Electromagnetic field distributions around conducting slabs, produced by eddy-current probes with arbitrary shape current-carrying excitation loops

The theoretical prediction of eddy-current probe output signals for various nondestructive testing (NDT) applications usually involves solution of the electromagnetic field due to a current-carrying excitation loop in the vicinity of a flawless conductor. The paper presents a general theory for the time-harmonic magnetic field distribution produced by an arbitrary shape current-carrying excitation loop around a linear, isotropic, homogeneous conducting slab. In this theory the authors develop a Fourier-integral-based model for computing the magnetic field distributions, which greatly simplifies the computation procedure. The main feature of the model is its ability to analyse two- and three-dimensional excitation geometry, with a similar degree of computation burden. This feature stems from the fact that in this model, knowledge of the field distribution at the place of the conductor surface in free space suffices to compute the field in the presence of the conductor. To demonstrate the accuracy of the model, the authors consider two special cases of an infinite straight wire and an elliptical loop exciter. The comparison of the results with those obtained using the conventional algorithms in the literature validates the model introduced in the paper. To show the generality of the model, the authors also present results associated with a solenoid exciter with a three-dimensional geometry for which no analytical solution is available in the literature