Lecture 14 Announcements

1. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

2. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

3. 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) BAE2022/BAE4400 Physical Properties of Biological Materials

4. The electromagnetic spectrum BAE2022/BAE4400 Physical Properties of Biological Materials

5. Relationship between frequency and wavelength l Plus Plus Wavelength = speed of light divided by frequency (miles between bumps = miles per hour / bumps per hour) l= Wavelength [m] n= Frequency [Hz] c = 3x108 m/s in a vacuum Minus Minus BAE2022/BAE4400 Physical Properties of Biological Materials

6. Relationship between frequency and wavelength l + - Antenna Plus Plus Minus Minus lKOSU= 3 x 108 / 97.1 x 106 lKOSU= 3 m lred= 6.40 x 10- 7 m = 640 nm Bohr’s Hydrogen = 5 x 10 - 11 m BAE2022/BAE4400 Physical Properties of Biological Materials

7. Plants light harvesting structure - model Jungas et. al. 1999 BAE2022/BAE4400 Physical Properties of Biological Materials

8. Light emission / absorption governed by quantum effects Planck - 1900 Einstein - 1905 One “photon” DE is light energy flux n is an integer (quantum) h is Planck’s constant n is frequency BAE2022/BAE4400 Physical Properties of Biological Materials

9. Frequency bands and photon energy BAE2022/BAE4400 Physical Properties of Biological Materials

10. Changes in energy states of matter are quantified Bohr - 1913 • Where Ek, Ej are energy states (electron shell states etc.) and frequency, n , 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 BAE2022/BAE4400 Physical Properties of Biological Materials

11. Measurement of reflected intensity –Typical Multi-Spectral Sensor Construction One Spectral Channel Photo-Diode detector / Amplifier Analog to Digital Converter CPU Optical Filter Illumination Collimator Radiometer Computer Target BAE2022/BAE4400 Physical Properties of Biological Materials

12. Measurement of reflected intensity - Fiber-Optic Spectrometer One Spectral Channel at a time Optical Glass Fiber Optical Grating Analog to Digital Converter CPU Element selection Computer Photo Diode Array BAE2022/BAE4400 Physical Properties of Biological Materials

13. 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 700 nm 400 nm 500 nm BAE2022/BAE4400 Physical Properties of Biological Materials

14. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

15. CIE XYZ model Y • Attempts to describe perceived color with a three coordinate system model X Z= luminance BAE2022/BAE4400 Physical Properties of Biological Materials

16. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

17. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

18. Silicon Responsivity BAE2022/BAE4400 Physical Properties of Biological Materials

19. Primary and secondary absorbers in plants • Primary • Chlorophyll-a • Chlorophyll-b • Secondary • Carotenoids • Phycobilins • Anthocyanins BAE2022/BAE4400 Physical Properties of Biological Materials

20. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

21. Radiation Energy Balance • Incoming radiation interacts with an object • and may follow three exit paths: • Reflection • Absorption • Transmission • a + t + r= 1.0 • a, t, andrare the • fractions taking each path • Known as: • fractional absorption coefficient, • fractional transmittance, and • reflectance respectively Il0 Il0r Il0 a Iout = Il0 t BAE2022/BAE4400 Physical Properties of Biological Materials

22. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

23. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

24. Solar Irradiance NIR UV BAE2022/BAE4400 Physical Properties of Biological Materials

25. Soil and crop reflectance BAE2022/BAE4400 Physical Properties of Biological Materials

26. Soil Reflectances - Oklahoma BAE2022/BAE4400 Physical Properties of Biological Materials

27. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

28. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

29. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

30. 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!!!!) BAE2022/BAE4400 Physical Properties of Biological Materials

31. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

32. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

33. 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) BAE2022/BAE4400 Physical Properties of Biological Materials

34. 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) BAE2022/BAE4400 Physical Properties of Biological Materials

35. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

36. 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 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 BAE2022/BAE4400 Physical Properties of Biological Materials

37. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

38. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

39. Electromagnetic properties Resistance, Capacitance and Dielectric Properties Example 4.2 pg 176 of handout BAE2022/BAE4400 Physical Properties of Biological Materials

40. 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) BAE2022/BAE4400 Physical Properties of Biological Materials

41. 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 BAE2022/BAE4400 Physical Properties of Biological Materials

42. 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 BAE2022/BAE4400 Physical Properties of Biological Materials