Three-dimensional impedance networks for modelling frequency dependent electrical properties of composite materials

Abstract

A three-dimensional impedance network model for describing the frequency dependent electrical properties of composite materials has been developed. The considered compounds consist of conducting particles dispersed in an insulating matrix and the ratio between the conductivities of the two phases is around seven decades. The character of the contacts between the particles will have a critical effect on the electrical characteristics. Two different types of contacts, represented by edge and face connections, are taken into account. A sharp edge connection gives an extremely localized field enhancement. Instead of trying to resolve this rapidly diverging electric field, an equivalent circuit element that reproduces the overall behaviour of the edge contact was introduced. The distribution of the filler grains also affects the electrical properties. The large agglomerates that appear in random distributions are not representative of the well-dispersed real materials. Several methods to create a more even than random dispersion of the conducting particles were therefore utilized. Simulations were performed and compared to measurements on ethylene–propylene–diene monomer rubber filled with silicon carbide grains. The calculations reproduce the general characteristics of the experimental results.