Simulation and experimental study on planar remote field eddy current detection of hidden defects in aircraft multilayer structure

Multi-layer metal flat structure is an important load-bearing component of the aircraft, with the characteristics of large thickness and complex structure. The structure is prone to produce various defects in the process of its use. The remote field eddy current detection technology is not limited by the skin effect and can penetrate the measured component with large thickness. In view of the large volume of traditional remote field eddy current sensor, which is difficult to apply to complex detection environment, a small-volume remote field eddy current sensor with coaxial placement and the differential structure of the detection coil is designed and developed. The simulation and experimental results show that the magnetic circuit structure and composite shield damping are beneficial to improve the detection capability of the sensor. Setting the balance coil greatly reduces the effect of the direct-coupled magnetic field on the detection coil and improves the sensitivity of the sensor. The detection signal of the remote field eddy current sensor is directly proportional to the defect equivalent volume, and within a certain defect size range, if the defect equivalent volume is similar, the remote field eddy current sensor is more sensitive to the defect depth.