基于编码压缩的钢板电磁超声Lamb波检测方法研究

Research on the detection method of the steel plate with Lamb wave EMATs based on phase coded pulse compression

针对大型金属板材构件导波检测中EMAT分辨率低、SNR差,难以用于小裂纹检测等难题,建立了基于Barker码脉冲压缩技术的Lamb波EMAT检测过程多物理场有限元模型,以含预制裂纹的5.6 mm厚钢板为检测对象,仿真和实验相结合,研究了永磁体宽度和高度、曲折线圈匝数、Barker码序列长度和码元长度等参数对EMAT检测回波的影响,验证了脉冲压缩技术在Lamb波EMAT检测中的有益效果。结果表明,基于脉冲压缩技术的EMAT经优化后,SNR比传统tone-burst激励方式高出了9.69 dB,可检出10 mm长和0.5 mm深的小裂纹,缺陷波SNR为23.47 dB。当Barker码码元中心频率为1 MHz时,脉冲压缩后的Lamb波包发生模态分离,但A_(0)模态的缺陷波SNR仍可达35.23 dB,这对提升Lamb波EMAT检测能力具有重要的工程应用价值。

The guided wave EMAT detection of large metal plate components has the problems of low resolution and poor SNR of the EMAT,which is challenging to be used for small crack detection.A multi-physical field finite element model of Lamb wave EMAT detection process based on the Barker code pulse compression technology is established to solve this issue.Taking a 5.6 mm thick steel plate with prefabricated cracks as the detection object,the effects of permanent magnet width and height,meander coil turns,the bit length of Barker code sequence,and subpulse duration on EMAT detection echo are studied by simulations and experiments.The beneficial effect of pulse compression technology in Lamb wave EMAT detection is evaluated.After optimization,results show that the SNR of the EMAT based on pulse compression technology is 9.69 dB higher than that of the traditional tone-burst excitation method.A small crack 10 mm long and 0.5 mm deep can be detected,and the SNR of the defect wave can reach 23.47 dB.When the center frequency of the Barker code subpulse is 1 MHz,the Lamb wave packet after pulse compression presents mode separation.However,the SNR of the A_(0) mode defect wave can still reach 35.23 dB,and it has essential engineering application value for improving the detection ability of the Lamb wave EMAT.