激光-仅线圈式 EMAT 的金属检测系统优化设计

在铝合金铸造和高温轧制过程中，采用非接触式无损检测技术实现在线监测与检测，对减小生产成本、保证生产线连续、提高产品成品率具有重要意义。首先，建立了以脉冲激光束激励和仅线圈式电磁超声换能器(EMAT)接收的铝合金Laser-EMAT检测过程有限元模型，分析了水膜表面约束机制以及硅钢聚磁结构对所激励的多模式超声波幅值的影响规律，研究了仅线圈式EMAT的励磁线圈和接收线圈的外径、内径、线径、层数等对超声波接收效率的影响；其次，开展了铝合金Laser-EMAT检测实验，验证了水膜表面约束机制、仅线圈式EMAT设计参数和硅钢聚磁结构对检测回波幅值的影响规律。研究结果表明，水膜表面约束下，采用硅钢材料作为励磁线圈的聚磁背板后，超声回波信号幅值增强了37.76%,信噪比增加了17.3 dB。在激光能量一定、光斑大小不变、励磁线圈外径为12.3 mm、内径为1.6 mm、线径为0.4 mm、层数为2层时，线圈阻抗与电路内阻一致，线圈获得的能量最多，其提供的径向偏置磁场最强。当接收线圈外径为14.1 mm、内径为1.7 mm、线径为0.26 mm时，超声波接收效率最佳。

Optimal design of metal detection system based on laser-coil only EMAT

In the process of aluminum alloy casting and high temperature rolling, non-contact nondestructive testing technology is used torealize online monitoring and detection, which is of great significance to reduce production costs, ensure the continuity of productionlines, and improve product yield. Firstly, the finite element model of the laser EMAT testing process of aluminum alloy, which is excitedby pulsed laser beam and received only by the coil electromagnetic ultrasonic transducer (EMAT), is established. The influence of waterfilm surface restraint mechanism and silicon steel magnetic structure on the amplitude of excited multi-mode ultrasonic wave is analyzed.The influence of the outer diameter, inner diameter, wire diameter, number of layers of the excitation coil and the receiving coil of thecoil electromagnetic ultrasonic transducer (EMAT) only on the ultrasonic receiving efficiency is studied. Secondly, the Laser EMAT testof aluminum alloy was carried out to verify the influence of water film surface constraint mechanism, coil only EMAT design parametersand silicon steel magnetic focusing structure on the detection echo amplitude. The results show that the ultrasonic echo signal amplitudeincreases by 37. 76% and the signal-to-noise ratio increases by 17. 3 dB when silicon steel is used as the magnetic back plate of theexcitation coil under the constraint of the water film surface. When the laser energy is constant, the spot size is constant, the outerdiameter of the excitation coil is 12. 3 mm, the inner diameter is 1. 6 mm, the wire diameter is 0. 4 mm, and the number of layers is 2,the coil impedance is consistent with the internal resistance of the circuit. The coil obtains the most energy and provides the strongestradial bias magnetic field. When the outer diameter of the receiving coil is 14. 1 mm, the inner diameter is 1. 7 mm, and the wire diameter is 0. 26 mm, the ultrasonic receiving efficiency is the best.