ECE 290: Senior Design Fall 2006
Electromagnetic Phantom for the Human Body
Final Report
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Enes Basic (EE) |
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Omar English (CompE) |
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Jason Deguzis (EE) |
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Dr. Rajeev Bansal (ECE)
Sponsor
MegaWave Corporation
200 Shrewsbury Street
Boylston, MA 01505
MegaWave Contact: Emanuel Merulla
Table of Contents
Executive Summary.......................................................................................................2
Sponsor Background.....................................................................................................2
Introduction....................................................................................................................2
Problem Statement........................................................................................................2
Project Specifications....................................................................................................3
Proposed Solution.........................................................................................................3
Tests Conducted...........................................................................................................5
Previous Research........................................................................................................5
Gel Medium...........................................................................................................5
Existing Liquid Solution.........................................................................................6
Proposed Testing..........................................................................................................6
Proposed Software Solution.........................................................................................7
Proposed Budget..........................................................................................................8
Timeline…………………………………………………………….....................................8
Appendix……………………………………………………………....................................9
I: Executive Summary
The proposal describes a senior design project that is currently being researched and designed for the MegaWave Corporation. Currently, MegaWave uses phantoms filled with a solution which imitates the electromagnetic properties of the human bodies in order to test antennas. The project aims at replacing this solution with another mixture which more accurately represents the afore mentioned electromagnetic properties of the human body. The simulating medium must be accurate for a frequency range of 20 MHz - 3000MHz. Also the medium with which the phantom will be filled should be stable, that is, it will not separate over time or due to small changes in temperature. A Laptop will control a network analyzer used to take measurements of an antenna under test that has been placed on the dummy. Once all measurements have been made, the laptop will process the data and display a horizontal radiation pattern for the antenna under test. The control software will be modified using Visual Basic. The code for the automated testing system should be modified so that graphs are automatically created after taking a measurement, as well as a way to easily compare the phantom test results with the human test results. The final mixture must be tested using the revised automated testing system developed last year for MegaWave Corporation.
II: Sponsor Background
Located in Bolyston, Massachusetts, MegaWave designs antennas for organizations such as DARPA, DOT, SOCOM, NASA, and the US Army and Navy. Founded in 1994, MegaWave began with development antennas for radio and television communication systems, and moved on to developing antennas for military use. Currently, MegaWave’s research includes direction finding antennas, genetically optimized antennas, and portable electronic device detection for aircraft.
III: Introduction
The process used by MegaWave for developing body worn antennas involves a filled phantom on a rotating platform. For a given frequency range, an antenna transmits a signal to the body worn antenna that’s placed on the phantom, which rotates a full 360 degrees, measuring signal strength at previously set intervals. While a human could undergo this test, the phantom has the advantage of being perfectly still for any amount of time. Considering these tests can take several hours to conduct, using the phantom is the more practical choice for testing.
IV: Problem Statement
In the past, the military has utilized communications that consisted of one soldier in a squad carrying a bulky antenna pack to keep in contact with headquarters. To move more efficiently in the field, antennas were soon integrated into the equipment that a soldier already carried, such as within body armor. With this evolution a new problem arose. The human body affected the properties of the antenna, and therefore a systematic way of testing body-worn antennas needed to be created. This was done last year by a senior design group sponsored by MegaWave Corporation. The final product was an automated system that through the use of a source antenna, body worn antenna mounted on a dummy, and a network analyzer, measured the antenna properties for a 360 degree rotation of the dummy. The dummy was filled with a saline solution that possessed similar electromagnetic properties to the human body.
As body worn antennas further developed, the need for a more accurate phantom arose. While the saline solution acted similar to the human body, it was determined that it was not precise enough for MegaWave’s research. Therefore, a new tissue-simulating medium is needed that more closely represents the electromagnetic properties of the human body. This would provide more accurate results when developing body-worn antennas, allowing them to be more efficient.
V: Project Specifications:
Environmental:
Testing:
Physical:
· should be cost effective and easy to prepare.
· should be easy to handle.
· can be inserted into the dummy as well as emptied without difficulty.
Software:
VI: Proposed Solution
Currently, the solution used at MegaWave is not an accurate enough representation of human tissues. The solution consists of 3.5g of salt per liter of water. For this concentration of salt, the permittivity ranges from 76-78. We are aiming for a medium that mimics muscle tissue, and to do that we will use values similar to those shown in the table below.
The proposed solution is to utilize both salt and sugar in the new mixture. Our research has shown that sugar added to a saline solution will decrease the permittivity slower then additional salt would. Considering the fact that muscle tissue and fat tissue are dominant in the human torso, we plan to concentrate on mimicking muscle tissue primarily and fat tissue secondarily.
Permittivity is a physical quantity that describes how an electric field affects and is affected by a dielectric medium, and is determined by the ability of a material to polarize in response to the field, and thereby reduce the field inside the material. Thus the permittivity relates to a materials ability to transmit an electric field. The response of normal dielectrics to external fields generally depends on the frequency of the field. This frequency dependence reflects the fact that a materials polarization does not respond instantaneously to an applied field. As a result the response is causal, and is treated as a complex function of the frequency to the applied electric field. Conductivity is a measurement of a material’s ability conduct an electric current. The loss tangent is the ratio of the complex part of the dielectric permittivity to the real part.
There are
several ways to predict the effective permittivity of a medium. The equations we
will be using are derived from Maxwell’s Equations.
Our main focus will be on the relationship of the loss tangent, conductivity,
and permittivity with regards to frequency.
VII: Tests Conducted
Graphs represent dielectric parameters when 100g of Sugar is diluted in 300ml of MegaWave’s Solution.
VIII: Previous Research
i. Gel Medium
There has been research on gel medium. This gel solution was based on the polyethylene powder and TX-150, a gelling agent. The gel used consisted essentially of Acrylamide (C3H5NO) polymerized in water with doping agents that were added to simulate electromagnetic properties of biological tissue. It has been used by authors to simulate high to low conductivity tissues in short wave ranges. Some of the pros are, that it is a solid elastic, easily shaped into complex forms, low cost and readily available. Some cons include that it is not easy to handle because bacteria or mold make it difficult to maintain the integrity of the gel. Also it would be difficult to fill a full body phantom with gel.
ii. Existing Liquid Solution:
In our research we have discovered a NTT-AT company in Tokyo, Japan that offers the tissue simulating liquid for small frequency bands. Sample of its Data is shown below.
Estimation of Body-Tissue Simulating liquid (http://www.emc-center.jp/index.html.en)
IX: Proposed Testing
Small scale testing will be conducted in the lab on campus using the network analyzer described in the Appendix. The testing will consist of mixing a salt and sugar solution, and measuring its properties to calculate its permittivity and conductivity. If time permits, the electromagnetic properties of a previously suggested gel solution will be analyzed. Getting the correct permittivity will require trial and error guided by approximate calculations and mixing the right amounts of salt and sugar. Once the correct mixture is found with an acceptable permittivity, and conductivity, large scale testing will be performed. This testing will involve using the automated antenna test developed by the previous Senior Design team. In this test we will be measuring the VSWR with antenna on body, and compare VSWR to phantom and body. We will also measure the vertical pattern on phantom and body and then compare the results.
Since contamination can be an issue, over winter intersession we will be testing solutions of salt, sugar, and water, to see under what conditions mold grows. Also, the use of preservatives may be used to prevent the growth of mold. This 30 day trial period should be sufficient in verifying if mold will grow.
X: Proposed Software Solution
The current software developed by the previous Senior Design team last year was not completed. The overall program was sufficient enough to do the automated testing of the antennas. However, several functionalities were omitted and various bugs were not resolved due to time constraints. We propose to add as many features and fix as many bugs as possible.
The features that will be added are listed below:
The bugs that need to be fixed are listed below.
o This will return the phantom back to the zero position. Upon returning no measurements will be taken. Currently the program hits an error upon
trying to return to zero while taking measurements.
XI: Proposed Budget
Digital Scale $180
Solutes $100
Phantom $350
Lab Equipment $100
Beakers, Stirring Rods, Graduated Cylinders,
Specimen Containers
Distilled Water
Other $100
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Total Cost $830
XII: Timeline
XIII: Appendix
Equipment we are going to be using:
The Network Analyzer is used to measure complex impedances VSWR, and the losses or gains in a device. It is capable of sweeping frequencies from 300 KHz to 3 GHz, and can be used in conjunction with the dielectric probe to determine additional electromagnetic properties.
The dielectric probe can be used to determine the incident, transmitted, and reflection signal strength of a sample. These values are then used to determine the permittivity, conductivity, and reflection coefficient of that sample.
General Experimental Setup utilizing Network Analyzer and Dielectric Probe
Additional Equipment includes:
To download this file:.pdf