IMMG Student Projects

2002 Industrial Project

Inverse Technique for Evaluation of Complex Permittivity of Materials

Student: Pawel Kopyt, Ph.D. Student at Warsaw University of Technology
Advisor: Vadim Yakovlev

Sponsored by The Ferrite Company, Inc.

Permittivity

Complex entity eps = eps ' - i eps '' where eps is dielectric constant, eps '' = eps /(2 eps f eps eps ) is loss factor, eps is electric conductivity, f is frequency, represents major aspects of behavior of dielectric materials in the electromagnetic field.

Difficulties and Peculiarities

Measurement requires very precise and accurate handling, and each experimental approach is associated with a specific calculation rule.
Permittivity cannot be measured directly; it is usually calculated via other measurable parameters (like reflection coefficient, phase, etc.).

Motivations for the Project

Despite all the progress in microwave technology, data on complex permittivity of many materials at many (higher) frequencies are still missing.
Knowledge of permittivity is a keystone controlling numerous applied problems in electronics, telecommunications, and microwave power engineering.

Common Problems

Determination of permittivity is a complex area of electrical engineering involving elaborate mechanical processing of the material samples.
Known techniques of measurement have different limitations (requirement of small sample dimensions, necessity of putting a sensor inside the material, etc.).

Engineers need to have a simple method of evaluation of permittivity of materials of arbitrary dimension and configuration.

Concept of the Project

Key Idea:

To avoid using special devices and associated calculation techniques for getting complex permittivity.
To replace a major part of measuring work by modeling of a corresponding structure.

Project Goal:

To force modeling software to run in a loop in order to match the measured and computed characteristics (for the unknown and known materials respectively) and thus determine permittivity for which these characteristics are matched.

Model and Experimental Setup

Reflection coefficient |S| in a frequency range is measured and computed
Section of a waveguide with a sample material (see Figure).

Experimental Phase:

|S| for the sample with unknown permittivity is measured by HP-8510B Network Analyzer.

Computational Phase:

|S| for the sample with known permittivity is computed with the use of QuickWave-3D (www.qwed.com.pl), conformal FDTD 3D full-wave EM simulator.

3D view of the waveguide with the sample material

Matching the Data - Computational Algorithm

(coming soon)

Anticipated Project Output

Algorithm incorporating efficient optimization process and error analysis guaranteeing quick convergence.
Computational procedure implemented in MATLAB.
Test results illustrating the accuracy of the method.
Data of evaluation of permittivity of unknown materials.

The web page is prepared on the basis of the material presented at the Departmental Meeting on the Prospective 2002-2003 Major Qualifying Projects, February 19, 2002.