Attend Lab 4: Dielectric Measurements

The dielectric properties (relative permittivity ɛ_r and conductivity σ (S/m)) of a material depend on the shape and nature of its molecules.  Water-based materials tend to have higher permittivity and conductivity than plastics and fats.  They are also generally non-magnetic, which means a relative permeability, μ­_r = 1. Knowledge of dielectric properties is useful for design specification. For instance, if we wanted to design a communication system for a cardiac pacemaker, we would need to know the dielectric properties of the tissue surrounding the device to determine size and power requirements of the system. There are generally two important tradeoffs in these designs. Higher dielectric materials have smaller wavelengths, so the antenna (which would ideally be half a wavelength) would be smaller. But these materials also generally have higher loss, so electromagnetic fields will attenuate more quickly and not travel as far into the body.

Biological tissues are made up mostly of water. The electrical properties of water depend on its temperature, frequency, and salinity.

• Online calculator for Water https://itis.swiss/virtual-population/tissue-properties/database/tissue-frequency-chart/ Links to an external site.

[1] S. Gabriel, R. Lau, C. Gabriel, “The Dielectric Properties of Biological Tissues II: Measurements in the Frequency Range 10 Hz – 20 GHz Links to an external site.” in Phys. Med. Biol., Vol. 41, 1996, pp. 2251-2269.

[2] C. Gabriel, “Compilation of the dielectric properties of body tissues at RF and microwave frequencies,” Final Technical Report, Occupational and Environmental Health Directorate Radiofrequency Radiation Division, Brooks Air force Base, TX, 1996.

• An online version can be accessed at:  http://niremf.ifac.cnr.it/docs/DIELECTRIC/Report.html Links to an external site.

Online Tissue Property Calculators (based on [2]:

• For different tissues: https://itis.swiss/virtual-population/tissue-properties/database/dielectric-properties/ Links to an external site.
• As a function of frequency: https://itis.swiss/virtual-population/tissue-properties/database/tissue-frequency-chart/ Links to an external site.

The wavelength and attenuation constant (or its inverse, skin depth) are two very important parameters when designing a communication system. Calculate attenuation constant α, propagation constant β, and wavelength λ for “Any Medium” from Table 7-1 in your textbook (Chapter 7-4), shown below.

A sample code for these calculations: compute_emvalues2.m Download compute_emvalues2.m

Theory:

Keysight App Note Dielectric Measurement 5989-2589.pdf Download Keysight App Note Dielectric Measurement 5989-2589.pdf

Kaatze 2006---Reference liquids for the calibration of dielectric sensors and measurement instruments.pdf Download Kaatze 2006---Reference liquids for the calibration of dielectric sensors and measurement instruments.pdf

Probe setup:

An initial setup of the probe is required, but has most likely been done by your TA. If not, see instructions:Dielectric Probe Lab Keysight Program Setup.docx Download Dielectric Probe Lab Keysight Program Setup.docx

Calibration:

A video from Keysight about calibrating the high temperature dielectric probe. It shows the small conductive disk placement between the shorting block and the dielectric probe. The software we are using is different, so the steps won't be exactly the same. It can be viewed here:  https://www.youtube.com/watch?v=vZi4UY2qQAw Links to an external site.

supporting material

Probe Spec Sheet:

N1501A_Technical_Overview_5992-0264.pdf Download N1501A_Technical_Overview_5992-0264.pdf

4a. Expected values for Fluids

• Kaatze 2006---Reference liquids for the calibration of dielectric sensors and measurement instruments.pdf Download Kaatze 2006---Reference liquids for the calibration of dielectric sensors and measurement instruments.pdf

4c.Variability of Food Product

• Matlab functions for mean Links to an external site. and standard deviation Links to an external site..

4d. Loss in Dielectrics

• Wikipedia Page on Dielectric Loss Links to an external site.

6a.Add to the Foodie Discussion

• Discussion Food Products