We consider three problems for the Helmholtz equation in interior and exterior domains in Rd , (d = 2, 3): the exterior Dirichlet-to-Neumann and Neumannto-Dirichlet problems for outgoing solutions, and the interior impedance problem. We derive sharp estimates for solutions to these problems that, in combination, give bounds on the inverses of the combined-field boundary integral operators for exterior Helmholtz problems.
Dean Baskin, Euan A. Spence, Jared Wunsch