Acoustic Vortices via Nonlocal Metagratings

Vortex beams carrying orbital angular momentum enrich the wave-matter interaction physics and show great potential applications, such as optical or acoustic tweezers and long-range signal communication. However, passive vortex generators commonly suffer from drawbacks of low efficiency and bulky configurations. In this work, by harnessing nonlocal coupling between subunits, we present a thin layer of metagratings to change efficiently the topological charge of a vortex beam in a waveguide. Our numerical and experimental results show that thin and planar metagratings can convert a plane-wave mode into first-, second-, and third-order vortex beams with nearly perfect efficiency (more than 99%). Our work breaks through the barrier to obtain highly efficient acoustic vortex beams and may offer opportunities for the development of devices for acoustic communication and manipulation.