Equations for the conductivity of macroscopic mixtures

Two equations which describe the conductivity (resistivity) of a wide variety of binary macroscopic conducting mixtures as a function of the conductivity of the components, the volume fraction of each, the space dimension and a single parameter are presented. These equations are interpolations between Bruggeman's symmetric- and asymmetric-effective-media theories. The parameter, possibly a fractal dimension, is determined from a critical composition; for example, in a metal-perfect-insulator mixture it is the metal-insulator transition point. Good agreement is found with a wide range of experimental data.