Analytical model for mutual inductance between two rectangular coils in driver pickup mode for eddy current testing

摘要

The electromagnetic induction method by means of eddy current plays an important role in non-destructive testing. In detecting a defect from the impedance variation, there is the driver pickup coils method, which arranges two coils on the one side of the tested material. In most studies, circular coils have been analysed. In this paper, the electromagnetic field and mutual inductance between two rectangular eddy current coils in driver pickup mode are calculated analytically for different sizes and arbitrary misalignment above a planar conductor. Firstly, the second-order vector potential formulation is used for the calculation of the fields produced by a rectangular transmitter coil of multi-turns and rectangular cross section placed on a conducting half-space. Then, the closed-form expressions are provided for the mutual inductance between two rectangular coils in free-space and its change due to the eddy current in the conducting half-space. Finally, the mutual inductance and its change are calculated for different frequencies, lift-off, distances and misalignments. The validity of the theoretical analysis and calculation is confirmed by the experiments.