Defect Detection and Depth Evaluation in Ferromagnetic Steel Using a Custom Magnetic Barkhausen Noise–Hysteresis Sensing System

Reliable inspection of ferromagnetic components requires measurements that relate defect indications to defect severity. This study extends a magnetic hysteresis (B–H) measurement platform with a dedicated magnetic Barkhausen noise (MBN) channel to examine depth-dependent responses in steel. Finite-element analysis was used to investigate changes in magnetic flux density and magnetic field strength caused by defects. Experiments covered crack-like and strip defects with nominal depths of 0.5–12 mm and 0.5–7 mm, respectively, using two probe sizes. The measured magnetic-field magnitude increased with defect depth, consistent with the simulated trend, whereas the MBN burst amplitude generally decreased. The tabulated peak amplitude, root-mean-square value and zero-field amplitude decreased within both defect series. The cycle-mean amplitude also decreased overall, following a small initial increase relative to the no-defect reference. Peak-field and width features increased with depth in both series, with different magnitudes and rates of change. The combined measurements connect changes in the local magnetic field with changes in the detected Barkhausen response and identify amplitude features as useful indicators for relative defect-depth assessment under the investigated conditions.