Effective Dielectric Constant of Heterogeneous Media

Abstract

A method for measuring the dielectric constant and conductivity of powders is described. Numerous formulas of earlier workers pertaining to the dielectric constant of porous media of low density are discussed. It is then shown that these relations incorrectly predict a value of the intrinsic dielectric constant which is a function of density. In an effort to develop a formula which would predict correctly the density dependence to at least a medium range of densities, a calculation is presented which expresses the effective dielectric constant of a given system as a function of particle shape, intrinsic dielectric constant, powdered density, and packing properties of powders composed of ellipsoidal particles. The formula involves the demagnetization coefficient and intrinsic dielectric constant of the powder particles. Data obtained from measurements of dielectric constant of magnetism oxide, silica, polystyrene, zinc oxide, etc., were applied to this formula and the intrinsic dielectric constants inferred agreed with bulk measurements by other workers, and the particle shapes derived from dielectric measurements agreed with other physical properties of the powder.