水下声学超材料中由两个面内伪磁场诱导的手性朗道能级
Chiral Landau levels induced by two in-plane pseudomagnetic fields in underwater acoustic metamaterials
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中文总结 AI 辅助
研究在水下声学超材料中引入两个垂直面内人工伪磁场实现手性朗道能级，通过在狄拉克点打开带隙合成伪磁场，经数值和实验证实其存在及特性，实现水下超声能量灵活操控，为水下声学控制提供新途径。
中文摘要 AI 辅助
手性零朗道能级构成拓扑保护的体态，可实现对声波传播的稳健控制。鉴于水下声学在海洋工程中的核心作用，在水下声学系统中实现这种朗道能级物理非常有必要。然而，现有研究主要限于空气传播声学系统，由于不可避免的流固相互作用，在水下声学中实现手性零朗道能级仍是挑战。本研究通过引入分别沿x和y方向的两个垂直面内人工伪磁场，在开放水下类表面声波平台实现了两种手性朗道能级，揭示了水中标量声场和固体中矢量弹性振动可在统一框架内联合操控。具体通过在狄拉克点战略性地打开带隙，将位置相关的有效质量项引入狄拉克哈密顿量，从而合成两个面内伪磁场，导致手性朗道能级出现，通过数值和实验得到证实。还展示了手性朗道能级的单向传播及其对缺陷的鲁棒性。此外，实现了对类表面声波携带的水下超声能量的灵活操控，包括波束分裂和任意波转向。在小尺寸水下拓扑超材料中也观察到了双带手性朗道能级。我们的工作为基于类表面声波的水下超声控制提供了新途径，为多带水下声学信号处理与检测以及水下声能收集带来了机遇。
英文摘要
The chiral zeroth Landau levels (LLs) constitute topologically protected bulk states that enable robust control of acoustic wave propagation. Given the central role of underwater acoustics in marine engineering, realizing such Landau-level physics in underwater acoustic systems is highly desirable. Nevertheless, existing studies have primarily been limited to airborne acoustic systems, and the implementation of chiral zeroth LLs in underwater acoustics remains a challenge due to the unavoidable fluid-solid interactions. In this study, we realize two kinds of chiral LLs in an open underwater spoof surface acoustic wave (SSAW) platform by introducing two perpendicular in-plane artificial pseudomagnetic fields (PMFs), oriented along the x and y directions, respectively, and reveal that scalar acoustic fields in water and vectorial elastic vibrations in solids can be jointly manipulated within a unified framework. Specifically, by strategically opening bandgaps at the Dirac points, position-dependent effective mass terms are introduced into the Dirac Hamiltonians, thereby synthesizing two in-plane PMFs. This results in the emergence of chiral LLs, which is confirmed both numerically and experimentally. The unidirectional propagation of the chiral LLs and their robustness against defects are also demonstrated. In addition, we achieve flexible manipulation of underwater ultrasonic energy carried by SSAWs, including beam splitting and arbitrary wave steering. Dual-band chiral LLs are also observed in small-scale underwater topological metamaterials. Our work provides a new route toward SSAW-based underwater ultrasonic control, opening opportunities for multiband underwater acoustic signal processing and detection, as well as underwater acoustic energy harvesting.
