Reduction of lift-off effect for pulsed eddy current testing based on equivalent magnetic circuit model analysis

摘要

Reducing the lift-off effect could enhance the accuracy and the application scope of pulsed eddy current testing. Firstly, an equivalent magnetic circuit model is established. As excitation current turns off, the magnetic field, which is generated by the induced eddy current in the specimen, is regarded as the magnetomotive force of the magnetic circuits. Secondly, the relationship between the magnetomotive force and the magnetic flux crossing the probe is presented. Finally, based on the relationship and the eddy current diffusion law in a conducting half-space, a method is proposed to reduce the lift-off effect. Analytic calculation results show that the method is effective and it is especially applicable to the thick specimen detection.