Far-field holography applied to an arbitrary geometry.

Abstract

An algorithm is developed for the reconstruction of the surface acoustic field from measurements of pressure made in the far field for a structure with arbitrary geometry. This inverse problem is ill-posed due to the presence of evanescentlike modes that decay very rapidly away from the surface making them difficult to reconstruct. The boundary elements method is applied. The presence of the evanescentlike field is treated by expanding surface normal velocity in a set of functions that form the eigenstates of radiated power, computed by diagonalizing the surface resistance operator, the sum truncated to remove the modes with negligible radiation. The algorithm is tested by applying it to scattering from a rigid cylinder with hemispherical endcaps. It is also applied to the radiation problem of a small piston located on the same cylinder, where the resolution attained on the surface is shown to increase with increasing frequency.