时变声超构材料中波拓扑传输效应

Topological wave transport is featured with the robust flow of waves that is related to topological quantities rather than geometric ones. Recently, the subject of topological wave transport has become a hotspot in acoustics, which had some significant consequences, such as designs of varied nonreciprocal acoustic topological insulators (TIs) and the prediction of one-way edge states that are immune to scattering of defects. However, those proposed acoustic TIs are mostly based on coupled ring cavities with high-speed air circulation inside, where the difficulties in increasing circulation velocity and airflow stability severely restrict the realization of topological sound transport. This project creatively adopts metafluid cylinders with the rotational speed accurately controlled by motors as the building blocks of acoustic TIs, and explores the robust wave transport in such time-varying acoustic metamaterials. The focus of this research project will be put on how to improve the dynamic stability of metafluid cylinders rotating at high-speed, how to guarantee synchronous rotation of arrayed metafluid cylinders, the establishment of appropriate physical model for calculations of the topological invariant (e.g., Chern number) and the frequency range where gapless topologically protected edge states locate, as well as the accurate measurement and controlling of topologically protected edge states in the time-varying metamaterials. With the successful implementation of this research project, we believe that some important breakthroughs in topological metamaterial-based devices will be achieved to manipulate sound in an unprecedented way.

拓扑传输效应是指波的传输特性取决于传播媒质的拓扑不变量而非几何属性。拓扑传输的概念在声学领域已产生了一些非常重要的影响，例如设计各种非互易声学拓扑绝缘体并预测存在不受缺陷影响且单向传输的拓扑保护边界态。然而，这些声学拓扑绝缘体大多基于相互耦合的环流腔。其中，如何提高气流的环流速度和稳定性严重地制约了声波拓扑传输的实现。本课题创新性地采用转速可精确控制的超构材料流体柱构建声学拓扑绝缘体，并研究声波在该时变超构材料中的拓扑传输效应。重点研究如何提高超构材料流体柱在高速旋转时的稳定性，如何保证相互耦合的超构材料流体柱阵列高速同步旋转，建立相应的物理模型来计算传播媒质的拓扑不变量(陈数)和无带隙拓扑保护边界态对应的频率范围，实现对时变声超构材料中拓扑保护边界态的精确测量和可控调节。相信本课题的顺利实施，必将在拓扑声学超构材料器件的研究和应用上产生一些重要的突破。

拓扑传输效应是指波的传输特性取决于传播媒质的拓扑不变量而非几何属性。拓扑传输的概念在声学领域已产生了一些非常重要的影响，例如设计各种基于声波赝自旋的声学拓扑绝缘体并预测存在不受缺陷影响且单向传输的拓扑保护边界态。然而，这些声学拓扑绝缘体大多数基于时间反演对称。其中，如何实现打破时间反演对称性的非互易声学拓扑绝缘体具有十分重要的意义。本课题采用转速可精确控制的超构材料环构建陈数声学拓扑绝缘体，实验上证实了声波在该时变超构材料中的拓扑传输效应(正反透射率对比大于5)。解决了超构材料环在高速旋转时的稳定性，保持相互耦合的超构材料环阵列的高速同步旋转(5转/秒)，并建立了相应的物理模型计算传播媒质的拓扑不变量(陈数)和无带隙拓扑保护边界态对应的频率范围(1930Hz至1970Hz)，实现对时变声超构材料中拓扑保护边界态的精确测量和可控调节。在声学领域，拓扑不变量和声波拓扑传输效应的相关研究有着重要的理论意义和潜在的应用价值。基于量子体系中拓扑不变量已有的丰富结果，声学系统中拓扑不变量的探究将开辟新的理论研究领域，促使声学理论的进一步发展。与传统的声波传输相比，声波的拓扑传输具有一些非常独特的性质：单一方向传输和在缺陷或无序处无散射(拓扑保护)。这些独特的性质使得声波的拓扑传输在声单向隔离、完美声吸收黑洞、声存储、声波调制和声换能器等方面具有诱人的应用前景。从物理本质上看，声波的拓扑传输属于一种非互易效应，而非互易声传输在声学领域是一个热门的研究方向。