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近年来，基于非厄米拓扑理论，人们通过调制声学晶体中的非互易耦合，揭示了体态向界面塌陷的趋肤效应.在这项研究中，我们实验设计了具有不同绕组数域之间的拓扑趋肤界面，以操纵能量聚焦到非厄米一维声腔链的中间或两端.首先，我们通过电声耦合的方法实现了两个声学腔之间的非互易耦合，并研究其特性.其次，我们将非互易耦合腔扩展成链状，通过调制非互易电-声耦合来构建趋肤界面的位置.实验结果表明，对于不同的非互易耦合分布，声音可以集中在中间界面或两端界面，并且通过改变非互易耦合方向，可以将趋肤界面从中间切换到两端.我们的研究结果为设计控制声音传播的先进拓扑声学装置提供了一个新平台.Topological insulators, which possess robust topologically protected properties for manipulating the wave propagation against the disorder and defects, have grown into a large research field in photonic and phononic crystals. However, the conventional topological band theory is used to describe a closed photonic/phononic crystal that is assumed to be Hermitian system. In fact, practical physical systems often couple with outside environment, and induce non-Hermitian Hamiltonian with complex eigenvalues. Recently, many novel topological properties have been induced by the interacting between non-Hermitian and topological phases, a prominent example is non-Hermitian skin effect that all eigenstates are localized to the boundary in open system, which different from the conventional topological edge states. The unique physical phenomenon has stimulated various applications, such as wave funneling, enhanced sensing, and topological lasing. In this work, we describe the non-Hermitian skin effect using winding numbers. The sign of the winding number determines the rotation direction of the loops in the complex frequency plane, which the sign can be controlled by the nonreciprocal coupling direction. In this context, we designed different topological skin interface between different domains with opposite winding numbers to manipulate the energy focusing to middle or two-end of non-Hermitian 1D acoustic cavity chain. In experiment, we used an electroacoustic coupling method, employing a unidirectional coupler composed of microphones, speakers, phase shifters, and amplifiers, to introduce positive and negative non-reciprocal couplings between the two acoustic cavities and studied the characteristics of these non-reciprocal couplings. Then, the non-reciprocal coupling cavities were extended into a chain structure, and the magnitude and sign of the non-reciprocal couplings were flexibly controlled using phase shifters and amplifiers. Through this method, we successfully constructed interfaces between different winding numbers, achieving a one-dimensional non-Hermitian skin effect at various interfaces. The experimental results indicate that the sound can be focused at middle interface or two-end interfaces for different nonreciprocal coupling distributions, and the skin interface can also be switched from middle to two-end by exchanging the nonreciprocal coupling direction of the domains. Our research results offer greater flexibility in the design of acoustic devices and may provide a new platform for exploring advanced topological acoustic systems for controlling sound propagation.
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Keywords:
- non-Hermitian skin effect /
- interface state /
- phononic crystal /
- resonant cavity
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