Highly Efficient Acoustic Metagrating with Strongly Coupled Surface Grooves

Typical acoustic refractive metasurfaces governed by the generalized Snell law require several types of subwavelength subunits to provide an extra phase gradient along the surface. However, current design strategies have several drawbacks; for instance, the complex subwavelength subunits result in inevitable viscous loss, and ignoring the coupling between adjacent subunits leads to low efficiency in wavefront manipulations, especially for large angles. To overcome these limitations, we propose a metasurface or metagrating composed of only one straight channel and several surface-etched grooves per period. By harnessing the nonlocal coupling between the channel and the grooves, and the evanescent modes inside them, superior feasible acoustic transmission manipulations can be achieved. Nearly perfect acoustic bending with transmission efficiency up to 95% is obtained in theory and experiments for an extremely large angle of 81 degrees. Our results extend the realm of acoustic metasurfaces and offer alternative opportunities for the development of highly efficient acoustic devices for wavefront manipulations.