Uberall H., Hughes R., Niemiec J.

We have obtained mathematical expressions for the acoustic response of a submerged wedge, whose outside is coated with a lossy material. Previously, solutions have been obtained for the case of Dirichlet or Neumann acoustic boundary conditions representing a sound-impenetrable wedge which is either rigid of soft; there seem to have been no investigations of the case where the wedge is coated, or where the coating is at least describable by an impedance boundary condition. The subject of the present study concerns this latter case, and consists of two parts: (a) obtaining a solution for the acoustic echo from a wedge characterized by an impedance boundary condition, and (b) obtaining an expression for the surface impedance that corresponds to a lossy acoustic coating on the wedge surface. The solution of (a) is found by an adaptation of existing theories, and of (b) by the transfer of an earlier approach from the electromagnetic to the acoustic domain. Solutions of the echo amplitude are found in the form of integral expressions for which asymptotic expansions can be found for large observer distances. Numerical solutions of the integral and hence of the scattering amplitude, were obtained for both an impenetrable wedge and for a coated wedge, at backscattering and at bistatic angles.