The waveguides with finite cross-section (such as rail, flat steel) are one of the most crucial configurations in infrastructure. When the shear horizontal (SH) guided waves are excited, the three-dimensional deformation of the elastomer will excite weak Lamb waves. In the finite cross-section waveguides, Lamb waves and SH waves are coupled together with each other. Mode coupling will influence the vibration direction of particles, resulting in wavelength changes of guided waves, which affects precise localization and quantification of defects. In this study, the SH0-like guided wave of flexural-like motion in the rectangular plate are analyzed theoretically. For the rectangular plate, the wavelength difference of SH0-like guided wave decreases with the increase of rectangular plate width and with the decrease of the excitation wavelength, respectively. The wave finite element method (WFEM) was used to calculate the dispersion curves of SH0-like guided wave, and the law of the wavelength changes is consistent with the theoretical analysis. Rectangular plates with different widths are selected and the excitation frequencies also vary according to different wavelengths. The changes of wavelengths and particle vibration direction are obtained by simulation, which are consistent with the theoretical analysis. The periodic-permanent-magnet (PPM) electromagnetic acoustic transducer (EMAT) with different wavelengths are constructed and used in the experiments to excite SH0-like guided wave. The wavelengths of experimental signal are calculated by two-dimensional fast Fourier transform (2DFFT), and the law of the wavelength changes are verified.

中文翻译：

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有限截面三维波导中SH导波与兰姆波的耦合


具有有限横截面的波导（如钢轨、扁钢）是基础设施中最关键的配置之一。当剪切水平（SH）导波被激发时，弹性体的三维变形将激发微弱的兰姆波。在有限截面波导中，兰姆波和SH波相互耦合。模式耦合会影响粒子的振动方向，导致导波波长变化，影响缺陷的精确定位和量化。本研究对矩形板中类弯曲运动的类SH0导波进行了理论分析。对于矩形板，类SH0导波的波长差分别随着矩形板宽度的增加和激发波长的减小而减小。采用波动有限元法(WFEM)计算了类SH0导波的色散曲线，其波长变化规律与理论分析一致。选择不同宽度的矩形板，激发频率也根据不同的波长而变化。通过模拟得到了波长和粒子振动方向的变化，与理论分析一致。构建了不同波长的周期永磁体（PPM）电磁声换能器（EMAT），并在实验中用于激发类SH0导波。通过二维快速傅里叶变换（2DFFT）计算实验信号的波长，验证了波长变化的规律。