  Metasurfaces based on geometric phase acquired from the conversion of the
optical spin states provide a robust control over the wavefront of light, and
have been widely employed for construction of various types of functional
metasurface devices. However, this powerful approach cannot be readily
transferred to the manipulation of acoustic waves because acoustic waves do not
possess the spin degree of freedom. Here, we propose the concept of acoustic
geometric-phase meta-array by leveraging the conversion of orbital angular
momentum of acoustic waves, where well-defined geometric-phases can be attained
through versatile topological charge conversion processes. This work extends
the concept of geometric-phase metasurface from optics to acoustics, and
provides a new route for acoustic wave control.
