Electromagnetic analysis of RFEC differential probes

A differential probe (DP) for defect detection in the remote field eddy current (RFEC) technique is proposed. The analysis of the DP response to a sinusoidal steady-state excitation and a sinusoidal pulse excitation has been carried out by an equivalent network model, which allows easy modeling of axisymmetric defects. In the case of a sinusoidal steady-state excitation, the possibility of having clearer defect detection with respect to the conventional phase shift output, exploiting the phase shift between the induced signals in the two pickup coils, is shown. The differential output signal is equally sensitive to outer and inner defects, while the signal amplitude decreases as the distance between the coils increases. In the case of a sinusoidal pulse excitation, the differential configuration allows defect detection, but the transient nature of the induced voltages presents the phase shift effect, and the differential probe output amplitude is lower than the conventional one