MODELING THE PERMITTIVITY OF COMPOSITE-MATERIALS WITH A GENERAL EFFECTIVE MEDIUM EQUATION

The purpose of this paper is to review the multiscattering models for spherical particles, quasistatic mixture laws, effective medium theories, percolation equations, and finally the general effective medium equation (GEM), which axe all used for modeling the dielectric properties of complex mixture materials. These are then used to analyse selected experimental results. Five different classes of composite materials, including carbon-resin mixtures (with various types of carbon) and a conducting polymer (in both air and water) have been selected. Comparisons between the experimental results and the theoretical fits obtained from the quasistatic laws (Looyenga, Kraszewski, Greffe, and Bottcher equations) and from the general effective medium (GEM) equation are then made. The GEM equation gives the best quantitative fit of the experimental data for these composite materials. This is almost certainly because the GEM equation is the only equation that can model the rapid changes in dielectric constants and conductivity that occur at and near the percolation threshold of the conducting particles in the dielectric matrix. Two parameters of the GEM equation, upsilon(c) or phi(c) (the percolation threshold) and t (an exponent) give some insight into the microstructures and the connectivity of the dispersed conducting particles.