Measurement methods for the permittivity of thin sheet dielectric materials

This paper presents a new method for the determination of the complex permittivity of thin sheet dielectric materials that are flexible and elastic. Instead of the traditional method to install a doughnut shape sample in the transverse plane used in transmission line methods, most widely used methods for broadband permittivity measurements, a thin sheet sample is installed onto the outer conductor of the coaxial transmission line. The proposed method has much large sensitivity compared to the traditional one and is a broadband technique useful for thin sheet materials. Measurement results and comparison with other approaches agree very well, particularly at high frequency range.

I. Introduction

Measurements of material properties in RF and microwave frequency regions have been getting more important, especially in the research fields, such as material science, microwave circuit design, absorber development, biological research, etc., as the frequency of the applications goes up to sub-millimeter wave range and the areas of the applications are being wider. Dielectric measurement is important because it can provide the electrical or magnetic characteristics of the materials, which proved useful in many research and development fields. The most widely used techniques in the microwave region are: cavity resonators, free space, open-ended coaxial probe, and transmission-line [1]–[4]. Among these techniques transmission-line techniques are the simplest methods for electromagnetic characterization in wideband frequencies for the growing number of wideband applications of various RF and microwave materials.