Optimization design method of excitation magnetic field in motion induced eddy current magnetic field testing

Abstract

In the process of production or long-time use of a thin metal plate, micro defects (micro particles or pores) will be produced in its interior. The number and size of these micro defects determine the quality of the thin metal plate, affecting its service life and factor of safety. Therefore, quantitative and accurate characterization of micro defects is a necessary to ensure the quality and safety of thin metal plate products. In this work, we study the application of motion induced eddy current magnetic field testing in electromagnetic testing to detect defects in conductive material and nonmagnetic material. The simulation results show that when the lift-ff distance and the surface remanence of the permanent magnet are determined, the size of the permanent magnet is positively correlated with the amplitude of the defect detection signal. The main reason is that in a motion induced electric field without defects, the amplitude of defect detection signal is linearly related to the current density mode at each point on the defect motion path. Increasing the size of the permanent magnet can effectively improve the current density mode. As a continuation of the above results, an optimization method for excitation magnetic field in motion induced eddy current magnetic field detection is proposed. The two types of permanent magnet arrays generated by this method generate larger amplitude defect detection signals than that by simple permanent magnets with the same volume and surface residual magnetism. The experimental results show that the excitation magnetic field arrangement designed by the above optimization method increases the signal amplitude by 80%–90% compared with that by traditional method. This optimization method conduces to improving the sensitivity of motion induced eddy current magnetic field detection methods.