电磁超声兰姆波换能器在金属板检测中的优化

Optimization of electromagnetic ultrasonic Lamb wave transducer used for detection of metal plate

为了提高电磁超声波在金属板中的传播距离,研究了金属板检测中的电磁超声兰姆波换能器的换能机理.通过分析兰姆波在金属板中传播的频散曲线,得出低频率范围内A0、S0模态兰姆波具有远传特性.对兰姆波换能器进行仿真计算,分析了在单极型永磁铁和马蹄形磁铁作用下,线圈受到的磁感应强度和洛伦兹力的分布情况,并对马蹄形兰姆波换能器进行了实验研究.结果表明,当激励频率为400 kHz时,S0模态兰姆波得到了有效抑制,使A0模态兰姆波幅值达到最大,传播距离可达18 m;在马蹄形磁铁作用下,兰姆波换能器的有效检测距离是单极型磁铁的1.8倍.

In order to increase the propagation distance of electromagnetic ultrasonic wave in the metal plate,the transducing mechanism of electromagnetic ultrasonic Lamb wave transducer used for the detection of metal plate was studied.Through the analysis on the dispersion curves of Lamb wave propagating in the metal plate,it is found that the Lamb wave with A0 and S0modes has the characteristics of long-distance propagation in the low frequency range.The simulation was performed for the Lamb wave transducer,and the distribution of both magnetic induction and Lorentz force suffered by the coil was analyzed under the action of unipolar permanent magnet and horseshoe-shaped magnet.In addition,the experimental study on the horseshoe-shaped Lamb wave transducer was performed.The results show that when the excitation frequency is 400 kHz,the Lamb wave with S0 mode can be effectively suppressed.Moreover,the amplitude of Lamb wave with A0 mode reaches the maximum value,and the propagation distance of 18 m can be achieved.Under the action of horseshoe-shaped magnet,the effective detection distance of Lamb wave transducer is 1.8 times as that of unipolar magnet.