A method is presented for the reconstruction of multiple cracks in conducting plate specimens. The impedance variation of a conventional eddy current testing (ECT) pancake coil is assumed to be the input of the targeted inverse problem. Cracks distributed in the degraded region of the material are modeled by infinitesimally thin cracks parallel with each other. The planes of the modelling cracks are in regular distance from each other. Based on numerical investigation, the validity and the limits of the described modelling are partially discussed. The signal of the probe is calculated by the solution of a boundary integral equation. The reconstruction is made in two steps. In the first step a rough crack distribution is obtained. In this step the signal is approximated by the superposition of the signals calculated for each individual crack, that is in this step the interaction between the cracks is neglected. In this step a pre-calculated data set is used to Speed up the calculations. In the second step of the reconstruction, the interaction of the cracks is also considered. The parameters describing the group of cracks are optimised by using deterministic optimisation method. The gradient of the objective function is evaluated using the sensitivity information which is also obtained by the solution of the mentioned integral equation. Numerical example is shown for the demonstration of the presented reconstruction method.
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