10/20/2015bae2022/bae4400 physical properties of biological materials 1 lecture 14 announcements...
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04/21/23 BAE2022/BAE4400 Physical Properties of Biological Materials
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Lecture 14 Announcements• HW#7 Due today
• Lab #4 this Wednesday, 3/5, in BAE Lab: Electromagnetism and Color
• Popcorn Design Problem due 3/7
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Electrical and magnetic properties
• Electromagnetic fields are propagated through and reflected by materials– Characterized as:
• Current flow at low frequencies• Magnetism in metals• Optical absorbance / reflectance in light
• Frequency is a major factor in the primary characteristics– Low frequency – “electrical” properties– High frequency – “optical” properties
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Fundamentals of high frequency electromagnetic waves (Light)
• Light = Energy (radiant energy)– Readily converted to heat
• Light shining on a surface heats the surface• Heat = energy
• Light = Electro-magnetic phenomena– Has the characteristics of electromagnetic
waves (eg. radio waves)– Also behaves like particles (e.g.. photons)
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The electromagnetic spectrum
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Relationship between frequency and wavelength
Plus
Minus Minus
Plus
Wavelength = speed of light divided by frequency
(miles between bumps = miles per hour / bumps per hour)
= Wavelength [m]= Frequency [Hz]c = 3x108 m/s in a vacuum
c
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Relationship between frequency and wavelength
Plus
Minus Minus
Plus
Antenna
+ -
KOSU = 3 x 108 / 97.1 x 106
KOSU = 3 m
red = 6.40 x 10- 7 m = 640 nmBohr’s Hydrogen = 5 x 10 - 11 m
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Plants light harvesting structure - model
Jungas et. al. 1999
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Light emission / absorption governed by quantum effectsPlanck - 1900
E nh E is light energy fluxn is an integer (quantum)h is Planck’s constant is frequency
E hp Einstein - 1905
One “photon”
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Frequency bands and photon energy
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Changes in energy states of matter are quantified
Bohr - 1913
h E Ek j
Where Ek, Ej are energy states (electron shell states etc.) and frequency, , is proportional to a change of state
and hence color of light. Bohr explained the emission spectrum of hydrogen.
Hydrogen Emission Spectra (partial representation)
Wavelength
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Measurement of reflected intensity –Typical Multi-Spectral Sensor Construction
Analog toDigitalConverter
Computer
One Spectral Channel
Photo-Diode detector/ Amplifier
Optical Filter
Collimator
Target
Illumination
CPU
Radiometer
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Measurement of reflected intensity - Fiber-Optic Spectrometer
OpticalGlass Fiber
Photo Diode Array
Optical GratingAnalog toDigitalConverter
Computer
CPU
Element selection
One Spectral Channel at a time
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Visual reception of color
• Receptors in our eyes are tuned to particular photon energies (hn)
• Discrimination of color depends on a mix of different receptors
• Visual sensitivity is typically from wavelengths of ~350nm (violet) to ~760nm (red)
Wavelength
400 nm 700 nm500 nm
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Quantification of color• Spectral measurements can be used to quantify
reflected light in energy and spectral content, but not very useful description of what we see.
• Tri-stimulus models – represent color as perceived by humans– Tri-stimulus models
• RGB - most digital work• CYM - print• HSI, HSB, or HSV - artists• CIE L*a*b*• YUV and YIQ - television broadcasts
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CIE XYZ model
• Attempts to describe perceived color with a three coordinate system model
X
Y
Z= luminance
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CIE Lab model
• An improvement of the CIE XYZ color model.
• Three dimensional model where color differences correspond to distances measured colorimetrically
• Hue and saturation (a, b) – a axis extends from green (-a) to red (+a)– b axis from blue (-b) to yellow (+b)
• Luminance (L) increases from the bottom to the top of the three-dimensional model
• Colors are represented by numerical values• Hue can be changed without changing the
image or its luminance.• Can be converted to or from RGB or other
tri-stimulus models
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Photo-Chemistry• Light may be absorbed and precipitate (drive) a chemical
reaction. Example: Photosynthesis in plants
6 6 62 2 6 12 6 2CO H O h C H O O
• The wavelength must be correct to be absorbed by some participant(s) in the reaction
• Some structure must be present to allow the reaction to occur
• Chlorophyll• Plant physical and chemical structure
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Silicon Responsivity
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Primary and secondary absorbers in plants
• Primary– Chlorophyll-a– Chlorophyll-b
• Secondary– Carotenoids– Phycobilins– Anthocyanins
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Chlorophyll absorbance
Chla: blackChlb: redBChla: magentaBChlb: orangeBChlc: cyanBChld: bueBChle: green
Source: Frigaard et al. (1996), FEMS Microbiol. Ecol. 20: 69-77
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Radiation Energy BalanceIncoming radiation interacts with an object and may follow three exit paths:
• Reflection• Absorption• Transmission
+ + = 1.0, , and are thefractions taking each pathKnown as:
fractional absorption coefficient,fractional transmittance, andreflectance respectively
I0
I0 I0
Iout = I0
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Internal Absorbance (Ai)• Lambert's Law - The amount of light absorbed is directly
proportional to the logarithm of the length of the light path or the thickness of the absorbing medium. Thus:
l = length of light path
k = extinction coefficient of medium• Normally in absorbance measurements the measurement is
structured so that reflectance is zero
klI
IA
outi
)1(log 0
klTI
IA
outi
1loglog 0
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Reflectance
– Ratio of incoming to reflected irradiance– Incoming can be measured using a “white”
reflectance target– Reflectance is not a function of incoming
irradiance level or spectral content, but of target characteristics
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0
100
200
300
400
500
600
700
0 250 500 750 1000 1250 1500 1750 2000Wavelength (nm)
Sp
ectr
al Irr
adie
nce
(w
/m^2
nm
)
Extraterrestrial SolarIrradience
Terrestial SolarIrradience
Adapted from Thekaekara, M. P. 1973.Solar Energy Outside the Earth's Atmosphere.Solar Energy, Vol 14, p 109.
Solar Irradiance
NIRUV
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Soil and crop reflectance
0
0.1
0.2
0.3
0.4
0.5
0.6
300 400 500 600 700 800 900 1000 1100
Wavelength (nm)
Fra
cti
on
al
Re
fle
cta
nc
e
43 Soils
27 Soybeans
25 Potatoes
9 Sunflower
73 Cotton17 Corn
P. S. ThenkabailR. B. SmithE. De PauwYale Center for Earth Observation
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Soil Reflectances - Oklahoma
0
0.2
0.4
0.6
0.8
1
350 400 450 500 550 600 650 700 750 800
Wavelength (nm)
Ref
lect
ance
(Fra
ctio
n)Tipton Stillwater
Perkins Mangum
Lahoma Haskell
Goodwell Ft. Cobb
Chickasha Altus
Agron. Stwr.
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Electromagnetic properties
Review:• Electromagnetic radiation is energy• Interaction with materials is affected by the
properties of the material• Can give indication of physical damage,
mold presence, foreign material, contaminating chemicals or ID of materials
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Electromagnetic properties
• ApplicationsNear-infrared: measuring moisture, % oils and
proteinsXrays: internal defectsMicrowaves: heating/cookingMagnetic properties: moisture content and
compositionGamma Rays: sterilization of food products
during processing
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Electromagnetic properties
• Electromagnetic radiation (ER) is transmitted in the form of waves
– Wavelength λ (lambda)– Frequency ν (nu)– λ ν = c, speed of light in a vacuum– 3.0 x 108
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Electromagnetic properties
• Xrays and gamma rays have shortest wavelengths 10-12 m and highest frequencies 1020 hz
• 60 cycle AC: 60 hz and 5 x 106 m (coast to coast distance for 1 wavelength!!!!)
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Electromagnetic properties
• Interactions with visible light, Infrared and UV radiation
– Used for sorting and quality evaluation– Iref = reflected– I1 = energy entering the object– I2 = energy striking the opposite face
after rectilinear transmission– Iout = leaving the opposite face
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Electromagnetic properties
– Transmittance: T=Iout/I0
– Absorbance: Ai=-log (I1/I2)
– Reflectance: R=Iref/I0
– Optical Density: log10(I0/Iout)• Amount of energy transmitted through
the material
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Electromagnetic properties
– Flourescence: excited by energy at a particular wavelength and then emits energy at a different wavelength (aflatoxin test for aspergillus...fungi)
– Delayed-light emission: radiation is emitted for a time after the exciting radiation is removed (chlorophyll)
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Electromagnetic properties Resistance, Capacitance and Dielectric
Properties
– Biological materials act as a combination of resistors and capacitors
– Varies with moisture content and internal structure
– Used to evaluate quality and composition– Dielectric loss factor is important in heating
(microwave)
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Electromagnetic properties Resistance, Capacitance and Dielectric
Properties
– Resistance:• measure by placing material between two
metal plates and incorporating into an electric circuit
– Value of R is inversely correlated with moisture content
– Pressure of plates and temperature also affect R
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Electromagnetic properties Resistance, Capacitance and Dielectric
Properties
– Resistivity: ρr (rho)R = (ρr L)/A ,
Ω-1m-1 or Siemen/m, S/m– Resistance and resistivity are variableSo…we use capacitance instead.In an AC circuit, capacitor causes a phase shift
between voltage and current. (perfect vacuum = 90°)
With biomaterials in place < 90°See Figure 11.5
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Electromagnetic properties Resistance, Capacitance and Dielectric
Properties
– Dielectric Properties: dielectric constant ε' and dielectric loss factor ε”.
– ε‘ = ability of material to store energy– ε” = ability of mateials to dissipate energy– Loss tangent = ε” / ε‘ – Rate of heat generation per unit volume (Q) at a
location inside material:– Q = 2πf ε0 ε”E2, where – f = frequency, ε0 = free space dc (8.854E-12
F/m), E = electric field
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Electromagnetic properties Resistance, Capacitance and Dielectric
Properties
– Distance waves will penetrate material before being reduced to 36.8% of original value….power penetration depth (δp)
δp = λ0((1+ (ε”/ ε‘)2)1/2)-1/2) / (2π(2 ε' )1/2
λ 0 = wavelengh in free space
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Electromagnetic properties Resistance, Capacitance and Dielectric
Properties
Example 4.2 pg 176 of handout
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Electromagnetic properties Resistance, Capacitance and Dielectric
Properties
Moisture content effects on dielectric properties
Pg 177 handout figure 4.18
Free water : found in capillaries (I)
Bound water: physically adsorbed to the surface of dry materials (II)
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Electromagnetic properties Resistance, Capacitance and Dielectric
Properties
Example of dielectric properties:
Page 183 handout Table 4.2
Measuring dielectric properties
pg 187 handout figure 4.23
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Electromagnetic properties HW #8 Due 3/14
Problem 1. Estimate the penetration depth of raw beef during cooking in a home microwave oven. Assume that dielectric properties are constant throughout heating.
Problem 2. Determine the angle of signal lag for wheat, corn and rice.
Problem 3. 11.2 in Stroshine book
Problem 4. 11.4 in Stroshine book