| Metal particulate polymer composites are fabricated and the d.c. conductivities and microwave dielectric constant from 8.5 GHz to 11.5 GHz are measured. The existing models are reviewed and compared with the experimental results. The microstructures of the composites are examined.;Six different elements (aluminum, copper, silver, nickel, carbon and silicon) as fillers are investigated. A number of different particle sizes of each element are studied. The distribution of the particle size is examined. Two thermosetting polymers are mainly used as matrices; a polyester and epoxy.;The effects of the type of element, the metal content and size and size distribution of the powder are documented. The dielectric constant of the composite is shown to be strongly dependent upon the dispersion of the particles in the matrix. For the same amount of metal content, the composite showing more clusters in the microstructure always gave a higher dielectric constant. The composite dielectric constant is shown to be invariant with the two polymeric matrices used when the dielectric constant of the composite is reduced by the dielectric constant of the matrix. No percolation phenomenon is observed for the samples in which the metal powder and polymer matrix are homogenously mixed.;The microstructure of the composite is significantly important in determining the electrical properties of the composite. The existing models which do not have a parameter to incorporate the effect of the microstructure always underestimate the dielectric constant of the composite. The Wu-McCullough model which does have a parameter of the microstructure, therefore, can predict the results better than the rest of models. |
