Research On Nondestructive Testing Theory Of Metal Material Based On Magnetoacoustic Tomography With Magnetic Induction

Non-destructive testing(NDT)technology based on magnetoacoustic tomography with magnetic induction(MAT-MI)is a newly emerged functional imaging modality for imaging the surface wave displacement of a metal plate.It combines the high penetration of ultrasound-based NDT and high sensitivity of electromagnetic NDT.It can accurately locate the defects on the surface of the metal plate.The idealized assumption of electrical homogeneity of the tested material may be invalid in many practical applications for metal materials with defects,resulting in significant distortions and artifacts in the surface wave images.In this dissertation,a method for solving the forward problem in NDT based on MAT-MI for nonferromagnetic metal plate is studied.A computer-simulated nonferromagnetic metal plate with anisotropic conductivity is constructed where its electrical conductivity is represented with a tensor.The metal plate is placed in a static magnetic field and an alternating excitation magnetic field stimulated by a meander coil placed over the metal plate.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 distribution map of the surface wave displacement.The defects can be clearly distinguished from the images because the surface wave rapidly attenuates at the defects.The conductivity tensor of the material can be flexibly adjusted to accurately simulate the distribution of acoustic source and surface wave displacement.