Acoustic orbital angular momentum Hall effect and realization using a metasurface

Abstract

Vortex beams with a twisted wavefront possess both intrinsic and extrinsic orbital angular momenta. Their coupling (viz. orbital-orbital coupling) leads to an orbital angular momentum Hall effect previously found in light, providing applications in light manipulation. Here an analogous orbital Hall effect in acoustics is reported via modeling vortex beam propagation in an inhomogeneous medium. A shift of the beam center perpendicular to the inhomogeneous direction is numerically observed to follow a path predicted by ray theory in the weak inhomogeneity approximation where the coupling and conservation of total angular momenta are identified. Experimental observation of the acoustic phenomenon with the aid of a gradient metasurface or a stratified fluid is proposed.