Research on crack monitoring technology of multilayer structure based on TMR-eddy current sensor

Abstract The flexible eddy current array sensor has the characteristics of flexibility, bendability and light weight, which has a great application prospect in the field of structural health monitoring. The traditional flexible eddy current array sensor is affected by the skin effect and the crack monitoring depth is relatively low. This paper proposes an eddy current array sensor which uses TMR (tunnel magneto-resistance) sensor as sensing channels. It reduces the excitation frequency and increases the eddy current skin depth. The TMR sensor realizes the quantitative monitoring of cracks by the array arrangement. First, the finite element model of the sensor is established, and the influence of the cracks on the different layers of the multilayer structure on the magnetic induction intensity at the test point is analyzed. The simulation and results show that when the crack passes through the sensor, the magnetic induction intensity at the three test points changes in sequence and gradually increases to the maximum value. The direct relative position of the maximum value of the three test points is approximately the same as the distance among the test points. Then, the simulated crack growth experiment of the corresponding sensor is carried out. The experimental results show that as the crack grows, the signals of the three TMR sensors on the eddy current sensor change in sequence, and the distance between the characteristic points is consistent with the distance between the TMR sensors. The output voltage of the sensor decrease with the crack depth increases. The experimental results are consistent with the simulation results, which further verifies the correctness of the simulation model.