electromagnetic earthing and coupling, electromagnetic shielding

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Mühendislik fakültesi ELEKTRONİK VE HABERLEŞME MÜHENDİSLİĞİ Electromagnetic Shielding A COURSE OFFERED BY Prof. Dr. Mustafa MERDAN Electromagnetic Earthing and Coupling Submitted by MSc. Student Mohammed Mahdi AboAjamm Student No. 1330145006

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Page 1: Electromagnetic earthing and coupling, Electromagnetic Shielding

Mühendislik fakültesi

ELEKTRONİK VE HABERLEŞME

MÜHENDİSLİĞİ

Electromagnetic Shielding

A COURSE OFFERED BY

Prof. Dr. Mustafa MERDAN

Electromagnetic Earthing and Coupling

Submitted by

MSc. Student

Mohammed Mahdi AboAjamm

Student No. 1330145006

Page 2: Electromagnetic earthing and coupling, Electromagnetic Shielding

What is electromagnetic shielding?

EM shielding (electromagnetic shielding) is the practice of

surrounding electronics and cables with conductive or magnetic

materials to guard against incoming or outgoing emissions of

electromagnetic frequencies (EMF).

EM shielding is conducted for several reasons. The most common

purpose is to prevent electromagnetic interference (EMI) from

affecting sensitive electronics. Metallic mesh shields are often used

to protect one component from affecting another inside a particular

device. In a smartphone, for example, a metallic shield protects

electronics from its cellular transmitter/receiver. Radiation shields

in mobile phones also decrease the amount of radio frequency (RF)

energy that might be absorbed by the user.

To increase the security of air gapped systems, EM shielding is

advised. Conventionally, physical isolation and a lack of external

connectivity have been considered adequate to ensure their

security. However, proof-of-concept attacks have demonstrated

that acoustical infection can be enabled by exploiting the

electromagnetic emanations of the system’s sound card.

Air-gapping is used in the military, government and financial

systems like stock exchanges. The measures are also used by

reporters, activists and human rights organizations working with

sensitive information.

A number of different materials and techniques are used for EM

shielding. Wires may be surrounded by a metallic foil or braid

Page 3: Electromagnetic earthing and coupling, Electromagnetic Shielding

shield to block errant EMI from the cased wires. Audio speakers

often have inner metallic casing to block EMI produced by the

drivers so they don’t affect TVs and other electronics. Complete

continuous enclosure is not necessary so long as any openings are

smaller than the electromagnetic waves that need to be blocked.

Special conductive paints can be used to prevent the EMF from

networks escaping the originating business to prevent

eavesdropping or wireless attacks. These techniques are like a

miniature Faraday cage, which can prevent signal corruption that

would cause electronics to perform unexpectedly.

Electronics may also have connections filtered for EMI by use of

electronic components like capacitors, ferrules and grounded wires

to minimize the effects of EMI noise -- even twisting wires

together with grounds can reduce lower interference.

Magnetic materials must be used for EM shielding in environments

where the magnetic fields are slowly varied below the 100Khz

range as a Faraday cage-type solution is ineffective in that

situation. With magnetic materials, the EMI is drawn into the

magnetic field of the shielding.

Page 4: Electromagnetic earthing and coupling, Electromagnetic Shielding
Page 5: Electromagnetic earthing and coupling, Electromagnetic Shielding

Fundamental Concepts

Knowledge of the fundamental concepts of EMI shielding will aid

the designer in selecting the gasket inherently best suited to a

specific design. All electromagnetic waves consist of two essential

components, a magnetic field, and an electric field. These two

fields are perpendicular to each other, and the direction of wave

propagation is at right angles to the plane containing these two

components. The relative magnitude between the magnetic (H)

field and the electric (E) field depends upon how far away the

wave is from its source, and on the nature of the generating source

itself. The ratio of E to H is called the wave impedance, Zw.

If the source contains a large current flow compared to its

potential, such as may be generated by a loop, a transformer, or

power lines, it is called a current, magnetic, or low impedance

source. The latter definition is derived from the fact that the ratio

of E to H has a small value. Conversely, if the source operates at

high voltage, and only a small amount of current flows, the source

impedance is said to be high, and the wave is commonly referred

to as an electric field. At very large distances from the source, the

ratio of E to H is equal for either wave regardless of its origination.

When this occurs, the wave is said to be a plane wave, and the

wave impedance is equal to 377 ohms, which is the intrinsic

impedance of free space. Beyond this point all waves essentially

lose their curvature, and the surface containing the two

components becomes a plane instead of a section of a sphere in the

case of a point source of radiation. The importance of wave

impedance can be illustrated by considering what happens when an

electromagnetic wave encounters a discontinuity. If the magnitude

of the wave impedance is greatly different from the intrinsic

Page 6: Electromagnetic earthing and coupling, Electromagnetic Shielding

impedance of the discontinuity, most of the energy will be

reflected, and very little will be transmitted across the boundary.

Most metals have an intrinsic impedance of only milliohms. For

low impedance fields (H dominant), less energy is reflected, and

more is absorbed, because the metal is more closely matched to the

impedance of the field. This is why it is so difficult to shield

against magnetic fields. On the other hand, the wave impedance of

electric fields is high, so most of the energy is reflected for this

case. Consider the theoretical case of an incident wave normal to

the surface of a metallic structure as illustrated in Figure below. If

the conductivity of the metal wall is infinite, an electric field equal

and opposite to that of the incident electric field components of the

wave is generated in the shield. This satisfies the boundary

condition that the total tangential electric field must vanish at the

boundary. Under these ideal conditions, shielding should be perfect

because the two fields exactly cancel one another. The fact that the

magnetic fields are in phase means that the current flow in the

shield is doubled.

Page 7: Electromagnetic earthing and coupling, Electromagnetic Shielding

Shielding effectiveness of metallic enclosures is not infinite,

because the conductivity of all metals is finite. They can, however,

approach very large values. Because metallic shields have less than

infinite conductivity, part of the field is transmitted across the

boundary and supports a current in the metal as illustrated in

Figure below. The amount of current flow at any depth in the

shield, and the rate of decay is governed by the conductivity of the

metal and its permeability. The residual current appearing on the

opposite face is the one responsible for generating the field which

exists on the other side.

Page 8: Electromagnetic earthing and coupling, Electromagnetic Shielding

RADIO FREQUENCY SHIELDING DEFINITIONS:

In any technical field of knowledge, a certain amount of special

terms unique to that field must be understood in order to

comprehend what is being presented. Therefore, this section is

placed deliberately here in the first chapter so that a working

vocabulary necessary to understanding the material presented can

be easily acquired by those not familiar with shielding prior to the

introduction of the technical concepts. Further definitions and

supporting terminology are given in Appendix A-I.

Absorber a material which absorbs electromagnetic energy by

converting the wave energy into heat.

Absorption Loss The attenuation of an electromagnetic wave as it

passes through a shield. This loss is primarily due to induced

currents and the associated heat loss. Ambient Level. Those levels

of radiated and conducted energy existing at a specified location

and time when a test sample is deenergized. Atmospheric noise

signals, both desired and undesired, from other sources and the

internal noise level of the measuring instruments all contribute to

the "ambient level." Antenna. A device employed as a means for

radiating or receiving electromagnetic energy. Aperture. An

opening in a shield through which electromagnetic energy passes.

Attenuation A general term used to denote a decrease in magnitude

of power or field strength in transmission from one point to

another caused by such factors as absorption, reflection, scattering,

and dispersion. It may be expressed as a power ratio or by decibels.

Bond. The electrical connection between two metallic surfaces

established to provide a low-resistance path between them.

Bonding The process of establishing the required degree of

electrical continuity between the conductive surfaces to be joined.

Conductive Interference. Undesired signals that enter or leave an

equipment along a conductive (wire or metallic) path.

Page 9: Electromagnetic earthing and coupling, Electromagnetic Shielding

Coupling Energy transfer between circuits, equipments, or

systems. Coupling, Free-Space. Energy transfer via

electromagnetic fields not in a conductor. Cutoff Frequency. The

frequency below which electromagnetic energy will not propagate

readily in a waveguide. dB. Decibel, a unit of voltage or power

ratio. Defined as follows: dB = 10 log P'21P 1 for power or dB =

20 log V2IVI for voltage. HdB" is commonly used to specify

shielding effectiveness since very large differences in the

input/output fields are generally required by the shielding

specification.

This means that if one watt of power impinges on the shield, then

only one millionth to one ten trillionth of a watt exits on the other

side. Degradation. A decrease in the quality of a desired signal

(i.e., decrease in the signalto- noise ratio or an increase in

distortion), or an undesired change in the operational performance

of equipment as the result of interference.

Earth Electrode System. A network of electrically interconnected

rods, plates, mats, or grids installed for the purpose of establishing

a low-resistance contact with earth.

The design objective for resistance to earth of this subsystem

should not exceed 10 O.

Electric Field. A vector field about a charged body. Its strength at

any point is the force which would be exerted on a unit positive

charge at that point.

Electromagnetic Compatibility (EMC). The capability of

equipment or systems to be operated in their intended operational

environment at designed levels of efficiency without causing or

receiving degradation owing to unintentional electromagnetic

interference.

Electromagnetic compatibility is the result of an engineering

planning process applied during the life cycle of the equipment.

The process involves careful considerations of frequency

allocation, design, procurement, production, site selection,

installation, operation, and maintenance.

Page 10: Electromagnetic earthing and coupling, Electromagnetic Shielding

Electromagnetic Interference (EMI). Any conducted, radiated, or

induced voltage which degrades, obstructs, or repeatedly interrupts

the desired performance of electronic equipment.

Electromagnetic Pulse (EMP). A large impulsive-type

electromagnetic wave generated by nuclear or chemical explosions

Facility A building or other structure, either fixed or transportable

in nature, with its utilities, ground networks, and electrical

supporting structures

Far Field The region of the field of an antenna where the radiation

field predominates, and where the angular field distribution is

essentially independent of the distance from the antenna. A variety

of guidelines is used; for some shielding calculations, 1/6th of a

wavelength has been found useful.

Fault An unintentional short circuit or partial short circuit (usually

of a power circuit) between energized conductors or between an

energized conductor and ground.

Field Strength A general term that means the magnitude of the

electric field vector (in volts per meter) or the magnitude of the

magnetic field vector (in ampere-turns per meter). As used in the

field of EMC/EMI, the term "field strength" shall be applied only

to measurements made in the far field and shall be abbreviated as

FS.

For measurements made in the near field, the term 44electric field

strength" (EFS) or "magnetic field strength" (MFS) shall be used,

according to whether the resultant electric or magnetic field,

respectively, is measured.

Filter. A device for use on power or signal lines, specifically

designed to pass only selected frequencies and to attenuate

substantially all other frequencies.

Ground the electrical connection to earth through an earth

electrode subsystem. This connection is extended throughout the

facility via the facility ground system, consisting of the signal

reference subsystem, the fault protection subsystem, and the

lightning protection subsystem.

Page 11: Electromagnetic earthing and coupling, Electromagnetic Shielding

Noise

In signal processing, noise is a general term for unwanted (and, in

general, unknown) modifications that a signal may suffer during

capture, storage, transmission, processing, or conversion.

Sometimes the word is also used to mean signals that are random

(unpredictable) and carry no useful information; even if they are

not interfering with other signals or may have been introduced

intentionally, as in comfort noise.

The IEEE Standard Dictionary defines noise as unwanted

disturbances superposed upon a useful signal that tend to obscure

its information content. This definition is versatile, since it applies

both to intrinsic and extrinsic noise (intrinsic noise is the noise

generated inside a system, while the term extrinsic noise designates

noise originating elsewhere).

Intrinsic Noise

This term refers to the noise generated inside an investigated

device or circuit. In linear systems the physical origin of noise is

the discrete nature of charge carriers. Consequently, the number of

carriers in some specific plane fluctuates in time. These

fluctuations are both universal and unavoidable.

Page 12: Electromagnetic earthing and coupling, Electromagnetic Shielding

A typical example is thermal noise, originating from the random

motion of free electrons inside a piece of conductive material.

Extrinsic Noise

The sources of extrinsic noise are situated outside the investigated

circuit, which merely acts as a receiving antenna; for this reason

this kind of noise is also called extraneous signals, or spurious

signals, or perturbations. According to its possible origins, two

main categories exist:

Environmental perturbations

such as sky noise (which includes strong broadband noise sources

like the Sun and the Milky Way), atmospheric noise (caused

mainly by lightning discharges in thunderstorms), manmade noise

(due to electric motors, arc welding, power lines, neon signs,

electrostatic discharge, electrical power equipment, radio and TV

broadcast services, motors, switches, spark plugs in ignition

systems, household appliances, cellular telephones, mobile radios,

etc.). All industrial perturbations are characterized by relatively

high amplitudes, and a spectrum that cuts off before reaching

visible wavelengths. Many are regular in form and periodic.

Page 13: Electromagnetic earthing and coupling, Electromagnetic Shielding

Crosstalk noise

Signals which are useful in one circuit, but unfortunately pass via

parasitic coupling into nearby circuits, where they are undesired

and therefore act as perturbations. As a general rule, the user

discovers the interference (i.e., the undesirable effect of spurious

signals) during operation and not before! Sometimes, such

coupling can be reduced by modifying the relative position of

various cables or equipment in a rack.

Thermal Noise

The physical origin of this noise is the thermal motion of free

electrons inside a piece of conductive material, which is totally

random.

Thermal noise is a consequence of the discrete nature of charge

and matter. At a microscopic level, thermal motion is a general

property of matter, regardless of temperature. Physical systems

containing a huge number of identical particles have a large

number of degrees of freedom, corresponding to the number of

ways in which energy can be stored in the system.

Page 14: Electromagnetic earthing and coupling, Electromagnetic Shielding

Diffusion Noise

The physical origin of diffusion noise is carrier velocity

fluctuations caused by collisions.

This noise is related to the diffusion process that results from

nonuniform carrier distribution. If carrier density increases at one

end of a semiconductor (for instance by illumination), it is a

natural tendency for the carriers to move towards the opposite end,

where the population is reduced. This is a diffusion process. Note

that no applied voltage is necessary to sustain it.

However, during their trip the electrons are scattered via collisions

with the lattice or with ionized impurity atoms. As a result, carrier

velocities are modified, and this represents a perturbation of the

regular diffusion tendency. As scattering occurs randomly, the

instantaneous value of the diffusion current is also random. This is

the mechanism of diffusion noise.

Quantum Noise

The quantified (discrete) nature of electromagnetic radiation

represents the fundamental origin of quantum noise. According to

quantum mechanics, electromagnetic energy is radiated or

Page 15: Electromagnetic earthing and coupling, Electromagnetic Shielding

absorbed in small discrete quantities, called photons. The energy of

a photon is related to the frequency of its associated radiation by

E = hf

Where h is Planck’s constant (h = 6.63 • 10−34 Js).

Consider a system exchanging thermal or optical energy with its

environment The bilateral flow of energy between the detector and

its environment has a fluctuation, according to the random number

of photons released or absorbed per second. This is called quantum

noise.

External Noise Sources

External noise sources can be grouped into two categories:

Natural noise sources,

Man-made noise sources.

Natural Noise Sources

For convenience, atmospheric noise, precipitation static, solar

noise, Galactic noise and hot-Earth noise are all grouped together

under ―Sky noise.‖ In practice, all quoted noise sources combine

with the celestial background in the radiation pattern of the

Page 16: Electromagnetic earthing and coupling, Electromagnetic Shielding

receiving antenna. Magnetic storms induced by solar flares have

the ability to induce damaging surges in power-line voltage,

destroying electrical equipment over a huge area. They also

dramatically affect signal propagation and sky noise.

Atmospheric Noise

This is defined as noise having its source in natural atmospheric

phenomena, mainly lightning discharges in thunderstorms. Their

location is time-variable, depending on time of the day, season of

the year, weather, altitude, and geographical latitude. As a general

rule, they are more frequently encountered in the equatorial region

than at temperate latitudes and above. However, the

electromagnetic waves produced by thunderstorms propagate at

thousands of kilometers via ionospheric sky wave. In the time

domain, this noise is characterized by large spikes against a

background of short random pulses. Its frequency spectrum

extends up to 20MHz and the spectral density is proportional to

1/f. Consequently, it mainly affects long-range navigation systems

(maritime radio), terrestrial radio broadcasting stations (LW, MW,

and SW) and to a considerably lesser extent, FM and TV reception.

Page 17: Electromagnetic earthing and coupling, Electromagnetic Shielding

Precipitation Static

This kind of noise is encountered in rain, snow, hail, and dust

storms in the vicinity of the receiving antenna. Its frequency

spectrum peaks below 10MHz. It can be substantially reduced by

eliminating sharp metallic points from the antenna and its

surroundings, and by providing paths to drain static charges that

build up on an antenna and in its vicinity during storms.

Galactic Noise

This is defined as noise at radio frequencies caused by disturbances

that originate outside the Earth or its atmosphere. Galactic noise

sources can be grouped into two classes: discrete sources and

distributed sources.

In the former category the chief source is the Sun, together with

thousands of known discrete sources, such as supernova remnant

Cassiopeia A, one of the most intense sources of cosmic radio

emission as viewed from Earth. The Sun is the most powerful

noise source, with its temperature of about 6000◦C and its

proximity to Earth. Its energy is radiated in a continuous mode,

and the frequency spectrum mainly covers the range from several

MHz up to several GHz. During quiescent periods, the Sun’s noise

Page 18: Electromagnetic earthing and coupling, Electromagnetic Shielding

temperature is about 700,000K at 200 MHz, and about 6000K at

30GHz. However, during sunspot and solar-flare activity these

values are considerably higher.

The distributed noise sources are the ionized interstellar gas clouds

in our Galaxy and a considerable number of extragalactic sources

known as radio galaxies. Depending on emission mechanisms, the

distributed noise sources are thermal or nonthermal. So-called

thermal noise sources are associated with random encounters of

electrons and ions in gas clouds, mostly ionized hydrogen.

Nonthermal noise sources (also called synchrotron radiation)

involve electrons moving in magnetic fields. This is a general

galactic phenomenon, encountered even in interstellar space.

Automotive Ignition Systems

There are two major sources: spark plugs and the current flowing

through the ignition system. Both are responsible for radiated

electromagnetic energy, which comes in bursts of short duration

pulses (nanoseconds), the burst width ranging from microseconds

to milliseconds. The frequency of the bursts depends on the

number of cylinders in the motor and the angular motor speed

(RPM). It can be reduced by using spark plugs with a built-in

Page 19: Electromagnetic earthing and coupling, Electromagnetic Shielding

interference suppressor and shielding the entire ignition system

(when possible).

Arc Welders

Typically, arc welders use an RF arc whose fundamental frequency

is around 2.8MHz . Their spectrum covers the 3 kHz to 250MHz

frequency range, but the fundamental remains at a significant level

even at a distance of several hundred meters. In radio receivers,

this noise is perceived as a ―frying‖ noise. The emission is

considerably reduced by improving welder grounding, using short

welding leads, shielding wiring, and avoiding proximity to power

lines.

Electric Motors

All high-power motors involved in electric transport systems

(underground, trains, conveyor belts, elevators, etc.) generate noise

when switched, but also do so in steady-state operation. Switching

produces transients which can reach several hundred volts as a

result of current interruption in an inductive load. In the steady

state, motor brushes are responsible for arc production, which

increases with aging. Besides radiation, these sparks generate

spurious signals that are conducted and distributed to nearby

Page 20: Electromagnetic earthing and coupling, Electromagnetic Shielding

systems by the power supply lines. The same problem (although

less aggressive) appears in all household appliances that use

electric motors (washing machines, vacuum cleaners, ventilators,

etc.). This noise can be reduced by inspecting the motor brushes

and changing them when necessary, as well as by adding a

capacitor of about 1 μF in parallel, to suppress sparks.

High-Voltage Transmission Lines

Noise from transmission lines peaks at 50 (60) Hz, and it can cause

interference at distances of several hundred meters. It is especially

perceptible in AM receivers. Transients associated with switching

of loads occur in bursts, and have rise times of a few nanoseconds;

amplitude spikes larger than 2KV are seldom observed. Another

major source of noise is the Corona effect, which consists in a

large number of discharges around the conductors of a power line.

This occurs when the electric field around the conductor exceeds

the value required to ionize the ambient gas (air), but is insufficient

to cause a spark. Discharges are initiated by the presence of small

irregularities in the conductor surface (like dust, pollen, snow, ice

crystals, etc.) and the resulting noise mainly affects AM

communication systems.

Page 21: Electromagnetic earthing and coupling, Electromagnetic Shielding

AC Supply Lines

The 220 (or 110)V supply lines connect all the rooms of a building

in a power distribution network, as well as all nearby buildings.

Besides its proper 50 (or 60) Hz fields and the transients caused by

switching various loads, the mains wiring constitutes an excellent

antenna, which picks up noise radiated in one room from

perturbing equipment and delivers it to all other rooms sharing the

same line. Hence, it propagates perturbations from one site to

another. In order to protect sensitive equipment, filters and surge

suppressors must be provided so that the bulk of energy is

absorbed before it claims victims. Various types of surge

suppressors exist, such as gas-discharge devices (which can handle

high power, but are slow) and semiconductor devices (using Zener

diodes).

Noise is generated in two distinct areas:

1) In the ionized gas column, which presents a small but

fluctuating resistance when the light is on?

2) In the associated circuitry, which includes a starter. Usually, the

starter is made of a bimetallic strip, which bends when the

temperature changes and abruptly breaks the current flowing

Page 22: Electromagnetic earthing and coupling, Electromagnetic Shielding

through an inductor. A voltage spike occurs, which is used to

trigger the discharge; however, this spike is also a source of

interference for nearby systems.

ISM Equipment

This category includes industrial equipment (such as relay-

controlled devices, electrical switching gear, laser cutters,

microwave ovens, etc.), scientific equipment (for instance, all sorts

of computer facilities), and medical equipment for intensive care

units, physical therapy facilities, electrosurgical units, diathermy,

CAT scanners, etc. The frequency spectrum of these noise sources

can extend up to several megahertz or even gigahertz.

Radio, Television, and Radar Transmitters

These are intentional emitters of electromagnetic waves that can

interfere with systems not intended for any form of reception. All

such transmitters have considerable power, since they must cover a

large area. Less powerful (but no less harmful) are electromagnetic

waves emitted by CB transmitters, cellular phones, mobile radios,

portable computers, and so forth.

Page 23: Electromagnetic earthing and coupling, Electromagnetic Shielding

Power Supplies

The major noise sources belonging to this category are DC/DC

converters and switching-mode power supplies. Both employ

switching transistors operating at frequencies up to 100 kHz. The

frequency spectrum is dominated by the fundamental and its

harmonics, but it extends well above the switching frequency

fundamental.

Triboelectric effect

This entails generating electrostatic charges of opposite sign when

two materials are rubbed together and separated, leaving one

positively charged and the other negatively charged. The term

triboelectricity refers to electricity produced by friction of two

dissimilar solids (as by sliding). In practice, this phenomenon

affects mainly the dielectric material within a coaxial cable. When

the cable bends, the metallic conductors slide along the dielectric

used to separate them (if the dielectric does not maintain

permanent contact with the metallic parts). A charge accumulation

appears in the equivalent capacitor formed between the metallic

shield and the inner conductor, separated by the insulator. This

Page 24: Electromagnetic earthing and coupling, Electromagnetic Shielding

charge fluctuates according to the rhythm of mechanical flexing of

the cable and hence acts as a noise source. This phenomenon is

especially pertinent when the coaxial cable is used to connect a

generator with high internal impedance to a high-value load (like

an electrometer). In this situation, the discharge of the equivalent

capacitor through the terminal impedances is slow, and additional

flexing of the cable causes additional charge to accumulate. For

instance, a coaxial cable terminated by 10-MΩ resistances

generates noise voltages by intermittent flexing which fluctuate

during 50% of the monitoring time around a few millivolts;

however, if the terminal resistances are lowered to 1MΩ, the noise

voltage level decreases to several hundred microvolts. If the cable

is terminated by low impedances, triboelectricity is no longer a

factor.

This kind of noise is critical in cables employed in vehicles,

satellite or airborne instruments, rockets, and military applications,

where vibration is unavoidable. The best solution is to reduce

vibration whenever possible; otherwise, special low-noise cable

can be used, where friction is reduced by an additional layer of

graphite.

Page 25: Electromagnetic earthing and coupling, Electromagnetic Shielding

Piezoelectric Effect

This is defined as the generation of a potential difference in a

crystal when a strain is introduced. In piezoelectric materials the

converse effect is also observed, namely that a strain results from

the application of an electric field. In practice, some circuit board

materials exhibit this effect. Consequently, they are vibration-

sensitive, and noise voltages can appear between conductors

connected to opposite sides, or between tracks situated on opposite

sides. To avoid this kind of noise, the only solution is to carefully

select circuit boards employing insulators that do not exhibit the

piezoelectric effect.

Noise Parameters

Normalized Power

Let us denote by V the effective (rms) value of the signal v(t)

applied across a resistor R. In this case the power dissipated is

P = V2/ R = RI2

Where I is the effective (rms) value of the current through the

resistor. By definition, the normalized power is the power

dissipated by a one-ohm resistance.

Page 26: Electromagnetic earthing and coupling, Electromagnetic Shielding

Noise Bandwidth

Is the bandwidth ( Δf ) of an ideal circuit (with rectangular power

transfer characteristic) such that the total transmitted noise power

is equal to that transmitted by the actual circuit.

IEEE Definition: the equivalent noise bandwidth is the frequency

interval, determined by the response frequency characteristics of

the system, that defines the noise power transmitted from a noise

source of specified characteristics.

Equivalent noise resistance

The equivalent noise resistance Rn is a quantitative representation

in resistance units of the spectral density Sv of a noise voltage

generator at a specified frequency.

And the relation between the equivalent noise resistance and the

spectral density Sv of the noise generator is

Rn = (πSv) / kTo

With To = 290 K.

Page 27: Electromagnetic earthing and coupling, Electromagnetic Shielding

Noise Ratio

The noise ratio N of a one-port is the ratio of: (1) the noise spectral

density (or mean square value) generated by the actual one port, to

(2) the same quantity generated by a hypothetical one-port of

identical impedance which produces only thermal noise.

Signal-to-Noise Ratio

The S/N ratio is the ratio of the value of the signal to that of the

noise (the two being expressed in a consistent way, as for example

peak signal to peak noise ratio, rms signal to rms noise ratio, peak-

to-peak signal to peak-to-peak noise ratio, etc.).

An exception occurs in television transmission, where the S/N ratio

is defined as the ratio of: (1) the maximum peak-to- peak voltage

of the video signal, including synchronizing pulse, to (2) the rms

value of the noise (because of the difficulty of defining the rms

value of the video signal or the peak-to-peak value of random

noise).

Page 28: Electromagnetic earthing and coupling, Electromagnetic Shielding

What is the earhing(grounding) system?

The electric potential of the conductors relative to the Earth's

conductive surface. The choice of earthing system can affect the

safety and electromagnetic compatibility of the power supply. In

particular, it affects the magnitude and distribution of short circuit

currents through the system, and the effects it creates on equipment

and people in the proximity of the circuit. If a fault within an

electrical device connects a live supply conductor to an exposed

conductive surface, anyone touching it while electrically connected

to the earth will complete a circuit back to the earthed supply

conductor and receive an electric shock.

Regulations for earthing system vary considerably among

countries and among different parts of electric systems. Most low

voltage systems connect one supply conductor to the earth

(ground).

A protective earth (PE), known as an equipment grounding

conductor in the US National Electrical Code, avoids this hazard

by keeping the exposed conductive surfaces of a device at earth

potential. To avoid possible voltage drop no current is allowed to

flow in this conductor under normal circumstances. In the event of

a fault, currents will flow that should trip or blow the fuse or

circuit breaker protecting the circuit. A high impedance line-to-

ground fault insufficient to trip the overcurrent protection may still

trip a residual-current device (ground fault circuit interrupter or

GFCI in North America) if one is present. This disconnection in

the event of a dangerous condition before someone receives a

shock, is a fundamental tenet of modern wiring practice and in

many documents is referred to as automatic disconnection of

supply (ADS). The alternative is defence in depth, where multiple

independent failures must occur to expose a dangerous condition -

reinforced or double insulation come into this latter category.

Page 29: Electromagnetic earthing and coupling, Electromagnetic Shielding

In contrast, a functional earth connection serves a purpose other

than shock protection, and may normally carry current. The most

important example of a functional earth is the neutral in an

electrical supply system. It is a current-carrying conductor

connected to earth, often, but not always, at only one point to avoid

flow of currents through the earth. The NEC calls it a groundED

supply conductor to distinguish it from the equipment groundING

conductor. Other examples of devices that use functional earth

connections include surge suppressors and electromagnetic

interference filters, certain antennas and measurement instruments.

Page 30: Electromagnetic earthing and coupling, Electromagnetic Shielding

The main reason for doing earthing in electrical network is for the

safety. When all metallic parts in electrical equipments are

grounded then if the insulation inside the equipments fails there are

no dangerous voltages present in the equipment case. If the live

wire touches the grounded case then the circuit is effectively

shorted and fuse will immediately blow. When the fuse is blown

then the dangerous voltages are away.

Page 31: Electromagnetic earthing and coupling, Electromagnetic Shielding

Purpose of Earthing:

1. Safety for Human life/ Building/Equipment:

a. To save human life from danger of electrical shock or

death by blowing a fuse i.e. To provide an alternative path

for the fault current to flow so that it will not endanger the

user

b. To protect buildings, machinery & appliances under fault

conditions.

c. To ensure that all exposed conductive parts do not reach a

dangerous potential.

d. To provide safe path to dissipate lightning and short

circuit currents.

e. To provide stable platform for operation of sensitive

electronic equipments i.e. To maintain the voltage at any

part of an electrical system at a known value so as to

prevent over current or excessive voltage on the

appliances or equipment .

2. Over voltage protection:

Lightning, line surges or unintentional contact with

higher voltage lines can cause dangerously high

voltages to the electrical distribution system. Earthing

provides an alternative path around the electrical

system to minimize damages in the System.

Page 32: Electromagnetic earthing and coupling, Electromagnetic Shielding

3. Voltage stabilization:

There are many sources of electricity. Every

transformer can be considered a separate source. If

there were not a common reference point for all these

voltage sources it would be extremely difficult to

calculate their relationships to each other. The earth is

the most omnipresent conductive surface, and so it was

adopted in the very beginnings of electrical distribution

systems as a nearly universal standard for all electric

systems.

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In a high-tech age, why is the concept of Earthing so

important?

What is most profound about Earthing is that it is so natural and

simple, and that it affects every aspect of human physiology. When

you ground yourself, the entire body readjusts to a new level of

functioning, the level, in fact, it seems to have been designed for

throughout evolution. Many people who have lived Earthed for

some years say that they do not want to go back to living

ungrounded. They feel the difference. Living Earthed broadly

elevates your quality of life to a level that seems not otherwise

possible.

Why does the Earth’s electric field transfer so easily to the

body?

The body is mostly water and minerals. It is a good conductor of

electricity (electrons). The free electrons on the surface of the

Earth are easily transferred to the human body as long as there is

direct contact. Unfortunately, synthetically-soled shoes act as

insulators so that even when we are outside we do not connect with

the Earth’s electric field. When we are in homes and office

buildings, we are also insulated and unable to receive the Earth’s

balancing energies.

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What is the difference between the Earth’s electric field and

the electric field used to conduct electricity in my home?

The Earth’s electric field is mainly a continuous direct current

(DC) producing field. Throughout history, life on the planet has

attuned our biology to this subtle field. By comparison, home

wiring systems in the U.S. use 60-cycle per second alternating

current (AC). Unless at very low frequency (less that 10 cycles per

second) and/or low power, alternating current is foreign to our

biology. AC, and other forms of man-made environmental

electromagnetic fields (EMFs) are being researched as possible

factors in a variety of stress-related responses. Many people are

sensitive to EMFs. Studies show an ―association,‖ but not cause

and effect, between livings near power lines (or exposure to EMFs

on the job) and higher rates of health problems.

How much “current” is actually being transferred from the

Earth's surface via the wire to a grounding product?

There is no constant measurable current flow beyond the

equalization charge that is instantly transferred to the body when a

person lies on a conductive sheet or makes contact with another

type of Earthing product. We are talking about numbers of

electrons in the trillions and quadrillions. Once the body is

grounded, the rate of influx changes, and the body will only absorb

that amount of electrons needed to maintain the same electrical

potential as the Earth and to restore what is lost in the body’s

metabolic processes. It may take many quadrillions to get the body

stable. As long as a person continues to be grounded, the body can

use the Earth as a natural reservoir, or ―power source,‖ of electrons

Page 35: Electromagnetic earthing and coupling, Electromagnetic Shielding

to maintain a ―topped up‖ homeostatic level that compensates for

any attrition of internal electrons. With connection to the Earth, it

would thus seem hard for the body to develop any electron

deficiency, and, theoretically, any chronic inflammation. The

actual amount of charge (electrons transferred) would vary

significantly based upon location of the body above the Earth

(voltage) and any potential electrostatic charge that has built up on

the body. The continuing amount of electrons absorbed by the

body to reduce metabolic and immune response free radicals

would also vary significantly between people depending upon their

life style and activity. This is all extremely difficult, if not

impossible, to measure.

What is the difference between the Earthing technology and

the use of magnets?

Although the use of magnets produces some therapeutic effects

when properly applied, magnets cannot provide free electrons, nor

can they connect the body with the naturally balancing electric

frequencies of the Earth. Earthing technology used inside your

home or office connects you with the Earth’s electrons in the same

way as if you were standing barefoot on ground outside.

Page 36: Electromagnetic earthing and coupling, Electromagnetic Shielding

Can I wear any type of footwear and still be earthed?

No. Standard plastic/rubber or composite soles do not conduct the

Earth’s electric energy. Most shoes today are made from those

materials. You need leather or hide soles, which used to be the

primary footwear materials in the past. Leather itself isn’t

conductive, but the foot perspires and the moisture permits

conduction of the energy from the Earth through the leather and up

into the body. In addition, moisture from walking on damp ground

or sidewalks could permeate up into the leather soled shoe.

Thickness of the sole can also be a factor, and specifically that a

very thick leather sole may not allow the moisture through.

Moccasins are the best type of natural conductive footwear.

Leather isn’t quite as good as bare feet on the ground but certainly

much, much better than standard soles that are insulating.

Page 37: Electromagnetic earthing and coupling, Electromagnetic Shielding

Hopefully soon shoe companies will begin making grounded

shoes.

Can I ground myself outside by wearing electrostatic discharge

(ESD) footwear?

ESD shoes are primarily designed for discharging static electricity

but to a degree they ground the body beneficially. They are better

than regular shoes but not as good as going barefoot. The

difference between grounding and static discharge is that

grounding instantly equalizes your body at Earth’s potential. Static

discharge, generally called a soft ground or a dissipative ground,

has an inline 1 meg ohm resistor in the ground cord which is

design to slowly bleed off static electrical charges (contact and

separation charges). These charges are created on the body by

clothing and shoes whenever you move your clothing with arm

movement or walk or sit on any synthetic material. The ESD

industry uses dissipative grounding to prevent a rapid discharge of

static electricity that might otherwise blow an electronic circuit or

sensitive chip.

Does Earthing occur if I work, stand, or walk barefooted on a

ceramic tile floor?

It depends on whether the tile floor sits on a concrete slab or on the

ground. If directly on a slab or ground, the energy could come

through. If the tile sits on plywood or some other kind of wood,

plastic, or vinyl understructure, you are not likely to get any

conductivity. It also depends on what kind of tile. Ceramic tile

Page 38: Electromagnetic earthing and coupling, Electromagnetic Shielding

with a glazed finish on the surface will, like glass, probably

prevent conductivity.

Can Earthing protect me from cell phone frequencies?

The protective potential of Earthing has not been tested yet on cell

phone exposure. There is no research indicating that Earthing will

or will not protect a person from exposure to cell phones signals,

microwave radiation, or radio frequencies. What we know is that

Earthing reduces significantly the induced body voltages generated

by simple exposure to common household 60 Hz EMFs

continuously emitted by all plugged-in electrical cords (even if the

appliance is off), internal wiring, and all ungrounded electrical

Page 39: Electromagnetic earthing and coupling, Electromagnetic Shielding

devices in the home or office. Based in the cases we have seen of

people extremely sensitive to such EMFs it is prudent to be

grounded as much as possible in the home or office.

If I sleep on the ground in a sleeping bag am I grounded?

The first thing you need to know is that Earthing products do not

operate on electricity, so it does not matter what the electrical

current is in your country (whether 110 volts or 240 volts, etc).

Earthing products simply allow the natural, gentle energy from the

Earth outside to be carried inside. When you make physical —

bare skin — contact with the Earthing product it is the same as if

you were standing or walking barefoot outside. This is what

creates the benefits of Earthing.

Our preference is that the products throughout the world be

connected to Earthing ground rods, however many people like the

idea of simply plugging them into an electrical outlet ground port

in their home or office. For people who live in tall apartment

buildings (high rises), a ground rod may not be feasible, and for

people who do not have a grounded electrical system in their home

or office, the only option is the ground rod.

The following explanation covers two options for connecting

Earthing products. The electrical terms ―ground‖ and ―Earth‖ have

the same meaning.

Page 40: Electromagnetic earthing and coupling, Electromagnetic Shielding

Earthing examples:

Page 41: Electromagnetic earthing and coupling, Electromagnetic Shielding

Factors affecting on Earth resistivity:

1. Soil Resistivity:

a. It is the resistance of soil to the passage of electric current.

The earth resistance value (ohmic value) of an earth pit

depends on soil resistivity. It is the resistance of the soil to

the passage of electric current.

b. It varies from soil to soil. It depends on the physical

composition of the soil, moisture, dissolved salts, grain

size and distribution, seasonal variation, current magnitude

etc.

c. In depends on the composition of soil, Moisture content,

Dissolved salts, grain size and its distribution, seasonal

variation, current magnitude.

2. Soil Condition:

a. Different soil conditions give different soil resistivity.

Most of the soils are very poor conductors of electricity

when they are completely dry. Soil resistivity is measured

in ohm-meters or ohm-cm.

b. Soil plays a significant role in determining the

performance of Electrode.

c. Soil with low resistivity is highly corrosive. If soil is dry

then soil resistivity value will be very high.

d. If soil resistivity is high, earth resistance of electrode will

also be high.

Page 42: Electromagnetic earthing and coupling, Electromagnetic Shielding

3. Moisture:

a. Moisture has a great influence on resistivity value of soil.

The resistivity of a soil can be determined by the quantity

of water held by the soil and resistivity of the water itself.

Conduction of electricity in soil is through water.

b. The resistance drops quickly to a more or less steady

minimum value of about 15% moisture. And further

increase of moisture level in soil will have little effect on

soil resistivity. In many locations water table goes down in

dry weather conditions. Therefore, it is essential to pour

water in and around the earth pit to maintain moisture in

dry weather conditions. Moisture significantly influences

soil resistivity

4. Dissolved salts:

a. Pure water is poor conductor of electricity.

b. Resistivity of soil depends on resistivity of water which in

turn depends on the amount and nature of salts dissolved

in it.

c. Small quantity of salts in water reduces soil resistivity by

80%. Common salt is most effective in improving

conductivity of soil. But it corrodes metal and hence

discouraged.

5. Climate Condition:

a. Increase or decrease of moisture content determines the

increase or decrease of soil resistivity.

b. Thus in dry whether resistivity will be very high and in

monsoon months the resistivity will be low.

Page 43: Electromagnetic earthing and coupling, Electromagnetic Shielding

6. Physical Composition:

Different soil composition gives different average

resistivity. Based on the type of soil, the resistivity of

clay soil may be in the range of 4 – 150 ohm-meter,

whereas for rocky or gravel soils, the same may be well

above 1000 ohm-meter.

7. Location of Earth Pit :

a. The location also contributes to resistivity to a great

extent. In a sloping landscape, or in a land with made up

of soil, or areas which are hilly, rocky or sandy, water runs

off and in dry weather conditions water table goes down

very fast. In such situation Back fill Compound will not be

able to attract moisture, as the soil around the pit would be

dry. The earth pits located in such areas must be watered

at frequent intervals, particularly during dry weather

conditions.

b. Though back fill compound retains moisture under normal

conditions, it gives off moisture during dry weather to the

dry soil around the electrode, and in the process loses

moisture over a period of time. Therefore, choose a site

that is naturally not well drained.

8. Effect of grain size and its distribution:

a. Grain size, its distribution and closeness of packing are

also contributory factors, since they control the manner in

which the moisture is held in the soil.

Page 44: Electromagnetic earthing and coupling, Electromagnetic Shielding

b. Effect of seasonal variation on soil resistivity: Increase or

decrease of moisture content in soil determines decrease or

increase of soil resistivity. Thus in dry weather resistivity

will be very high and during rainy season the resistivity

will be low.

9. Effect of current magnitude:

a. Soil resistivity in the vicinity of ground electrode may be

affected by current flowing from the electrode into the

surrounding soil.

b. The thermal characteristics and the moisture content of the

soil will determine if a current of a given magnitude and

duration will cause significant drying and thus increase the

effect of soil resistivity.

10. Area Available:

a. Single electrode rod or strip or plate will not achieve the

desired resistance alone.

b. If a number of electrodes could be installed and

interconnected the desired resistance could be achieved.

The distance between the electrodes must be equal to the

driven depth to avoid overlapping of area of influence.

Each electrode, therefore, must be outside the resistance

area of the other.

Page 45: Electromagnetic earthing and coupling, Electromagnetic Shielding

11. Obstructions:

The soil may look good on the surface but there may be

obstructions below a few feet like virgin rock. In that

event resistivity will be affected. Obstructions like

concrete structure near about the pits will affect

resistivity. If the earth pits are close by, the resistance

value will be high.

12. Current Magnitude:

A current of significant magnitude and duration will

cause significant drying condition in soil and thus

increase the soil resistivity.

Page 46: Electromagnetic earthing and coupling, Electromagnetic Shielding

Measurement of Earth Resistance by use of Earth Tester:

1. For measuring soil resistivity Earth Tester is used.

2. It has a voltage source, a meter to measure Resistance in

ohms, switches to change instrument range, Wires to connect

terminal to Earth Electrode and Spikes.

3. It is measured by using Four Terminal Earth Tester

Instrument. The terminals are connected by wires as in

illustration.

4. P=Potential Spike and C=Current Spike. The distance

between the spikes may be 1M, 2M, 5M, 10M, 35M, and

50M.

5. All spikes are equidistant and in straight line to maintain

electrical continuity. Take measurement in different

directions.

6. Soil resistivity =2πLR.

7. R= Value of Earth resistance in ohm.

8. Distance between the spikes in cm.

9. π = 3.14

10. P = Earth resistivity ohm-cm.

11. Earth resistance value is directly proportional to Soil

resistivity value.

Page 47: Electromagnetic earthing and coupling, Electromagnetic Shielding

Measurement of Earth Resistance (Three point method)

Page 48: Electromagnetic earthing and coupling, Electromagnetic Shielding

Measure Correct Grounding System Impedance of

Electromagnetic Field:

Measurement of the grounding system impedance of a substation

or power plant is often required immediately after construction, in

order to verify that the design calculations correctly predict the

performance of the system. Years later, new measurements are

sometimes required to check that the performance of the grounding

system has not deteriorated. This type of measurement, however,

which is typically carried out using the fall-of-potential method, is

plagued by a number of potential problems: conductive coupling

between the grid under test and the remote current return electrode,

especially for soil structures with low resistivity over high;

inductive coupling between current and voltage test leads;

inductive coupling between test leads and grounding grid

conductors; inductive coupling between test leads and power line

static or neutral wires; additional grounding provided by power

line static and neutral wires, which lowers the apparent impedance

of the grounding grid.

Plant grounding system, its ground impedance is usually measured,

in order to validate the design calculations. The fall-of-potential

method, also known as the ―3-pin‖ method, is typically used. The

test method consists in essence of causing a test current to flow

through the soil, from the grounding system under test to a remote

current return electrode, while the resulting potential rise of the

grounding system is measured with respect to a sufficiently distant

potential reference electrode. Typically, several potential rise

values are measured for increasingly distant reference electrode

positions, in order to confirm that the full potential rise has been

Page 49: Electromagnetic earthing and coupling, Electromagnetic Shielding

measured. The potential rise divided by the test current yields the

ground impedance. For small grounding systems that are isolated

from any other ground electrodes and have sufficient clearance

from nearby grounded structures, this test is usually as simple as it

sounds.

On the other hand, for larger grounding systems or those that are

not electrically isolated from other ground electrodes, a plethora of

problems can occur, which is why a distinct IEEE standard was

written to address the testing of such large systems. The following

points must therefore be considered:

Page 50: Electromagnetic earthing and coupling, Electromagnetic Shielding

1. The ground impedance of a large grounding system tends to be

low. As a result, the measured grid potential rise is small and

undesirable effects, such as induced voltages, that would otherwise

go unnoticed, can become large enough to alter the measured

signal considerably. Stray noise also becomes a greater issue, but

can usually be handled by frequency-selective test gear.

2. Since the potential rise of the grounding system is small, it is

more susceptible to earth potentials transferred from the remote

current return electrode, so this latter must be placed further away

than for a small grounding system. Indeed, IEEE Standard 81.2

indicates that a separation distance of 6.5 times the maximum

diagonal of a rectangular grounding system is required to achieve

95% accuracy. As this paper will show, the actual required

separation distance is a function of soil structure.

3. As a result of this large separation distance, long test leads are

required.

4. A long lead carrying an ac test current is apt to induce

significant voltages in the test lead used to measure the potential

rise of the grounding system, if the two leads are run parallel to

one another or at an acute angle to one another. Induced voltages

do not decrease rapidly as a function of separation distance

between leads, so increasing the spacing between them is of

limited effectiveness.

5. The current-carrying test lead can also induce voltages in long

grounding grid conductors, if there is any parallelism or an acute

angle between them, thus altering the distribution of test current in

the grounding system and its measured impedance.

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6. Test current injected into a long grounding grid can induce

significant voltages in the test lead that measures the potential rise,

if this test lead is run parallel or at an acute angle to the grounding

grid.

7. The above concerns would be eliminated by the use of a very

low frequency test signal. However, for large grounding grids or

even smaller ones in low resistivity soils (the size of concern is

strongly related to soil resistivity), the 50 or 60 Hz reactance of the

grounding grid conductors make a major contribution to the total

grid impedance. A very low frequency test signal would not

reproduce the inductive choke effect that these conductors exhibit

at power frequency and therefore provide false results,

underestimating the grounding system impedance. It is important

that the test signal be carefully chosen to avoid this pitfall.

Guidance in the selection of the appropriate test frequency is one

important part of this paper’s contribution.

8. When a grounding system is connected to other ground

electrodes, as is the case for an operating station, whose grounding

grid is typically connected to lightning shield wires (or other types

of ground return conductors), the effective size of the grounding

system is increased and all of the above problems are compounded,

with the lightning shield wires introducing additional inductive

coupling problems. Furthermore, since the objective of the test is

to measure the ground impedance of the station, it is desirable to

somehow exclude the supplemental grounding provided by the

exterior electrodes.

Page 52: Electromagnetic earthing and coupling, Electromagnetic Shielding

Ground impedance measurements can be influenced by the

following factors:

1. Size of grounding system.

2. Distance from the grounding system of the remote test

current return electrode and the potential reference

electrode.

3. Soil resistivity and layering.

4. Test signal frequency.

5. Angle and separation distance between test leads.

6. Type of lightning shield wire.

7. Separation between test leads and power lines.

8. Separation between test current injection point and potential

rise measurement point on grounding system.

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Page 54: Electromagnetic earthing and coupling, Electromagnetic Shielding

Coupling

In electronics and telecommunication, coupling is the desirable or

undesirable transfer of energy from one medium, such as a metallic

wire or an optical fiber, to another medium, including fortuitous

transfer.

Coupling is also the transfer of electrical energy from one circuit

segment to another. For example, energy is transferred from a

power source to an electrical load by means of conductive

coupling, which may be either resistive or hard-wire. An AC

potential may be transferred from one circuit segment to another

having a DC potential by use of a capacitor. Electrical energy may

be transferred from one circuit segment to another segment with

different impedance by use of a transformer. This is known as

impedance matching. These are examples of electrostatic and

electrodynamics inductive coupling.

Page 55: Electromagnetic earthing and coupling, Electromagnetic Shielding

Types of coupling:

1. Electrical conduction:

a. Hard-wire

b. Resistive

c. Natural conductor

2. Electromagnetic induction:

a. Electrodynamic -- commonly called inductive coupling,

also magnetic coupling

b. Electrostatic -- commonly called capacitive coupling

c. Evanescent wave coupling

3. Electromagnetic radiation:

a. Radio -- wireless telecommunications

b. Electromagnetic interference (EMI) -- Sometimes called

radio frequency interference (RFI), is unwanted coupling.

Electromagnetic compatibility (EMC) requires techniques

to avoid such unwanted coupling, such as electromagnetic

shielding.

c. Microwave power transmission

4. Other kinds of energy coupling:

Acoustic.

Page 56: Electromagnetic earthing and coupling, Electromagnetic Shielding

What is electromagnetic coupling?

Electromagnetic coupling is a phenomenon common to electrical

wiring and circuits where an electromagnetic field in one results in

an electrical charge in another. It is often referred to as inductive

coupling because the process occurs due to electrical inductance,

where a transferring of electromagnetic properties from one

location to another occurs without physical contact taking place. In

order for electromagnetic coupling to take place, there must be a

change in the electromagnetic field that is generating it. For this

reason, direct current (DC) devices do not produce the effect, but it

is common in alternating current (AC) circuits. The principle of

electromagnetic coupling was discovered by Michael Faraday and

Joseph Henry in 1831, and is known as Faraday's Law.

When an AC current in a circuit or wire induces a voltage in

another wire, it is usually due to the fact that they are both in close

proximity to each other, such as in the electrical windings that

transformers have. This is not always true, however, and coupling

at a distance that is unintentional, called cross talk, can occur with

radio and telephone transmissions as well. Intentional

electromagnetic coupling is the principle that transformers are

based upon, where current can be stepped up or stepped down in

voltage in a secondary wire winding based on the current level in a

primary winding on the device.

Since electromagnetic radiation is a dual condition in nature where

electromagnetic waves are composed of both electrical and

magnetic properties, couplings are also of two types. An electrical

Page 57: Electromagnetic earthing and coupling, Electromagnetic Shielding

coupling results when a positive or negative charge density in a

wire or circuit changes, and this repels like charges in another

circuit wire. The process of repelling like charges in nearby wire

causes them to move within the wire, and this is the definition of

what electrical current is. This form of current flow is often

referred to as charge coupling or capacitance coupling.

Magnetic coupling is the flip side of this effect. As a current flows

in a wire, it generates a magnetic field. With AC current, this

magnetic field will fluctuate and cause a changing magnetic field

in coupled circuits or wires. Magnetic fields are directly

perpendicular to electric fields in electromagnetic coupling, so

altering a magnetic field in one circuit can alter the current flow in

another.

The principle of electromagnetic coupling is what all modern

electric motors, relays, and transformers are built upon. Electrical

generators also utilize it, as do a wide variety of communications-

related devices; from citizen's band (CB) radios to televisions and

wireless door locks for buildings and automobiles. It can also be

detrimental to how a circuit functions and cause interference in

telecommunications. In this case, it's often referred to as

electromagnetic interference (EMI). Not all EMI is unintentional,

however, as it can be used as a form of carrier wave to enhance

signal strength as well.

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Page 59: Electromagnetic earthing and coupling, Electromagnetic Shielding

Electromagnetic coupling is used in communications-related

devices like CB radios.

Page 60: Electromagnetic earthing and coupling, Electromagnetic Shielding

Coupled Structures:

As frequency of an electrical signal becomes greater, the

corresponding wavelength be-comes commensurable with the

dimensions of the signal-carrying lines. As this happens,

geometrical parameters of the signal-carrying lines may no longer

be neglected when de-signing electronic circuits, for potentials and

currents are no longer constant along the length of the lines and

per-unit-length line parameters, viz. resistance, inductance,

conductance, and capacitance significantly affect propagation of

the signal along the line. Thus, the problem of designing the lines

acquires another domain, spatial, in addition to the time domain.

The signal-carrying lines used in microwave circuits are usually

referred to as transmission lines, as any other line employed to

convey energy, e.g. transmission lines in electrical power

engineering, where the problem of the line design also has to

account for variation of potentials and currents along the length of

the line and per-unit-length parameters, but due to immense

lengths of the lines rather than high operating frequency.

Transmission lines employed in microwave circuits typically have

two main missions: (1) transfer of electromagnetic energy between

circuit elements, and (2) serving as wave guiding media for

creation of separate circuit elements such as couplers, filters,

baluns (balanced-to-unbalanced transformers), etc.

When two or more unshielded transmission lines supporting

propagation of time-varying electromagnetic fields are placed in

close proximity, see figure below, they demonstrate

electromagnetic coupling between each other due to excitation of

the electromotive forces in the line affected by the time-varying

fields of the other line, which gives rise to additional per-unit-

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length parameters, viz. mutual capacitance, which describes

interaction between the lines in terms of voltages, and mutual

inductance, which describes interaction between the lines in terms

of currents. Such structures are called parallel edge-coupled

structures, if the lines lie in a common plane, or broadside-coupled

structures, if the lines are placed one above the other.

A general representation of coupled lines

A graphical representation of these in a strip line wave guiding

medium is given in figure below (a strip line waveguide consists of

a signal conductor placed between two ground planes as shown in

the figure). The distance to which the lines should be brought

together in order for appreciable electromagnetic coupling to

appear is defined relative to the distance between the signal lines

and the lines, serving as electric potential reference, referred to as

grounds. Generally, the distance between the signal lines should

Page 62: Electromagnetic earthing and coupling, Electromagnetic Shielding

not be much greater than the distance between the lines and the

ground in order not to confine electro-magnetic fields only around

the signal lines.

Electromagnetic coupling between transmission lines may be

classified as either desirable or parasitic. Desirable coupling is

created intentionally in the structures that operationally depend on

interaction of the electromagnetic fields supported by the lines.

Such structures include couplers, filters, and baluns. Parasitic

coupling, also referred to as crosstalk, is an unwanted effect

observed in closely spaced interconnecting traces or lumped

elements that operate on either high frequencies or pulses with

sharp edges. High levels of parasitic coupling may significantly

deteriorate electrical performance of the circuits; therefore

parasitic coupling should be accounted for when designing circuits

with high density of arrangement of elements and additional

measures should be taken to decrease the influence of crosstalk.

Representation of edge-coupled (a) and broadside-coupled (b)

structures in strip line wave guiding medium

Page 63: Electromagnetic earthing and coupling, Electromagnetic Shielding

The Need for Compact Tight Couplers

Couplers have been used extensively in a wide variety of

microwave applications, including power division/combining and

signal sampling. The majority of couplers provide coupling levels

within the 8 – 40-dB range. However, several applications require

greater levels of coupling, up to 3-dB, which corresponds to

division of incoming power into two equal halves. One such

application is the active antenna array, where usage of compact

components is critical.

An active antenna array is a combination of transmit/receive

modules (TRM), each per-forming the functions of final

amplification for transmitted signals, preliminary amplification for

received signals, and control of the phase and amplitude of these

signals to electronically steer the antenna beam. In order for an

active antenna array to operate properly within the whole

frequency and spatial range, the spacing between the TRMs should

be no greater than half-wavelength at the highest operating

frequency. For instance, an active antenna array operating in free

space at 30 GHz must have TRMs spaced no further than 5 mm

from each other. This gives appreciation of how compact, yet

complex enough each TRM should be to meet the aforementioned

functional requirements. Moreover, TRMs must be of low cost in

order for active antenna arrays to be economically feasible since

virtually thousands of TRMs are required for high gain active

antenna arrays. This requires increased levels of circuit integration

to make fabrication less expensive.

Notwithstanding being faced with this multitude of engineering

and economic problems, each TRM’s power amplifier is required

to output high power, which is a contradictory requirement for

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solid-state active devices, being the backbone of monolithic

microwave integrated circuits (MMIC), to be of small size and

feature a high output power at high operating frequency. Hence,

summation of output power from a number of power amplifiers is

a must for high overall transmit output power of each TRM.

Power combining networks consist of a number of branches with

power amplifiers, each fed from a common signal source through a

power divider that divides the input signal be-tween the branches.

Amplified signals from the output of each branch power amplifier

are combined into a common output signal with the help of a

power combiner. Power-combining networks of this type are called

corporate networks. An example of such a network is given in

below figure. Here, the output power of the network is twice the

output power of each branch. In addition to the advantage of power

combining, this network pro-vides redundancy: if one of the

branch amplifiers fails, the whole network remains operational,

though with half the normal output power.

Both power dividers and power combiners in the corporate power-

combining networks are the same microwave devices, viz. 3-dB

directional couplers, and are four-port reciprocal devices, which

means that any port can serve as the input port and the remaining

ports will serve as relevant output ports.

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Power-combining corporate network employing couplers

The most popular couplers are the SML edge-coupled couplers

owing to their simplicity and optimum area utilization. They are

often implemented in the planar wave guiding media, which are

the waveguides of choice in the prevailing majority of small-scale

micro-wave circuits. However, the SML edge-coupled couplers are

unable to attain the 3-dB level of coupling due to prohibitively

narrow gaps between the signal traces required for as tight a level

of coupling as 3 dB, which compromises the very possibility of

fabrication of such couplers. Therefore, microwave designers

having conventional circuit fabrication technologies at their

disposal have to resort to other, more complex coupler

configurations such as multi-dielectric layer broadside-coupled

strip lines (see Fig. a), which greatly increases production

complexity, especially in MMIC’s; multi-line couplers such as the

Lange coupler (see Fig. b), which are not optimum from the area

utilization point of view and require wire jumpers, which add

parasitic inductances; or branch-line couplers (see Fig. c), which

are neither compact in area, nor wide in frequency bandwidth.

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increasing the level of coupling with retaining feasibility of the

coupled-line structures may be attained by following one or both of

the following methods: (1) enlarging the area of metal interface in

the field interaction volume of the coupled structure, or (2)

applying dielectric materials with high relative permittivity.

a) Broadside strip line coupler (cross-sectional view)

b) Lange coupler (top view)

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Branch-line coupler (top view)

Following the latter approach might significantly deteriorate high-

frequency performance of microwave devices fabricated using

dielectric materials with high relative permittivity.

Therefore, following the first approach could be considered more

beneficial to obtain simple 3-dB couplers.

In MMICs, or small-scale circuit environment, optimum

enlargement of metal interface area with respect to chip area

utilization may be achieved by exploring the third, tradition-ally

unused, dimension, viz. the height of metal structures serving as

signal lines. The fabrication technology that allows production of

small-scale tall metallic structures combined with the precision and

aptitude for large-scale fabrication of integrated circuits is the deep

X-ray lithography (DXRL) and its spin-off techniques such as

LIGA (DXRL with replication).

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Principle of Electromagnetic Coupling:

A transmission line representing a system of N+1 non-touching

conductors, where one of the conductors acts as the reference of

zero potential (in other words, N transmission lines with a common

reference placed in proximity to each other) can generally support

N independent, or normal, propagation modes, each one described

with a unique propagation constant and nonzero voltages and

currents [12]. When the media, where the system is located is

homogeneous, i.e. electromagnetic waves propagating along the

conductors do not experience refraction, the modes will be

transverse electromagnetic (TEM) and they, still being

independent, will have identical propagation constants. When one

of the N transmission lines is excited with a time-varying signal, N

sets of voltages and currents will be excited in the system due to

the electromagnetic coupling. The essence of the electromagnetic

coupling may be readily seen from Faraday’s Law (2.1) stating that

any change in the magnetic environment produces opposing

electromotive force:

where electric field intensity E is tangential to contour C and

normal to magnetic flux density B passing through an arbitrary

surface S bounded by C. For a stationary system, counteracting

electromotive force will be induced by any temporal change of

perpendicular magnetic field. Written in terms of field components

after performing vector operations, Faraday’s Law may be

presented as follows:

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Where Et and Bn are mutually orthogonal components of electric

and magnetic fields respectively. One of the implications of (2.2) is

that if there are two closely spaced conductors and the first one is

acted upon by magnetic field produced by current in the second

conductor, there will be induced electromotive force emf causing

flow of current in the first conductor in the direction opposing the

change of magnetic field. Thus, electromagnetic coupling is

established between the two conductors via magnetic-flux linkage

as shown in Figure:

Magnetic-flux linkage between two conductors

In case if time-varying magnetic flux is caused by harmonic

current, (2.2) may be written in the phasor form as:

Where ω is the operating angular frequency. It is clear from (2.3)

that in order for electro-magnetic coupling to exist in a stationary

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system of conductors, one of them must be driven from an AC

source.

Directional Couplers

A four-port microwave device demonstrating electromagnetic

coupling is called a ―directional coupler‖. The simplest example of

the directional coupler is a pair of unshielded transmission lines

placed closely to each other and having a common reference of

zero potential. Assuming that the lines are identical and the cross

section of the coupled part does not change along its entire length,

i.e. the coupled part is uniform and symmetrical, as shown in Fig.

2.2, then the scattering matrix, [S], of such a network will be as

follows, provided the network is ideally matched to the

characteristic impedance of the network at all four ports:

a) A two-line four-port uniformly coupled symmetrical section

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If the network is not built of any nonreciprocal media, it shows

reciprocal properties, which means that any port can serve as input

and remaining ports will serve as appropriate output ports.

Depending on the direction that the coupled wave travels, which in

its turn depends on the geometry of the coupler, coupled power

will appear either at Port 3 or at Port 4 as shown in Fig. a) In the

former case, the coupler will be backward-wave, and in the latter –

forward-wave. Assuming a backward-wave directional coupler, i.e.

the coupler where the coupled wave on the secondary line

propagates in the direction opposite to the direction of the wave on

the primary line, the elements of matrix (2.4) will have the

following meaning when Port 1 acts as the input: S12 –

throughput, S13 – coupling, S14 – isolation. By the virtue of

reciprocity, the remaining elements of matrix (2.4) correspond to

the above as follows: S23 = S14, S24 = S13, S34 = S12. So when

the input is assigned to Port 1, Port 2 becomes direct (through)

port, Port 3 – coupled port, and Port 4 – isolated. Ideally, no power

should appear at the isolated port or S14 should be zero, i.e. all

power should be divided between the direct and coupled ports with

the following relation being true:

In this case, the [S] matrix of the coupler looks like:

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Performance of couplers is described with the help of the following

four main parameters:

Where P1, P2, P3, and P4 are levels of power at the input, direct,

coupled, and isolated ports respectively.

The coupling factor K shows the fraction of input power that is

electromagnetically coupled to the output port; the directivity

factor D indicates the ability of the coupler to isolate between the

forward and backward waves, where one of them is the coupled

wave de-pending on the coupler type; and isolation factor I is the

measure of the coupler’s ability to deter the useful power from

traveling to the isolated port. The isolation factor is linearly

connected to the above quantities as follows:

I = K + D, dB

The ideal coupler, as described by [S]-matrix (2.6), would have

infinite isolation and directivity.

From the energy conservation law, in order for a network to be

lossless its [S] matrix should be unitary, which means that each

matrix column should be orthogonal to the conjugates of other

columns and parallel to its conjugate. It can be easily seen from

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(2.5) and (2.6) that a directional coupler matched at all four ports is

ideally lossless. Complimentarily, it may be inferred from the

energy conservation condition that any lossless, reciprocal four-

port network matched at all ports is a directional coupler.

Therefore, directional couplers may be designed for the condition

of being simultaneously lossless, reciprocal, and matched at all

ports. Unlike directional couplers, three-port couplers, such as

Wilkinson coupler, have to be lossy in order to be reciprocal and

matched at all ports [13].

A special case of the directional coupler in which the signals at the

two output ports are equal (which corresponds to the 3-dB level of

coupling) and differ in phase by 90 degrees is called ―hybrid‖.

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Magnetic field coupling(Inductive coupling):

Magnetic field coupling (also called inductive coupling) occurs

when energy is coupled from one circuit to another through a

magnetic field. Since currents are the sources of magnetic fields,

this is most likely to happen when the impedance of the source

circuit is low.

Consider the two circuits sharing a common return plane shown in

Fig. 1. Coupling between the circuits can occur when the magnetic

field lines from one of the circuits pass through the loop formed by

the other circuit. Schematically, this can be represented by a

mutual inductance between the two signal wires as shown

below:

Two circuits above a signal return plane.

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Schematic representation of the circuits in the above fig

including inductive coupling.

In most cases, a convenient closed-form equation for calculating

the mutual inductance will not be available. However, we can often

estimate the mutual inductance by estimating the percentage of the

total magnetic flux generated by the first loop that couples the

second loop. For example, suppose the two wires in the example

above are 20 mm above the plane and separated by 5 mm. We

could visualize the magnetic flux lines that wrap the current in line

1 as shown in figure:

More intuitive schematic representation of the circuits

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If the wire radius in the example above is 0.6 mm, we could

calculate the self-inductance of the source circuit using the

equation for the inductance per unit length of a wire over a

conducting plane,

The self-inductance is the total flux divided by the current while

the mutual inductance is the flux that couples both loops divided

by the current. Therefore the mutual inductance can be expressed

as a fraction of the self-inductance,

We might estimate that somewhere between 50% and 80% of the flux

couples both circuits. If we were to assume 60%, then our estimate of

the mutual inductance would be,

Of course, there are more accurate ways of determining the mutual

inductance between two circuits. Electromagnetic modeling

software is often used for this purpose when it is necessary to

determine crosstalk levels more precisely. There are also a number

of closed-form equations that can be applied to specific

(1)

(2)

(3)

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geometries. In fact, for the case of two thin wires above an infinite

ground plane, there is a relatively simple closed form expression

[1],

Where h1 and h2 are the heights of the two wires above the plane,

s is the distance between the two wires and the wire radius is small

relative to the height and separation. Applying this equation to the

example above,

The difference between the estimate (3) and the calculation in (5)

is less than 2 dB. Estimates within a few dB are usually accurate

enough to indicate whether a potential crosstalk problem exists.

To calculate the crosstalk due to magnetic field coupling, we start

with the current in the source circuit, since the current is the source

of the magnetic field. The voltage induced in the second circuit can

be expressed as,

(4)

(5)

(6)

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VLOOP2 is the voltage induced in the entire loop of the circuit.

The fraction of this voltage that will appear across the load can be

expressed as,

Since, I1 = VRL1/RL1, the crosstalk due to magnetic field

coupling can be expressed as,

(7)

(8)

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Magnetic Resonance and Magnetic Induction -

What is the best choice for my application?

Loose coupling or tight coupling between the Tx and Rx coils?

Inductive power transfer works by creating an alternating magnetic

field (flux) in a transmitter coil and converting that flux into an

electrical current in the receiver coil. Depending on the distance

between the transmit and receive coils, only a fraction of the

magnetic flux generated by the transmitter coil penetrates the

receiver coil and contributes to the power transmission. The more

flux reaches the receiver, the better the coils are coupled.

A higher coupling factor improves the transfer efficiency, and

reduces losses and heating. Applications with a larger distance

between the transmit and receive coils operate, by definition, as a

loosely coupled system. In loosely coupled systems, only a fraction

of the transmitted flux is captured in the receiver. That means that

loosely coupled systems have higher electromagnetic emissions,

making them less suitable for applications with tight EMI or EMF

requirements.

Loosely coupled systems trade-off larger distance at the cost of

lower power transfer efficiency and higher electromagnetic

emissions. This may be suitable choice in applications where

tightly aligned coils is impractical, but less suitable for applications

with tight EMI or EMF of efficiency requirements.

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Tightly coupled systems, because of their higher efficiency, tend to

produce less heat which is an advantage is products with tight

thermal budgets such as modern smartphones.

The transmit and receive coils are tightly coupled when (a) the

coils have the same size, and (b) the distance between the coils is

much less than the diameter of the coils.

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Operate the coils at resonance or off-resonance?

From the beginning of inductive power transmission, resonant

circuits have been used to enhance the efficiency of power

transmission. As early as 1891, Nicola Tesla used resonance

techniques in his first experiments with inductive power

transmission. Systems with a low coupling factor generally use a

resonant receiver and resonant transmitter to improve power

transfer efficiency.

You might expect that operating tightly coupled coils at resonance

offers the best performance. That combination, however, is not

used in practice because two tightly coupled coils cannot be both

in resonance at the same time. This is one of the counter-intuitive

effects that make power electronics such an interesting subject.

Most Qi transmitters use tight coupling between coils. In that

configuration, the best results are achieved by operating the

transmitter at a frequency that is slightly different from the

resonance frequency of the Qi receiver. Off-resonance operation

gets you the highest amount of power at the best efficiency.

Single coil or multi-coil?

Tightly coupled coils are sensitive to misalignment. That’s why

most Qi transmitters use multiple coils. This increases the

complexity of the transmitter design, but improves the horizontal

(X, Y) freedom of positioning. Coil arrays can cover large areas.

for example, ConvenientPower’s WoW5 transmitter.

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Another advantage of multi-coil systems is that they help localize

the magnetic flux, reducing EM emissions, and make it possible to

charge multiple receivers concurrently.

Here are some examples of transmitters that use overlapping coils.

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Coils don't need to overlap either. Solutions with non-overlapping

coils can be easier easy to assemble.

Multi-coil transmitters can charge several receivers at the same

time, simply by powering the coils underneath the receiver.

Multi-coil transmitters also allow the wireless power ecosystem to

scale with increasing power levels that devices demand, by

powering multiple coils underneath the receiver. The first smart

phones needed 3W, todays require over 7.5W and growing

A loosely coupled system can achieve multi-device charging with

a single transmitter coil; provided it is much larger than the

receiver coils and the provided the receivers can tune themselves

independently to the frequency of the single transmitter coil.

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References

1. E. C. Niehenke, R. A. Pucel, and I. J. Bahl, ―Microwave and Millimeter-Wave

Integrated Circuits,‖ IEEE Transactions on Microwave Theory and Techniques,

vol. 50, No. 3, pp. 846–857, March 2002.

2. http://en.wikipedia.org/wiki/Electromagnetism#cite_note-1

3. Anatoly Tsaliovich, Electromagnetic Shielding Handbook For Wired And

Wireless Emc Applications, Kluwer Academic

4. http://en.wikipedia.org/wiki/Noise_(signal_processing)

5. B. A. Kopp, M. Borkowski, and G. Jerinic, ―Transmit/Receive Modules,‖ IEEE

Transactions on Microwave Theory and Techniques, vol. 50, No. 3, pp. 827–834,

March 2002.

6. G. I. Haddad and R. J. Trew, ―Microwave Solid-State Active Devices,‖ IEEE

Transactions on Microwave Theory and Techniques, vol. 50, No. 3, pp. 760–779,

March 2002.

7. F. H. Raab et al, ―Power Amplifiers and Transmitters for RF and Microwave,‖

IEEE Transactions on Microwave Theory and Techniques, vol. 50, No. 3, pp.

814–826, March 2002.

8. Practical Guide to Electrical Grounding, Library Of Congress Catalog Card

Number: 99-72910, 1999 ERICO, Inc.

9. http://en.wikipedia.org/wiki/Inductive_coupling

10. C. R. Paul, Introduction to Electromagnetic Compatibility, 2nd Ed., Wiley Series

in Microwave and Optical Engineering, 2006.

11. http://en.wikipedia.org/wiki/Coupling_%28electronics%29

12. D. M. Pozar, Microwave Engineering, Addison-Wesley Publishing Company,

1990.

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