A modified boundary integral equation for solving the exterior Robin problem for the Helmholtz equation in three dimensions

A boundary integral equation with modified fundamental solution to solve the exterior Robin problem for Helmholtz’s equation is considered. A specific choice of the coefficients of these added terms ensure the unique solvability and, in addition, they can be chosen to ensure the minimization of the least-squares difference of the modified and the exact Green’s function or the minimization of the condition number. Numerical results are reported showing the robustness and the superconvergence of the new method.