Collaborative non-local topology optimization of gradient acoustic metasurfaces for broadband extreme reflection modulation

To control the complex energy flow between neighboring microstructures for realizing the extreme acoustic functionality using a large-scale non-local metamaterial, here this paper shows that a collaborative non-local topology-optimization methodology is developed to construct gradient acoustic metasurfaces with smooth boundaries for the broadband large-angle reflection. An inverse-designed non-local acoustic metasurface is numerically and experimentally validated to support the large reflection angles within the low-frequency broadband range while maintaining high efficiency greater than 98.9%. It is further revealed that the strong non-local energy exchange between the multiple adjacent optimized microstructures can enable arbitrary surface impedances, thus obtaining efficient large-angle anomalous reflection from 52 degrees to 90 degrees. The present collaborative non-local topology-optimization methodology is not only applicable to airborne acoustic waves, but also can be extended to the customization of efficient wave functionalities of elastic and underwater acoustic metasurfaces. (C) 2025 Acoustical Society of America.