Impedance acoustic cloaking

The paper addresses a new approach to passive acoustic cloaking, which is an alternative to the well-known approach of transformation optics. It is shown first that the scattered acoustic field of a body is completely determined by special surface impedances defined at the body surface. The surface impedances of a non-scattering, i.e. acoustically transparent, body of any geometry are then derived explicitly, and a thin coating is proposed that can provide such impedances with controlled accuracy. The coating represents a doubly periodic surface structure made of elements of sub-wavelength size. The computer simulation shows that the coating being placed on any body can render it non-scattering and, hence, invisible to all acoustic observation systems in a range of low and medium frequencies. The width of the range and the coating efficiency depend on the number of internal couplings introduced between the coating elements.