A baseline-free defect localization method in thin plates is proposed and tested. In this proof-of-concept work, a steel ball pressed against an aluminum plate is used to mimic a surface contact defect. The technique takes benefit of a repetitive nonlinear pump-probe interaction with a backpropagation imaging algorithm. High-frequency probe waves are periodically emitted by a piezoelectric patch transducer glued to the plate. Propagated flexural waves are recorded using a distributed array of transducers. At the same time, a continuous low-frequency pump vibration provided by a shaker fixed to the plate modulates the contact state. By combining multiple probe signals, the contact can be successfully localized. Contrast of the localization images is finally improved by a factor of 3 to 5 by implementing a modified version based on synchronous detection of the imaging algorithm.

中文翻译：

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各种固体接触的泵浦探针定位技术

提出并测试了无基线薄板缺陷定位方法。在此概念验证工作中，将钢球压在铝板上以模拟表面接触缺陷。该技术利用反向传播成像算法，实现了重复的非线性泵浦-探针相互作用。高频探针波由粘贴在板上的压电贴片换能器周期性地发射。使用分布式换能器阵列记录传播的弯曲波。同时，由固定在板上的振动器提供的连续的低频泵振动会调节接触状态。通过组合多个探测信号，可以成功定位触点。