Three-dimensional large-scale acoustic invisibility cloak with layered metamaterials for underwater operation

A class of three-dimensional acoustic cloak for underwater operation is designed by using a multi-area coordinate transformation method. To overcome the difficulty of achieving materials with the ideal parameters of the cloak in nature, layered metamaterials consisting of mercury and water are designed based on effective medium theory. The acoustic properties of the layered metamaterials can be characterized by the anisotropic densities and isotropic modulus, which can satisfy the material requirements of the cloak shell. This design has many advantages over previous designs of acoustic cloak, including a large cloaking area, omnidirectional invisibility, broad working frequency and easier design methodology. Our transformation strategy and method of metamaterials design offer a cost-effective way and efficient technique for fabricating a large-scale cloak. Excellent invisibility is achieved by using simulations based on the finite element method. The good cloaking performances have demonstrated great potential in the promotion of the practical applications of a large-scale acoustic cloak, especially for low-frequency sound manipulation underwater.