  Typical acoustic refractive metasurfaces governed by generalized Snell law
require several types of subwavelength subunits to provide an extra phase
gradient along the surface. This design strategy, however, has several kinds of
drawback. For instance, the inevitable viscous loss brought out by the complex
subwavelength subunits, and the negligence of the coupling between adjacent
subunits which leads to low-efficiency in wavefront manipulation, especially
for large angles. To overcome these limitations, we propose a new type of
refractive metasurface composed of only one straight channel and several
surface-etched grooves per period. By harnessing the nonlocal coupling between
the channel/grooves, and the evanescent modes inside them, superiorly feasible
acoustic transmission manipulations can be achieved. Nearly perfect acoustic
bending with transmission efficiency up to 95% is demonstrated with theory and
experiments for an extremely large angle of 81 degree. The reported results
introduce a novel concept of acoustic metasurfaces and offer a real leap
towards the development of high-efficient acoustic devices for wavefront
manipulation.
