A solution methodology is presented in this article to compute the effectiv
e permittivity for a multiphase lattice of dielectric and/or conducting sph
eres at low frequencies. It is assumed that the lattice is effectively isot
ropic. This methodology relies on two central developments. The first is a
T-matrix solution for a multiphase lattice of spheres immersed in a uniform
electric field. This solution is presented in a succinct matrix-vector not
ation and is valid for any lattice type. The second development is a simple
and accurate equation for the effective permittivity that incorporates all
mutual coupling between the spheres. Results are shown in this article for
three situations. The first is a two-phase system of conducting spheres (u
sed for verification) and the second is a dielectric-conductor (cermet comp
osite) lattice of spheres. The third and final result is from a lattice con
taining a cluster of conducting spheres. It is suggested that this last mat
erial type displays a behavior in between that of random materials and two-
phase lattices due to "permittivity enhancement" at low volume fraction. It
is also shown that the Maxwell Garnett formula is not nearly as accurate f
or this cluster lattice, also because of this enhancement effect. (C) 2000
American Institute of Physics. [S0021-8979(00)02116-2].