Enhancement method of magnetic flux leakage signals for rail track surface defect detection

Magnetic flux leakage (MFL) detection is widely used for non-destructive testing of rails, pipelines and storage tanks. The leakage magnetic field (LMF) of a defect, especially a small defect, is usually weak. To find small defects on the rail surface, here a ferrite is added in an LMF sensor to reduce the reluctance to increase the magnetic intensity above the defects. The effects of the cross-sectional shape and size of a ferrite are studied by simulation and experiments, and the suitable dimensions for signal enhancement are found. To suppress the interference caused by the variation of the lift-off distance, two Hall sensors are introduced and a differential circuit is designed for signal post-processing. From the finite element simulation and experiments, it is shown that the MFL signals with a ferrite are significantly increased.