Measurement of foam plastics permittivity with the resonance method using a waveguide-dielectric resonator

The rapid development of electronic technology is characterized by continuous expanding the potentials of new types of created elements, devices and systems that use porous plastics. Therefore, it is necessary to study the main electrophysical characteristics of these materials. The effective solution to this problem is impossible without the accurate determination of the dielectric constant (e ). This paper presents two methods of measuring the relative low e (1.02...1.1) of foams using a cylindrical waveguide-dielectric resonator on the evanescent waveguide. The measurements of the e were carried out for four types of foams in the frequency range 10...12 GHz and the estimation errors are presented. In the “direct” method the test material is used as a dielectric element of the resonator. In the “indirect” method the dielectric element is made from ftoroplast, and the test material filled the evanescent sections of the waveguide. The investigations have shown that the “indirect” method gives a decrease of the measurement error in 2.5–5 times compared to the “direct” one. But the “direct” method is easier and allows to measure any permittivities.