Sweeping frequency balanced electromagnetic field distortion effects under buried cracks

Electromagnetic testing (ET) possesses the advantages of strong adaptability and low sensitivity to environmental conditions, enabling effective identification of surface cracks. However, its accuracy in detecting buried cracks is often constrained by the limitation of skin depth. To address this issue, this paper proposes sweeping frequency balanced electromagnetic technology (SFBET) and systematically investigates the disturbance characteristics of buried cracks on the sweeping balanced electromagnetic field, leading to the discovery and definition of a new characteristic parameter independent of skin depth-the amplitude zero-point frequency (AZF). First, a finite element model is established to simulate the disturbance behavior of buried cracks on the balanced electromagnetic field, and the formation mechanism of the amplitude zero-point (AZ) is revealed. Subsequently, an experimental platform for buried crack detection is constructed to validate the simulation results. Finally, the quantitative relationship between the crack buried depth and the AZ is analyzed. The results demonstrate that, under sweeping frequency excitation, the skin depth varies dynamically; buried cracks significantly disrupt the balanced state of the electromagnetic field, causing distortions in both its propagation direction and amplitude; during the sweeping process, a zero-amplitude point emerges near the crack edge, and the corresponding excitation frequency exhibits an exponential relationship with the crack buried depth, with a fitting correlation coefficient exceeding 0.99.