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中国物理学会期刊

基于Aharonov-Bohm囚禁的声学局域现象

CSTR: 32037.14.aps.74.20241717

Acoustic localization phenomenon based on Aharonov-Bohm cage

CSTR: 32037.14.aps.74.20241717
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  • 声子晶体能带理论为声场调控提供了重要的理论基础. 基于声学平带特征, 可有效控制声波局域与扩散现象. 本文通过设计声学正负耦合结构, 在准一维声学菱形晶格中构建等效规范场, 并利用声学Aharonov-Bohm囚禁效应产生的全平带调控声场局域. 研究表明, 相比于零通量结构, 引入 \pi 通量的等效规范场后, 在有限菱形晶格体内和边界位置均可有效控制声波局域. 这类Aharonov-Bohm囚禁效应诱导的局域态对对称结构微扰具有拓扑鲁棒性, 表明局域模式依赖于 \pi 通量等效规范场的拓扑特征. 此外, 通过平带本征态激发, 可获得与不同本征态对应的声学平带局域态. 进一步将不同的平带局域态叠加, 调控特定位置的声波幅值和相位, 实现具有丰富声场特征的复合型平带局域态. 因此, 利用一种声学Aharonov-Bohm笼拓扑结构可实现不同类型的声学局域态. 这些局域态可在不同晶胞位置激发, 且在不同带隙频率均具有较强的束缚声波的能力, 实现了宽带的声场局域调控. 本文研究结果不仅为利用等效规范场调控声场局域提供理论指导, 而且在发展声波控制器件方面具有潜在的应用前景.

     

    The energy band theory of acoustic crystal provides an important theoretical foundation for controlling the features of sound fields. By utilizing the acoustic flat bands, the sound wave can be effectively modulated to realize the acoustic localization and diffusion. In this work, an artificial gauge field is used to design a system supporting multiple acoustic flat bands, leading to the emergence of diversified acoustic localizations. Initially, cavity resonators, linked with different connectivity based on the field profiles of acoustic resonators, are employed to emulate coupled pz-dipole modes of atomic orbitals.
    According to the band order of in-phase and out-of-phase modes in two coupled cavities, it can be confirmed that the cross-linked and V-shaped-linked tube structures can achieve the positive coupling and negative coupling, respectively. By introducing positive and negative coupling into a rhombic loop, a synthetic gauge field can be formed due to the \pi flux phase accumulation of acoustic wave in the loop. Correspondingly, the different geometric phases of acoustic wave in different paths are analogous to the Aharonov-Bohm caging effect. Due to the Aharonov-Bohm caging effect, the introduce of \pi -flux into a rhombic loop causes the dispersion bands to collapse into dispersionless flat bands, providing the opportunity for controlling the localizations of sound fields. According to the finite structures of the cases with and without gauge fluxes, the eigenmodes and energy ratios are analyzed to investigate the sound field distributions. Compared with the zero-flux structure, the acoustic localization can be realized in the bulk and edge of a finite rhombic sonic crystal after introducing an artificial gauge field with a \pi flux in each plaquette. Here the localized states, induced by Aharonov-Bohm caging effect, are topologically immune to symmetrical structure disorder, indicating that the localized mode relies on the topological feature of the \pi -flux artificial gauge field. Additionally, based on the excitation of flat band eigenstates, the acoustic flat band bound states corresponding to different eigenstates can be obtained. By superimposing acoustic flat band bound states, the amplitude and phase of sound wave can be manipulated at specific locations, realizing the composite flat band bound states with rich acoustic field patterns.
    Therefore, we achieve different types of acoustic localized states in an acoustic topological Aharonov-Bohm cage. These localized states can be excited in any primitive cell of the rhombic lattices, and possess the remarkable ability to trap sound waves at different bulk gap frequencies, which achieves the broadband sound localizations. At the eigenfrequencies of flat bands, the localized states will be transformed into the extended states, exhibiting acoustic filtering functionality. Therefore, the acoustic Aharonov-Bohm cage is promising for applications at bandgap and flat band frequencies. The findings in this work provide the theoretical guidance for exploring the acoustic localized states with artificial gauge field, and can realize potential applications in acoustic control devices.

     

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