  We provide a rigorous derivation of an asymptotic formula for perturbations
in the resonance values caused by the presence of finite number of anisotropic
imperfections of small shapes with constitutive parameters different from the
background conductivity. The asymptotic expansion is carried out with respect
to the size of the imperfections. The main feature of the method is to yield a
robust procedure making it possible to recover information about the location,
shape, and material properties of the anisotropic imperfections.
