1. 15/20/2015BAE2023 Physical Properties of Biological Materials 1 Spectroscopy

2. 25/20/20152 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

3. 35/20/20153 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)

4. 45/20/20154 The electromagnetic spectrum

5. 55/20/20155 Relationship between frequency and wavelength Plus Minus Plus Wavelength = speed of light divided by frequency (miles between bumps = miles per hour / bumps per hour)  = Wavelength [m]  = Frequency [Hz] c = 3x10 8 m/s in a vacuum

6. 65/20/20156 Relationship between frequency and wavelength Plus Minus Plus Antenna +- KOSU = 3 x 10 8 / 97.1 x 10 6 KOSU = 3 m red = 6.40 x 10 - 7 m = 640 nm Bohr’s Hydrogen = 5 x 10 - 11 m

7. 75/20/20157 Plants light harvesting structure - model Jungas et. al. 1999

8. 85/20/20158 Light emission / absorption governed by quantum effects Planck - 1900  E is light energy flux n is an integer (quantum) h is Planck’s constant is frequency Einstein - 1905 One “photon”

9. 95/20/20159 Frequency bands and photon energy

10. 105/20/201510 Changes in energy states of matter are quantified Bohr - 1913 Where E k, E j 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

11. 115/20/201511 Measurement of reflected intensity – Typical Multi-Spectral Sensor Construction Analog to Digital Converter Computer One Spectral Channel Photo-Diode detector / Amplifier Optical Filter Collimator Target Illumination CPU Radiometer

12. 125/20/201512 Measurement of reflected intensity - Fiber-Optic Spectrometer Optical Glass Fiber Photo Diode Array Optical Grating Analog to Digital Converter Computer CPU Element selection One Spectral Channel at a time

13. 135/20/201513 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 nm 500 nm

14. 145/20/201514 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

15. 155/20/201515 CIE XYZ model Attempts to describe perceived color with a three coordinate system model X Y Z= luminance

16. 165/20/201516 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

17. 175/20/201517 Photo-Chemistry Light may be absorbed and precipitate (drive) a chemical reaction. Example: Photosynthesis in plants 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

18. 185/20/201518 Silicon Responsivity

19. 195/20/201519 Primary and secondary absorbers in plants Primary –Chlorophyll-a –Chlorophyll-b Secondary –Carotenoids –Phycobilins –Anthocyanins

20. 205/20/201520 Chlorophyll absorbance Chla: black Chlb: red BChla: magenta BChlb: orange BChlc: cyan BChld: bue BChle: green Source: Frigaard et al. (1996), FEMS Microbiol. Ecol. 20: 69-77

21. 215/20/201521 Radiation Energy Balance Incoming radiation interacts with an object and may follow three exit paths: Reflection Absorption Transmission  +  +  = 1.0 , , and  are the fractions taking each path Known as: fractional absorption coefficient, fractional transmittance, and reflectance respectively I 0  I 0  I 0 I out = I 0 

22. 225/20/201522 Internal Absorbance ( A i ) 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

23. 235/20/201523 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

24. 245/20/201524 Solar Irradiance NIR UV

25. 255/20/201525 Soil and crop reflectance

26. 265/20/201526 Soil Reflectances - Oklahoma

27. 275/20/201527 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

28. 285/20/201528 Electromagnetic properties Applications Near-infrared: measuring moisture, % oils and proteins Xrays: internal defects Microwaves: heating/cooking Magnetic properties: moisture content and composition Gamma Rays: sterilization of food products during processing

29. 295/20/201529 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 10 8

30. 305/20/201530 Electromagnetic properties Xrays and gamma rays have shortest wavelengths 10 -12 m and highest frequencies 10 20 hz 60 cycle AC: 60 hz and 5 x 10 6 m (coast to coast distance for 1 wavelength!!!!)

31. 315/20/201531 Electromagnetic properties Interactions with visible light, Infrared and UV radiation –Used for sorting and quality evaluation –I ref = reflected –I 1 = energy entering the object –I 2 = energy striking the opposite face after rectilinear transmission –I out = leaving the opposite face

32. 325/20/201532 Electromagnetic properties –Transmittance: T=I out /I 0 –Absorbance: A i =-log (I 1 /I 2 ) –Reflectance: R=I ref /I 0 –Optical Density: log 10 (I 0 /I out ) Amount of energy transmitted through the material

33. 335/20/201533 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)

34. 345/20/201534 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)

35. 355/20/201535 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

36. 365/20/201536 Electromagnetic properties Resistance, Capacitance and Dielectric Properties –Resistivity: ρ r (rho) R = (ρ r L)/A, Ω -1 m -1 or Siemen/m, S/m –Resistance and resistivity are variable So…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

37. 375/20/201537 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 ε 0 ε”E 2, where –f = frequency, ε 0 = free space dc (8.854E-12 F/m), E = electric field

38. 385/20/201538 Electromagnetic properties Resistance, Capacitance and Dielectric Properties –Distance waves will penetrate material before being reduced to 36.8% of original value….power penetration depth (δ p ) δ p = λ 0 ((1+ (ε”/ ε‘) 2 ) 1/2 ) -1/2 ) / (2π(2 ε' ) 1/2 λ 0 = wavelengh in free space

39. 395/20/201539 Electromagnetic properties Resistance, Capacitance and Dielectric Properties Example 4.2 pg 176 of handout

40. 405/20/201540 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)

41. 415/20/201541 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

42. 425/20/201542 Electromagnetic properties 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