MULTIPOLE EXPANSION TECHNIQUE FOR ELECTROMAGNETIC SCATTERING BY BURIED OBJECTS

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Abstract
A conceptually simple technique is introduced to solve the electromagnetic scattering by buried objects. The technique applies the multipole expansions in two-medium half spaces accompanied with their generalized Sommerfeld integrals to represent the scattering waves. Since the modal fields of the expansions all satisfy the boundary conditions on the planar air-earth interface, the scattering problem is reduced to solving the expansion coefficients by matching the boundary conditions on a sphere. Hence the method is very similar to that of the scattering in an infinite space using the method of separation of variables. Scattering results of buried conducting and dielectric spheres are presented. Some polarization anomalies of the scattered electric field components are observed on the earth surface. The technique can be directly applied to solve the scattering by buried non-spherical objects when the finite element method is used to treat the scatterer boundaries and inhomogenuities.