Detection mechanism and magnetic field distribution characteristics for plate remote-field eddy-current testing

One advantage of remote field eddy current technology is that it is not limited by the skin effect; the technology can be used to detect defects in the inner or the outer wall of a pipeline. Studies have also found the remote field eddy current phenomenon while detecting plate conductors. Remote field eddy current technology is usually used in pipeline material defect detection. If applied to plate material defect detection, the measurable range of defect depths can be greatly extended. In the present study the finite element method was selected for numerical electromagnetic analysis of magnetic flux density distribution disturbances in the induction coil, which are induced by two typical defects: rectangular slots and flat-bottom holes. The present study found that, the distribution of magnetic flux density is similar for defects on either the lower or the upper surface, though the changes in magnetic flux density caused by defects on the lower surface are smaller than those caused by the same kind of defects on the upper surface. There is also an intuitive correspondence between the magnetic flux density distribution and the shape of the defect.