A New Dual Magnetic Sensor Probe for Lift-off Compensation in Magnetic Flux Leakage Detection

For in-line inspection of ferromagnetic materials, magnetic flux leakage (MFL) detection is the most common nondestructive testing method. The measured signals of the MFL detection are affected by many factors, especially the lift-off of sensors. In addition, in practical inspection applications, due to mechanical vibration, the lift-off of sensors will continue to fluctuate throughout the detection process. To address the problem, this paper proposes a new type of probe with dual vertical distributed magnetic sensors for MFL detection. This paper also presents a solution for implementing the dual magnetic sensor probe on the circuit board. According to the proposed probe structure and the magnetic dipole model, the analytical solutions of the current sensor lift-off and the defect depth are given. The solutions are verified by the finite element simulation and physical experiments. Furthermore, the sensor lift-off compensation experiments are carried out under different lift-off values. The simulation and the experiments prove that the solution of the defect depth and the lift-off compensation of probes are in line with the engineering application.