Based on the Huygens-Fresnel principle, a metasurface structure is designed to generate a
sound vortex beam in airborne environment. The metasurface is constructed by a thin planar
plate perforated with a circular array of deep subwavelength resonators with desired phase
and amplitude responses. The metasurface approach in making sound vortices is validated
well by full-wave simulations and experimental measurements. Potential applications of
such artificial spiral beams can be anticipated, as exemplified experimentally by the torque …