Acoustic cloaking by the wave flow method

The methods for calculating acoustic cloaking that is implemented by the wave flow method are reviewed, and the efficiency of this technique for cloaking regions with symmetries of three types is analyzed. It is shown that the main problem in implementing acoustic cloaking is the formation of an anisotropic medium with inhomogeneous components of the density tensor and bulk modulus, which change in a wide range and have limiting values of a or 0 at the cloaking-region boundaries. Some estimates are obtained, according to which a stratified medium composed of a sequence of layers with different densities and compressibilities appears to be more promising, because it (i) is more easy to implement and (ii) opens possibilities for broadband cloaking. Analysis of different versions of the cloaking-region symmetry revealed that, using a layered medium, one can implement efficient acoustic cloaking only in the case of a spherically symmetric region.