Active Acoustic Cloaking Spherical Shells

The scheme of efficient and practical directional active acoustic cloaking is proposed in contrast to the attractive though hard to utilize concept of passive acoustic cloaking which is based on composite acoustic metamaterials or negative index materials. In this paper, the scattering cancellation is planned to occur in a desired direction such as backscattering in far-field, with great interests in SONAR (Sound Navigation and Ranging) applications. The invisibility of the target object/region occurs due to a surrounding spherical cloaking shell composed of a casing layer stimulated by a radially polarized piezoelectric bonded layer. With concerns regarding the feasibility of the proposed configuration, the electrical excitation is limited only to its monopole mode (breathing mode). An illustrative numerical example is presented in order to investigate the practicability of the configuration especially with emphasis on required voltage and power supply.