When estimating a structural health monitoring (SHM) system, its defect sensitivity and area/distance coverage are most important factors. For commonly used guided wave sparse array system, it usually requires a reference state as the baseline which is not available in many cases. In comparison, phased array technique typically does not need the baseline in simple structures and it had been successfully used in nondestructive testing (NDT). However, currently developed phased array systems employed omni-directional transducers routinely, where the wave energy is distributed equally along all directions thus it is not favorable for long-distance detection. In this work, bidirectional piezoelectric transducers were used to form a linear phased array system, which can generate/receive shear horizontal (SH) wave with high energy concentration. Firstly, the configuration of the employed transducer composed by antiparallel d15 piezoelectric strips (APS) was presented. Then the total focusing method (TFM) employed for defect detection was introduced. After validating the radiation pattern of SH wave generated by the APS, the properties of beam steering for the proposed phased array was investigated. Finally, experiments were carried out to validate its performance in detection of various defects. Results indicated that even for a 1 mm through-thickness hole 700 mm away, the proposed phased array system can still detect it accurately, which is much better than previous SHM systems. Dual defects including a crack and a hole can also be clearly detected without baseline. The high-sensitivity of the proposed system was attributed to the employed bidirectional transducer which can generate non-dispersive SH0 wave with high energy concentration. This proposed SH wave phased array system will provide a high-performance SHM method for plate-like structures.

中文翻译：

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基于双向SH波相控阵的高灵敏度远距离结构健康监测系统

在评估结构健康监测 (SHM) 系统时，其缺陷敏感性和面积/距离覆盖是最重要的因素。对于常用的导波稀疏阵列系统，通常需要一个参考状态作为基线，这在很多情况下是不可用的。相比之下，相控阵技术通常不需要简单结构的基线，它已成功用于无损检测（NDT）。然而，目前开发的相控阵系统通常采用全向换能器，波能沿各个方向均匀分布，不利于远距离探测。在这项工作中，双向压电换能器被用来形成一个线性相控阵系统，它可以产生/接收具有高能量集中的剪切水平（SH）波。首先，介绍了由反平行 d15 压电条 (APS) 组成的换能器的配置。然后介绍了用于缺陷检测的全聚焦法（TFM）。在验证了 AP​​S 产生的 SH 波的辐射方向图后，研究了所提出的相控阵的波束控制特性。最后，进行了实验以验证其在检测各种缺陷方面的性能。结果表明，即使对于 700 mm 外的 1 mm 通孔，所提出的相控阵系统仍然可以准确地检测到它，这比以前的 SHM 系统要好得多。也可以在没有基线的情况下清楚地检测包括裂纹和孔洞在内的双重缺陷。所提出系统的高灵敏度归因于所采用的双向换能器，该换能器可以产生具有高能量集中的非色散 SH0 波。这种提出的 SH 波相控阵系统将为板状结构提供一种高性能的 SHM 方法。