Size-Dependent Bruggeman Approach for Dielectric-Magnetic Composite   Materials
  Expressions arising from the Bruggeman approach for the homogenization of dielectric-magnetic composite materials, without ignoring the sizes of the spherical particles, are presented. These expressions exhibit the proper limit behavior. The incorporation of size dependence is directly responsible for the emergence of dielectric-magnetic coupling in the estimated relative permittivity and permeability of the homogenized composite material. 
A. Lakhtakia and T.G. Mackay