The effective medium approximations: Some recent developments

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. (C) 1998 Academic Press Limited.