A Novel Leakage Magnetic Field Enhancement Method Based on Permeability Perturbation

The magnetic flux leakage (MFL) testing method is widely applied in detecting ferromagnetic materials, such as steel pipes. In order to protect the magnetic sensor, nonferromagnetic wear-resistant materials are placed between the sensor and the tested workpiece by conventional MFL. However, the leakage magnetic field (LMF) decays exponentially in the air, reducing the sensitivity. To improve the sensitivity of MFL, a novel approach for enhancing the LMF based on permeability perturbation is proposed in this article. The ferromagnetic materials are used as the medium between the sensor and the workpiece. The ferromagnetic medium generates a magnetic permeability perturbation area under the effect of the LMF, changing the magnetic reluctance in this local area. The difference in the magnetic reluctance in the medium influences the magnetizing field, and an additional LMF is formed, which enhances the LMF. Experiments found that the enhancement effects of different magnetic mediums with different magnetic characteristics were different. Different materials' enhancement mechanism was analyzed by considering the saturated magnetization. Compared with conventional MFL, the method proposed in this article can increase the LMF and improve the sensitivity of MFL.