Effective medium theory for large particulate size composites

The present study extends our previous work that concerned the effective pe rmittivities and absorptivities of particulate composites consisting of gra phite-type microsphere inclusions in a dielectric matrix, and their suitabi lity as radar-absorbing materials. Whereas in that work spheres of one size (radius a=50 mum) had been considered only, we here study the dependence o f the results on the sphere radius of up to one or several millimeters, and find sizable effects on permittivities for a greater than or equal to1 mm, and below that for the absorptivities, indicating the increasing importanc e of multiple scattering effects. While the multiple-scattering formulas ut ilized here are based on a low-frequency approximation, we devise a modific ation of these formulas in order to extend their validity to higher frequen cies (or larger particle sizes). (C) 2001 American Institute of Physics.