Scattering by a composite sphere and effective medium approximations

To investigate the accuracy of three selected effective medium approximations (Bruggeman, Maxwel Garnett and an extended effective medium approximation), we compare the scattering, absorption and extinction cross sections obtained using the effective medium approximations with those utilizing the exact solution of the Maxwell equations for a composite sphere containing an arbitrarily located spherical inclusion. For the considered case of an acrylic sphere containing water inclusions at centimeter wavelengths, we find that all considered effective medium approximations provide scattering, absorption and extinction cross sections within 1% accuracy, for the inclusion size parameter up to about 0.5. The traditional effective medium approximations (Bruggeman and Maxwell Garnett) lead to considerable errors for larger values of the size parameter. The extended effective medium approximation allows larger inclusions, however, its accuracy decreases with increasing inclusion size. For the considered case of an acrylic sphere with water inclusions, the accuracy of the extended effective medium approximation is within 10% for the inclusion size parameters up to 5. (C) 1998 Elsevier Science B.V.