A perturbation technique applied to the finite ele- ment modelling of eddy-current nondestructive testing (ECNDT) problems is developed for taking into account differential probes. It concerns a h−conform formulation. The source term of the formulation is directly determined by the projection of the unperturbed field in a relatively small region around the defect. The voltage change due to the presence of the flaw is calculated by performing an integral over the defect and a layer of elements in the exterior domain that touch its boundary. The considered test case involves a shielded differential probe scanning the surface of a metal specimen for the detection of flaws.
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