Sound scattering from underwater elastic sphere shell covered with multilayered medium approximated acoustic cloak

The anechoic performance and mechanism of underwater elastic sphere shell covered with coating is studied at low frequency. The acoustic cloak must be anisotropic material, which is designed with homogeneous isotropic materials on the basis of effective medium approximation theory. The analytic expression of scattering sound field from underwater elastic sphere shell covered with multilayered medium is formulated. The scattering form function, resonance mode, acoustic field distribution of elastic sphere shell covered and uncovered with multilayered medium is computed. And the sound scattering characteristics and mechanism of transmission are analyzed. The results show that inside the multilayered medium, the direction of transmission is changed, the acoustic field is gradually deflected, and the acoustic energy flux is guided around the target, which reduce the scattering intensity at lower frequency, but also the acoustic intensity of target's surface is very weak. Excepting the first resonance peak in spectrum produced by zero order subwave, the other resonance modes of elastic sphere shell are not excitated and the multilayered medium has suppression of sphere shell resonance.