Orthogonality relation for a three-dimensional scattering electromagnetic field in a dispersive medium

Considering a scattering field by a perfectly conducting sphere as a typica l example, we develop a method to derive an orthogonality relation for a th ree-dimensional scattering electromagnetic field in a dispersive dielectric medium. Each orthogonal mode is composed of the doublet of the incident pl ane field and the scattering spherical plane field. The scattering field in cludes the near field in the vicinity of the scatterer. Expanding the total field energy stored in the whole space using the derived orthogonality rel ation, we show that the total field energy is expressed as the sum of the e nergies of independent harmonic oscillators.