We propose an ultrathin membrane-type active acoustic metasurfaces with deep-subwavelength thickness for arbitrarily steering the transmitted acoustic wavefront in real-time via adjustment of the static voltage distribution. The underlying mechanism is that the change of tension on the middle membrane by the stresses introduced by the voltage exerted on the piezoelectric layers modulates the surface phase profile. The performance of the resulting device is numerically demonstrated via versatile wave-steering phenomena. Our design with functionality and flexibility opens up possibility for the design of active acoustic functional devices and may find important application in diverse fields such as acoustic communication.

We propose a design for topological phononic crystals comprising Helmholtz resonators to give rise to tunable interface states by adjusting the side length and rotation angle of the cavities. The underlying mechanism is that the modulation of edge modes changes the interface state by controlling local resonance elements and breaking mirror symmetry. The performance of the resulting device is numerically demonstrated via the production of robust topological valley transport along a prescribed path for incident waves of different frequencies. Our design helps to improve the design of tunable topological insulators and may find important applications in diverse fields such as acoustic communications.

As a key component of various acoustic systems, acoustic beam splitter (BS) finds important application in many scenarios, yet are conventionally based on the assumption that the acoustic waves propagate as easily when incident from either input or output side. It would therefore be intriguing, from the viewpoints of both science and technology, to break through this limit by realizing acoustic BSs supporting asymmetric transmission. Here we propose the concept of one-way acoustic BS capable of splitting acoustic beam incident from the input port into multiple beams while effectively reducing the backward transmission from any of the output ports. Furthermore, our design enables flexibly adjusting the number and angle of output beams by blocking the unused line defects. The numerical results verify the theoretical predictions and demonstrate the phenomenon of one-way acoustic BS at the predesigned frequency. Our design with functionality and flexibility bridges the gap between acoustic diodes and BSs and may enable novel multi-functional devices with great application prospects in diverse fields such as acoustic integrated circuits and acoustic communication.