Realization of controllable acoustic acceleration beams via flexible active surfaces

The generation of acoustic acceleration beams is a research hotspot that has attracted increasing interest recently. In this article, we propose to generate controllable acoustic acceleration beams by using a flexible active surface with homogeneous phase and amplitude distributions. Thus, the active surface does not necessarily require very complex electronic control systems. Analytically, we show that the beam trajectories can be related to the shape of flexible active surfaces via the technique of inverse Legendre transformation. Consequently, we can directly create diffraction-suppressed acoustic beams along curve trajectories in space. We numerically and experimentally demonstrate that the acoustic beam projected from a bent active surface propagates along the predesigned path, which is in good agreement with theoretical prediction. We envision that the active soft acoustic surface may have versatile applications in the fields of medical treatment, particle manipulation and acoustic communication.