Nonlocal Ventilating Metasurfaces

Nonlocal metasurfaces, by harnessing the nonlocality, have shown their unparalleled capacities for the efficiency of wave-front manipulation. Here, we demonstrate that nonlocality can be served as a powerful tool to achieve a dramatical enhancement in working bandwidth, showcased by an acoustic open metasurface encoding the exceptional property of allowing airflow while blocking sound transmission. Our design is a binary metaunit composed of two parts, a central orifice and a surrounding helical blade. We show that the transmission spectrum can be tailored by leveraging the hybrid nonlocal effect from the synergy of radiation coupling and direct coupling, the latter provided by a physical connection between the two parts. Verified by simulations and experiments, such a hybrid nonlocal open metasurface consistently blocks more than 90% of incident energy in the range from 600 to 1900 Hz across four adjacent transmission dips. Our finding may pave a way for noise blocking in a flowing-fluid-filled circumstance, more essentially, sets out an efficient approach for broadband wave manipulation in a hybrid nonlocal way.