Optimization of Magneto-Optical Imaging Visualization of Micro-Defects Under Combined Magnetic Field Based on Dynamic Permeability

The existing magneto-optical imaging of weld defects is carried out under a constant magnetic field or alternating magnetic field. The magneto-optical image (MOI) is easy to saturate under a constant magnetic field, resulting in the loss of defect information. It is very difficult to realize magneto-optical imaging of micro-defects under alternating magnetic fields. Therefore, magneto-optical imaging under a combined magnetic field is proposed in this article. Firstly, the effect of dynamic permeability on the law of magnetization of defects is analyzed. Then, through simulation experiments, the magnetic flux leakage law of defect samples under constant magnetic field, alternating magnetic field, and combined magnetic field are analyzed. Finally, the magneto-optical imaging experiment is used to study the imaging law of wire cutting grooves under different magnetic field excitation. The experimental results show that compared with constant magnetic field and alternating magnetic field, the difference of leakage magnetic field under combined magnetic field excitation is more obvious. This shows that using a combined magnetic field for imaging detection can effectively improve the disadvantage that it is difficult to realize an MOI of micro-defects under an alternating magnetic field.