A novel experimental technique based on point contact and Coulomb coupling is devised and optimized for ultrasonic imaging of bulk and guided waves propagation in piezo-ceramics. The Coulomb coupling technique exploits the coupling and transfer of electric field to mechanical vibrations by excitation of phonons. The point contact excitation and detection technique facilitates the spatial-temporal imaging of ultrasonic waves. The motivation of this research is the diagnosis and localization of surface cracks in the piezoelectric sensors and actuators. The underlying principle of the detection scheme is that any discontinuity on the surface causes high localization of electric gradient. The localized electric field at the defect boundaries enables then to behave as secondary passive ultrasonic sources resulting in strong back reflections. However, due to the interference between transmitted and reflected wave components from rigid boundaries and defect, the resolution on the localization of the damage is challenging. Therefore, an algorithm based on the two-dimensional spectral decomposition is utilized for selective suppression of the transmitted wave. The algorithm includes data transformation and vectorization in polar coordinates for efficient spectral decomposition. In the spectral domain, the complex wave component (phase and amplitude) are suppressed for the transmitted wave field. The reflected wave component in the spectral domain is retained and retrieved back using inverse spectral transformation. The algorithm is successful in retaining and exemplifying only the reflected wave sources arising from the strong scattering of ultrasonic waves from the surface and sub-surface defects. In summary, a novel experimental technique based on Coulomb coupling and spectral decomposition technique has been implemented for localization of surface defect in piezo-ceramic structures.

中文翻译：

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使用双点接触激励和检测方案激励的超声波在压电陶瓷中的损伤定位

设计并优化了一种基于点接触和库仑耦合的新型实验技术，用于压电陶瓷中体波和导波传播的超声成像。库仑耦合技术通过声子的激发利用电场与机械振动的耦合和转移。点接触激发和检测技术促进了超声波的时空成像。这项研究的动机是压电传感器和执行器中表面裂纹的诊断和定位。检测方案的基本原理是表面上的任何不连续性都会导致高度定位的电场梯度。缺陷边界处的局部电场能够充当次级无源超声源，从而导致强烈的背反射。然而，由于刚性边界和缺陷的透射和反射波分量之间的干扰，损伤定位的分辨率具有挑战性。因此，基于二维谱分解的算法被用于透射波的选择性抑制。该算法包括极坐标中的数据转换和矢量化，以实现高效的光谱分解。在谱域中，传输波场的复波分量（相位和幅度）被抑制。谱域中的反射波分量被保留并使用逆谱变换取回。该算法成功地仅保留和举例说明了由超声波从表面和次表面缺陷的强散射引起的反射波源。总之，一种基于库仑耦合和光谱分解技术的新型实验技术已被用于压电陶瓷结构中表面缺陷的定位。