On the Surface-Integral-Equation-Based Characteristic Mode Expansion of Dielectric Body With Internal Excitations

In this communication, the completeness of surface-integral-equation (SIE)-based characteristic modes (CMs) in the modal expansion for the dielectric body is addressed. It is found that, when the excitation source is positioned inside the dielectric body, the conventional spurious-free SIE-based CMs alone are inadequate for fully characterizing the internal scattered fields and the nonradiating CMs arisen from the Chang-Harrington CM formulation will contribute to the internal fields. A numerical example where a lossless dielectric ball is excited with an internal electric dipole is provided. Theoretical analysis and numerical results demonstrate that, in the presence of internal excitations, both the radiative CMs and the nonradiative CMs should be employed to fully characterize the internal scattered fields.