Kubrusly Alan C, Freitas Miguel A, von der Weid Jean Pierre, Dixon Steve
IEEE Trans Ultrason Ferroelectr Freq Control. 2018 Jul;65(7):1239-1249. doi: 10.1109/TUFFC.2018.2835299.
Shear horizontally (SH) guided waves, generated by periodic permanent magnet arrays, have been used previously in nondestructive evaluation of metal plates and pipes. When an SH guided wave interacts with a defect or a change in sample thickness, the incident SH wave may undergo mode conversion. Analysis of mode conversion is complicated, due to the interference of several propagating modes in the received signal that can often temporally overlap. This paper proposes a mode selection technique to help understand the interaction of SH guided waves with changes in sample thickness. Using an understanding of the propagation characteristics of the guided waves, SH guided waves are sequentially generated and detected on both surfaces of the plate, capturing four distinct waveforms. By superposition of the detected signals, symmetric modes can be clearly separated from antisymmetric modes in the processed received signals. For this method to work well, the transducers used should have very similar responses and be precisely positioned on exactly opposite positions either side of the plate. Finite element simulations are also performed, mirroring the experimental measurements, and the results correlate well with the experimental observations made on an 8-mm-thick plate with a region of simulated wall thinning machined into the sample.
由周期性永磁体阵列产生的水平剪切（SH）导波，此前已用于金属板和管道的无损检测。当SH导波与缺陷或样品厚度变化相互作用时，入射的SH波可能会发生模式转换。由于接收到的信号中几种传播模式的干扰常常在时间上重叠，模式转换的分析很复杂。本文提出一种模式选择技术，以帮助理解SH导波与样品厚度变化的相互作用。利用对导波传播特性的理解，在板的两个表面上依次产生并检测SH导波，捕获四个不同的波形。通过对检测信号的叠加，可以在处理后的接收信号中将对称模式与反对称模式清晰地分离。为使该方法有效，所使用的换能器应具有非常相似的响应，并精确地定位在板两侧完全相对的位置。还进行了有限元模拟，以反映实验测量情况，结果与在一块8毫米厚的板上进行的实验观察结果很好地相关，该板上加工有一个模拟壁厚减薄的区域。
