Effective dielectric response of polydispersed composites

We generalize the concept of renormalized polarizability introduced in a recently developed effective-medium theory to the case of polydispersed composites. We deal with a homogeneous and isotropic ensemble of spherical inclusions with a continuous distribution of sizes. The theory accounts for the correlated fluctuations among the induced dipole moments and the induced internal field within the long-wavelength dipolar approximation. The statistical properties of the ensemble enter in the final result through the two- and three-particle distribution functions. Numerical results are presented for a system of silver spheres in gelatin with a log-normal distribution of radii. The roles played by the dipolar fluctuations and by the size-dependent relaxation time, due to the surface scattering of the electrons, are analyzed and compared.