Modulation of out-of-plane reflected waves by using acoustic metasurfaces with tapered corrugated holes.

In this paper, modulation of reflected wavefront out of the incident plane by a tunable acoustic metasurface is investigated based on the fully generalized Snell's law in the three-dimensional space. The metasurface is constructed by a square lattice of circular holes with gradient annular bumps. The phase shift is tuned by changing the volume of water filled in the holes. The acoustic wave steering out of the incident plane and the out-of-plane acoustic focusing with the oblique incidence at the subwavelength scale are demonstrated numerically by selecting suitable distributions of water depth. The numerical results show that the wavefront of the reflected wave can be manipulated over a wide frequency range; and the gradient design of the unit cells can suppress the parasitic reflection. The present work is relevant to the practical design of novel acoustic devices.