An effective medium method for calculation of the T matrix of aggregated spheres

An effective medium approach is developed for describing the radiative scattering characteristics of large-scale clusters of spheres. The formulation assumes that the waves exciting each sphere in the cluster can be described by a regular vector harmonic expansion, centered about a common origin of the cluster, and characterized by an effective propagation constant m(e)k. By combining this description with the multiple sphere interaction equations a 'homogeneous' T matrix of the cluster is derived, which is analogous to using the effective propagation constant models of the Varadans in conjunction with Waterman's EBCM. However, it is shown that the homogeneous T matrix will not automatically satisfy energy conservation because it cannot account for dependent scattering effects among the spheres. A 'discrete' formulation of the T matrix is then developed which retains the effective medium description of the exciting field yet provides for energy conservation. Illustrative calculations show that the effective medium T matrix can provide accurate predictions of the cross sections and scattering matrices of clusters containing a large number of uniformly packed spheres, yet this approximation uses a fraction of the computational time required for an exact solution. (C) 2001 Published by Elsevier Science Ltd.