周向导波电磁超声探头(EMAT)设计与优化

摘要

To inspect oil and gas pipelines by using SHO mode guided circumferential ultrasonic wave,a novel electromagnetic acoustic transducer (EMAT) for guided circumferential wave was designed. The EMAT has two structural features,a carbon steel sheet is on top of all the magnets and small nonmagnetic blocks are placed between adjacent magnets. To improve its transduction efficiency, ANSYS software was used to optimize some geometric parameters of EMAT. The optimal result is the carbon steel sheet should be thicker than 1 mm, and the wire spacing of the coil should be as small as possible. Experiments on a tube 200 mm in OD and 4 mm in wall thickness indicate that the EMAT optimized can excite the SHO mode guided wave effectively.%为了利用SH0模超声周向导波检测油气管道纵向裂纹,提出了一种新的周向导波电磁超声探头(EMAT)结构设计,其结构特点是磁铁顶部放置碳钢片,相邻磁铁之间放置非磁性材料片.为了提高周向导波EMAT的换能效率,采用ANSYS仿真对其结构参数进行了优化.优化的结果为:磁铁顶部应放置厚度大于1mm的碳钢片,线圈中导线间距要尽量小.在直径200 mm壁厚、4mm的管材上进行实验,结果表明,优化设计后的探头能有效地激励出周向SH0导波.