Magnetic flux leakage detection based on a sensitivity-enhanced fiber Bragg grating magnetic field sensor

We propose a sensitivity-enhanced fiber Bragg grating (FBG) magnetic field sensor for magnetic flux leakage (MFL) detection. The testing system consists of the FBG, suspended strain concentration structure, and two ceramic tubes bonded on a Terfenol-D base. We show the relation between the MFL and the width and depth of the crack, the lift-off of the sensor away from the surface of the workpiece, and the angle between the orientation of the sensor and the magnetization direction. The experimental results are very consistent with those obtained from finite element analysis simulations. The sensitivity of the sensor is increased to 81.11 pm/mT for increasing magnetic fields and 91.55 pm/mT for decreasing magnetic fields. The MFL test demonstrates that the sensor can identify a crack with a width of 0.5 mm and depth of 2 mm in an 8 mm thick workpiece. To the best of our knowledge, the magnetic field sensor proposed in this work has the highest sensitivity compared with the same types of sensors. Moreover, the application of an FBG-Terfenol-D based magnetic field sensor in the MFL test shows good performance. Compared with traditional electrical MFL testing technologies, the sensitivity-enhanced optical fiber magnetic field sensor has a higher resolution and longer survival time in harsh environments.