电导率各向异性金属薄板感应式磁声图像的仿真

为了给金属薄板感应式磁声(MAT-MI)成像算法的研究提供数据源,提出一种电导率各向异性金属薄板表面MAT-MI图像的数值仿真方法。建立含缺陷的电导率各向异性金属薄板仿真模型,并将其置于静磁场中。将通入交变电流的折线线圈置于金属薄板上方,对金属薄板在静磁场和交变磁场共同作用下产生的感应涡流以及声源(即洛伦兹力)进行数值仿真,得到金属薄板表面波位移分布的灰度图像。仿真实验结果表明,根据表面波位移在缺陷处迅速衰减的特性,可从图像中准确地识别并定位金属薄板表面的缺陷。忽略金属材料的电导率各向异性会降低成像质量,进而导致对缺陷的误判。通过提高表面波位移信号的信噪比可改善成像质量。减小提高距离或增大激励电流频率,可提高系统对微小缺陷和不规则缺陷检测的分辨力。 

Simulation of magnetoacoustic tomography with magnetic induction images of metal sheet with anisotropic conductivity

A method for numerically simulating MagnetoAcoustic Tomography with Magnetic Induction (MAT-MI) images of a metal sheet with anisotropic conductivity is proposed to provide image data for research and performance testing of Non-Destructive Testing (NDT) based on MAT-MI.A computer-simulated metal sheet with anisotropic conductivity is constructed and placed in a static magnetic field.A meander coil is placed over the metal sheet to stimulate an alternating excitation magnetic field.The induced eddy current and the acoustic source,i.e.,Lorentz force,generated by the static and alternating magnetic field are numerically simulated to obtain the gray-scale images of the surface wave displacement.The simulation results show that the defect on the metal sheet surface can be clearly identified and located from the images according to the characteristics of rapid attenuation of the surface wave at the defects.Ignoring the conductivity anisotropy of metal materials will reduce the imaging quality and lead to misjudgment of defects.The imaging quality can be improved through increasing the signal-to-noise ratio of the measured displacement signal of surface waves.The resolution to detect small and irregular defects can be improved by reducing the lift-off distance and increasing the excitation current frequency.