Acoustic scattering from layered pentamode materials.

Abstract

While receiving less attention in the literature than in the field of electromagnetic scattering, theoretical efforts to define and create acoustic skins capable of reducing scattered energy from obstacles by way of mimicking coordinate transformations through use of meta-materials have begun. The present work extends recent analysis of Norris by considering a variety of acoustic skins, from those comprised of fluid layers which are isotropic in bulk moduli with anisotropic density to those having anisotropic bulk moduli and isotropic density. In all but pure inertial types, fluid layers comprising the skins are pentamode materials governed by a special scalar acoustic equation for pseudo-pressure derived by Norris. In most cases presented, material properties of the fluid/pentamode layers are based upon target values specified by continuously varying properties resulting from theoretical coordinate transformations geared to minimize scattered pressure limited by realistic goals. The present work analyzes acoustic skins for the specific case of plane wave scattering from an acoustically hard sphere. An initial exploration of the parameter space defining such skins (for example, material properties of its constituent layers and operating frequency) is undertaken with a view toward “optimal” design. [Work supported by the NAVSEA Newport In-House Laboratory Individual Research (ILIR) Program.]