Flux-Directional Orthogonal Differential Probe for Low-Frequency Eddy-Current Nondestructive Testing

Eddy current probes are widely used to enable non-contact, high-speed detection in the operation and maintenance of metal pipelines and sheets. This study proposes a spatially orthogonal differential eddy current probe based on magnetic flux directional extraction to address the issue of weak detection signals during low-frequency eddy current testing of millimeter-scale surface defects on metal sheets. A simulation model of the probe is developed using COMSOL Multiphysics to analyze the magnetic flux distribution and induced electromotive force (EMF) characteristics of both traditional runway-shaped and refined spatially orthogonal differential probes during defect detection. An experimental platform is constructed to compare defect signals of varying sizes at different detection speeds. Simulation results indicate that the induced EMF amplitude in the detection coil of the refined probe is approximately 3.3 times greater than that of the traditional runway-shaped differential eddy current probe. Experimental findings confirm that the refined probe, operating at 2 m/s, can reliably detect defects with a width and depth of 0.5 mm.