Electromagnetic scattering from large aspect ratio lossy dielectric solids in a conducting medium

The spheroidal T-matrix formalism developed by Hackman/sup 1-3/ and Sammelmann/sup 4-6/ for acoustic scattering is extended to electromagnetic scattering from lossy dielectric solids in a conducting medium. The spheroidal T-matrix formalism exhibits superior performance with respect to the spherical T-matrix formalism for objects that deviate appreciably from a spherical shape. Both acoustic (elastic) and electromagnetic scattering are solutions of the vector Helmholtz equation. In the case of elastic wave scattering, the displacement field has 3 degrees of freedom corresponding to the 2 polarization states of the shear wave and the longitudinal mode. In the case of electromagnetic scattering, the electric (magnetic) field has 2 polarization states corresponding to left and right-handed photons, but lacks a longitudinal mode. The T-matrix description of electromagnetism mimics the T-matrix description of elastic wave scattering in the absence of a longitudinal mode. Indeed, the stress tensor of the displacement is replaced by the exterior derivative of the electric field in Betti´s identity in the derivation of the T-matrix formalism of scattering from a lossy dielectric solid. Continuity of the displacement and surface traction is replaced by continuity of the tangential components of the electric and magnetic fields in the boundary conditions. In the case of a time harmonic field, the presence of a finite conductivity in the medium is represented by the insertion of an imaginary component of the wavenumber that is proportional to the conductivity in the medium. In the case of complex wavenumber, the Helmholtz equation is no longer a self-adjoint operator, and the S-matrix is no longer unitary. This article describes some of the features unique to scattering in seawater due to the large conductivity of the medium.