Semi-analytical calculation of the impedance of a differential sensor for eddy current non-destructive testing

In this contribution, we aim at the modelling of the impedance of a differential sensor in eddy-current non-destructive testing. This mode of control is very common in the detection of abrupt geometrical and electromagnetic variations, disturbances generated by slow variations of dimensions and temperature being in particular not observed. We develop a direct semi-analytical model of a voltage-excited system. The formulation is based upon the use of coupled electric circuits. It provides a particular form of the differential impedance, which clarifies the role of the electromagnetic and geometric characteristics. This form of impedance will allow the investigation of non-destructive testing by means of differential sensors and will facilitate the development of real-time inversion procedures. The model is validated by results published in the literature. We exploit it in order to study various electric and geometrical parameters of the control system.