  Optical geometric-phase metasurface provides a robust and efficient means for
light control by simply manipulating the spatial orientations of the in-plane
anisotropic meta-atoms, where polarization conversion plays a vital role.
However, the concept of acoustic geometric-phase modulation for acoustic field
control remains unexplored because airborne acoustic waves lack a similar
optical polarization conversion process. In this work, a new type of acoustic
meta-atom with deep subwavelength feature size is theoretically investigated
and further applied to acoustic field engineering based on the so-called
acoustic geometric phase. Herein, tunable acoustic geometric-phase modulation
of designated order is obtained via the near-field coupled orbital angular
momentum transfer process, and the topological charge-multiplexed acoustic
geometric phase endows our meta-arrays with multiple functionalities. Our work
extends the capacity of acoustic meta-arrays in high-quality acoustic field
reconstruction and offers new possibilities in multifunctional acoustic
meta-holograms.
