CAPACITANCE AND DIELECTRIC-BREAKDOWN OF METAL LOADED DIELECTRICS

The authors review and extend analytic, numerical and experimental work on the capacitance, C(f), and dielectric breakdown field, Eb(f), of a simple insulator containing volume fraction, f, of randomly located metal inclusions. In the case of spherical inclusions, they find Eb(f)=Eb(0)/(1+kc(ln V/mod ln f mod)alpha). V is the sample volume divided by the average volume of an inclusion, kcis a constant and 1/2< alpha <1 for large ln V/mod ln f mod. In the dilute inclusion limit, the statistics of the dielectric breakdown field are shown to be of a modified Gumbel form. The scaling theory of capacitance in composites with percolation microstructures is outlined, and the authors discuss extensions to include hard core repulsion between inclusions. They have fabricated many samples of paraffin wax (a simple insulator) containing various concentrations of stainless-steel spheres (size range 10-65 mu m). The capacitance and dielectric breakdown field of these samples is presented and the results are compared with theory. © 1990 IOP Publishing Ltd.