Investigation of optimal time-domain feature for non-surface defect detection through a pulsed alternating current field measurement technique

The detectability of an alternating current field measurement (ACFM) for non-surface defects is improved by a pulsed alternating current field measurement (PACFM) technique. In this paper, the optimal time-domain feature of the PACFM technique for non-surface defect detection is investigated by numerical and experimental methods. In the simulation, the numerical model of the PACFM technique is built by the finite element software COMSOL. The mechanism for non-surface defect detection and the time-domain feature of the response signal are studied. It indicates that the value measured after the peak time has a better detection sensitivity and signal to noise ratio than the conventional peak value. Finally, the PACFM detection system is set up and the experimental results indicate that the 1.5 ms time point measured value in the response signal is the optimal time-domain feature for non-surface defect detection. For non-surface defects, the maximum changes in normalized B _x signals for the time point 1.5 ms are always larger than that for the peak time. When detecting surface defects, the maximum change in the normalized B _x signal for the peak time is always larger than that for the time point after the peak time. This phenomenon can be used to effectively classify surface defects and non-surface defects. (paper)