Electromagnetic propagation in close-packed disordered suspensions

Multiple-scattering theory is used to evaluate the effective dielectric function {ε}({ω}) for disordered systems in which spherical inclusions are densely packed in a host medium. We compare the well-known quasicrystalline approximation (QCA) with Roth's effective-medium approximation (EMA). Both approaches are studied in the long-wavelength limit and, also, in the regime where the wavelength and particle diameter are comparable. In the long-wavelength case, the QCA reduces to the elementary Maxwell-Garnett formula. By contrast, the EMA is shown to include the effects of local-field fluctuations. The QCA and EMA are applied to two situations of experimental interest: (1) a strong-scattering system comprised of metal spheres embedded in a KCl matrix, and (2) a weak-scattering system made of pressed Al₂{O}₃$ particles. In both cases there are significant differences between the two approximation schemes and the EMA is generally to be preferred.