Methods for improving sensitivity of crack quantitative monitoring of flexible eddy current array sensor

Flexible eddy current array sensor has the characteristics of flexibility and light weight. It has a wide application prospect for surface crack monitoring of metal structures. In order to solve the problem of low sensitivity of crack identification of traditional flexible eddy current array sensor, the methods of changing the spacing between the excitation coil and the sensing coil (SES) of the sensor and pasting the permalloy film on one side of the sensor are adopted to improve the sensitivity of crack identification. Firstly, a finite element model is established to analyze the influence of the permalloy film on the eddy current density on the surface of the specimen and the influence of the SES on the sensitivity of crack identification of the sensor. The simulation results show that when the SES increases from 0.1 mm to 0.4 mm, the sensitivity of the three sensing coils of the sensor to crack identification increases by 144.96%, 181.63% and 136.36%, respectively. And the sensitivity of the sensor to crack identification is improved when the permalloy film is stuck on the upper surface of the sensor, which is up to 81.88%. Then, the experimental results show that when the SES increases from 0.1 mm to 0.4 mm, the sensitivity of the three sensing coils to crack identification increases by 114.68%, 161.66% and 131.24%, respectively. The sensitivity of the sensor to crack identification is increased by 68.21% when the permalloy film is pasted on the surface of the sensor. The error between simulation results and experimental results is introduced by lift-off. The research results can be used to improve the sensitivity of crack identification.