To build this model, we made assumptions deduced from various numerical results obtained from an electromagnetic finite element code. For each position of the coil, the impedance change can be derived, knowing the distribution of eddy currents around the flaw. We then chose to build a parametric model to approximate eddy currents around the flaw. We then chose to build a parametric model to approximate eddy current distributions. These distributions are discretized into elementary current loops, whose shape is parameterized. Assuming some hypothesis, the intensity of each current loop and the impedance change can be determined. as computation time is still too long, eddy current distributions are approached by some few average elementary current loops. The impedance change is calculated from these average current loops.

As a first step, we consider the case of a rectangular crack, normal to the surface of an infinite plate to validate the model. Details of the model and comparison between model and experimental results will be given.