  When a composite containing nonlinear dielectric particles suspended in a
host medium is subjected to a sinusoidal alternating current (ac) electric
field, the dielectric response of the composite will generally consist of ac
fields at frequencies of higher-order harmonics. For an electrorheological (ER)
solid under structure transformations due to external fields, we apply the
Ewald-Kornfeld formulation to derive the local electric fields and induced
dipole moments explicitly, and then we perform the perturbation expansion
method to extract their fundamental and third-order harmonics analytically. It
is shown that the degree of anisotropy of the ER solid can affect these
harmonics significantly. Our results are well understood in the spectral
representation theory. Thus, it seems possible to perform a real-time
monitoring of the structure transformation by measuring the nonlinear ac
responses of ER solids.
