基于有限元法的激光声磁检测系统优化研究

针对激光超声和电磁超声两种非接触式检测方式在实验中操作复杂和灵敏度低，以及难以观察不同参数对相关物理场造成的影响等问题，文中将有限元法应用到激光声磁混合式检测当中，采用数值分析方法分析了脉冲激光与电磁超声换能器之间的匹配关系对检测灵敏度的影响，研究了激光声磁检测系统的优化设计依据。利用有限元软件建立了激光声磁检测系统的仿真模型，通过正交数值仿真分析了高斯激光脉冲激励超声的温度场和位移场特性，进而观测了电磁超声换能器参数变化对检测灵敏度的影响。结果表明:螺旋型线圈接收的电压信号能正确反应由入射激光在固体中发生热膨胀效应产生的超声位移场，当磁体的高宽比为 1.5 倍时，驱肤层处磁场强度分布最优，提离距离对换能效率的影响呈现负指数变化规律，评价了不同接收间距处电磁超声换能器的接收性能。

Optimization of the laser-EMAT detection system based on FEM

To solve the complicated operation problems of the laser ultrasonic method and the low sensitivity of electromagnetic acoustic transducers, that both have noncontact characteristics in their respective detection processes. It is difficult to observe the effects of different parameters on the relevant physical fields. In this paper, the finite element simulation method was used to analyse the influence of the matching relationship between the pulsed laser and the electromagnetic ultrasonic transducer on the detection sensitivity, and the optimal design basis of the laser sound-magnetic detection system was studied. The simulation model of the laser acoustic-magnetic detection system was established by using finite element software. The characteristics of the temperature field and displacement field of ultrasonic excitation by a Gaussian laser pulse were analysed through orthogonal numerical simulation, and the influence of the parameter change of the electromagnetic ultrasonic transducer on the detection sensitivity was observed. The results indicate that the voltage signal received by the spiral coil can correctly respond to the ultrasonic displacement field generated by the thermal expansion effect of the incident laser in the solid. When the height to width ratio of the magnet was 1.5 times, the magnetic field intensity distribution at the driving layer was optimal, and the effect of the lifting distance on the energy conversion efficiency presented the law of negative exponential. The receiving performance of the electromagnetic ultrasonic transducer at different receiving spacings was evaluated.