Finite element modeling of pulse Eddy current NDT phenomena

Transient electromagnetic fields for nondestructive testing (pulse eddy current methods) have been used experimentally for such applications as coating thickness measurements [1] and the inspection of reactor fuel tubing.[2] The lack of suitable models to facilitate understanding of the interaction of the pulsed field with the test specimen has hindered a wider acceptance of the method as a tool in NDT. Two models, based on the finite element technique, are described. A through transmission arrangement of a source and pickup coil with a conductive plate separating the two coils is modeled. The first model, used for a periodic current pulse source, makes use of the Fourier series of the source current to solve a steady-state problem for each significant harmonic. The harmonic solutions are then summed to calculate the total EMF in the pickup coil. The second model provides a transient time stepping solution for a single current pulse applied to the source coil. In both cases, axisymmetric geometries are studied using a magnetic vector potential formulation. Solutions are compared with experimental results.