Free-Space Time Domain Position Insensitive Technique for Simultaneous Measurement of Complex Permittivity and Thickness of Lossy Dielectric Samples

Abstract

A novel time domain measurement technique is proposed to facilitate the simultaneous measurement of electrical properties (complex relative permittivity) and geometrical parameters (thickness) of the material under test (MUT). The overall process is noninvasive and noncontacting, which uses the measured scattering data of the MUT in the equivalent time domain or spatial domain. The effective time domain scattering data are employed to detect the primary and secondary peaks of the overall reflection and transmission coefficients. To this end, a novel algorithm is proposed to obtain the complex permittivity and thickness of the MUT in terms of extracted reflection and transmission power peaks. From the practical point of view, the main advantage of the proposed scheme is that one avoids the complicated calibration procedure normally required to define the reference plane. For increasing the accuracy of the overall reconstruction process, an automated optimization procedure based on parameter sensitivity analysis is proposed, which uses standard time gating procedure to implement the corresponding direct problem. The proposed technique is validated by extracting the relative permittivity, the dielectric loss (effective conductivity), and the thickness of various standard materials, such as polyethylene, Plexiglas, PVC, mortar, nylon, and so on, and comparing the extracted data with their values available in the literature.