Separation of Lift-off and Defect Depth Features in Magnetic Sensor based Pulsed Eddy Current Signals

摘要

This paper focuses on defect characterisation independent of the lift-off effects using lift-off point of intersection (LOI) and the separation of these two parameters in pulsed eddy current (PEC) measurements for ferrous and non-ferrous materials. It reveals, amongst other things, that the first order derivative of the normalised PEC response maintains the LOI feature, which otherwise is not apparent in ferromagnetic materials using current methods; lift-off effects in ferrous materials vary strongly with the second order derivative of the normalised PEC response and the LOI can be used for defect estimation in a magnetic sensor-based PEC. These two characteristics provide a means of separating lift-off effects from the defect.