Microwave characterization of filled polymers

Interest in filled polymers has expanded in recent years as investigators h ave recognized the great flexibility allowed by these materials to suit par ticular properties such as electrical, mechanical, and/or coupling between these properties. This article describes the work undertaken to investigate the microwave response of two different types of samples: one with carbon black or silica particles embedded in a linear low-density polyethylene, an d the other with carbon black particles or carbon fibers embedded in an epo xy resin. We report broad-band (30 MHz-14 GHz) measurements of the complex permittivity of these materials obtained by measuring the scattering parame ters (S parameters) of a microstrip line loaded with a rectangular sample o f the test material. The experimental results presented give access to data which can be rationalized in terms of a combination of Bruggeman's self-co nsistent model with Jonscher's phenomenological analysis. This analytical a pproach yields data that are in good correspondence with experimental data in terms of the concentration dependence of inclusions within the polymeric matrixes and demonstrates large practical capabilities for analyzing the e lectromagnetic properties of these materials at microwave frequencies becau se it allows one to make an explicit connection between these properties an d the experimentally accessible parameters. (C) 2001 American Institute of Physics.