Design of multi-directional acoustic cloaks using two-dimensional shape optimization and the boundary element method

Acoustic cloaking is a technique that seeks hiding objects in a sound field by reducing or cancelling their scattered sound pressure. Incident waves are restored to as close as possible their original undisturbed form after hitting the cloaked object. One technique for achieving this goal is the design of additional scatterers around the object, which, properly distributed and shaped, can create cloaking at the design frequency. A newly developed numerical technique combining the Boundary Element Method (BEM) with shape optimization is applied in this work for two-dimensional cloaking of a cylinder. The shapes of the scatterers are optimized for the cloaking of the whole setup with waves impinging on the cylinder from several different directions. The results show a measure of the amount of cloaking depending on the direction at the range around the design frequency. The optimization results are compared with existing one-directional cloaks. The impact of visco-thermal acoustic losses in the cloaking design is also evaluated by means of a BEM implementation with losses.