基于电磁超声换能器阵列的管道螺旋导波传播规律研究

螺旋导波因在管道超声导波层析成像中的巨大应用价值，近年来受到研究者们的重视。阐述管道螺旋导波的激发/接收条件、传播路径和波前形状等规律。建立FE模型，研究由圆环波前S₀模态兰姆波在管道上形成螺旋导波的过程。组建了双环24阵元的电磁超声换能器阵列及试验系统，170 kHz下激发圆环波前S₀模态兰姆波在管道中产生螺旋导波，试验研究了激励源所在圆周及管段上的波动场信号特征。仿真和试验结果表明，管道螺旋导波实质上是兰姆波在曲面上的传播形态，可由管道某处点源激发兰姆波产生，主要存在于波动场的近场。由于管道结构的封闭性，兰姆波的波前在管道上反复交叉前行，形成了螺旋传播路径。从波源到管道上任意一点的螺旋导波传播路径有无数条，各阶螺旋角不连续。利用螺旋导波进行管段检测提供了缺陷的多角度入射信息，对缺陷高分辨率检测具有重要意义。

Helical Mode Guided Waves in Pipe Observed by Electromagnetic Acoustic Transducer Array

As the raising application of guided wave tomography for pipelines, helical mode guided waves have received the attention of researchers in recent years. Helical mode guided waves generating/receiving method, the propagation path and wave fronts shape characteristics are studied. An FE model is established to study the process of helical mode guided waves in pipeline generated by omini-directional S₀ mode Lamb wave. A two-ring 24-elements electromagnetic acoustic transducers array and its supplementary experiment system is set up. Omini-directional single S₀ modal Lamb wave is excited at the frequency of 170 kHz to produce helical mode guided waves in the pipeline. The experiment is conducted to study the propagation characteristics of helical mode guided wave in circumference of the excitation source and the pipe. The simulation and experimental results show that the helical guided wave in pipeline is essentially the propagation of Lamb wave on the curved surface. When Lamb wave is generated from a point source in the pipeline, due to the closure of the pipeline, wave fronts continue to cross with each other and form helical propagating guided waves. There are countless helical propagation paths from the source to the receiver. The spiral angles of each order helical mode are not continuous. Helical mode guided waves provide multi-angle incidence and more information of defects, which is of great significance for defects high-resolution detection.