Sweeping alternating current field measurement method for buried crack inspection

To address the limitations of traditional electromagnetic testing (ET) technology in detecting buried cracks due to the skin effect and skin depth, this paper proposes a novel sweeping alternating current field measurement (SACFM) method. This method leverages the dynamic variation of skin depth under sweeping frequency excitation and utilises the amplitude zero frequency (AZF) as a characteristic parameter to evaluate the burial depth of cracks, enabling precise detection of buried cracks. First, the influence mechanism of excitation frequency on buried crack detection is thoroughly analysed and a comprehensive theoretical model for SACFM is established based on the principles of alternating current field measurement (ACFM). Subsequently, an SACFM experimental platform is constructed, and systematic experiments are performed on cracks with varying burial depths. The results demonstrate that the skin depth exhibits dynamic changes during frequency sweeps. Crucially, a distinct amplitude zero (AZ) appears at the edges of buried cracks, and a strong exponential relationship exists between AZF and the burial depth of cracks, with a correlation coefficient exceeding 0.99. By integrating SACFM with ACFM, precise localisation of buried cracks can be achieved.