Lewin's homogenization formula revisited for nanocomposite materials

The applicability of Lewin's homogenization formula is restricted to composite materials wherein: (a) the inclusions are small relative to wavelength in the host material and the inclusion material; (b) the real parts of the permittivities (and/or the permeabilities) of the host and inclusion materials have the same sign, for weakly nondissipative materials; and(c) the volume fraction of the inclusion material is less than approximately 0.3.