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Dielectric and Thermal Properties
of Materials at Microwave Frequencies
RF Cafe Quiz #45

All RF Cafe quizzes would make perfect fodder for employment interviews for technicians or engineers - particularly those who are fresh out of school or are relatively new to the work world. Come to think of it, they would make equally excellent study material for the same persons who are going to be interviewed for a job.

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Note: Many answers contain passages quoted in whole or in part from the text.

Handbook of Dielectric and Thermal Properties of Materials at Microwave Frequencies - RF Cafe Featured BookThis quiz is based on the information presented in Handbook of Dielectric and Thermal Properties of Materials at Microwave Frequencies, by Theodore Anderson. This book is a wealth of information of dielectric characteristics of biological tissues in plants, animals, as well as for ceramics, soils and minerals. Particular attention is paid to properties in the ISM frequency bands. Extensive sources for similar studies are provided.

Also consider: USAFSAM-TR-85-73
Radiofrequency Radiation Dosimetry Handbook (4th Edition)
This is the mother of all such references for SAR studies.

1.  What is a serious reason for uneven distribution of the thermal field in lossy media?

a)  Lossiness
b)  Temperature gradients
c)  Thermal runaway
d)  Impurities

2.  What is the mechanism for generating heat in dielectric materials via microwaves?

a)  Dipole polarization where polar molecules try to align themselves with the applied field
b)  High internal friction
c)  High temperature gradients
d)  Atomic molecularity

3.  What name is given to a resonant cavity method for measuring complex dielectric permittivity of lossy materials?

a)  Spatial injection method
b)  Surface current method
c)  Skin effect method
d)  Perturbation method

4.  What does heat capacity of a material measure?

a)  Ability to accumulate heat by increasing its temperature
b)  Amount of heat contained
c)  Absolute temperature
d)  Relative temperature

5.  What are the main mechanisms for interaction between EM waves and biological (e.g., brain) tissue?

a)  Oscillation of polar water molecules and ions
b)  Radiation of conductive salts
c)  Conduction of mineral imputities
d)  All the above

6.  Which list represents materials ordered from least to most polar high frequency dielectric properties.

a)  PVC, rubber, polyethylene
b)  Rubber, PVC, polyethylene
c)  Polyethylene, rubber, PVC
d)  All have equal polar properties at high frequency

7.  Which property is very important in affecting temperature distribution in liquids heated by microwaves?

a)  Density
b)  Conductivity
c)  Dielectric constant
d)  Viscosity

8.  Which body component has the highest conductivity in the 915 MHz ISM band?

a)  Cerebrospinal fluid
b)  Brain
c)  Bone marrow
d)  Tongue

9.  Which body component has the lowest conductivity in the 915 MHz ISM band?

a)  Blood
b)  Brain
c)  Bone marrow
d)  Tongue

10.  What typically happens to conductivity of body tissues as frequency across the ISM bands is increased?

a)  Increases
b)  Decreases
c)  Does not change
d)  Initially increases, then decreases

Need some help? Click here for the answers and explanations.


Posted  8/9/2012

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