Measurement of lift-off using the relative variation of magnetic flux in pulsed eddy current testing

• The process of penetration and loss of the eddy currents in a metal plate is studied.
• A new feature is proposed for the measurement of lift-off.
• How to obtain the key parameters of the feature from the testing signals is provided.
• The validity of the feature is verified by simulations and experiments.
• The feature is suitable when the lift-off is large and the plate is ferromagnetic.

Measurement of lift-off can be used to assess the thermal insulation thickness and it has the potential to reduce the lift-off effect in pulsed eddy current testing. In this paper, first, the relative variation of magnetic flux is proposed as a feature for the measurement of lift-off. And then, how to directly obtain the key parameters of the feature from the testing signals is provided. At last, the validity of the feature is verified by simulations and experiments, respectively. The results show that the feature is suitable when the lift-off is tens of millimeters and the plate is ferromagnetic.