THE EFFECTIVE-MEDIUM APPROXIMATIONS - SOME RECENT DEVELOPMENTS

We provide a brief and highly selective review of the Landauer-Bruggem an 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 t hen describe extensions of this approach to random composites with cub ic nonlinearities in addition to a dominant linear term, and to compos ites in which the components have a fluctuating conductivity ('conduct ivity noise'). Finally, we mention one novel application: to conductiv ity noise in a random composite of normal metal (N) and perfect conduc tor (S). It is shown that the extension of the EMA leads to a predicti on of a frequency range in which the conductivity noise has a 1/omega frequency dependence, even if the noise in the individual components i s frequency independent. (C) 1998 Academic Press Limited.