A perturbation approach for the modelling of eddy current nondestructive testing problems with differential probes

A perturbation technique applied to the finite element modelling of eddy-current nondestructive testing (ECNDT) problems is developed for taking into account differential probes and multiply connected domains. It concerns a h-conform formulation. The source term of the formulation is directly determined from the unperturbed field and 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