Boundary layer techniques for solving the Helmholtz equation in the presence of small inhomogeneities

We consider solutions to the Helmholtz equation in two and three dimensions. Based on layer potential techniques we provide for such solutions a rigorous systematic derivation of complete asymptotic expansions of perturbations resulting from the presence of diametrically small inhomogeneities with constitutive parameters different from those of the background medium. It is expected that our results will find important applications for developing effective algorithms for reconstructing small dielectric inhomogeneities from boundary measurements.  2004 Elsevier Inc. All rights reserved