A surface integral equation formulation for low-frequency scattering from a composite object

A surface integral equation formulation is derived for low-frequency scattering from a composite object. This formulation allows those algorithms for finding loop-tree basis on simple surfaces to be applied to the complicated interfaces of a composite object. By including the residue term in the kappa operator, the present formulation induces the interface boundary conditions automatically, and the resultant matrix equation can be solved directly without using the O(N-2) number-of-unknown-reduction scheme. Numerical results validate that the algorithm is stable even at extremely low frequencies and for closely spaced structures.