线圈自激励电磁超声换能器设计及特性研究  

EMAT Design of Self-excitation with Coils and Its Characteristics Study

作　　者：何健鹏[1] 徐科 任威平 

机构地区：[1]北京科技大学高效轧制国家工程研究中心,北京100083 [2]北京科技大学钢铁共性技术协同创新中心,北京100083

出　　处：《机械工程学报》2017年第16期134-140,共7页Journal of Mechanical Engineering

基　　金："十二五"国家科技支撑计划(2012BAB19B06);教育部博士点基金(20120006110033)资助项目

摘　　要：提出一种线圈自激励电磁超声换能器模型,该换能器无需磁铁提供静态磁场,可以避免磁铁对铁磁性材料吸附带来的不利影响,同时可以大大降低换能器质量。通过有限元仿真和试验结合的方法对所设计的换能器性能进行研究,随着提离距离提高,A_0兰姆波的衰减速率要快于S_0兰姆波,这是由于S_0兰姆波主要由磁致伸缩力引起的面内振动产生,动态磁场在6 mm提离距离时仍然具有较大水平分量。与之相比,A_0兰姆波主要由动态洛伦兹力引起,感应涡流强度及动态磁场强度在大于3 mm提离距离后都有明显衰减,动态洛伦兹力引起的面外振动衰减迅速。线圈自激励换能器可以在6 mm提离距离激励较纯净S_0兰姆波,优于传统换能器3 mm提离距离。最后,对两种兰姆波指向性进行研究,波长较长的S_0兰姆波具有更大的检测范围。An electromagnetic acoustic transducer（EMAT） model of self-excitation with coils is proposed. The new EMAT can avoid attraction between the magnet and ferromagnetic particles, as there is no need of magnet providing field. Furthermore, the weight of the EMAT reduces dramatically. Characteristics of the EMAT are investigated by both finite element and experimental methods. A_0 Lamb wave attenuates more rapidly than S_0 Lamb wave. At the lift-off distance of 6 mm, the dynamic magnetic field still has a large horizontal component to excite S_0 Lamb wave by magnetostriction mechanism. In comparison, A_0 Lamb is mainly generated by dynamic Lorentz force. Both the current density and the dynamic magnetic field attenuate markedly after 3 mm, leading to the rapid decrease of out-of-plane vibration produced by dynamic Lorentz force. The coil-only EMAT is able to generate pure S_0 Lamb at the lift-off of 6 mm. This distance is much higher than traditional EMATs, which is usually lower than 3 mm. Finally, directionality of the lamb waves is studied and S_0 Lamb is more suitable for wide range detection because of the longer wavelength.

关 键 词：电磁超声 兰姆波 洛伦兹力 磁致伸缩力 提离距离 

分 类 号：TP212[自动化与计算机技术—检测技术与自动化装置]