The series calculation model for the magnetic field of coil above arbitrary layer conductive plates

In calculation the magnetic field of the coil above multilayer conductive plates, time consuming and implementation difficulties are the main problems. A series expansion method was proposed to calculate the magnetic field, based on the Maxwell equations, the magnetic vector potential and solution region truncation. The conductive plates were extended to arbitrary layers and the expression for the magnetic field change of the coil was derived in the form of series. When the radius of truncated region and the number of summation terms were selected properly, and some terms were precomputed, the computation time can be reduced considerably and at the same time preserve the computational accuracy. The magnetic field change of the coil above a conductive half space was calculated at different frequencies with series approach and finite element method respectively, the results agreed very well and confirmed the suitability of the proposed series expansion calculation model and its application prospect in forward model of eddy current testing for defect quantitative measurement.