Recent Development of MESSINE, a 3D Eddy Current Model

Abstract : In the 1996 QNDE Conference, we presented a parametric forward model [1], which has been recently named MESSINE (Model for Electromagnetic Simplified Simulation In Nondestructive Evaluation), to predict eddy current signal. The proposed model first discretizes the eddy current distribution into current loops. A parametric description of the shape of these loops is given according to the observation of the results obtained with a three-dimensional finite element code which provides a realistic distribution of the induced currents. The loops’ inductances and resistances are then calculated. By considering the system constituted of the coil and the current loops as a « multi-transformer», their current intensity is determined. The impedance change, which is the component of the eddy current signal, can then be deduced. The model was validated in the case of axisymmetric configurations. Comparisons with both analytical (Dodd and Deeds [2]) and numerical models showed very good agreements. Then the proposed model was applied to three-dimensional configurations. Impedance changes of a coil along rectangular through-wall slot were calculated. Comparisons with experimental results show a fairly good agreement for the impedance change phases, but a poorer one for the impedance change amplitudes. Investigations were made to improve the parametric description of the current loop deformation. One of the solutions to improve the parametric description is presented here.