Multi-frequency electromagnetic scattering from inhomogeneous bodies using shifted frequency equivalence

The surface integral formulation of EM scattering from a homogeneous body involves using internal and external equivalencies. Imposing the continuity of the fields at the boundary renders the unknowns defined at the surface. For an inhomogeneous body, no such surface formulation is available yet, and furthermore one has to repeat at the same volume integral equation solution at each frequency of interest. In this work, the shifted frequency internal equivalence is reported which allows the usage of the same data in numerical calculations, at least over a frequency band. Utilization of this equivalency is demonstrated using a simple inhomogeneous dielectric/magnetic slab example.