A hybrid FEM / SBR method to compute scattering by large bodies with small protruding scatterers

A hybrid method that combines the finite-element method (FEM) and the shooting-and-bouncing-ray (SBR) method is presented to compute scattering by large bodies with small protruding scatterers. In the method, the field equivalence principle is employed to replace the protruding scatterers by a set of equivalent electric and magnetic currents. The total scattered field then becomes the superposition of the field scattered by the large body without protrusions, which is calculated with the use of the SBR method, and the field radiated by the equivalent currents in the presence of the large body, which is also calculated with the use of the SBR method with the aid of the reciprocity theorem. The required equivalent currents are computed with the use of the FEM, which permits the handling of complex material composition of the protrusions. Two-dimensional examples are presented to demonstrate the feasibility of the proposed method.