Attend Lab 4: Dielectric Measurements

Due No Due Date
Points 100

ECE 3305 Lab 4Dielectric Measurements

Introduction

Pre-Lab: Please complete the pre-lab assignments each week before coming to the lab.

Lab attendance: Lab attendance is required this week in order to complete the measurements. If you are unable to attend your lab due to illness, please contact your TA and arrange a later date to complete this lab.

No lab next week: Next week, there is no in person lab, and you can use that time to write your report.

What is due: The report for this lab is due before your next lab.

PRE-Lab

Download Files for Lab 4

Please download the following files and bring them with you to the lab (preferably on your laptop).

Lab 4 Handout Download Lab 4 Handout Please take a moment to read it over and make sure you have all the necessary gear to perform the project in lab.

Samples

Please bring a soft/pliable food product to measure. Fruits, applesauce, pudding, lunch meats, and similar soft products are good choices. I'd like you to see variability, so materials that have a little variability will be especially interesting.

Pre-Lab

Learn about Dielectric Properties of Body Tissues. See below.
Calculate the attenuation and wavelength of materials. See below.

Tutorials and Support Materials for each section of lab

Prelab: 1. Dielectric Properties of Biological Materials

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.

Prelab: 2. ATTENUATION AND WAVELENGTH

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.

table 7-1.jpg

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

3. THE DIELECTRIC PROBE

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.