Magnetic saturation effect and optimizsation design of inductive coil sensors in MFL testing

In the magnetic flux leakage (MFL) detection of steel wire ropes (SWRs), an inductive coil with a ferrite core is often used as the sensor for detection. This paper points out that the ferrite core in the current MFL test sensors also exhibit the magnetic saturation effect (MSE), and analyzes the related MSE theory. Based on the analysis of the existing open-loop magnetiser, through simulation and experiments, the existence of the ferrite core’s MSE was verified. By conducting comparative tests under different magnetisation intensities, a stronger magnetisation intensity actually leads to a decrease in the detection signal under the same conditions. This is the manifestation of the MSE. Therefore, six experimental groups set up, including different-sized ferrite cores, different magnetisation intensities of open-loop magnetisers, and different number of coil turns, and carried out on-site tests. The experimental results not only demonstrated the existence of the MSE, provided effective methods to suppress the MSE. The newly designed sensor avoids the MSE and has better Signal-to-noise ratio (SNR) and peak signal-to-noise ratio (PSNR) in on-site actual detection. Meanwhile, this research also provided ideas for the design of the ferrite core in MFL sensors, and offers important theoretical guidance for MFL sensor optimisation.