Asymptotic Expansions for Resonances in the Presence of Small   Anisotropic Imperfections
  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. 
M. Gozzi, A. Khelifi
math-ph math.MP