Defects in periodic structures can always result in localization of various waves, such as Anderson localization, line defect photonic crystal waveguides, and locally resonant sonic metamaterials. Due to the unique physical properties of localization, it has found applications in many functional devices including optical/acoustical tweezers, laser cavities, spatial modulators, and detectors. Here, we introduce two defects into an acoustic waveguide with perfect periodicities and experimentally observe the related two defect modes and their coupling effects. The double defects can cause the two extraordinary transmissions in the forbidden band of periodic structures, and the induced acoustic localization is quite different from that in a single defect that the measured sound pressure along the axis of the waveguide shows the maximum in each defect. The measured sound pressure also indicates that the localization of defect modes has in-phase or out-of-phase characteristics, which change alternately with increasing number of periods between the defects. When the distance between the two defects increases, the defect coupling turns to be weaker and the transmitted peaks fuse together as one. Finally, the defect mode disappears for a larger distance. The experiments also reveal that the localization of double defects is very sensitive to the defect geometry. The maximum sound pressure of defect modes with a longer wavelength always appears in the longer defect. Based on our findings, the acoustic localization can be efficiently manipulated by the regulation of structures with defects, which may pave the way for various functional devices in wave control engineering.

中文翻译：

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波纹波导中基于缺陷模式耦合的声局部化处理

周期性结构中的缺陷总是会导致各种波的局域化，例如安德森局域化，线缺陷光子晶体波导和局域共振声超材料。由于定位的独特物理特性，它已在许多功能设备中得到应用，包括光/声镊子，激光腔，空间调制器和检测器。在这里，我们将两个缺陷引入具有完美周期性的声波导中，并通过实验观察相关的两个缺陷模式及其耦合效应。双重缺陷会在周期性结构的禁带中引起两次异常传输，并且感应声的定位与单个缺陷中的声定位非常不同，沿波导轴的测得的声压在每个缺陷中显示出最大值。测得的声压还表明缺陷模式的定位具有同相或异相特性，它们随着缺陷之间的周期数增加而交替变化。当两个缺陷之间的距离增加时，缺陷耦合会变弱，并且透射的峰会融合在一起。最终，缺陷模式消失了更长的距离。实验还表明，双重缺陷的定位对缺陷的几何形状非常敏感。具有较长波长的缺陷模式的最大声压始终出现在较长的缺陷中。根据我们的发现，可以通过调节有缺陷的结构来有效地控制声学定位，这可能为波控制工程中的各种功能设备铺平了道路。