Wang Xu, Dong Ruizhi, Li Yong, Jing Yun
Institute of Acoustics, School of Physics Science and Engineering, Tongji University, Shanghai 200092, People's Republic of China.
Graduate Program in Acoustics, The Pennsylvania State University, University Park, PA 16802, United States of America.
Rep Prog Phys. 2023 Oct 10;86(11). doi: 10.1088/1361-6633/acfbeb.
Acoustic metasurfaces are at the frontier of acoustic functional material research owing to their advanced capabilities of wave manipulation at an acoustically vanishing size. Despite significant progress in the last decade, conventional acoustic metasurfaces are still fundamentally limited by their underlying physics and design principles. First, conventional metasurfaces assume that unit cells are decoupled and therefore treat them individually during the design process. Owing to diffraction, however, the non-locality of the wave field could strongly affect the efficiency and even alter the behavior of acoustic metasurfaces. Additionally, conventional acoustic metasurfaces operate by modulating the phase and are typically treated as lossless systems. Due to the narrow regions in acoustic metasurfaces' subwavelength unit cells, however, losses are naturally present and could compromise the performance of acoustic metasurfaces. While the conventional wisdom is to minimize these effects, a counter-intuitive way of thinking has emerged, which is to harness the non-locality as well as loss for enhanced acoustic metasurface functionality. This has led to a new generation of acoustic metasurface design paradigm that is empowered by non-locality and non-Hermicity, providing new routes for controlling sound using the acoustic version of 2D materials. This review details the progress of non-local and non-Hermitian acoustic metasurfaces, providing an overview of the recent acoustic metasurface designs and discussing the critical role of non-locality and loss in acoustic metasurfaces. We further outline the synergy between non-locality and non-Hermiticity, and delineate the potential of using non-local and non-Hermitian acoustic metasurfaces as a new platform for investigating exceptional points, the hallmark of non-Hermitian physics. Finally, the current challenges and future outlook for this burgeoning field are discussed.
声学超表面因其在声学消失尺寸下先进的波操控能力，处于声学功能材料研究的前沿。尽管在过去十年取得了重大进展，但传统声学超表面在根本上仍受其基础物理和设计原理的限制。首先，传统超表面假设单元胞是解耦的，因此在设计过程中对它们进行单独处理。然而，由于衍射，波场的非局域性会强烈影响效率，甚至改变声学超表面的行为。此外，传统声学超表面通过调制相位来工作，通常被视为无损系统。然而，由于声学超表面亚波长单元胞中的区域狭窄，损耗自然存在，这可能会损害声学超表面的性能。虽然传统观念是尽量减少这些影响，但一种反直觉的思维方式已经出现，即利用非局域性以及损耗来增强声学超表面的功能。这导致了一种由非局域性和非厄米性驱动的新一代声学超表面设计范式，为使用二维材料的声学版本来控制声音提供了新途径。这篇综述详细介绍了非局域和非厄米声学超表面的进展，概述了近期声学超表面的设计，并讨论了非局域性和损耗在声学超表面中的关键作用。我们进一步概述了非局域性和非厄米性之间的协同作用，并阐述了使用非局域和非厄米声学超表面作为研究非厄米物理标志——奇异点的新平台的潜力。最后，讨论了这个新兴领域当前面临的挑战和未来展望。
