Convergence performance of flexural wave in the unconventional acoustic black hole

Two-dimensional traditional acoustic black hole (ABH) embedded in the plate has been recognized as a highly effective tool for wave energy harvesting, which enables wave trajectories to converge into a confined area. Traditional ABH is a rotational symmetrical circular indentation, and the residual thickness platform is always located in the center. This type of ABH has been widely investigated in previous study. However, the discussion on the structure configuration and layout of the residual thickness platform is rare. In this paper, two types of unconventional ABHs embedded in the plate are proposed and studied, namely "Heteromorphic ABH" and "Eccentric ABH," which represent that the shape of indentation is no longer a circle and the inner platform is not located in the center, respectively. These unconventional ABHs can also converge the flexural wave, but the focalization phenomenon is obviously distinct from that of the traditional ABH. The converging performances are characterized through the ray-tracing method based on the geometrical acoustic method. The validation of calculated results is conducted using the finite element simulation. Moreover, the effects of ABH geometric parameters are investigated in detail. The unconventional ABH demonstrates the multiplicity in structure and shows the potential of the flexible manipulation for flexural waves.