Lift-Off Effect of Koch and Circular Differential Pickup Eddy Current Probes  

作　　者：Guolong Chen Zheng Cao Shuaishuai Zhang Ji Wei Wei Gao Wuyin Jin 

机构地区：[1]School of Mechanical and Electrical Engineering,Lanzhou University of Technology,Lanzhou 730050,China

出　　处：《Chinese Journal of Mechanical Engineering》2024年第2期283-293,共11页中国机械工程学报（英文版）

基　　金：Supported by Gansu Provincial Natural Science Foundation of China(Grant No.22JR5RA229);National Natural Science Foundation of China(Grant Nos.51807086,12162021);Hongliu Youth Found of Lanzhou University of Technology and Gansu Provincial Outstanding Graduate Student Innovation Star of China(Grant No.2021CXZX-453).

摘　　要：A flexible or planar eddy current probe with a differential structure can suppress the lift-off noise during the inspection of defects.However,the extent of the lift-off effect on differential probes,including different coil structures,varies.In this study,two planar eddy current probes with differential pickup structures and the same size,Koch and circular probes,were used to compare lift-off effects.The eddy current distributions of the probes perturbed by 0°and 90°cracks were obtained by finite element analysis.The analysis results show that the 90°crack can impede the eddy current induced by the Koch probe even further at relatively low lift-off distance.The peak-to-peak values of the signal output from the two probes were compared at different lift-off distances using finite element analysis and experimental methods.In addition,the effects of different frequencies on the lift-off were studied experimentally.The results show that the signal peak-to-peak value of the Koch probe for the inspection of cracks in 90°orientation is larger than that of the circular probe when the lift-off distance is smaller than 1.2 mm.In addition,the influence of the lift-off distance on the peak-to-peak signal value of the two probes was studied via normalization.This indicates that the influence becomes more evident with an increase in excitation frequency.This research discloses the lift-off effect of differential planar eddy current probes with different coil shapes and proves the detection merit of the Koch probe for 90°cracks at low lift-off distances.

关 键 词：Eddy current testing Differential pickup probe Fractal Koch curve Flexible eddy current probe 

分 类 号：TG115.28[金属学及工艺—物理冶金] TG665[金属学及工艺—金属学]