Suppressing sensor lift-off effects on cracks signals in surface magnetic field measurement technique

As in the eddy current technique, a major problem for crack measurement in the surface magnetic field measurement (SMFM) technique is the lift-off distance of the sensor. The nonzero value of lift-off distance tends to smear out the discontinuity in the SMFM crack signal, causing errors in crack characterization. The paper presents a method for sensor lift-off evaluation and crack signal restoration in the SMFM technique. The method employs a deconvolution technique and uses a suitable cost function based on the relations available for electromagnetic field distributions at the metal surface. Simulation results are presented to demonstrate the accuracy of the method.