed a physicomathematical model to
calculate the temperature distribution on the surface and inside the bulk of biological
object exposed to electric field with frequency of 40.68 MHz for therapeutic purposes.
It was shown that temperature is strongly high in deep tissues at this frequency of
electric field.
Masaki Fujimoto et al., 2006, analyzed the correlation the SAR and the
maximum temperature increase in child and adult human head models exposed to
electromagnetic field from a dipole antenna. It was found that no clear difference of the
SAR and temperature increase between child and adult human head model.
Deshan Yang et al., 2007, expanded the bioheat diffusion equation to
propose a new method for studying the high temperature tissue ablation. The
combination of specific heat and effective specific heat, temperature dependent, were
added into the bioheat equation. The microwave ablation of bovine liver was
numerically simulated by using the new equation. The simulated result was compared
to the ex vivo results. It was shown that simulation results of temperature profiles by
using the modified bioheat equation had more accurate prediction.
Deshan Yang et al., 2007, measured the temperature changes of bovine
liver tissue during ex vivo microwave ablation and water content of ablated tissue
lesions. Moreover, they examined the relationship between the water content and tissue
temperature because they suggested that tissue temperature changes may be directly
related to tissue water related phenomena during microwave ablation, including
evaporation, diffusion, condensation and tissue water composition. The simulation
results shown that the tissue water content were significant related to temperature
change.
Yogender Aggarwal et al., 2008, analyzed the heat flow between body
core and skin surface when the environmental temperature was change with fixed
relative humidity and wind velocity. They developed the mathematical models of
thermoregulation in the human body and at its periphery for different body segments.
The simulation results show that the internal temperature distributions of hand, arm, leg
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and feet segments were good results and observed to be trend with the previous work
under ambient environmental conditions.
T. Wessapan et.al. 2011, used the Finite Element Method via COMSOL
Multi Physics program to calculate the SAR and temperature distributions in several
organs inside human body model exposed to electromagnetic field at frequencies of 915
MHz and 2450 MHz. The figuration of 2-D several organs inside human body model is
shown in figure 1.6. The simulation results of the SAR and temperature distributions on
several organs inside human body model are shown in figure 1.7 and 1.8, respectively.
Figure 1.6 The 2-D human body model
Figure 1.7 The SAR distributions inside human body model (a) 915 MHz (b) 2450
MHz
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Figure 1.8 The temperature distributions at frequencies 915 MHz and 2450 MHz with
times (a) 1 minute (b) 10 minute (c) constant time
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1.2.2 Extremely low frequency
For a last few decades, there was the consciousness of the biological effects
on the human body for people from electromagnetic radiation due to high-voltage
overhead transmission lines. A.M. Qabazard measured of the electromagnetic field near
electric power transmission lines were taken at an incremental distance away from the
tower in Kuwait. These values were compared with the electromagnetic field physical
and calculated results near the 275 kV Ring Road electric power transmission lines. The
field results were based on the ICNIRP guidelines for limiting exposure to
electromagnetic fields and the WHO recommended standards, A.M. Qabazard, 2007.
The techniques to calculate the electric and magnetic fields around the area of high-
voltage transmission lines have been developed by many researchers by using theory
and simulation or measurement. The simulation methods of electromagnetic field which
propagated from the high-voltage overhead transmission lines to the environment were
used by several techniques. The image theory was used by L. Li and G.Yougang to
calculate the value of magnetic field environment near high-voltage transmission lines
which have 110, 220, 330 and 500 kV of voltage on the line passing area at residential,
non-residential and difficult traffic area. It was shown that the magnetic flux densities
deduced rapidly with the distance increased from the transmission lines, (L. Li and
G.Yougang, 1998). The Finite Difference Method (FDM), based on four-point formula,
and presented the first and second derivatives on the boundary using more than two grid
points on one side of the boundary in order to improve the accuracy of approximation,
was used by S.M. Al Dhalaan to simulate the electromagnetic field which propagated
from the high-voltage overhead transmission lines to the environment. It was described
the observation and analysis of electromagnetic field in proximity of Al-Qaseem Saudi
Tower Transmission Lines, and investigated the feasibility of magnetic field reduction
by optimization of phase relationship in 3-phase systems, (S.M. Al Dhalaan, 2003). The
Charge Simulation Method, was used by L. Xu et al. to compute the power frequency
electric field of overhead transmission lines between the different conditions such as
different phase order for double circuit and different arrangement of line in single circuit
or double circuit, (L. Xu et al., 2006). The Finite Element Method (FEM), S.Tupsie
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et.al. was developed this method by MATLAB program to simulate the electromagnetic
field radiating to the atmosphere around the high-voltage 500 kV of overhead
transmission lines. The simulation of six types long distance distributing transposition
will not affect changing of electric field and magnetic field which surround the
transmission lines (S.Tupsie et.al., 2009). For FEM, P. Dhana Lakshmi et al. used to
analyze the magnetic field distribution around single-circuit and double-circuit of 500
kV overhead transmission lines under normal loading and short-circuit conditions. The
results of the normal loading case revealed that the magnetic fields from both single-
circuit and double-circuit, at a level of 1 m above the ground that were assumed to be
the level of human working, did not excess the maximum allowance when complied
with the ICNRP standard, (P. Dhana Lakshmi et al., 2011).
There is concern about the biological effects in human body exposed to
electromagnetic radiation in extremely low frequency, 50/60 Hz, due to the high-voltage
overhead transmission lines. The biological effects have been studied to investigate its
harmful on living bodies especially on human beings from worldwide researchers.
Some of these researches which were studied the effects in human body due to
extremely low frequency of electromagnetic radiation are shown as,
H. Yildirim and O. Kalenderli, 1998, computed the electric field
distribution around a three phase 380 kV transmission line by using Charge Simulation
Method. The induced currents on human body standing underneath this high voltage
overhead transmission line was obtained using computed electric field values. The
computed induced current densities were evaluated with respect to the safety limit, it
was found that these current densities were below the safety limit of 10 mA/m2.
Li Hongjie et al., 2000, evaluated the electric fields and induced currents
when the workers was performing in a 330 kV power system by using a model of man
and with a full sized 1:1 power tower. The electric field computation was performed by
charge simulation method and it was checked by experiment. It can be evaluated the
maximum electric gradient along the ladder and induced currents in human body, the
maximum errors of the numerical and experimental results can be in range of 10%.
Hu Yi et al., 2005, analyzed and calculated the system parameters, the
over-voltage level and its statistical distribution during the process of live work on the
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1000 kV transmission line, and developed the full set screening cloths for worker. The
electric field intensity on human body surface inside and outside of the screening cloths
at different working positions was measured. It indicated that the climbing worker
should dress screening cloths and mask, because the results shown that the electric field
intensity inside cloths and mask were very different with the outside.
M. A. Abd-Allah, 2006, calculated the maximum, minimum and average
magnetic fields in the organs inside human body, by a standard human model, which is
under central line conductor, under outermost conductor and at the edge of right-of-
way. The maximum and average current densities, and the specific absorption rate
(SAR) in these organs are calculated and discussed. It was found that the magnetic field
was varied only about 2% along the brain and by about 1% along the heart. The kidney
had low values of current density and SAR and the brain absorbed the maximum power
under the outermost conductor.
S.M. El-Makkawy, 2007, studied the biological effects in human body
who were standing under a high voltage transmission line as shown figure 1.9. The
electric field from this transmission line was calculated by using Boundary Element
Method (BEM). The induced currents and current densities on the human body at the
top of head, middle of the neck, middle of the waist and the middle of the legs, were
obtained using computed locally enhanced electric field values. These electric field
distributions within human body were studied as a function of height of conductors of
three phase 380 kV line over the ground plane as shown in figure 1.10.
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Figure 1.9 The 2-D human body model
Figure 1.10 The electric field distribution due to 380 kV transmission lines
C. A. Belhadj, 2008, calculated the profiles of electric and magnetic
fields along live-line workers exposed to body from the 132 kV transmission line of
Saudi Electricity Company (SEC). Both electric and magnetic fields values had been
generated using EPRI’s work station software, the electric field was based on the
Charge Simulation Method, while the magnetic field was based on Biot-Savart law.
These profiles were compared to the universal standards such as IEEE standard C95.6,
ICNIRP guidelines ACGIH threshold Limit Values and to NRPB. It was found that the
highest electric and magnetic fields exposure level for the SEC 132 kV transmission
line were well below the recommended the international standards limit.
180
mm
400
mm
200 mm
120 mm
600 mm
900
mm
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N.M. Maalej et al., 2009, used the Visible Human (VH) to investigate
the induced electric fields and current densities in human body tissues and organs of a
worker standing 2 m away from conductor phase C of double-circuit 132 kV and 60 Hz
transmission line. Charge Simulation Method and the Bio-Savart law had been used for
computation of external electric and magnetic fields. Finite-difference time-domain
technique was used to calculate the internal induced electric field and circulating current
densities in organs more than 40 different tissues of the VH with 3 mm voxel size. The
simulation indicated that the computed external electric and magnetic fields were below
the limits set by the IEEE standards for external exposure for live-line workers.
L. Kai et al., 2010, developed and tested the screening cloths for live
working on 1000 kV AC transmission line. The electric field intensity on the different
parts of body and the current passing through human body were measured in equal-
potential process. It was found that the screening cloths for live working on 1000 kV
AC transmission line can be made of material with shielding efficiency was not less
than 60 dB, while the face shielding mask was not less 20 dB. The electric field intensity
at the inside and outside of these screening cloths and face shielding mask were very
different.
A. Z. El Dein et al. (2010), computed the electric field distribution
around three phase 500 kV transmission line by using Charge Simulation Method, with
the presence and absence of the human model. This models was shown as figure 1.11.
It was found that the electric field around the transmission lines with the presence of
human body model under the transmission lines which had small height compared with
overhead transmission lines, had no change when compared with the absence of human
body. Only the local electric field around the human body was perturbed, as shown in
figure 1.12.
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Figure 1.11 The model of human body standing under overhead transmission lines
Figure 1.12 The contour of electric field under overhead transmission lines with the
absence and presence of human body
In Thailand, the largest AC 500 kV overhead transmission lines was
constructed by EGAT both of single-circuit and double-circuit. S.Tupsie et.al., 2009,
used the Finite Element Method that was developed by MATLAB program to simulate
the magnitude of electric field and magnetic field distributions in the environment
around the transmission line conductors. The configuration of four-bundled, double-
a
L
H
Ground level
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circuit, 500 kV power transmission line is shown in figure 1.13. The simulation results
of electric and magnetic fields of these studies were shown as figure 1.14.
Figure 1.13 Configuration of four-bundled, double-circuit, 500 kV transmission lines
(a) Electric field distribution (b) Magnetic field distribution
Figure 1.14 The simulation of electric field (a) and magnetic field (b) distribution due
to high-voltage transmission line
P. Pao-la-or et.al., 2010, calculated the magnetic field distribution due
to 500 kV overhead transmission lines by using Finite Element Method. The magnetic
field distributions due to double-circuit in figure 1.13 and single-circuit in figure 1.15
were selected to analyze. The simulation results of magnetic field distribution were
shown in figure 1.16.
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Figure 1.15 The configuration of single-circuit overhead transmission lines
(a) single-circuit (b) double-circuit
Figure 1.16 The magnetic field distributions (a) single-circuit (b) double-circuit
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1.3 Research objectives
The main purposes of this research are as follows;
1) To develop the coupled mathematical models of electromagnetic field
emitted from microwave heat source or high-voltage overhead transmission lines and
the effects inside human body model.
2) To investigate the effects on several organs inside human body model
both of exposed to high frequency and extremely low frequency electromagnetic fields
under various conditions.
3) To compare the electric fields and the effects inside human body
between the simulation results and the universal standard limitations from the
International Commission on Non-Ionizing Radiation Protection (ICNIRP).
4) To provide guidelines which will help the government in
implementing policies for the management of residents in community living near the
high-voltage transmission lines.
1.4 Scope of research
1) Analysis of specific absorption rate and heat transfer inside human
body exposed to high frequency of electromagnetic radiation, microwave
a. Two propagation modes
b. Four operating frequencies
c. Three power densities
d. Nine organs inside human body
2) Analysis of electric field and induced current density inside human
body exposed to extremely low frequency of electromagnetic radiation from high-
voltage overhead transmission lines
a. Two configurations of overhead transmission lines
b. One voltage of overhead transmission lines
c. Five organs inside human body
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1.5 Expected benefits
1) The developed mathematical models will be enable us to get more
practical predictions of the biological effects on several tissues inside human body
during exposed to electromagnetic fields both of high frequency and extremely low
frequency in range of non-ionizing radiation.
2) The obtained simulation results of biological effects can be applied to
a wide range of problems related to the electromagnetic field exposures from the
utilization of electromagnetic wave in range of non-ionizing radiation such as
microwave or transmission lines.
3) This work will give us an understanding of the characteristics of the
biological effects inside human body exposed to electromagnetic field in range of non-
ionizing radiation frequency. It can be guided to protect these electromagnetic fields do
not exceed the limitation which set by ICNIRP.
1.6 Research Procedure
The study and research procedure consist of the following steps:
1) Literature reviews.
2) Study on the fundamental theory of electromagnetic field distributions
in range of non-ionizing radiation frequency and the biological effects from these
electromagnetic fields.
3) Develop the mathematical models and numerical scheme that
considers electromagnetic field propagation and the biological effects on tissues inside
human body model.
4) Compare the some simulation results from the developed
mathematical models from the experimental results or the previous work from literature
review with the same conditions for the accuracy of the developed mathematical
models.
5) Calculate the emitted electromagnetic field from source, induced
electromagnetic field and biological effects inside human body. For high frequency,
source and biological effects are microwave and SAR, respectively. For extremely low
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frequency, source and biological effects are high-voltage overhead transmission lines,
respectively.
6) Study the biological effects on several organs inside human body
model exposed to electromagnetic fields both of high frequency and extremely low
frequency in range of non-ionizing radiation.
7) Explain and discuss the biological effects inside human body on
physical parameters of electromagnetic field.
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Figure 1.17 Research procedure
SAR and heat transfer inside human body exposed to high
frequency
(Microwave)
Induced current density inside human body exposed to ELF
(HV transmission lines)
Mathematical model
- EM wave propagation
- SAR distribution
- Heat transfer
Mathematical model
- EM wave propagation
- Current density distribution
Verify the accuracy of the
mathematical model
Simulated results
- Electric filed
- SAR
- Temperature
- Current density
Studied parameters
- Frequency
- Power density
- Property of tissues
Numerical Analysis of Biological Effects inside Human Body during Exposed
to Non-Ionizing Electromagnetic Fields
Ref. code: 25595410300163SME
CHAPTER 2
THE RELATED THEORY
2.1 Electromagnetic wave propagation
In recent years, the utilizations of non-ionizing electromagnetic wave are
rapidly increasing around the world. Electromagnetic wave can be propagated from the
source to any medium. Maxwell was able to unify all of the theories of electricity and
magnetism into one concise set of four formulas known as Maxwell’s equation. It is
the mathematical equations which can be described how electric field and magnetic
field are created by electric charges and electric currents, in addition they give
relationships between these fields. The set of four vector-differential equations that
govern all of electromagnetic wave propagation are shown as equation (2.1)-(2.4).
∇ ∙ �⃗⃗� = 𝜌 (Gauss’s law) (2.1)
∇ ∙ �⃗� = 0 (Gauss’s law for magnetic field) (2.2)
∇ × �⃗� = − 𝜕�⃗⃗⃗�
𝜕𝑡 (Faraday’s law) (2.3)
∇ × �⃗⃗� = 𝜕�⃗⃗⃗�
𝜕𝑡 + 𝐽 (Ampere’s circuital law) (2.4)
where �⃗� is electric field intensity (V/m), �⃗⃗� is electric flux density (C/m2), �⃗� is magnetic
flux density (T), �⃗⃗� is magnetic field intensity (A/m), and 𝐽 is current density (A/m2),
is charge density (C/m2). The constitutive relations of these quantities are shown as:
�⃗⃗� = 휀�⃗� (2.5)
�⃗� = 𝜇�⃗⃗� (2.6)
𝐽 = 𝜎�⃗� (Ohm’s law) (2.7)
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where is permittivity (F/m), is permeability (Tm/A), and is conductivity (m).
For the fourth law of Maxwell’s law, Ampere’s law, it can be written in term
of mathematical identity as equation:
∇ × (∇ × �⃗⃗� ) = ∇(∇ ∙ �⃗⃗� ) − ∇2�⃗⃗� (2.8)
From equations (2.2), equation (2.8) becomes to:
∇ × (∇ × �⃗⃗� ) = −∇2�⃗⃗� (2.9)
Consider the left side of equation (2.9) with Ampere’s circuital law and the institutive
relations,
∇ × (∇ × �⃗⃗� ) = ∇ × (휀𝜕�⃗⃗⃗�
𝜕𝑡+ 𝜎�⃗� ) (2.10)
∇ × (∇ × �⃗⃗� ) = 휀𝜕𝜕𝑡
(∇ × �⃗� ) + 𝜎(∇ × �⃗� ) . (2.11)
From Faraday’s law,
∇ × (∇ × �⃗⃗� ) = −휀𝜇𝜕𝜕𝑡
(𝜕�⃗⃗�
𝜕𝑡) − 𝜎𝜇
𝜕�⃗⃗�
𝜕𝑡 (2.12)
or ∇ × (∇ × �⃗⃗� ) = −휀𝜇𝜕2�⃗⃗⃗⃗�
𝜕𝑡− 𝜎𝜇
𝜕�⃗⃗⃗⃗�
𝜕𝑡 (2.13)
Thus, −휀𝜇𝜕2�⃗⃗⃗⃗�
𝜕𝑡− 𝜎𝜇
𝜕�⃗⃗⃗⃗�
𝜕𝑡 = −∇2�⃗⃗� (2.14)
∇2�⃗⃗� − 휀𝜇𝜕2�⃗⃗⃗⃗�
𝜕𝑡− 𝜎𝜇
𝜕�⃗⃗⃗⃗�
𝜕𝑡 = 0 (2.15)
It is call the wave equation for magnetic field propagation. The same as
electric field propagation, Helmholtz equation:
∇2�⃗� − 휀𝜇𝜕2�⃗⃗⃗�
𝜕𝑡− 𝜎𝜇
𝜕�⃗⃗⃗�
𝜕𝑡 = 0 (2.16)
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If there is a source of time-harmonic electromagnetic wave at some point in
the space, the electric field and magnetic field will be propagated in the space in time-
harmonic. The time-harmonic magnetic field intensity is sinusoidal as figure 2.1
Figure 2.1 The sinusoidal wave
The time-harmonic magnetic propagation in space can be written as:
�⃗⃗� = 𝐻 sin 𝜃 �̂� (2.17)
A time-harmonic signal can be transformed into the frequency domain by
using phasor in polar plot in figure 2.2.
Figure 2.2 The polar plot of phasor
Im
Re
𝐻 𝐻 sin 𝜃
𝐻 cos 𝜃
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The magnitude of magnetic field intensity can be written in form of phasor
as equation:
𝐻 = 𝐻 cos 𝜃 + 𝑗𝐻 sin 𝜃 (2.18)
where 𝜃 = 𝜔𝑡 = 2𝜋𝑓𝑡. From Euler’ identity, 𝑒𝑗𝜔𝑡 = cos 𝜔𝑡 + 𝑗 sin 𝜔𝑡
𝐻 = 𝐻𝑒𝑗𝜔𝑡 (2.19)
Therefore, 𝜕�⃗⃗�
𝜕𝑡 = 𝑗𝜔�⃗� (2.20)
𝜕2�⃗⃗�
𝜕𝑡2 = −𝜔2�⃗� (2.21)
The wave equation for time-harmonic magnetic field intensity can be written
as equation:
∇2�⃗⃗� + 𝜔2휀𝜇�⃗⃗� − 𝑗𝜔𝜎𝜇�⃗⃗� = 0 (2.22)
∇2�⃗⃗� − 𝑗𝜔𝜇(𝜎 + 𝑗𝜔휀)�⃗⃗� = 0 (2.23)
The version of Helmholtz wave equation for time-harmonic magnetic field
intensity is generally written in the form
∇2�⃗⃗� − 𝛾2�⃗⃗� = 0 (2.24)
where 𝛾 = √𝑗𝜔𝜇(𝜎 + 𝑗𝜔휀) is called the propagation constant. The same as magnetic
field intensity, the Helmholtz wave equation for time-harmonic electric field intensity
is generally written in the form
∇2�⃗� − 𝛾2�⃗� = 0 (2.25)
From equation (2.22) and (2.24), we have
𝛾2 = −𝜔2휀𝜇 + 𝑗𝜔𝜎𝜇 . (2.26)
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Now if we consider 𝛾 = 𝛼 + 𝑗𝛽 , we can write 𝛾2 as:
𝛾2 = (𝛼2 − 𝛽2) + 𝑗2𝛼𝛽 . (2.27)
The real parts of equation (2.26) and (2.27) must be equal, the same as
imaginary parts. We can solve for and in terms of the material’s constitutive
parameters as:
𝛼 = 𝜔√𝜇휀2
(√1+ (𝜎𝜔휀
)2− 1) (2.28)
𝛽 = 𝜔√𝜇휀2
(√1+ (𝜎𝜔휀
)2+ 1) (2.29)
These equations can be used to find and for any medium. The materials
in high frequency of electromagnetic wave can be considered low-loss dielectric,
(𝜎/𝜔휀) ≪ 1. We can reduce equation (2.28) and (2.29) for this special case by applying
a binomial series expansion to the value within the interior square root portion of the
equations. The expansion is
(1 + 𝑥)𝑛 = 1 + 𝑛𝑥 +𝑛(𝑛−1)
2!𝑥2 + …
and for 𝑥 ≪ 1, it can be approximated as
(1 + 𝑥)𝑛 = 1 + 𝑛𝑥
(1 + (𝜎
𝜔𝜀)2)1/2
= 1 +1
2(
𝜎
𝜔𝜀)2
Inserting this approximation into equation (3.28) and (3.29):
𝛼 = 𝜎2√
𝜇휀 (3.30)
𝛽 = 𝜔√𝜇휀 (3.31)
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2.1.1 Uniform plane wave propagation
In fact, most sources of electromagnetic wave are classified as incoherent and
unpolarized because they consist of a random mixture of waves having different spatial
characteristics, frequencies, phases, and polarization states. However, for better
understanding of electromagnetic waves propagation and polarization in particular, it is
easiest to just consider coherent uniform plane waves; these are sinusoidal waves of one
particular direction, frequency, phase, and polarization state. For the uniform plane
waves, electromagnetic waves such as microwave, are traveling in free space or another
homogeneous isotropic non-attenuating medium. They are properly described as
transverse waves, meaning that a plane wave's electric field vector, �⃗� , and magnetic
field, �⃗⃗� , are in directions perpendicular to the direction of wave propagation; �⃗� and
�⃗⃗� are also perpendicular to each other. Considering a monochromatic uniform plane
wave of frequency f or angular frequency, let’s take the direction of uniform
electromagnetic wave propagation as in the z-axis. The transverse waves of the �⃗� and
�⃗⃗� fields must contain components only in the x and y directions, respectively, whereas
𝐸𝑧 = 𝐻𝑧 = 0. A vertically polarized electromagnetic wave propagation of wavelength
has its electric field vector, �⃗� , oscillating in the vertical direction. The magnetic field,
�⃗⃗� , is always at right angles to it, and both are perpendicular to the direction of
propagation as shown in figure 2.3.
Using complex notation, we understand the instantaneous physical electric
and magnetic fields to be given by the real parts of the complex quantities occurring in
the following equations. As a function of time t and spatial position z-axis, for a plane
wave in the +z direction, the fields have no dependence on x or y directions. To make
use of the Helmholtz equations for time-harmonic fields, let’s consider an x-polarized
plane wave traveling in z direction. For electric field
�⃗� (𝑧) = 𝐸𝑥 �̂� (2.32)
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(http://www.dannex.se/theory/1.html)
Figure 2.3 The uniform plane wave propagation
Recall for a uniform plane wave that the fields do not vary in the transverse
direction, x-y plane. The electric field can only be a function of z. The Laplacian of �⃗�
becomes a straightforward second derivative as:
𝑑2𝐸𝑥
𝑑𝑧2 − 𝛾2𝐸𝑥 = 0 (2.33)
This is a second order, linear, homogeneous differential equation. A possible
solution of this equation for the magnitude of electric field is
𝐸𝑥 = 𝐴𝑒−𝛾𝑧 (2.34)
We can substitute 𝐴 = 𝐸𝑜+ for the electric field amplitude of the
electromagnetic wave propagation in z-direction at 𝑧 = 0. It can be written as
�⃗� 𝑥 = 𝐸𝑜+𝑒−(𝛼+𝑗𝛽)𝑧𝑖 ̂ (2.35)
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From the Faraday’s law, ∇ × �⃗� = − 𝜕�⃗⃗⃗�
𝜕𝑡
∇ × �⃗� 𝑥 = −𝑗𝜔𝜇�⃗⃗� 𝑦 (2.36)
Evaluating the curl of �⃗� 𝑥,
∇ × �⃗� 𝑥 = −(𝛼 + 𝑗𝛽)𝐸𝑜+𝑒−(𝛼+𝑗𝛽)𝑧𝑗̂ (2.37)
From equation (2.36) and (2.37), we get the magnetic field in y-direction as equation
�⃗⃗� 𝑦 = (𝛼 + 𝑗𝛽)
𝑗𝜔𝜇𝐸𝑜
+𝑒−(𝛼+𝑗𝛽)𝑧𝑗 ̂ (2.38)
Let’s define the intrinsic impedance of the medium, . It is the ratio of the
magnitude of electric field and magnetic field in the same medium. It is constant for
any medium. It can be written as:
𝜂 = 𝑗𝜔𝜇
𝛼 + 𝑗𝛽 (2.39)
or 𝜂 = √𝑗𝜔𝜇
𝜎 +𝑗𝜔휀 (2.40)
2.1.2 Reflection and transmission of uniform plane wave
In practice, the uniform plane waves always have obstacles in their path. Let’s
consider a time-harmonic electromagnetic wave incident from medium 1, with
constitutive parameters, 𝜇𝑟1, 휀𝑟1, 𝜎1 , to medium 2, with constitutive parameters,
𝜇𝑟2, 휀𝑟2, 𝜎2. We will consider 2 cases of the incident uniform plane wave, normally and
obliquely incidents.
2.1.2.1 Normally incident
Let’s consider a time-harmonic x-polarized electric field normally incident
from medium 1 at the boundary of medium 2. If we set 𝐸𝑜 is the amplitude of the electric
field at the location of planar boundary separating the two medium. It is easier to carry
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out the upcoming calculations using phasors, and assume that the reflected and
transmitted uniform electric field maintains x-direction. The incident, reflected, and
transmitted fields are indicated with i, r, and t, respectively. Medium 1 and 2 are
indicated with 1 and 2, respectively. The normally incident plane wave from medium 1
to medium 2 results in a reflected wave and transmitted wave is shown in figure 2.4.
Figure 2.4 The plane wave incident from medium 1 to medium 2 results in a reflected
wave and transmitted wave (Wentworth, 2005)
There are the set of electric field and magnetic field polarized equations for
incident, reflected, and transmitted fields as:
Incident fields:
�⃗� 𝑖 = 𝐸𝑜𝑖𝑒−𝛾1𝑧 �̂� (2.41)
�⃗⃗� 𝑖 = 𝐸𝑜
𝑖
𝜂1𝑒−𝛾1𝑧 𝑗̂ (2.42)
Reflected fields:
�⃗� 𝑟 = 𝐸𝑜𝑟𝑒𝛾1𝑧 �̂� (2.43)
Medium 1 Medium 2
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�⃗⃗� 𝑟 = −𝐸𝑜
𝑟
𝜂1𝑒𝛾1𝑧 𝑗̂ (2.44)
Transmitted fields:
�⃗� 𝑡 = 𝐸𝑜𝑡𝑒−𝛾2𝑧 �̂� (2.45)
�⃗⃗� 𝑡 = 𝐸𝑜
𝑡
𝜂2𝑒−𝛾2𝑧 𝑗̂ (2.46)
where 𝐸𝑜𝑖 , 𝐸𝑜
𝑟 , and 𝐸𝑜𝑡 represent the amplitudes for the incident, reflected, and
transmitted electric field intensities at the boundary z = 0. The boundary conditions for
electric and magnetic fields of the two medium are related to tangential fields, therefore,
�⃗� 𝑡1 = �⃗� 𝑡2 (2.47)
�⃗⃗� 𝑡1 = �⃗⃗� 𝑡2 (2.48)
We get the magnitude of electric field
𝐸𝑜𝑖 + 𝐸𝑜
𝑟 = 𝐸𝑜𝑡 . (2.49)
For magnetic field,
𝐸𝑜
𝑖
𝜂1 −
𝐸𝑜𝑟
𝜂1 =
𝐸𝑜𝑡
𝜂2 (2.50)
or 𝐸𝑜𝑖 − 𝐸𝑜
𝑟 = 𝜂1𝜂2
𝐸𝑜𝑡 (2.51)
Using equation (2.49) and (2.51), we get the equation relating the amplitude
of reflected electric fields to the incident electric field as shown in equation:
𝐸𝑜𝑟 =
𝜂2 − 𝜂1
𝜂2 + 𝜂1𝐸𝑜
𝑖 = 𝐸𝑜𝑖
or = 𝐸𝑜
𝑟
𝐸𝑜𝑖 =
𝜂2 − 𝜂1
𝜂2 + 𝜂1 (2.52)
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where is reflection coefficient. The ratio of transmitted electric fields to the incident
electric field as shown in equations:
𝐸𝑜 𝑡 =
2𝜂2𝜂2 + 𝜂1
𝐸𝑜𝑖 = 𝜏𝐸𝑜
𝑖
or = 𝐸𝑜
𝑡
𝐸𝑜𝑖 =
2𝜂2𝜂2 + 𝜂1
(2.53)
where is transmission coefficient.
2.1.2.2 Oblique incident
Figure 2.5 shows the oblique incident electromagnetic field from medium 1
to medium 2. In the figure, the propagation directions of incident, reflected, and
transmitted waves are �̂�𝑖, �̂�𝑟, and �̂�𝑡, respectively. The plane of propagation directions
are in the x-z plane, perpendicular to y-direction. The incident angle, 𝜃𝑖, the reflected
angle, 𝜃𝑟, and the transmitted angle, 𝜃𝑡, are the angles with the normal to the boundary.
Figure 2.5 The oblique incident electromagnetic field from medium 1 to medium 2
(Wentworth, 2005)
x
z
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Any uniform plane wave incident on the boundary of the medium can be
decomposed into a pair of polarization. The first polarization, the electric field is
perpendicular or transverse to the incident plane wave. It is called the perpendicular
polarization, or more commonly, the transverse electric polarization (TE). Another
polarization, the electric field is parallel to the incident plane wave. In this case, the
magnetic field is transverse to the incident plane wave. It is called the parallel
polarization or the transverse magnetic polarization (TM).
2.1.2.2.1 TE Polarization
Consider TE polarization in figure 2.6, the electric field intensity vector is
directed out of the page. We superimpose an artificial pair of axes x and z for the
incident electric field and magnetic field are,
�⃗� 𝑖 = 𝐸𝑜𝑖𝑒−𝛾1𝑧′ 𝑗̂ (2.54)
and �⃗⃗� 𝑖 = 𝐸𝑜
𝑖
𝜂1𝑒−𝛾1𝑧′ (−�̂�′) (2.55)
Figure 2.6 The TE polarization (Wentworth, 2005)
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Figure 2.7 shows a pair of axis (𝑥′ and 𝑧′) superimposed on coordinate system
to find equivalence 𝑧′ and -𝑖̂′ . By trigonometry arguments, we can relate 𝑧′ to the
original coordinate system for electric field as shown in figure 2.7(a):
�⃗� 𝑖 = 𝐸𝑜𝑖𝑒−𝛾1(𝑥 sin𝜃𝑖+𝑧cos𝜃𝑖) 𝑗̂ (2.56)
For magnetic field from figure 2.7 (b)
�⃗⃗� 𝑖 = 𝐸𝑜
𝑖
𝜂1𝑒−𝛾1(𝑥 sin𝜃𝑖 + 𝑧 cos𝜃𝑖) (− cos 𝜃𝑖 �̂� + sin 𝜃𝑖�̂�) (2.57)
Figure 2.7 A pair of axis (𝑥′ and 𝑧′) superimposed on coordinate system to find
equivalence 𝑧′ and -�̂�′ (Wentworth, 2005)
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There are the set of reflected and transmitted electric field and magnetic field
for TE polarization equation:
Reflected fields:
�⃗� 𝑟 = 𝐸𝑜𝑟𝑒−𝛾1(𝑥 sin𝜃𝑟 − 𝑧 cos𝜃𝑟) 𝑗̂ (2.58)
�⃗⃗� 𝑟 = 𝐸𝑜
𝑟
𝜂1𝑒−𝛾1(𝑥 sin𝜃𝑟 − 𝑧 cos𝜃𝑟)(−cos 𝜃𝑟 �̂� + sin𝜃𝑟�̂�) (2.59)
Transmitted fields:
�⃗� 𝑡 = 𝐸𝑜𝑡𝑒−𝛾2(𝑥 sin𝜃𝑡 + 𝑧 cos𝜃𝑡) 𝑗̂ (2.60)
�⃗⃗� 𝑡 = 𝐸𝑜
𝑡
𝜂2𝑒−𝛾2(𝑥 sin𝜃𝑡 + 𝑧 cos𝜃𝑡)(−cos 𝜃𝑡 �̂� + sin 𝜃𝑡�̂�) (2.61)
When 𝛾1 > 𝛾2 , as incident angle, 𝜃𝑖, increases from normal incident, the
transmitted angle, 𝜃𝑡, increases more rapidly until at critical angle, 𝜃𝑐. It is the incident
angle for transmitted angle reached 90. It can be written from Snell’s law as:
𝜃𝑐 = sin−1 (𝛾2
𝛾1) (2.62)
If the incident angle is greater than the critical angle, the electric fields cannot
transmit from medium 1 to medium 2. The total reflection of the wave will be occurred.
Returning to equation (2.49) at the boundary, since 𝜃𝑖 = 𝜃𝑟, it can be expressed as:
𝐸𝑜
𝑖 − 𝐸𝑜𝑟
𝜂1cos 𝜃𝑖 =
𝐸𝑜𝑡
𝜂2cos 𝜃𝑡 (2.63)
or 𝐸𝑜𝑖 − 𝐸𝑜
𝑟 = 𝐸𝑜𝑡 𝜂1
𝜂2
cos𝜃𝑡cos𝜃𝑖
(2.64)
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The reflection coefficient, , and the transmission coefficient, , of the
oblique incident uniform plane wave in TE polarization can be expressed as:
TE = 𝜂2 cos𝜃𝑖 − 𝜂
1cos𝜃𝑡
𝜂2 cos𝜃𝑖 + 𝜂1cos𝜃𝑡 (2.65)
𝜏TE = 2𝜂2cos𝜃𝑖
𝜂2 cos𝜃𝑖 + 𝜂1 cos𝜃𝑡 (2.66)
2.1.2.2.2 TM Polarization
The oblique incidence of a TM polarization is indicated in figure 2.8. All of
the magnetic fields are tangential to the boundary, but only the x component of the
electric field is tangential. The reflection and transmission of the TM polarization
analysis reveals the same as for the TE polarization by similar geometric arguments as
before.
Figure 2.8 The TM polarization (Wentworth, 2005)
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There are the set of incident, reflected and transmitted electric field and
magnetic field for TM polarization equation:
Incident fields:
�⃗� 𝑖 = 𝐸0𝑖𝑒−𝛾1(𝑥 sin𝜃𝑖 + 𝑧 cos𝜃𝑖)(cos 𝜃𝑖 �̂� − sin 𝜃𝑖�̂�) (2.67)
�⃗⃗� 𝑖 = 𝐸0
𝑟
𝜂1𝑒−𝛾1(𝑥 sin𝜃𝑖 + 𝑧 cos𝜃𝑖) 𝑗̂ (2.68)
Reflected fields:
�⃗� 𝑟 = 𝐸0𝑟𝑒−𝛾1(𝑥 sin𝜃𝑟 − 𝑧 cos𝜃𝑟)(cos 𝜃𝑟 �̂� + sin 𝜃𝑟�̂�) (2.69)
�⃗⃗� 𝑟 = −𝐸0
𝑟
𝜂1𝑒−𝛾1(𝑥 sin𝜃𝑟 − 𝑧 cos𝜃𝑟) 𝑗̂ (2.70)
Transmitted fields:
�⃗� 𝑡 = 𝐸0𝑡𝑒−𝛾2(𝑥 sin𝜃𝑡 + 𝑧 cos𝜃𝑡)(cos 𝜃𝑡 �̂� − sin 𝜃𝑡�̂�) (2.71)
�⃗⃗� 𝑡 = 𝐸0
𝑡
𝜂2𝑒−𝛾2(𝑥 sin𝜃𝑡 + 𝑧 cos𝜃𝑡)𝑗̂ (2.72)
Employing the boundary conditions, the reflection coefficient, , and the
transmission coefficient, , of the oblique incident uniform plane wave in TM
polarization can be expressed as:
TM = 𝜂2 cos𝜃𝑡 − 𝜂
1cos𝜃𝑖
𝜂1 cos𝜃𝑖 + 𝜂2cos𝜃𝑡 (2.73)
𝜏TM = 2𝜂2cos𝜃𝑖
𝜂1 cos𝜃𝑖 + 𝜂2 cos𝜃𝑡 (2.74)
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2.1.3 Standing wave
Standing wave is the superposition of the opposite travelling two waves in
the same medium. For the uniform plane wave, the standing wave occurs in the first
medium where containing the incident wave and reflected wave from the boundary of
both medium. The standing wave pattern of uniform plane wave in a lossless medium
reflecting off a second medium at z = 0 is shown in figure 2.9.
Figure 2.9 The standing wave pattern of uniform plane wave in a lossless medium
(Wentworth, 2005)
The maximum and minimum amplitudes of standing wave are related to the
reflected coefficient, , as in equation:
𝐸𝑚𝑎𝑥 = 1 + |Γ| (2.75)
𝐸𝑚𝑖𝑛 = 1 − |Γ| (2.76)
The ratio of the maximum to the minimum amplitudes of standing wave is
called the standing wave ratio, SWR. It can be expressed as:
𝑆𝑊𝑅 = 1 + |Γ|
1 − |Γ| (2.77)
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2.2 Electromagnetic wave propagation of overhead transmission lines
The mathematical models are developed to calculate the distribution of
electromagnetic wave around the phase conductors of the high-voltage and extremely
low frequency overhead transmission lines system. The general form of Maxwell’s
equation is simplified to demonstrate the electromagnetic wave distribution. Ampere’s
law can be described electric and magnetic field propagation in the environment as
equation:
∇ × �⃗⃗� = 𝜕�⃗⃗⃗�
𝜕𝑡 + 𝐽 . (2.78)
The first term of the right hand side is displacement current density. 𝐽 is the
total current density, consists of velocity current density, 𝐽 𝑣 = 𝜎(𝑣 × �⃗� ) , induced
current density, 𝐽 𝑖 = 𝜎�⃗� , external current density, 𝐽 𝑒 . The Ampere’s law can be
written again as:
∇ × �⃗⃗� = 𝜕�⃗⃗⃗�
𝜕𝑡 + 𝐽 𝑒 + 𝜎(𝑣 × �⃗� ) + 𝜎�⃗� . (2.79)
The magnetic field distribution can be calculated by curl of magnetic vector
potential as equation (2.80):
�⃗� = ∇ × 𝐴 (2.80)
The relation between magnetic flux density and magnetic field is in equation
(2.81):
�⃗� = 𝜇�⃗⃗� (2.81)
The electric field distribution due to high-voltage overhead transmission lines
composes of static electric field and alternating electric field. The static electric field
can be calculated by gradient of electric scalar potential, while the alternating electric
field is associated with magnetic field. It can be calculated by time derivative of
magnetic vector potential as equation:
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�⃗� = − ∇𝑉 −𝜕�⃗⃗⃗�
𝜕𝑡 (2.82)
The first term in the right hand side of equation (2.82) is the electric field due
to gradient of electric potential from conductor lines to anywhere around them. The
intensity of this electric field depends on the distance from conductor lines. The second
term is the time-harmonic electric field due to alternating current of the transmission
lines. The electric displacement in the medium is in equation as:
�⃗⃗� = 휀�⃗� (2.83)
For the time-harmonic electromagnetic wave, the propagation of electric field
and magnetic flux density with the angular frequency can be written as equations:
�⃗� = 𝐸𝑒−𝑗𝜔𝑡�̂� (2.84)
�⃗⃗� = 𝐻𝑒−𝑗𝜔𝑡�̂� (2.85)
Thus, the Ampere’s law for time-harmonic electromagnetic wave
propagation can be written as:
∇ × 𝜇−1�⃗� = 𝑗𝜔�⃗⃗� + 𝐽 𝑒 + 𝜎 (𝑣 × (∇ × 𝐴 )) + 𝜎 (−∇𝑉 − 𝜕𝐴
𝜕𝑡)
∇ × 𝜇−1(∇ × 𝐴 ) = 𝑗𝜔휀(−∇𝑉 − 𝑗𝜔𝐴 ) + 𝐽 𝑒 + (𝜎𝑣 × (∇ × 𝐴 )) + 𝜎(−∇𝑉 − 𝑗𝜔𝐴 )
∇ × 𝜇−1(∇ × 𝐴 ) = −𝑗𝜔휀∇𝑉 + 𝜔2휀𝐴 + 𝐽 𝑒 + (𝜎𝑣 × (∇ × 𝐴 )) − 𝜎∇𝑉 − 𝑗𝜔𝜎𝐴
∇ × 𝜇−1(∇ × 𝐴 ) = − (𝜎 + 𝑗𝜔휀)∇𝑉 − (𝑗𝜔𝜎 − 𝜔2휀)𝐴 + 𝐽 𝑒 + (𝜎𝑣 × (∇ × 𝐴 ))
((𝑗𝜔𝜎 − 𝜔2휀)𝐴 ) + (∇ × 𝜇−1(∇ × 𝐴 )) − (𝜎𝑣 × (∇ × 𝐴 )) = − (𝜎 + 𝑗𝜔휀)∇𝑉 + 𝐽 𝑒
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The behavior of the medium in extremely low frequency of electromagnetic
is a conductor. In this case, 𝜎 is much greater than 𝜔휀, 𝜎 ≫ 𝜔휀 . The gradient of
voltage is decreased in the distance, ∇𝑉 = −∆𝑉
𝐿 . The Ampere’s law becomes:
(𝑗𝜔𝜎 − 𝜔2휀𝑜휀𝑟)𝐴 + ∇ × (𝜇𝑜−1𝜇𝑟
−1(∇ × 𝐴 )) − (𝜎𝑣 × (∇ × 𝐴 )) = 𝜎∆𝑉
𝐿+ 𝐽 𝑒 (2.86)
2.3 The propagation of electromagnetic wave in biological tissues
The biological tissues behave a dielectric material in electromagnetic
propagation. The lossy nature can be attributed to finite conductivity, polarization loss,
or a combination of the two. With finite conductivity, the electric field gives rise to a
current density, 𝐽 = 𝜎�⃗� . Polarization loss comes about from the energy required of
the field to flip reluctant dipoles. This loss mechanism is proportional to frequency.
Recalling Ampere’s circuital law:
∇ × �⃗⃗� = 𝜎�⃗� + 𝑗𝜔(휀′ − 𝑗휀′′)�⃗� (2.87)
where 휀′ and 휀′′ are the real part and the imaginary part of the permittivity that accounts
for the polarization losses. It can be rearranged as:
∇ × �⃗⃗� = [𝜎𝑒𝑓𝑓 + 𝑗𝜔휀′]�⃗� (2.88)
It is apparent that we can account for both conductivity and the polarization
losses by an effective conductivity given by, 𝜎𝑒𝑓𝑓 = 𝜎 + 𝜔휀′′. Now the propagation
constant is complex, with an attenuation constant greater than zero. A standard measure
of losses in a dielectric is given by the loss tangent, represented by figure 2.10.
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Figure 2.10 Loss tangent of electromagnetic propagation in dielectric
The loss tangent is typically applied when discussing dielectric material, for
which a small value is desirable. The imaginary part of equation (2.88), is the
displacement current density. The vector sum of the real and imaginary parts is the total
current density, ∇ × �⃗⃗� . We define as the angle by which the displacement current
density leads the total current density. The tangent of this angle is called the loss
tangent, can be write as:
tan 𝛿 = 𝜎𝑒𝑓𝑓
𝜔휀′ (2.89)
The loss tangent is affected to the attenuation of electromagnetic wave in the
biological tissues. The penetration depth (Dp) is defined as the distance within biological
tissue at which the electromagnetic wave density has decreased to 𝑒−1 or 36.8% of its
initial value at the surface (Dincer and Rosen, 2007):
𝐷p = 1
2𝜋𝑓𝑣
√휀𝑟′ (√1+(tan)
2− 1)
2
. (2.90)
Im
Re
∇ × �⃗⃗� 𝜔휀′�⃗�
𝜎𝑒𝑓𝑓�⃗�
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Where 휀𝑟′ is the relative dielectric constant, tan 𝛿 is the loss tangent which
provides an indication of how well the biological tissues can be penetrated by an
electrical field and how it dissipates electrical energy as heat, and υ is the speed of
electromagnetic wave (m/s). The penetration depth of the electromagnetic wave which
penetrates within the biological tissues is calculated using equation (2.90), which shows
how it depends on the dielectric properties of the dielectric material and frequency of
electromagnetic wave. It is shown that the penetration depth is greatly dependent on the
frequency of electromagnetic wave, it will be increased if the frequency of
electromagnetic wave is decrease. In real biological tissue, the relative permittivity and
conductivity are varied with the frequency of electromagnetic wave. Figure 2.11
represents a schematic view for the variation of the relative permittivity and
conductivity of biological tissue for a wide frequency range of electromagnetic wave.
For the relative permittivity, it decreases as the frequency increases. It is opposite for
the conductivity of biological tissue.
Figure 2.11 A schematic view for the variation of the relative permittivity and
conductivity of biological tissue for a wide frequency range of electromagnetic wave.
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2.4 Interactions of electromagnetic wave with biological tissues
2.4.1 High frequency of electromagnetic wave
For the high frequency of electromagnetic wave such as microwave, the
penetration dept is low. Most of the electromagnetic wave is not passed through the
biological tissue, if the size of biological tissue is greater than the penetration depth.
Human tissues are generally lossy mediums for electromagnetic wave with finite
electric conductivity. They are usually neither good dielectric materials nor good
conductors. The energy of electromagnetic wave is absorbed by the tissues when
electromagnetic wave propagates through the human tissues. The interaction of
electromagnetic fields with biological tissues can be defined in term of the specific
absorption rate (SAR). It is defined as the power dissipation rate normalized by
material density (Kanai et al., 2007). The specific absorption rate is given by
𝑆𝐴𝑅 = 𝜎𝜌|𝐸|2 (2.91)
where E is the root mean square electric field (V/m), is the conductivity (S/m) and ρ
is mass density of the tissue (kg/m3) and is the conductivity of the tissue.
The absorbed energy of electromagnetic wave can be changed to thermal
energy. The heat source density inside biological tissue will be occurred. It can be
written as:
𝑄 = 𝜌 ∙ 𝑆𝐴𝑅 (2.92)
𝑄 = 𝜎𝐸2 (2.93)
From equation (2.89), 𝜎 = 2𝜋𝑓휀𝑟′ 휀𝑜 tan 𝛿
𝑄 = 2𝜋𝑓휀𝑟′ 휀𝑜 tan 𝛿 𝐸2 (2.94)
where E is electromagnetic field intensity; f is microwave frequency; is angular
velocity of microwave; r is relative dielectric constant; 0 is dielectric constant of air
and tan is dielectric loss tangent coefficient.
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The heat source density is directly proportional to the frequency of the
applied electric field and dielectric loss tangent coefficient and root-mean-square value
of the electric field. The temperature in the biological tissue will be increased due to
heat source. It means that during an increasing of tan of biological tissues, energy
absorption and heat generation are also increased. While tan is small, microwave will
penetrate into biological tissue without heat generation. However, the temperature
increase depends on other factors such as specific heat, size and characteristic of
biological tissue.
The heat transport in biological tissues is complicated because it involve with
metabolic heat generation, thermal conduction of tissues, convection and blood
perfusion in the biological tissues. For human body, there are two sets of blood vessels
in the blood circulatory system for carrying blood from the heart to all parts of tissues
inside the body and get back to the heart by the pumping action of the heart, artery and
vein vessels. Figure 2.12 shows the blood circulatory system of human body. The blood
flows from the heart to the tissues through the artery vessels and flows back to the heart
through the vein vessels.
Figure 2.12 The blood circulatory system of human body (Datta and Dekker, 2002)
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The mathematical model of bioheat equation is usually used to describe the
heat transport in biological tissues. It can be derived for an idealized biological system
with blood vessels through it as shown in figure 2.13
Figure 2.13 Idealized biological tissue systems (Datta and Dekker, 2002)
For an idealized biological tissue system with blood vessels, some
assumptions of the biological tissue model are made:
1. It is a homogeneous material with isotropic thermal properties, same
in all directions.
2. The blood capillaries are isotropic.
3. The large blood vessels are ignored.
4. The temperature of blood is at arterial temperature but quickly reaches
the tissue temperature by the time.
The bioheat equation model was initially developed by Pennes (Pennes,
1948). The simplest form of Pennes’ bioheat equation can be expressed as:
𝜌𝐶𝜕𝑇
𝜕𝑡 = ∇ ∙ (𝑘∇𝑇) + 𝑄𝑚𝑒𝑡 + 𝑄𝑝 + 𝑄𝑒𝑥𝑡. (2.95)
Where is the biological tissue density (kg/m3), C is the heat capacity of
biological tissue (J/kg K), k is thermal conductivity of biological tissue (W/m K), T is
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the biological tissue temperature ( C ). The first term in the right hand side of equation
(2.91) is the heat conduction in biological tissue. 𝑄𝑚𝑒𝑡 is the metabolism heat source
(W/ m3). 𝑄𝑝 is the heat transfer by blood perfusion. The heat transfer from the blood to
the biological tissue is proportional to temperature difference between the blood
temperature and biological temperature as equation:
𝑄𝑝 = 𝜌𝑏𝐶𝑏𝜔𝑏(𝑇𝑏 − 𝑇). (2.96)
Where bT is the blood temperature ( C ),
b is the blood density (kg/m3), bC
is the specific heat capacity of blood (J/ kg K), b is the blood perfusion rate (1/s). For
the external heat source, 𝑄𝑒𝑥𝑡 is electromagnetic wave heat source density (W/m3). It is
equal to the resistive heat which is generated by the electromagnetic wave power
absorbed, which is defined as
𝑄𝑒𝑥𝑡 = 1
2𝜎organ|𝐸|2 (2.97)
where 𝜎organ = 2𝜋𝑓휀𝑟′ 휀𝑜
The Pennes’ bioheat equation was implemented in various biological
research works because the simplicity of the Pennes bioheat model.
2.4.2 Extremely low frequency of electromagnetic wave
In the extremely low frequency electromagnetic field, biological tissues
behave as electrolytic conductors and insulator at the same time as they are made of
polar molecules, such as water. Charges inside biological tissues, positive and negative
ions, will be moved to the surface in response to the electric field when they exhibit
conductor. In case of insulator, the external electric field will be reduced by relative
permittivity property inside human body according to the following equation:
�⃗� 𝑖𝑛 = �⃗⃗⃗� 𝑒𝑥𝑡휀𝑟
(2.98)
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The current density inside human body can be evaluated by electric field
distribution which is occurred on each surface of organs inside human body. It can be
expressed as:
𝐽 = 𝜎𝐸 + 𝐽𝑒 (2.99)
where 𝐽𝑒 is the external current density. The equation of continuity in the static form of
current density can be expressed as:
∇ ∙ 𝐽 = 0 (2.100)
∇ ∙ (𝜎𝐸 + 𝐽𝑒) = 0 (2.101)
−∇ ∙ (𝜎∆𝑉 − 𝐽𝑒) = 0 (2.102)
If the current density source inside human body is 𝑄𝑖, unit A/m3.
−∇ ∙ (𝜎∆𝑉 − 𝐽𝑒) = 𝑄𝑖 (2.103)
The in-plane conductive media assumes that the electric potential varies only
in the x-y plane and it constant in z-direction. This implies that the stationary electric
field, E, is tangential to the x-y plane. The surface current density, unit A/m2, on the
medium with thickness d in z-direction can be expressed as:
−∇ ∙ 𝑑(𝜎∆𝑉 − 𝐽𝑒) = 𝑑𝑄𝑖 (2.104)
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CHAPTER 3
THE EFFECTS INSIDE HUMAN BODY MODEL EXPOSED
TO HIGH FREQUENCIES OF NON-IONIZING
ELECTROMANETIC WAVE
3.1 Introduction
Electromagnetic wave is a one heat source that is an attractive alternative
over conventional heating methods because electromagnetic wave in range of
microwave that penetrates the surface is converted into thermal energy within the
material. The utilizations of electromagnetic wave have been used in many industrial
and household applications such as heating process or drying process. In recent years,
these utilizations are increasing rapidly because of the several advantages of
electromagnetic wave heating source such as high speed start up, selective energy
absorption, instantaneous electric control, no pollution, high energy efficiency and high
product quality (Rattanadecho et al., 2009, Suwannapum et al., 2011). Rapid
development of electromagnetic energy applications causes an increase in public
concern about health risks from electromagnetic energy emitted from various sources
(Wessapan et al., 2011, 2012). The power absorption of electromagnetic wave induces
temperature increase on organs in the human body. The specific absorption rate (SAR)
criteria have been used to obtain the dosimetric data and to gain further understanding
of the biological tissues absorption characteristic of the human body (Nishizawa et al.,
1999). The temperature increase of organs is one of the main tasks in the evaluation of
the human risk related to the exposure to the human body to electromagnetic wave
(Samaras et al., 2007).
The computational analysis is used to study the distributions of SAR and
temperature in human body because these distributions cannot be measured directly to
the alive human body due to ethical consideration. In present day, the experimental data
on the correlation of SAR levels to the temperature increase on organs in the human
body are still sparse. Most previous studies of a human body exposed to an
electromagnetic wave did not consider heat transfer cause an incomplete analysis to
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result. The earlier studies of heat transfer in human tissues used the general bioheat
equation to investigate that (Pennes, 1998). Thereafter, coupled model of Maxwell’s
equation and bioheat equation were used to model human tissues exposed to
electromagnetic wave to explain the electromagnetic wave propagation and heat
transfer in tissues in the human body. There are some research have been studied
temperature distribution over the surface and various biotissues exposed to
electromagnetic wave (Yang et al., 2007, Ozen et al., 2008). The SAR distributions of
skin, fat and muscle tissues in human body with three-layer physical model were
simulated by S. Nishizawa (Nishizawa et al., 1999). The heat transfer in liver tissue for
liver cancer treatment using microwave coaxial antenna was studied by P.
Keangin (Keangin et al., 2011). However, most studies of temperature increase induced
by electromagnetic wave have not been considered in a realistic domain of the human
body with complicated organs of several types of tissues. Our research group has tried
to numerically investigate the temperature increase in human tissue subjected to
electromagnetic fields in many problems, such as Wessapan et al. studied SAR and
temperature distributions in the human head and the human eye due to mobile phone
radiation at several frequencies (Wessapan et al., 2011, 2012). Moreover, they used the
human body model which has 10 organs in the human trunk to simulate the SAR and
heat transfer in these organs exposed to electromagnetic wave at frequencies of 915
MHz and 2450 MHz which are characterized propagation in TE mode (Wessapan et al.,
2011), and studied the effects of dielectric shield on SAR and temperature increase in
the human body at the frequencies of 300 MHz, 915 MHz, 1300 MHz and 2450 MHz
(Wessapan et al., 2011). However, these works were not considered these effects on
organs when the electromagnetic wave propagated from source in different propagation
mode.
The work described in this paper is substantially extended from our previous
work (Wessapan et al., 2011) by further puts the focus on the effects of wave
propagation mode, operating frequency, radiated power of electromagnetic wave and
exposure time. In this paper, a 2-D human cross section model (Shiba et al., 2009) is
used to simulate the distribution of SAR and temperature in these organs exposed to
electromagnetic wave. There are four frequencies of electromagnetic wave in range of
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microwave at 300 MHz, 915 MHz, 1300 MHz and 2450 MHz are chosen to simulate
these distributions because the energy of these frequencies can be converted to thermal
energy. Each frequency has radiated power of 10 W, 50 W and 100 W. Furthermore,
the comparison of biological effects on organs due to particular mode of
electromagnetic wave propagation, TE mode and TM mode, are considered. The
Maxwell’s equation and the bioheat equation are used to investigate electromagnetic
wave propagation and heat transfer on organs exposed to electromagnetic wave,
respectively. The obtained values provide an indication of limitations that must be
considered for temperature increases due to localized electromagnetic wave energy
absorption.
3.2 Numerical simulation
Most of industrial electromagnetic wave heating systems generate high
power electromagnetic wave to use in various applications such as industrial microwave
system as shown in figure 3.1. The leakage electromagnetic wave from the heating
source can cause significant thermal damage on sensitive organs within the human
body. Therefore, to approach reality, it is necessary to investigate the temperature
distribution on organs in the human trunk due to the leakage electromagnetic wave. It
is assumed that the propagation of electromagnetic wave is uniform plane wave. For
ethical consideration, it is difficult to measure these distributions directly to the alive
human body. The computational analysis is selected to investigate the distributions of
SAR and temperature in human body. The system of governing equations as well as
initial and boundary conditions are solved numerically using the finite element method
(FEM) via COMSOLTM Multiphysics to demonstrate the phenomenon occurs within
the human body exposed to electromagnetic wave.
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Figure 3.1 The leakage electromagnetic wave from the industrial microwave
3.2.1 Human model
Figure 3.2 shows the 2-D human body model which is used in this study is
obtained by image processing technique from the work of (Shiba et al., 2009). The side
view cross section through the middle plane of the human trunk model has a dimension
of 400 mm in width and 525 mm in height which composes of nine internal organs in
human trunk which are skin, fat, muscle, bone, large intestine, small intestine, bladder,
stomach and liver. These organs have different dielectric and thermal properties. The
thermal properties of tissues are given in Table 3.1 and the dielectric properties of
tissues at the frequencies of 300 MHz, 915 MHz, 1300 MHz and 2450 MHz are given
in Table 3.2. The thermal properties of these tissues are constant because there are only
a slight change of temperature is noticed along the exposure time.
Figure 3.2 Cross sectional model of human body
stomach
large intestine
bladder
skin
liver
muscle
small intestine
fat y
x
bone
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Table 3.1 Thermal property of tissues (Wessapan et al., 2011)
Table 3.2 Dielectric properties of tissues (Wessapan et al., 2011)
organs
300 MHz 915 MHz 1300 MHz 2450 MHz
(S/m)
r
(S/m)
r
(S/m)
r
(S/m)
r
skin 0.35 48.41 0.92 44.86 1.25 43.56 2.16 41.79
fat 0.06 6.55 0.09 5.97 0.10 5.80 0.13 5.51
muscle 1.08 55.45 1.33 50.44 1.42 48.96 1.60 46.40 bone 2.10 44.80 2.10 44.80 2.10 44.80 2.10 44.80
large intestine 2.04 53.90 2.04 53.90 2.04 53.90 2.04 53.90
small intestine 3.17 54.40 3.17 54.40 3.17 54.40 3.17 54.40 bladder 0.69 18.00 0.69 18.00 0.69 18.00 0.69 18.00
stomach 2.21 62.20 2.21 62.20 2.21 62.20 2.21 62.20
liver 1.69 43.00 1.69 43.00 1.69 43.00 1.69 43.00
3.2.2 Equation of electromagnetic wave propagation analysis
The mathematical models are developed to predict SAR and temperature
distributions within the human body exposed to electromagnetic wave. It is assumed
that electromagnetic wave leaks from industrial electromagnetic wave heating system.
This electromagnetic wave propagates in x-direction and penetrates into the human
body from front to back of human body as shown in figure 3.1. To simplify the
computational analysis, some of the following assumptions are used in this paper,
1. It is assumed that the electromagnetic wave is plane wave.
2. The human body in which electromagnetic wave interact with human
proceeds in free space.
3. The free space is truncated by scattering boundary condition.
4. The dielectric properties of tissues are uniform and constant.
organs
(kg/m3)
K
(W/mK)
c
(J/kgK)
b
(1/s)
skin 1125 0.35 3437 2.00 10-2
fat 916 0.22 2300 4.58 10-4
muscle 1047 0.60 3500 8.69 10-3
bone 1038 0.44 1300 4.36 10-4
large intestine 1043 0.60 3500 1.39 10-2
small intestine 1043 0.60 3500 1.74 10-2
bladder 1030 0.56 3900 0.000
stomach 1050 0.53 3500 7.00 10-3
liver 1030 0.50 3600 1.72 10-2
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3.2.3 Governing equations
In this study, the two propagation characteristic of electromagnetic wave
which leaks from electromagnetic wave heating system to the human body is assumed
in two circumstances: (i) TE mode and (ii) TM mode. The induced biological effects on
organs in human body due to the two propagation modes of electromagnetic wave are
compared. The propagation of electromagnetic wave in human body is calculated by
Maxwell’s equation (Spiegel et al., 1984), which mathematically describes the
interdependence between electric and magnetic fields. The general forms of Maxwell’s
equation are simplified to the following expressions:
- Transverse Electric mode (TE mode) (Wessapan et al., 2011)
∇ × (1
𝜇𝑟∇ × 𝐸𝑧) − (휀𝑟 −
𝑗𝜎
𝜔𝜀𝑜) 𝑘𝑜
2𝐸𝑧 = 0. (3.1)
-Transverse Magnetic mode (TM mode)
∇ × ((1
𝜀𝑟−𝑗𝜎
𝜔𝜀𝑜
)(∇ × 𝐻𝑧)) − 𝜇𝑟𝑘𝑜2𝐻𝑧 = 0. (3.2)
Where 휀𝑜 = 8.8542 × 10−12 F/m is the permittivity of free space and 𝑗 = √−1 is
imaginary number.
3.2.4 Boundary conditions
The electromagnetic wave is emitted from the high power electromagnetic
wave heating system and leaks to the environment. It propagates in x-direction to strike
in front of the human body and moves through the back. It is assumed that the
electromagnetic wave which strikes the human body is characterized by uniform plane
wave with the power the same as source. Figure 3.3 shows an electromagnetic wave
propagation port in the left boundary of considered domain with a specified power,
where 1 and 2 refer to the first medium and the second medium of each organ inside
human body model, respectively,
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𝑆 = ∫(𝐸−𝐸1)∙𝐸1
∫𝐸1∙𝐸1 . (3.3)
For the boundary conditions along the interfaces between different medium
such as air and organs or organs and organs, they are considered continuity boundary
conditions,
𝑛 × (𝐻1 − 𝐻2) = 0. (3.4)
For the outer sides of the tissue boundaries are truncated as scattering
boundary conditions,
𝑛 × (∇ × 𝐸𝑧) − 𝑗𝑘𝐸𝑧 = −𝑗𝑘(1 − 𝑘 ∙ 𝑛)𝐸𝑜𝑧𝑒−𝑗𝑘∙𝑟 (3.5)
Figure 3.3 Boundary conditions for electromagnetic wave propagation and heat
transfer
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3.2.5 Equation of heat transfer in human body
To solve the thermal problem, the temperature distribution in the human body
has been evaluated by the bioheat equation according to Maxwell’s equations. The
temperature distribution corresponds to the SAR. This is because the SAR within the
human body distributes, owing to energy absorption. Thereafter, the absorbed energy is
converted to thermal energy, which increases the organs temperature. Heat transfer
analysis of the human body is modeled in two dimensions. To simplify the problem, the
following assumptions are made:
1. Human organ is bio-material with uniform and constant thermal
properties.
2. There is no phase change of substance within the organ.
3. There is no energy exchange throughout the human model.
4. There is no chemical reaction within the organ.
3.2.6 Governing equations
The energy of electromagnetic wave is absorbed by tissue organs, when it
penetrates into the human body. The temperature of tissues in human body will be
increased, according to the absorbed energy is converted to thermal energy. These
temperature distributions inside the human model are obtained by Pennes’ bioheat
equation as equation (3.6). The transient bioheat equation effectively explains the
phenomenon of heat transfer within the human body, it can be written as (Pennes, 1998):
𝜌𝐶𝜕𝑇
𝜕𝑡= ∇ ∙ (𝑘∇𝑇) + 𝜌𝑏𝐶𝑏𝜔𝑏(𝑇𝑏 − 𝑇) + 𝑄𝑚𝑒𝑡 + 𝑄𝑒𝑥𝑡. (3.6)
where is the organ density (kg/m3), C is the heat capacity of organ (J/kg
K), k is thermal conductivity of orgas (W/m K), T is the organ temperature ( C ), bT
is the temperature of blood ( C ), b is the density of blood (kg/m3), bC is the specific
heat capacity of blood (J/ kg K), b is the blood perfusion rate (1/s), metQ is the
metabolism heat source (W/ m3) and extQ is the external heat source term
(electromagnetic wave heat-source density) (W/ m3).
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In this analysis, the metabolism heat source is negligible, heat conduction and
blood flow in each organ is approximated by the term ∇ ∙ (𝑘∇𝑇) and 𝜌𝑏𝐶𝑏𝜔𝑏(𝑇𝑏 − 𝑇),
respectively. For the external heat source, Qext, this analysis is electromagnetic wave
heat source density (W/m3). It is equal to the resistive heat which is generated by the
electromagnetic wave power absorbed, which is defined as
𝑄𝑒𝑥𝑡 = 1
2𝜎organ|𝐸|2 (3.7)
where 𝜎organ = 2𝜋𝑓휀𝑟′ 휀𝑜.
3.2.7 Boundary conditions
Heat transfer is considered only in the human body domain, which is not
including the surrounding space. The boundary of human body which contacts the air
is considered to be a thermal insulation boundary condition, defined as,
𝑛 ∙ (𝑘∇𝑇) = 0. (3.8)
It is assumed that no contact resistance occurs between the internal organs in
human body. Therefore, the boundary conditions of the internal organs are assumed to
be a continuous.
𝑛 ∙ (𝑘𝑢∇𝑇𝑢 − 𝑘𝑑∇𝑇𝑑) = 0. (3.9)
3.2.8 Interaction of electromagnetic wave and human organs
Human organs are generally lossy mediums for electromagnetic wave with
finite electric conductivity. When electromagnetic wave propagates into these organs,
the energy of electromagnetic wave propagation is absorbed by the tissue. SAR of
electromagnetic wave energy in organ is defined as a power dissipation rate normalized
by organs density (Wessapan et al., 2011), which is given by the following equation:
𝑆𝐴𝑅 = 𝜎𝜌|𝐸|2. (3.10)
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3.2.9 Initial condition for heat transfer
In this analysis, the temperature distribution inside the human body is
assumed to be uniform. The thermoregulation mechanisms and the metabolic heat
generation of each organ have been neglected to illustrate the clear temperature
distribution. Therefore, the initial temperature of the human body is defined as
𝑇(𝑡𝑜) = 37 °C (3.11)
3.2.10 Penetration Depth
The penetration depth (Dp) is defined as the distance within material at which
the electromagnetic wave density has decreased to 37% of its initial value at the surface
(Wessapan et al., 2011):
𝐷p = 1
2𝜋𝑓𝑣
√휀𝑟′ (√1+(tan)
2− 1)
2
(3.12)
where 휀𝑟′ is the relative dielectric constant, tan 𝛿 is the loss tangent which provides an
indication of how well the material can be penetrated by an electrical field and how it
dissipates electrical energy as heat, and υ is the speed of electromagnetic wave (m/s).
The penetration depth of the electromagnetic wave which penetrates within
the material is calculated using equation (3.12), which shows how it depends on the
dielectric properties of the dielectric material and frequency of electromagnetic wave.
It is shown that the penetration depth is greatly dependent on the frequency of
electromagnetic wave, it will be increased if the frequency of electromagnetic wave is
decrease.
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3.3 Simulation procedure
The finite element method is used to analyze the transient problems. The
computational scheme is to assemble a finite element model and compute a local heat
generation term by performing an electromagnetic calculation using organ properties.
In order to obtain a good approximation, a fine mesh is specified in the sensitive areas.
This study provides a variable mesh method for solving the problem as shown in figure
3.4. The model of bioheat equation and Maxwell’s equation are solved. All
computational processes are implemented using COMSOLTM Multiphysics, to
demonstrate the phenomena that occur within the human body exposed to
electromagnetic fields. The electromagnetic power absorption at each point is computed
and used to solve the time-dependent temperature distribution. All steps are repeated,
until the required exposure time is reached. The 2-D model is discretized using
triangular elements and the Lagrange quadratic is used to approximate temperature and
SAR variation across each element. Convergence tests are carried out to identify a
suitable number of elements required. The convergence test leads to a grid with
approximately 90,000 elements. It is reasonable to assume that, with this element
number, the accuracy of the simulation results is independent of the number of elements
and therefore save computation memory and time.
Figure 3.4 An initial two-dimensional finite element mesh of human cross section
model
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3.4 Results and Discussions
The coupled mathematic models of heat transfer and electromagnetic wave
propagation is used to simulate SAR and temperature distributions on organs in human
body exposed to electromagnetic wave which have four frequencies of 300 MHz, 915
MHz, 1300 MHz and 2450 MHz. The influence of wave propagation mode, operating
frequency, and radiated power of the electromagnetic wave source are systematically
investigated.
3.4.1 Verification of the model
It must be noted in advance that it is not possible to make a direct comparison
of the model in this study and the experimental results. In order to verify the accuracy
of the present numerical model, the simple case of the simulated results is then validated
against the numerical results with the same geometric model obtained by Nishizawa and
Hashimoto (Nishizawa et al., 1999). The horizontal cross section of three-layer human
tissues as shown in figure 3.5 is used in the validation case. In the validation case, the
leakage power density exposed to the electromagnetic frequency of 1300 MHz is 1
mW/cm2. The results of the selected test case are illustrated in figure 3.6 for SAR
distribution in the human body. Table 3.3 clearly shows good agreement in the
maximum value of the SAR of tissues between the present solution and that of
Nishizawa and Hashimoto. This favorable comparison lends confidence in the accuracy
of the present numerical model. It is important to note that there may be some errors
occurring in the simulations that are generated by the input dielectric properties and the
numerical scheme.
It is shown that the maximum SAR of organs calculated in the present study
and Nishisawa’s models are in good agreement, the maximum difference is about
3.88%. This comparison lends confidence in the accuracy of these models to simulate
SAR and temperature distributions in human body in this study.
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Figure 3.5 Geometry of the validation model obtained from the paper (Wessapan et
al., 2011).
Figure 3.6 Comparison of the calculated SAR distribution to the SAR distribution
from the paper (Wessapan et al., 2011)
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Table 3.3 Comparison of the results obtained in the present work with those of
Nishizawa and Hashimoto
Power (W)
Present
work
Published
work
%
difference
SARmax in skin
SARmax in fat
SARmax in muscle
0.212
0.198
0.116
0.220
0.206
0.120
3.63
3.88
3.33
3.4.2 Influence of exposure time of electromagnetic wave
Figure 3.7 shows the maximum temperature increases in human body
exposed to electromagnetic wave propagation in TE and TM mode plane wave at the
frequency of 300 MHz, 915 MHz, 1300 MHz and 2450 MHz in various exposure times.
It is found that the maximum temperature increases in the human body at these
frequencies are approach to steady state after five minutes of exposure time, except for
the frequency of 300 MHz from both of propagation mode, the temperature is rising
continuously. This is because the high penetration depth of the 300 MHz frequency
causes localizing thermal runaway in deep organs which is shown in equation (3.12).
The SAR distributions at low frequency are higher than that of high frequency, but at
300 MHz has low SAR value because its penetration depth is too high compared to that
of other frequencies. The electromagnetic wave can penetrate into the human body and
the absorbed energy is distributed in each organ of the human body as shown in figure
3.8.
The maximum temperature increases at the high frequency of 1300 MHz and
2450 MHz for both TE and TM mode propagation have a very similar distribution trend
at each radiated power as shown in figures 7(c) and 7(d). This is because in this
frequency range they have low penetration depth of the electromagnetic wave into the
human body. While at the low frequency of 300 MHz, the maximum temperature
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increases in case of TM mode, is higher than that of TE mode. This is because the
resonance of standing wave is becoming a dominant phenomenon in the fat (which will
be discussed later). The energy of this resonance ability to be absorbed in the fat,
thereafter, it is converted to thermal energy and its transfer to other organs. This
phenomenon causes significant high temperature increase within organs.
At the frequency of 915 MHz, it is illustrated the different behavior of the
maximum temperature increases to the frequency of 300 MHz. It is found that the
temperature increases of TE mode are higher than that of TM mode. This is because the
maximum SAR obtained from TE mode occurred in the skin, is very different from fat
as shown in figure 3.8. Therefore, a significant amount of thermal energy transfers from
skin to fat. It is found that the maximum temperature occurs in the fat because it has
low thermal conductivity and low blood perfusion rate. While the maximum SAR
obtained from TM mode occurs in the fat, but not much different from the contiguous
organs. This is because thermal energy spread out from fat to these organs. Thus, the
maximum temperatures of organ in human body exposed to electromagnetic wave at
915 MHz of TM mode are lower than that of TE mode.
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(a) 300 MHz (b) 915 MHz
(c) 1300 MHz (d) 2450 MHz
Figure 3.7 The maximum temperature increase on organs in human body due to
electromagnetic wave at frequencies of 300 MHz, 915 MHz, 1300 MHz and
2450 MHz in various exposure time.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 10 20 30 40 50 60
Maxim
um
tem
per
atu
re in
crea
se
(C
)
Time (min)
TE 10 W
TE 50 W
TE 100 W
TM 10 W
TM 50 W
TM 100 W
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 10 20 30 40 50 60
Maxim
um
tem
per
atu
re in
crea
se (C
)
Time (min)
TE 10 W TE 50 W
TE 100 W TM 10 W
TM 50 W TM 100 W
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 10 20 30 40 50 60
Max
imum
tem
per
ature
incr
ease
(
C)
Time (min)
TE 10 W
TE 50 W
TE 100 W
TM 10 W
TM 50 W
TM 100 W
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 10 20 30 40 50 60
Max
imum
tem
per
ature
incr
ease
(
C)
Time (min)
TE 10 W
TE 50 W
TE 100 W
TM 10 W
TM 50 W
TM 100 W
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(a) TE mode
(b) TM mode
Figure 3.8 SAR distribution on organs in human body exposed to electromagnetic
wave which are propagated in (a) TE mode (b) TM mode at power 100 W and
exposure time 20 minutes in various frequencies.
.
0
5
10
15
20
25
30
35S
AR
(W
/kg)
300 MHz
915 MHz
1300 MHz
2450 MHz
0
50
100
150
200
250
300
350
SA
R (W
/kg)
300 MHz
915 MHz
1300 MHz
2450 MHz
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3.4.3 Influence of the power of electromagnetic wave
The relation between the maximum SAR and electromagnetic wave radiated
power which is propagated in TE and TM mode is shown in figure 3.9. The exposure
times at 20 minutes are selected to study because the maximum temperature increases
in human body due to electromagnetic wave are steady for both of frequencies and
propagation mode, except at 300 MHz which are shown in figure 3.7.
Figure 3.9 shows the maximum SAR depends on the radiated power, it will
be increased if the radiated power is higher. The increasing is inversely to the frequency
of electromagnetic wave, because the penetration depth in human body of the lower
frequency is high, except at frequency 300 MHz in TE mode, it is the most slowly
increasing of the maximum SAR because it is very high of penetration depth. This is
because the energy of electric field distributes many organs in human body. The
maximum SAR at frequency 300 MHz in TM mode is the most rapidly increasing in
various powers of source, because the resonance of the electric field standing wave in
the fat is very strong due to the large different thermal and dielectric properties with
each others as shown in Table 3.1 and Table 3.2. From electromagnetic theory, the
reflection to the first medium and the transmission to the next medium of
electromagnetic wave can be occurred at the surface when it propagates in
discontinuous medium. The standing wave of electric or magnetic field will be occurred
at the first medium due to the combination of incident and reflected field if they have
opposite phase, normally when it propagates from low density to strike high density
medium. The dominant standing wave of electromagnetic field which is propagated in
TE mode is magnetic field, while propagated in TM mode is electric field. These fields
will be increased in the medium which has many standing waves due to the resonance
of these standing waves inside. Thus, the total electric and magnetic field of each organ
are from the penetration field and the resonance. Therefore, SAR value of organ is
obtained from electric field, its dielectric property and density as shown in equation
(3.10). Moreover, the maximum SAR from TM mode is higher than that of TE mode at
each frequency because the dominant standing wave of TM mode is electric field which
causes to SAR value.
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For consideration of the maximum temperature increases, it is found that most
of them are corresponding to the maximum SAR as shown in figure 3.10. For TE mode,
the maximum temperatures at the extremely high and low frequencies are slowly
increases, while at 915 MHz is the most rapidly increase in this propagation mode. For
TM mode, the maximum temperature increase at 300 MHz is the most rapidly while
2450 MHz is the most slowly temperature increase, corresponding to the maximum
SAR.
(a) TE mode
(b) TM mode
Figure 3.9 The maximum SAR on organs of each electromagnetic wave power of
heating source which are propagated in (a) TE mode (b) TM mode.
y = 0.0321x
y = 0.3263x
y = 0.2677x
y = 0.1623x
0
10
20
30
40
50
0 20 40 60 80 100
Max
imum
SA
R (
W/k
g)
Power (W)
300 MHz
915 MHz
1300 MHz
2450 MHz
y = 3.3522x
y = 0.4598x
y = 0.3875x
y = 0.246x
0
10
20
30
40
50
0 20 40 60 80 100
Max
imum
SA
R (
W/k
g)
Power (W)
300 MHz
915 MHz
1300 MHz
2450 MHz
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(a) TE mode
(b) TM mode
Figure 3.10 The maximum temperature increase on organs of each power of heating
source which are propagated in (a) TE mode (b) TM mode.
y = 0.0018x
y = 0.0047x
y = 0.0036x
y = 0.0019x
0
0.1
0.2
0.3
0.4
0.5
0.6
0 20 40 60 80 100
Max
imum
tem
per
ature
incr
ease
(C
)
Power (W)
300 MHz
915 MHz
1300 MHz
2450 MHz
y = 0.0057x
y = 0.0026x
y = 0.0038x
y = 0.002x
0
0.1
0.2
0.3
0.4
0.5
0.6
0 20 40 60 80 100
Max
imum
tempe
rature
incre
ase (
C)
Power (W)
300 MHz
915 MHz
1300 MHz
2450 MHz
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3.4.4 SAR distribution in human body
Figure 3.11 shows the SAR distribution evaluated on the vertical section of
the human body in which the maximum SAR value occurs. For consideration of the
SAR distribution on organs in human body exposed to electromagnetic wave at
frequencies of 300 MHz, 915 MHz, 1300 MHz and 2450 MHz, the cases of 100 W and
exposure time at 20 minutes are investigated. It is evident that the dielectric properties,
as shown in Table 3.2, can become significant to SAR distributions in human organ
when electromagnetic energy is exposed in these organs. The electric field is attenuated
within the human body, owing to the energy absorbed in organs. The SAR in particular
organ is given by equation (3.10), it is found that the high values of SAR occur in the
periphery region of the body, skin and fat. The SAR distributions at low frequency are
higher than that of high frequency of electromagnetic wave in the same organs, because
the penetration depth of low frequency is high. But at frequency 300 MHz in TE mode
has low SAR because it is very high penetration depth of this frequency when compares
with other frequencies, the electromagnetic wave can moves through many organs in
human body and distributes the energy on each organ, as shown in figure 3.11(a).
For TM mode, it is found that the SAR values on each organ which is exposed
to electromagnetic wave in TM mode are higher than that of TE mode for all organs
and frequencies. This is because the standing wave on each organ can be occurred by
the summation of the transmitted electromagnetic field from previous organ and
reflected electromagnetic field from the boundary of the next organ. It contributes to
the resonance of standing wave in each organ, the energy of the resonance of standing
wave will be absorbed by organs. The dominant standing wave on organs from wave
propagation in TE mode is magnetic field, while from wave propagation in TM mode
is electric field. Thus, the absorbed energy from electric field on each organ which
exposed to electromagnetic wave in TM mode is higher than that of TE mode. Figure
3.11(b) shows the SAR value at frequency 300 MHz in TM mode is too high on fat
when compares with other frequencies and organs, because the dielectric constant of fat
is too different from the contiguous organs while the others are similar to each
contiguous organ as shown in Table 3.2, the reflected coefficient of electric field is very
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high, it causes strong standing wave on fat. The resonance of standing wave on fat at
frequency 300 MHz in TM mode is significant because it has high penetration depth
and strong standing wave, it has very high SAR when compare to other organs,
frequencies of electromagnetic wave and propagation mode.
a) TE mode
b) TM mode
Figure 3.11 SAR distribution of human body exposed to electromagnetic wave at
frequencies of 300 MHz, 915 MHz, 1300 MHz and 2450 MHz which are propagated in
(a) TE mode (b) TM mode at power 100 W and exposure time 20 minutes.
SAR (W/kg)
SAR (W/kg)
35
30
25
20
15
10
5
0
300 MHz 915 MHz 1300 MHz 2450 MHz
35
30
25
20
15
10
5
0
300 MHz 915 MHz 1300 MHz 2450 MHz
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3.4.5 Temperature distribution in the human body
Figure 3.12 shows the temperature distribution in the human body at the same
cases of the SAR consideration. It is found that the temperature increases are
corresponding to the SAR distributions because the absorbed energy on each organ is
converted to thermal energy. Although the SAR on the inner organs are quite different
from the periphery organs of the body as shown in figure 3.8, but the temperature
increases are not quite different. Not only SAR is important value to cause the
temperature increase in the human body, but the thermal and dielectric properties which
are shown in Table 3.1 and Table 3.2 are also important. The bioheat equation in
equation (3.6) shows that thermal energy can be transfer to the contiguous organs due
to conduction and blood perfusion terms. The heat source of each tissue is SAR, while
heat sink is heat transfer to other organs by factors of thermal conductivity and blood
perfusion rate.
For TE mode, the maximum temperature increases are inversely to frequency,
except at 300 MHz because it has low SAR in this case. The maximum temperature of
high frequencies of 915 MHz, 1300 MHz and 2450 MHz are occurred on fat at 37.46C,
37.36C and 37.19C, respectively. This is because fat has low thermal conductivity
and blood perfusion rate as shown in Table 3.1, causes low heat sink on fat. While the
maximum temperature at frequency 300 MHz is occurred on bladder, 37.14C. This is
because this frequency has high penetration depth, it can penetrate into bladder. This
organ is very large and don’t have blood perfusion rate.
For TM mode, the most of maximum temperature is obtained from 300 MHz
at 37.50C on fat because it has very high SAR on fat. Figure 3.8(b) shows that the
temperature increases on organs of 300 MHz are not quite different, although the SAR
value on fat is very high when compare with other organs. This is because of heat
transfer from fat to the contiguous organs. The maximum temperatures which are
obtained from 915 MHz, 1300 MHz and 2450 MHz are occurred on skin at 37.26C,
37.37C and 37.20C, respectively. It is found that the temperature increases which are
obtained from both of TE mode and TM mode at high frequency are not different. The
maximum temperature increase from all frequencies and propagations mode in this
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work is 0.50 C, this temperature is much lower than the thermal damage temperature
within the range of 1-5C.
Figure 3.12 Temperature distribution of human body exposed to electromagnetic wave
at frequencies of 300 MHz, 915 MHz, 1300 MHz and 2450 MHz which are propagated
in (a) TE mode (b) TM mode at power 100 W and exposure time 20 minutes.
Temperature
(C) 37.50
37.40
37.30
37.20
37.10
37.00
300 MHz 915 MHz 1300 MHz 2450 MHz
a) TE mode
37.14 C 37.46 C
37.36 C 37.19 C
Temperature
(C) 37.50
37.40
37.30
37.20
37.10
37.00
300 MHz 915 MHz 1300 MHz 2450 MHz
b) TM mode
37.50 C 37.26 C 37.37 C 37.20 C
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3.4.6 The maximum SAR and temperature on organs in the human body
From the previous section, the steady state temperature after exposure for 20
minutes at the radiated power of 100 W, are selected to study the organs which have the
maximum SAR and temperature. Figure 3.13 shows the temperature distribution on
tissues in human body exposed to electromagnetic wave at frequencies of 300 MHz,
915 MHz, 1300 MHz and 2450 MHz which are propagated in TE mode and TM mode.
Table 3.4 and Table 3.5 show the organs which have the maximum SAR and
temperature from TE mode and TM mode, respectively. It is found that the maximum
SAR from TE mode at frequencies of 915 MHz, 1300 MHz and 2450 MHz occur in the
skin. These values are 32.6 W/kg, 26.9 W/kg and 16.2 W/kg, respectively. Thereafter,
thermal energy transfers from skin to fat, the maximum temperatures occur on fat,
because at low conductivity and blood perfusion rate on fat. These values are 37.46C,
37.36C and 37.19C, respectively. At 300 MHz, which has high penetration depth, the
maximum SAR occurs on muscle, 3.2 W/kg, and the maximum temperature occurs on
the next organ, bladder, 37.14C.
For TM mode, it is found that the maximum SARs occur on fat at all
frequencies, because of the resonance of the electric field standing wave is very strong.
These values are 335.5 W/kg, 46.0 W/kg, 38.7 W/kg and 24.6 W/kg, respectively. The
maximum temperatures occur in the skin because thermal energy from fat spread out to
the contiguous organs, except at 300 MHz is still on fat because of very high SAR when
compared to the others. These values are 37.50C, 37.26C, 37.37C and 37.20C,
respectively.
Comparing to the ICNIRP limit, SAR value for occupational exposure is 10
W/kg. It is found that most of the resulting of SAR values are exceeded the ICNIRP
limit for all cases of frequencies and propagation modes when the electromagnetic
radiated power is 100 W, especially at 300 MHz in TM mode.
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(a) TE mode
(b) TM mode
Figure 3.13 Temperature distribution on tissues in human body exposed to
electromagnetic wave at frequencies of 300 MHz, 915 MHz, 1300 MHz and 2450
MHz which are propagated in (a) TE mode (b) TM mode at power 100 W and
exposure time 20 minutes.
0
0.1
0.2
0.3
0.4
0.5
0.6T
emper
ature
incr
ease
(
C)
300 MHz
915 MHz
1300 MHz
2450 MHz
0
0.1
0.2
0.3
0.4
0.5
0.6
Tem
per
ature
incr
ease
(
C)
300 MHz
915 MHz
1300 MHz
2450 MHz
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Table 3.4 The organ in human body which has the maximum SAR and
temperature in TE mode
Power
(W)
300 MHz
915 MHz
1300 MHz
2450 MHz
10
50
100
SAR
T
SAR
T
SAR
T
SAR
T
muscle
muscle
muscle
bladder
bladder
bladder
skin
skin
skin
fat
fat
fat
skin
skin
skin
fat
fat
fat
skin
skin
skin
fat
fat
fat
Table 3.5 The organ in human body which has the maximum SAR and temperature
in TM mode
Power
(W)
300 MHz
915 MHz
1300 MHz
2450 MHz
10
50
100
SAR
T
SAR
T
SAR
T
SAR
T
fat
fat
fat
fat
fat
fat
fat
fat
fat
skin
skin
skin
fat
fat
fat
skin
skin
skin
fat
fat
fat
skin
skin
skin
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3.5 Conclusions
This study presents the numerical simulation of SAR and temperature
distributions on organs in human body exposed to electromagnetic wave at the
frequencies of 300 MHz, 915 MHz, 1300 MHz and 2450 MHz. The influence of
electromagnetic wave propagation mode at each frequency in various exposure time
and power of electromagnetic wave are investigated. The results show that the
maximum temperature are approch to steady after 5 minutes of exposure time, it
depends on the power of electromagnetic wave.
For the distribution of SAR consideration, the maximum SARs within the
human body which are exposed to electromagnetic wave propagation in TM mode are
higher than that of TE mode at each frequency for all cases of radiated power. The
maximum SARs occur at skin when electromagnetic wave propagated in TE mode for
all frequencies, except at the frequency 300 MHz. It occurs at muscle because it has
high penetration depth. In TM mode, they occur at fat for all frequencies because of the
resonance of electric field standing wave on fat. These maximum SAR values are
proportional to the power of electromagnetic wave but the power of electromagnetic
wave is not affected to the organs which have the maximum SAR, it is the same organ
for all frequencies and propagation modes even though the power of electromagnetic
wave is increasing.
For the distribution of temperature consideration, the maximum temperatures
in the human body occur at the contiguous organs of the organs which have the
maximum SAR, because of heat transfer of these organs. They occur at bladder from
the frequency 300 MHz and fat from the frequencies of 915 MHz, 1300 MHz and 2450
MHz for all powers of electromagnetic wave in TE mode. These organs has the lareg
size, the effect of heat is increasing of temperature more than transfer to other organs.
While they occur at skin from the frequencies of 915 MHz, 1300 MHz and 2450 MHz
for all powers of electromagnetic wave in TM mode. This is because fat is a tiny region
at the position of the maximum SAR. Except at the frequency 300 MHz in TM mode,
the maximum temperature still occurs at fat. This is because it has very high SAR and
the large size of fat.
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Moreover, it is found that the temperature distribution is not related only
electric field, but the dielectric property, thermal property, blood perfusion and
penetration depth of organs at each frequency of electromagnetic wave are significant
too. However, mode of electromagnetic wave propagation is important to cause the
SAR and tempertaure distributions. The electromagnetic wave at frequency 300 MHz
which is propagated in TE mode is little affected to SAR and temperature distributions
in human body, while 300 MHz in TM mode is significant to cause the SAR and
temperature distributions.
For the future work, these models will be developed for 3-D simulation for
better understanding of the realistic situation of the interaction between the
electromagnetic wave and the organs in human body. Moreover, these effects will be
calculated from other electromagnetic sources such as electromagnetic wave which is
propagated from high power transmission lines.
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CHAPTER 4
THE EFFECTS INSIDE HUMAN BODY MODEL EXPOSED
TO EXTREMELY LOW FREQUENCY OF NON-IONIZING
ELECTROMANETIC WAVE
4.1 Introduction
During the last few decades, the electrical power demand in Thailand
increases very rapidly. In order to fulfill the vast need of electrical power in the large
city, the high-voltage OHTLs are constructed to carry electricity from the power plant
to the very long distance electrical power station with minimizes the power loss of
electricity. In Thailand, the Electricity Generating Authority of Thailand (EGAT) has
been constructed the enlarge transmission capacity by installing high voltage power
transmission lines, the maximum voltage is 500 kV (Pao-la-or et al., 2008; Tupsie et
al., 2009; Pao-la-or et al., 2010). The electromagnetic field can be generated by the
high-voltage power transmission lines. The strength of the electromagnetic field is
proportional to the magnitude of voltage of transmission lines. There is concern about
the possible health hazards for general public from these extra high voltage OHTLs,
because they can generate electromagnetic field to the environment. For the improving
of living standard, the consciousness of environment protection and health for people
who live near the passing transmission lines area and the worker who climb on the high-
voltage post to maintain the transmission lines needs to be increasing. The extremely
low frequency (ELF) of 50-60 Hz is a very important health concern. Some international
organizations have provided guidelines to limit electromagnetic field which is exposed
to human body by the extremely low frequency (ELF) of 50 Hz such as The
International Commission on Non-Ionizing Radiation (ICNIRP). It has been suggested
that if there is any harmful effect to health due to the electromagnetic field, induced
current may cause this effect (ICNIRP, 2010). The amount of the current, even if a
human is directly under a transmission line, is extremely small. These biological effects
from extremely low frequency electric and magnetic fields have been studied to
investigate its harmful on living bodies especially on human beings from worldwide
researchers (Furse, et al., 1996; Stuchly, et al., 1997; Yildirim et al., 1998; Hongjie et
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al., 2000; Siauve et al., 2003; King, et al., 2004; Abd-Allah, 2006; Gonzalez et al.,
2007; El-Makkawy, 2007; Duyan et al., 2008; Min, et al., 2009; Maalej et al., 2009; El
Dein, et al., 2010; Darabant et al., 2012). However, these quantities are difficult to
measure. Therefore, the numerical methods are used to calculate electric and magnetic
fields which are emitted from high voltage OHTLs and induced current inside human
body. Many researchers both of power electrical engineering and biomedical
engineering fields have developed the techniques to calculate the electric and magnetic
fields around the area of high voltage OHTLs by using theory and simulation such as
Image Theory Method (ITM) (Li et al., 1998), Charge Simulation Method (CSM)
(Ismail et al., 1998; Santos Jr. et al., 2010), Finite Element Method (FEM) (Pao-la-or
et al., 2008; Tupsie et al., 2009; Pao-la-or et al., 2010). These quantities were compared
with guidelines for limiting the exposure which set by The International Commission
on Non-Ionizing Radiation (ICNIRP). However, most studies of the electric field,
magnetic field and induced current density are calculated at the surface of human body.
They have been not considered theses effects inside human body with complicated
organs of several types of tissue. However, most studies of the effects are not considered
theses effects inside human body with complicated organs of several types of tissue.
In this work, uses the Finite Element Method to calculate the extremely low
frequency electromagnetic field, 50 Hz, which is emitted from 500 kV OHTLs. This
power line is the maximum voltage which is installed in Thailand. For the biological
effects, the induced electric field and current density inside a 2-D human cross sectional
model which has several organs inside such as brain, lungs, heart, liver and intestine
exposed to extremely low frequency electromagnetic field and high voltage are
calculated. These calculated quantities will be compared with the ICNIRP limitation.
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4.2 Formulation of the problem
The electromagnetic fields are emitted from the 500 kV overhead
transmission lines both of single-circuit and double-circuit high-voltage transmission
lines which are installed by EGAT in Thailand. The power transmission lines are three
phases and frequency 50 Hz for both of single-circuit and double-circuit. There are 4-
bundled conductors as illustrated diagrammatically by figure 4.1 for single-circuit and
figure 4.2 for double circuit. They show the 2-D cross section at mid-span (maximum
sag allowance) of conductors. For both circuit types, the height of the lowest conductor
are 13.00 m above the ground level and phase conductors are 795 MCM (diameter =
0.02772 m) while overhead ground wires (OHG) are 3/8 inch (diameter = 0.009114 m).
The maximum current load density is 3.15 kA per phase (Tupsie et al., 2009).
Figure 4.1 The 2-D cross section diagrammatically the single-circuit of 500 kV
overhead transmission lines
OHG1 OHG1
10.65 m 10.65 m
10.65 m 10.65 m
13.6 m
13.0 m
26.6 m
0.457 m
OHG1 OHG2
35.0 m 35.0 m
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11.0 m 11.24 m
9.40 m
13.64 m
15.84 m
13.51 m
0.457 m
OHG1 OHG2
11.0 m
13.0 m
48.51 m
Figure 4.2 The 2-D cross section diagrammatically the single-circuit of 500 kV
overhead transmission lines
4.3 Methods and Models
The first step in evaluating the biological effects of a certain exposure to
electromagnetic field due to high voltage OHTLs on several organs inside human body
is the determination of electric field and its spatial distribution on human body.
Thereafter, the induced electric field and current density distributions inside human
body are considered. The system of the governing equations as well as initial and
boundary conditions are solved numerically using the Finite Element Method (FEM)
via COMSOLTM Multiphysics to demonstrate the phenomenon occur within the human
body exposed to electromagnetic field.
The 2-D human body model which is used in this study has the height of 1.80
m. It composes of five internal organs in human trunk and head such as brain, lungs,
heart, liver, and intestine. The shapes of these organs are expressed by cylinders,
spheroids and circle as shown in figure 4.3. These organs have different dielectric
properties at the frequency of 50 Hz as shown in Table 4.1 (Gandhi et al., 1992;
Wessapan et al., 2011). The relative permeability (r) is 1 and relative permittivity (r)
OHG1 OHG2
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of all organs is 2 × 107. The system of the governing equations as well as initial and
boundary conditions are solved numerically using the Finite Element Method (FEM)
via COMSOLTM Multiphysics.
Table 4.1 Dielectric property of tissues
Figure 4.3 The 2-D human body model
Organs (kg/m3) (S/m)
Body 1062 0.2160
Brain 1050 0.0533
Lung 1050 0.0684
Liver 1030 0.0367
Heart 1058 0.0827
Intestine 1043 0.5220
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4.4 Governing equations
4.4.1 Electromagnetic field distribution
The electromagnetic field emits from high voltage overhead transmission
lines to the environment around phase conductors. Mathematical models are developed
to predict the electromagnetic field distribution around phase conductors. For overhead
transmission lines, high voltage and extremely low frequency system, the most
important field for biological effects inside human body is electric field (C. Peratta,
2010). The electric field distribution in the area under phase conductors at mid-span
where is human body standing is investigated. To simplify the problem, the assumptions
are made.
1. The high-voltage overhead transmission lines are in 2-D cross section.
2. The wire conductors at mid-span are straight lines perpendicular to
cross section.
3. The computational space is truncated by scattering boundary
condition.
4. There is no interference of electromagnetic fields due to each
conductor phase line.
The electromagnetic field propagation in space can be calculated by
Maxwell’s equation. It can be described electric and magnetic field distributions. The
general form of Maxwell’s equation is simplified to demonstrate the electromagnetic
field distribution as the following equation:
(𝑗𝜔𝜎 − 𝜔2휀𝑜휀𝑟)𝐴 + ∇ × (𝜇𝑜−1𝜇𝑟
−1(∇ × 𝐴 )) − (𝜎𝑣 × (∇ × 𝐴 )) = 𝜎∆𝑉
𝐿+ 𝐽𝑒 (4.1)
The magnetic field distribution can be calculated by curl of magnetic vector
potential as equation:
�⃗� = ∇ × 𝐴 (4.2)
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The electric field distribution due to high voltage overhead transmission lines
composes of static electric field and alternating electric field. The static electric field
can be calculated by gradient of electric scalar potential, while the alternating electric
field is associated with magnetic field. It can be calculated by time derivative of
magnetic vector potential as equation:
�⃗� = − ∇𝑉 − 𝜕�⃗⃗⃗�
𝜕𝑡 (4.3)
The first term in the right hand side of equation (4.3) is the electric field due
to gradient of electric potential from conductor lines to anywhere around them. The
intensity of this electric field depends on the distance from conductor lines. The second
term is the time-harmonic electric field due to alternating current of the transmission
lines. It can be derived from equation (4.3) and Maxwell’s equation as:
∇⃗⃗ × �⃗� = − 𝜕�⃗⃗⃗�
𝜕𝑡 (4.4)
The propagation of time-harmonic of magnetic flux density with the angular
frequency can be written as equation:
�⃗⃗� = 𝐻𝑒−𝑗𝜔𝑡�̂� (4.5)
Thus, the relation between time-harmonic electric field and magnetic flux
density as shown in equation:
∇ × �⃗� = 𝑗𝜔𝜇�⃗⃗� (4.6)
∇ × �⃗⃗� = (𝜎 + 𝑗𝜔휀)�⃗� (4.7)
The electrical conductivity, permittivity and permeability in air are very low.
For extremely low frequency of electromagnetic field, the right hand side of equation
(4.6) and equation (4.7) are approximately to zero. Therefore, the dominant of electric
field distribution around the high-voltage transmission lines with extremely low
frequency is electric field due to the gradient of electric potential.
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4.4.2 Electric field and current density distributions inside human body
In the extremely low frequency electromagnetic field, biological tissues
behave as electrolytic conductors and insulator at the same time as they are made of
polar molecules, such as water. Charges inside biological tissues, positive and negative
ions, will be moved to the surface in response to the electric field when they exhibit
conductor. In case of insulator, the external electric field will be reduced by relative
permittivity property inside human body according to the following equation:
�⃗� 𝑖𝑛 = �⃗⃗⃗� 𝑒𝑥𝑡휀𝑟
(4.8)
The current density inside human body can be evaluated by electric field
distribution which is occurred on each surface of organs inside human body. It can be
expressed as (El Dein et al., 2010):
𝐽 = 𝜎𝐸𝑖𝑛 (4.9)
To simplify the problem for calculating the electric field and current density
distributions inside human body, the assumptions are made.
1. Human body organs are biomaterial with the constant dielectric
properties.
2. There is no energy exchange throughout the human body.
3. There is no chemical reaction within the organs.
4. Human body model is standing on ground under overhead
transmission lines at mid-span.
4.5 Boundary conditions
The electromagnetic field is emitted from high-voltage overhead
transmission lines to the environment and strikes the human body which is standing
under high-voltage overhead transmission lines at the mid-span. Therefore, the
boundary conditions for electromagnetic field distribution are shown in figure 4.4
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(a) Single circuit (b) Double circuit
Figure 4.4 Boundary conditions
4.6 Calculation procedure
In this work, The Finite Element Method is selected to analyze the problems.
It is implemented in COMSOLTM Multiphysics program to demonstrate the
phenomenon of electromagnetic field distribution and biological effects inside human
body exposed to electric field due to high voltage overhead transmission lines both of
single-circuit and double-circuit. The 2-D model is discretized using triangular
elements. The Lagrange quadratic is used to vary the electric field propagation from
high voltage overhead transmission lines, induced electric field distribution and current
on several organs inside human body across each element. In order to obtain a good
approximation, a fine mesh is specified in the sensitive area. The convergence test of
the average electric fields at the height 1 m from ground is carried out to identify the
suitable number of element required. Figure 4.5 shows that the average electric fields
are stable after number of element more than 400,000 elements for single circuit and
500,000 elements for double-circuit. In order to save time and material of computation,
the number of mesh element which is selected to use in this work are 484220 elements
for single circuit and 564809 elements for double-circuit.
Continuity
(n̂ × (H⃗⃗ 1 − H⃗⃗ 2) = 0)
Electric Insulation
(n̂ × H⃗⃗ = 0)
Ground (𝑉 =0)
Ground (𝑉 =0)
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Figure 4.5 The convergence test of the maximum electric field at the high 1 m above
ground
4.7 Results and Discussions
In this work, the Finite Element Method is used to analyze the effects on
several organs inside human body model exposed to electric field due to high-voltage
overhead transmission lines. The electric field distribution in the area under 500 kV
overhead transmission lines at mid-span both of single-circuit and double-circuit are
calculated. Thereafter, the induced electric field and current density distributions on
several organs inside human body exposed to electric field due to transmission lines are
systematically investigated.
4.7.1 Verification of the models
It must be noted that it is difficult to make a direct comparison of the models
in this study with the experimental results because there is no measured report of the
500 kV overhead transmission line configurations. In order to verify the accuracy of the
present numerical models, the electric field distribution of the simulated result is then
0
1
2
3
4
5
6
7
8
9
10
0 200 400 600 800 1000
Av
era
ge e
lctr
ic f
ied
in
ten
sity
(k
V/m
)
Number of mesh elements (x103)
sigle-circuit
double-circuit
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validated against the numerical result with the same configuration of double-circuit 500
kV overhead transmission lines which are installed in Thailand, obtained by S.Tupsie,
et al. (Tupsie et al., 2009).
The comparison of the electric field distribution of double-circuit 500 kV
overhead transmission lines between the reference and present simulated results without
human body model are illustrated in figure 4.6. It is seen that the pattern of electric field
distribution in present simulated result is similarly as the reference simulated result,
both of low and high electric field region and characteristic of equi-electric field lines.
Moreover, the electric field distribution at 1 m above ground in the area under 500 kV
overhead transmission lines at mid-span is compared. This area is the place of human
body standing. Figure 4.7 clearly shows a good agreement of the reference and present
simulated electric field distributions. The relative root mean square (RMS) deviation is
used to quantify the comparison. It is found that the RMS deviation is equal to 2.35%.
(a) (b)
Figure 4.6 The pattern of electric field distribution of reference and present simulated
results, (a) Reference simulated result, (b) Present simulated result
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Figure 4.7 The comparison of the reference and present simulated electric field
distributions at 1 m above ground under high voltage overhead transmission lines.
4.7.2 Electromagnetic field distribution
The electromagnetic field propagates to the environment around the
transmission line conductors. Figure 4.8 (a) and 4.8 (b) show the simulation results of
electric field distributions which are emitted from 500 kV overhead transmission lines
with frequency 50 Hz of single-circuit and double-circuit, respectively. The arrows in
figure 4.8 are shown the direction of the electric field due to gradient of electrical
potential around transmission lines in the plane. It can be seen that the direction is from
conductors to ground. It is seen that the electric field intensity in the area between phase
line conductors is very high when compare with the area under transmission line
conductors. This is because of the electric field due to gradient of electrical potential in
equation (4.3) shows that it depends on the distance from transmission line conductors.
The intensity of time-harmonic electric field is not change at any point in the area as
shown in equation (4.6). Thus, the magnitude of electric field due to high-voltage
overhead transmission lines and extremely low frequency is constant at each point.
0
2
4
6
8
10
12
14
-35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35
Ele
ctri
c fi
eld (
kV
/m)
Distance from mid-tower (m)
Reference
Present
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a) Single-circuit
b) Double-circuit
Figure 4.8 The electric field distributions due to overhead transmission lines
Figure 4.9 shows that the electric field distributions at some levels above
ground under overhead transmission lines. It is seen that the average electric field
intensities at the level near the phase conductors are higher than that of the level near
the ground. For the maximum electric fields, at the levels near the ground occur at the
same place at the middle of the transmission lines but at the levels near the conductor
lines occur beneath the conductor lines. The average and the maximum electric field
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intensity distributions due to the double-circuit are higher than that of single-circuit but
not much.
The human body model has the height of 1.80 m. The effects inside human body
are caused by the electric field intensity in range 1 m to 2 m above ground. Table 2
shows the comparison of the averages and the maximum of electric field intensity at
each height above ground. The average electric intensities at the levels from 1 m to 2 m
are in the range of 5.95 – 11.90 kV/m for single-circuit and 6.49-13.10 kV/m for double-
circuit. The maximum electric field intensities at the levels from 1 m to 2 m are in the
range of 10.55 – 21.12 kV/m for single-circuit and 10.92-22.08 kV/m for double-circuit.
The guidelines for limiting exposure to electric field for occupational and general public
exposures which set by ICNIRP are 10 kV/m and 5 kV/m, respectively. It is seen that
the maximum incident electric field on human body model which stands under 500 kV
overhead transmission lines at mid-span is higher than that of safety limit for both of
occupational and general public exposures.
Figure 4.9 Electric field distributions under high-voltage overhead transmission lines
0
25
50
75
100
125
150
175
200
225
-35 -25 -15 -5 5 15 25 35
Ele
ctr
ic f
ield
(k
V/m
)
Distance from the center of tower at mid-span
single-circuitdouble-circuit
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4.7.3 Electric field distribution inside human body
Human body is standing under high-voltage overhead transmission lines at
mid-span. Because of the height of human body model is 1.80 m, the maximum incident
electric field on human body model due to these transmission lines in the levels in range
of 1 m to 2 m above the ground are 10.55 – 21.12 kV/m for single-circuit and 10.92-
22.08 kV/m for double-circuit as shown in Table 4.2. The effects inside human body
due to the electric field from double-circuit are selected to investigate because the
electric field intensities are higher than that of single-circuit at the same level. Because
the human body is ground when compare to high-voltage overhead transmission lines,
the direction of incident electric field perpendicular to the surface of human body model
as shown in figure 4.10 (a). The behavior of biological tissues exposed to extremely low
frequency is electrolytic conductor. The electric charges inside the biological tissues
will be move to the surface of each tissue response to the electric field. The amount of
electric charges inside each tissue organ will be reduced because they can be trapped at
the interface of tissue organs when exposed to extremely low frequency. The induced
electric field will be occurred inside tissue organs because of the electric charges which
are trapped on the surface. Figure 4.10 (b) shows the intensities of induced electric field
of each organ inside human body. It is seen that the intensities are very high at the
surface of each organ while are vanished inside organs, because almost of electric
charges are trapped on the surfaces at the extremely low frequency. For the large organs,
the electric charges can be trapped on the surface less than the small organs because the
distance of charge carrier between the surfaces of each organ is longer than that of small
organ. Some of them will be moved back to inside organ before strike the surface due
to alternating of electromagnetic field 50 Hz. Thus, the induced electric fields of small
organs are higher than large organs as shown in figure 4.10 (b).
For the behavior of biological tissue organs, it is not only electrolytic
conductor but also insulator at the same time. The electric field inside human body
model of each organ can be reduced by relative permittivity which is shown in Table
4.1. The induced electric field of each organ inside human body can be calculated by
equation (4.8). The maximum induced electric field are occurred on the top of both
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lungs, 253.98 V/m. This is because there are a lot of charge carriers in the large area
between collarbones move to the surface of neck and both of lungs and they have high
incident electric field. While the maximum electric field intensity on intestine is lower
than other organs, 15.79 V/m, because the incident electric field is low and it has large
organ.
Table 4.2 Average and maximum electric fields under overhead transmission lines at
each height above ground both of single-circuit and double-circuit
h (m)
Average electric field
(kV/m)
Maximum electric field
(kV/m)
Single Double Single Double
1 5.95 6.49 10.55 10.92
2 11.90 13.10 21.12 22.08
3 17.87 19.49 31.77 32.80
5 29.85 32.56 53.43 54.79
7 41.91 45.76 76.03 77.61
10 60.27 65.90 115.20 118.25
13 77.96 85.94 198.31 204.30
(a) (b)
Figure 4.10 Induced electric field inside human body
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4.7.4 Current density distribution inside human body
The induced current densities are conduction current density resulting by the
transport of charges of each organ due to induced electric field which is given by
equation (4.9). The current densities are occurred on the interface of each organ.
Although the induced electric field intensity on the organ is high, it is not meant the
current density is high too because the electrical conductivities of each tissue are
different. Figure 4.11 shows the maximum current density on the organs inside human
body model. The maximum current densities on the surface of the body on the top of
lungs, brain, lungs, heart, liver and intestine are 54.86, 5.97, 3.78, 4.92, 3.64 and 8.24
A/m2, respectively.
Figure 4.11Current density inside human body
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4.7.5 Comparison distribution patterns between electric field and current
density on several organs inside human body
Figure 4.12 shows the extrusion lines inside human body at the level of 0.92,
1.10, 1.38 and 1.52 m above ground for comparison the distribution patterns between
the electric field and current density inside human body model at same level. The
maximum electric field is occurred on the surface of each organ because charges are
accumulated from another organ at the interface of them. For current density, it depends
on electrical conductivity and electric field intensity of each organ inside human body
as show in equation (4.9).
Figure 4.12 The extrusion lines at 4 levels inside human body
Figure 4.13 shows the extrusion line at the level 0.92 m. It passes arms, body
and intestine. The maximum electric field intensities in this line occur on the surface of
body both of the interfaces with intestine and skin. They are very low in the internal of
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each organ as shown in figure 4.13 (a). The pattern distribution of current density does
not much different from the pattern distribution of electric field. But the maximum
current density on the surface of body at the interfaces with intestine are a little bit
higher than that of skin as shown in figure 4.13 (b). This is because the electrical
conductivity of intestine and body are higher.
Figure 4.14 shows the extrusion line at the level 1.10 m. It passes arms, liver
and body. The maximum electric field intensities in this line occur on the interfaces
between liver and body as shown in figure 4.14 (a). It is seen that the electric field on
the surface of body at the interface with air on the right side is higher than that of the
left side. This is because the area of body on the right side is much larger than the left.
Charge carriers in the body on the right can be moved to surface much more than the
left. For the current density pattern in Fig.14 (b), it tends to electric field pattern, except
at the surface on the left side of liver. The current density on the surface of liver is very
low when compared with the current density of the body, because electrical conductivity
of liver very low.
Figure 4.15 shows the extrusion line at the level 1.38 m. It passes arms, lungs
and body. The maximum electric field intensities in this line occur on the interfaces
between body and lungs at the top of lung as shown in figure 4.15 (a). It is seen that the
electric field intensities inside lungs at the top position and the area between both of
lungs do not vanish. This is because the shape on the top of lungs are sphere, charges
can be trapped higher than that the straight surface. While the electric field intensity in
area between both of lungs is not vanish because it is near the heart. The current density
pattern tends to electric field pattern, except it drops inside the lungs as shown in figure
4.15 (b). This is because lungs have low conductivity.
Figure 4.16 shows the extrusion line at the level 1.52 m. It passes only body
at neck and shoulder. It is seen that the maximum electric field intensity occurs on the
neck because of the charges which are moved from the area between collarbones as
shown in figure 4.16 (a). The current density pattern is the same as electric field pattern
because it occurs inside only one organ as seen in figure 4.16 (b).
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a) Electric field b) Current density
Figure 4.13 The distribution patterns inside human body at the height 0.92 m above
ground
a) Electric field b) Current density
Figure 4.14 The distribution patterns inside human body at the height 1.10 m above
ground
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a) Electric field b) Current density
Figure 4.15 The distribution patterns inside human body at the height 1.38 m above
ground
a) Electric field b) Current density
Figure 4.16 The distribution patterns inside human body at the height 1.52 m above
ground
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4.8 Conclusions
This work is studied the distribution of electric field which are emitted from
high-voltage overhead transmission lines with 500 kV and 50 Hz both of single-circuit
and double-circuit configurations. These electric field can affect to the biological in the
area of this field. The human body model which have internal sevral organs is selected
to investigate the effect from the electric field. The induced electric fied and induced
current density distributions on several organs inside human body model which is
standing under overhead transmission lines at mid-span are investigated.
For the distribution of electric field intensities which are emitted from high-
voltage overhead transmission lines, the average intensities in the area under
transmission line conductors depend on the distance from the transmission line
conductors for both of configurations. It is high intensity in the level near the phase line
conductors and it is lower at the level near the ground. The average electric field
intensities from single-circuit is lower than that of double-circuit at each level but not
too much. This is because of the electric field depends on the voltage of transmission
lines, it is not depend on configuration. The maximum electric field at the level near the
ground occur at the middle between phase lines of tower but occur beneath the phase
line conductors at the high level near the phase line. The maximum electric fields on
human body model at mid-span of configurations are 10.55 – 21.12 kV/m for single-
circuit and 10.92-22.08 kV/m for double-circuit. This electric field intensity exceeds
the guideline of safety limiting electric field exposure for occupational and general
public exposure which set by ICNIRP, 10 kV/m and 5 kV/m, respectively.
The incident electric field will be reduced inside human body model because of
the relative permittivity of tissue organs. This electric field can induce the internal
electric field inside human body model because it behaves electrolytic conductor and
insulator at the same time. The induced electric field is proportional to electric charges
which are trapped on the surface of each organ. The intensity of small organs is higher
than large organs because the electric charges of small organs can be trapped at the
surface more than large organs. The maximum induced electric field intensity inside
human body is 253.98 V/m, it is occurred at the body on the top of lungs.
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In extremely low frequency, induced current density is most important for the
biological effects. The guideline of safety limiting current density for occupational and
general public exposure were set by ICNIRP, 10 mA/m2 and 2 mA/m2, respectively. It
depends on electric field intensity and electrical conductivity of each tissue. Figure 13-
16 show that the induced current densities are occurred at the interface of each organ
the same as electric field. The maximum induced current density is not depends on
electric field intensity only but it depends on electrical conductivity of each organ. The
maximum induced current density inside human body is 54.86 A/m2, it is occurred in
the interface between body and lungs at the top of lungs. This is because they have high
induced electric field intensity and electrical conductivity. Although the induced electric
field intensity on intestine is lowest but the maximum induced current density is higher
than that of other organs, except body region. This is because the electrical conductivity
of intestine is highest when compare with the others. However, the maximum induced
current density which is occurred inside human body for all organs are much less than
the guideline of safety limiting current density for occupational and general public
exposure which set by ICNIRP.
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CHAPTER 5
OVERALL CONCLUSIONS
This study presents the numerical simulation of the biological effects on
several organs inside human body exposed to electromagnetic wave with frequency in
range of non-ionizing radiations. Some of the organs in the human trunk such as skin,
muscle, fat, bladder, intestines, heart, lungs, liver and brain are selected to investigate
the biological effects due to electromagnetic wave. The effects on biological tissues
depend on the frequency of electromagnetic wave. The behavior of biological tissues
exposed to high frequency is insulator while extremely low frequency is conductor. This
is because the biological tissue properties, conductivity and permittivity, are varied with
frequency of the electromagnetic wave. Thus, the biological effect on tissues exposed
to high frequency is heat inside tissues and induced current density for extremely low
frequency.
For the high frequency of electromagnetic wave, the source of wave is
microwave. The effects of physical parameters such as operating frequency, power
density, and exposure time, on distribution of specific absorption rate (SAR) and
temperature profiles within each organ inside human body are systematically
investigated. The selected operating frequencies are 300 MHz, 915 MHz, 1300 MHz
and 2450 MHz. The selected power densities are 10 W, 50 W, and 100 W. The slected
exposure times are 5, 10, 20, 30, 40,50 60 minutes. The results show that the maximum
temperature are approch to steady after 5 minutes of exposure time, it depends on the
power of electromagnetic wave. This study, the influence of wave propagation in
transverse electric field polarization (TE mode) and transverse magnetic field
polarization (TM mode) are considered. The conclusions of the SAR and temperature
distributions on several organs inside human body exposed to high frequency of
electromagnetic wave both of TE and TM polarizations can be summarized as:
- For TE polarized consideration, the maximum SARs occur at
skin for all frequencies, except at the frequency 300 MHz. It occurs at muscle for 300
MHz because it has high penetration depth. The maximum temperatures in the human
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body occur at the contiguous organs of the organs which have the maximum SAR,
because of heat transfer of these organs. They occur at bladder from the frequency 300
MHz and fat from the frequencies of 915 MHz, 1300 MHz and 2450 MHz for all powers
of electromagnetic wave. These organs has the lareg size, the effect of heat is increasing
of temperature more than transfer to other organs.
- For TM polarized consideration, the maximum SARs occur at fat
for all frequencies because of the resonance of electric field standing wave on fat. The
maximum temparetures from the frequencies of 915 MHz, 1300 MHz and 2450 MHz
for all powers of electromagnetic wave occur at skin. This is because fat is a tiny region
at the position of the maximum SAR. For the frequency of 300 MHz, the maximum
temperature still occurs at fat. This is because it has very high SAR and the large size
of fat.
Moerover, the maximum SAR values are proportional to the power of
electromagnetic wave but the power of electromagnetic wave is not affected to the
organs which have the maximum SAR, it is the same organ for all frequencies and
propagated polarizations even though the power of electromagnetic wave is increasing.
The temperature distribution is not related only electric field, but the dielectric property,
thermal property, blood perfusion and penetration depth of organs at each frequency of
electromagnetic wave are significant too. However, the propagated polarization of
electromagnetic wave is important to cause the SAR and tempertaure distributions. The
electromagnetic wave at frequency 300 MHz which is propagated in TE polarization is
little affected to SAR and temperature distributions in human body, while 300 MHz in
TM polarization is significant to cause the SAR and temperature distributions.
For the extremely low frequency of electromagnetic wave, the source of wave
is high-voltage overhead transmission lines, 500 kV and 50 Hz. The configurations of
overhead transmission lines are single-circuit and double-circuit with three phases. The
biological effect on organs inside human body is current density due to the incident
electric field intensity on each organ. It is found that the average electric field intensities
in the area under overhead transmission lines depend on the distance from the
transmission line conductors for both of configurations. The average electric field
intensities from single-circuit is lower than that of double-circuit at each level but not
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too much. This is because of the electric field depends on the voltage of transmission
lines, it is not depend on configuration. The maximum electric field at the level near the
ground occur at the middle between phase lines of tower but occur beneath the phase
line conductors at the high level near the phase line. This electric field intensity exceeds
the guideline of safety limiting electric field exposure for occupational and general
public exposure which set by ICNIRP.
In extremely low frequency, induced current density is most important for the
biological effects. The maximum induced current density is not depends on electric field
intensity only but it depends on electrical conductivity of each organ. The maximum
induced current density inside human body is 54.86 A/m2, it is occurred in the interface
between body and lungs at the top of lungs. This is because they have high induced
electric field intensity and electrical conductivity. Although the induced electric field
intensity on intestine is lowest but the maximum induced current density is higher than
that of other organs, except body region. This is because the electrical conductivity of
intestine is highest when compare with the others. However, the maximum induced
current density which is occurred inside human body for all organs are much less than
the guideline of safety limiting current density for occupational and general public
exposure which set by ICNIRP.
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CHAPTER 6
RECOMMENDATIONS FOR FUTURE WORK
In this study, the biological effects on several organs inside human body
exposed to electromagnetic wave are simulated using the finite element method (FEM)
via COMSOLTM Multiphysics program. It demonstrates the phenomenon occurs within
the human body exposed to electromagnetic wave with frequency in range of non-
ionizing radiation. The sources of electromagnetic wave are microwave, high
frequency, and high-voltage overhead transmission lines, extremely low frequency.
There is no considered the effects due to electromagnetic wave which is middling
frequency between those frequencies. The organs inside human body models are two
dimensions with constant dielectric and thermal properties. However, the biological
tissues are functional to the frequency of electromagnetic wave. In case of extremely
low frequency, the organs inside human body model are not realistic, they are ideal
geometric shapes. Thus, it may be affected the accuracy of the simulation results. For
future work, some ideas will be added for studying the biological effects from
electromagnetic wave with frequency in range of non-ionizing radiations. They can be
summarized as follows:
1. The three dimensions will be used in this study.
2. The effects from middling frequency of electromagnetic wave in
range of non-ionizing radiation will be considered.
3. The organs inside human body model are realistic.
4. The frequency-dependent dielectric properties of human tissues are
needed.
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REFERENCES
Articles
P. Rattanadecho, N. Suwannapum, and W. Cha-um, Interactions Between
Electromagnetic and Thermal Fields in Microwave Heating of Hardened Type
I-Cement Paste Using a Rectangular Waveguide (Influence of Frequency and
Sample Size), ASME J. Heat Transfer, 131, 2009, p. 082101.
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buildup induced inside unsaturated porous media subjected to microwave
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Liver Cancer Modeling Treated Using a Microwave Coaxial Antenna, Applied
Thermal Engineering, 31(16), November 2011, pp. 3243-3254
P. Keangin, T. Wessapan, and P. Rattanadecho, An Analysis of Heat Transfer in Liver
Tissue During Microwave Ablation Using Single and Double Slot Antenna,
International Communications in Heat and Mass Transfer, 38, 2011, pp.
757-766
T. Wessapan, S. Srisawatdhisukul, and P. Rattanadecho, Numerical Analysis of
Specific Absorption Rate and Heat Transfer in the Human Body Exposed to
Leakage Electromagnetic Field at 915 MHz and 2450 MHz, Journal of Heat
Transfer, 133(5), 2011, pp. 051101.1-13
T. Wessapan and P. Rattanadecho, Specific Absorption Rate and Temperature Increase
in Human Eye Subjected to Electromagnetic Fields at 900 MHz, ASME journal
of Heat Transfer, 2011
T. Wessapan, S. Srisawatdhisukul, and P. Rattanadecho, Specific Absorption Rate and
Temperature Distributions in Human Head Subjected to Mobile Phone
Radiation at Different Frequencies, International journal of Heat and Mass
Transfer, 55 (1-3), 2012, pp. 347-359
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T. Wessapan, S. Srisawatdhisukul, and P. Rattanadecho, The effects of dielectric Shield
on specific Absorption Rate and Heat Transfer in The Human Body Exposed to
Leakage Microwave energy, International Communications in Heat and
Mass Transfer, 38, 2011, pp. 255-262
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Surrounding an Energy Transmitting Coil for a Wireless Capsule Endoscope,
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Proceeding of The 6th International Conference on Properties and
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PUBLICATIONS
Conferences
Siriwitpreecha A., Wessapan T., and Rattanadecho P., Computational Analysis of SAR
and Temperature Distribution in Human Body Exposed to Microwave, The
second TSME International Conference on Mechanical Engineering
(TSME-ICoME), 19-21 October, 2011, Krabi, Thailand
Siriwitpreecha, A., Rattanadecho, P. and Wessapan, T., Comparison of SAR
Distribution inside Human Body Exposed to EM Wave between TM and TE
Mode at 300 MHz, Siam Physics Congress SPC 2012, 9-12 M a y , 2 0 1 2 ,
Ayuthaya, Thailand
Siriwitpreecha, A., and Rattanadecho, P., Analysis of Electric Field Distribution and
Induced Current Density on Human Body due to 500 kV Overhead
Transmission Lines, Siam Physics Congress SPC 2013, 21-23 Ma rch, 201 3,
Chiangmai, Thailand
Siriwitpreecha, A., and Rattanadecho, P., Numerical Analysis of Current Density inside
Human Body Exposed to Electric Field under HV and ELF Transmission Lines,
Siam Physics Congress SPC 2014, 26-29 M a rch, 2 0 14, Nakhonratchasima,
Thailand
Siriwitpreecha, A., and Rattanadecho, P., Analysis of Biological Effect inside Human
Body Exposed to Extremely Low Frequency due to Overhead Transmission
Lines, Siam Physics Congress SPC 2015, 20-22 May, 2011, Krabi, Thailand
International Journals
Siriwitpreecha, A., Rattanadecho, P. and Wessapan, T., The influence of wave
propagation mode on specific absorption rate and heat transfer in human body
exposed to electromagnetic wave, International Journal of Heat and Mass
Transfer, Vol.65, pp.423-434, 2013.
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Sirwitpreecha A. and Rattanadecho P., Numerical Analysis of Biological Effects on
Several Organs inside Human Body Exposed to Electric Field from 500 kV
OHTLs, Songklanakarin Journal of Science and Technology, (Submitted)
Sirwitpreecha A. and Rattanadecho P., Numerical Analysis of Electric Field and
Current Density on Several Organs inside Human Body due to 500 kV Overhead
Transmission Lines, Computational and Applied Mathematics, (Submitted)
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BIOGRAPHY
Name Apichart Siriwitpreecha
Date of birth 10 January, 1973
Education profiles Bachelor of Science in Physics (B.Sc)
Prince of Songkla University, 1995
Master of Science in Nuclear Technology (M.Sc.)
Chulalongkorn University, 1999
Work experience 1999 – 2006: Lecturer, Department of Industrial
Physics and Medical Instrumentation, Faculty of
Applied Science, King Mongkut’s University of
Technology North Bangkok
2006 – present: Assistant Professor, Department
of Industrial Physics and Medical Instrumentation,
Faculty of Applied Science, King Mongkut’s
University of Technology North Bangkok
Ref. code: 25595410300163SME