David Stroud, Department of Physics, The Ohio State University, Columbus, Ohio 43210-1106

We provide a brief and highly selective review of the Landauer-Bruggeman effective-medium approximation as applied to random composite media. We first discuss this approximation as applied to linear composites, i. e., to those materials in which there is a linear relation between a curl-free electric field and a divergence-free current density. We then describe extensions of this approach to random composites with cubic nonlinearities in addition to a dominant linear term, and to composites in which the components have a fluctuating conductivity (``conductivity noise''). Finally, we mention one novel application: to conductivity noise in a random composite of normal metal (N) and perfect conductor (S). It is shown that the extension of the EMA leads to a prediction of a frequency range in which the conductivity noise has a 1/omega frequency dependence, even if the noise in the individual components is frequency-independent.

PACS Nos. 42.70.Nq, 42.65.Pc, 78.66.Sq