Complex permittivity of low loss thermoplastic composites using a resonant cavity method

Abstract

SUMMARY: The use of high energy rate joining of fibre-reinforced thermoplastic (FRTP) composites using microwaves has yielded promising preliminary results [1][2][3] and more research is being carried out so that the technology can find its application in manufacturing industries shortly. Methods such as the dielectric probe and waveguide transmission have been successfully used to measure the dielectric constant (ε′) of low loss thermoplastic composites but they cannot give reliable results when used to measure the dielectric loss (ε″) [4][5][6]. This paper describes a convenient laboratory based method designed to obtain ε′, ε ″ and hence loss tangent (tan δ) for low loss thermoplastic composite materials like glass fibre reinforced (33%) low density polyethylene [LDPE/GF(33%)]. The method is called the resonant cavity method and the schematic diagram of the set up and that of the cavity is depicted in Fig.1 and Fig. 2 respectively..