Wideband Optimization Process for EM Characterization of Low-Losses Dielectric and Dispersive Materials in a Quasi-TEM Cell

Abstract

This paper presents an original wideband method (from 1 MHz to 1 GHz) for the characterization of dielectric and dispersive materials. The method is based on a full-wave calculation technique using the finite-difference time-domain (FDTD) method combined with a fast optimization process. The S-parameters are the metrics which have to be minimized. Only two S-parameters measurements of a quasi-TEM structure with and without the sample under test (SUT) are required. In parallel, the experiment is faithfully reproduced by simulation through the FDTD method still without and with the SUT model. This enables to determine the electromagnetic properties of the SUT by adjusting its properties in simulation in order to match the measured S-parameters of the cell thanks to the optimization process. The main advantage of the proposed method lies in the fact that no machining process of the sample is required provided that: 1) the size of the sample enables to insert it within the quasi-TEM cell; 2) the position of the SUT in the propagating device is known accurately; and 3) the insertion of the SUT sufficiently modifies the S-parameters of the quasi-TEM structure. The experimental results obtained on different dielectrics or ferrite samples are provided showing excellent agreements with results given in the literature or by the manufacturers.