1. Lecture 14 Announcements
HW#11 Due today
Monday’s lecture by Dr. Brusewitz (movie about processing in the cotton industry)
HW#12 Due Monday 3/5
HW#13 Due Friday 3/9
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

2. Electromagnetic properties (cont)
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
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

3. Electromagnetic properties (cont)
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
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

4. Electromagnetic properties (cont)
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
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

5. Electromagnetic properties (cont)
Xrays and gamma rays have shortest wavelengths m and highest frequencies 1020 hz
60 cycle AC: 60 hz and 5 x 106 m (coast to coast distance for 1 wavelength!!!!)
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

6. Electromagnetic properties (cont)
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
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

7. Electromagnetic properties (cont)
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
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

8. Electromagnetic properties (cont)
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)
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

9. BAE2022/BAE4400 Physical Properties of Biological Materials
Electromagnetic properties (cont) 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)
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

10. BAE2022/BAE4400 Physical Properties of Biological Materials
Electromagnetic properties (cont) Resistance, Capacitance and Dielectric Properties
Resistance:
measure by placing material between two metal plates and incorporating in an electric circuit
Value of R is inversely correlated with moisture content
Pressure of plates and temperature also affect R
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

11. BAE2022/BAE4400 Physical Properties of Biological Materials
Electromagnetic properties (cont) Resistance, Capacitance and Dielectric Properties
Resistivity: ρr (rho)
R = (ρr L)/A ,
Ω-1m-1 or Siemen/m, S/m
Resistance and resistivity is variable
So…we use capacitance instead.
In an AC circuit, capacitor causes a phase shift between voltage and current. (perfect and vacuum = 90°)
With biomaterials in place < 90°
See Figure 11.5
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

12. BAE2022/BAE4400 Physical Properties of Biological Materials
Electromagnetic properties (cont) 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
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

13. BAE2022/BAE4400 Physical Properties of Biological Materials
Electromagnetic properties (cont) 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
Λ0 = wavelengh in free space
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

14. BAE2022/BAE4400 Physical Properties of Biological Materials
Electromagnetic properties (cont) Resistance, Capacitance and Dielectric Properties
Example 4.2 pg 176 of handout
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

15. BAE2022/BAE4400 Physical Properties of Biological Materials
Electromagnetic properties (cont) 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)
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

16. BAE2022/BAE4400 Physical Properties of Biological Materials
Electromagnetic properties (cont) Resistance, Capacitance and Dielectric Properties
Example of dielectric properties:
Page 183 handout Table 4.2
Measuring dielectric properties
pg 187 handout figure 4.23
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

17. Electromagnetic properties HW #13
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.
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials

18. Cotton Products Processing HW #12
Problem 1. List 3 physical properties that must be considered in the handling of the products in the video.
Problem 2. List all of the conveyance systems you observe in the video.
11/23/2018
BAE2022/BAE4400 Physical Properties of Biological Materials