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

The rapid advancement of electronic technology is characterized by continuous expanding the potentials of new-type elements, devices and systems with the use of porous plastics being developed. Therefore, it is necessary to study the main electrophysical characteristics of these materials. The effective solution to this problem is impossible without accurate estimation of the dielectric constant (ε). This paper presents two methods for measuring the relative low ε (1.02...1.1) of foams using a cylindrical waveguide-dielectric resonator based on the evanescent waveguide. The measurements of ε were carried out for four types of foam plastic in the frequency range of 10...12 GHz. 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 fluoroplastic-4 (polytetrafluorethylene), and the test material fills 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 one to measure any permittivity. ©2016 by Begell House, Inc.