Tailoring of diversified sound vortices using curved impedance-matched acoustic metasurfaces

Abstract

Acoustic vortex beam, which carries the orbital angular momentum, has attracted great interest in recent years. In this paper, we propose a novel curved impedance-matched metasurface constructed with tunable units, which are filled with mixed gases with different refractive indices. It converts an acoustic point source to vortex beam with nearly unity transmittance in a broad frequency bandwidth. By arranging the units, we demonstrate topological charge modulation and rotated direction shifting for acoustic vortex beams. In addition, combining with phase superposition effect, we introduce double curved metasurfaces model. A vortex beam can transform into another vortex beam with different energy flows conveniently. The proposed methods open up an effective avenue for tailoring acoustic vortex fields and provide possibility for applications such as particles trapping, acoustic communication and biomedical engineering.