The defect state in periodic structures usually leads to a pass band in the forbidden bandgap and energy localization at the position of geometric change. In this paper, we have introduced periodic cavities into a symmetric structure composing of two separated phononic crystals to construct the defect state in the forbidden band and realize the temperature tuning of the defect state. The proposed structure is composed of two mirror-symmetric phononic crystals, with triangular steel arrays embedded in water. These two phononic crystals have opposite rotation angles possessing different topological properties, and the relative position of them leads to a forbidden band for the underwater ultrasonic waves. Interestingly, the periodic cavities between the boundaries of the phononic crystals result in a peak in the forbidden bandgap, which behaves as energy localization inside the cavities. The simulated results reflect the spectral and spatial characteristics of the defect state of this structure and exhibit the temperature tuning of the mentioned defect state. The designed structure provides a valid platform to filter the ultrasonic waves in fluid via controlling temperature, and the defect state manipulations benefit the smart structures of wave propagation, such as acoustic switches and underwater sound waveguides.

中文翻译：

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声子晶体之间周期性空腔引起的缺陷态的温度调谐

周期性结构中的缺陷态通常导致禁带隙中的通带和几何变化位置的能量局域化。在本文中，我们将周期腔引入由两个分离的声子晶体组成的对称结构中，以构建禁带中的缺陷态并实现缺陷态的温度调谐。所提出的结构由两个镜像对称的声子晶体组成，三角形钢阵列嵌入水中。这两种声子晶体具有相反的旋转角，具有不同的拓扑性质，它们的相对位置导致了水下超声波的禁带。有趣的是，声子晶体边界之间的周期性空腔导致禁带隙中的峰值，它表现为腔内的能量定位。模拟结果反映了该结构缺陷态的光谱和空间特性，并表现出上述缺陷态的温度调谐。所设计的结构提供了一个有效的平台，通过控制温度来过滤流体中的超声波，缺陷状态的操纵有利于波传播的智能结构，如声学开关和水下声波导管。