Evaluation of Coating Thickness Using Lift-Off Insensitivity of Eddy Current Sensor

Defect detection in ferromagnetic substrates is often hampered by nonmagnetic coating thickness variation when using conventional eddy current testing technique. The lift-off distance between the sample and sensor one of main obstacles for measurement coatings on Based thin-skin effect insensitive inductance (LII), a simplified iterative algorithm proposed reducing multifrequency sensor. Compared to previous techniques compensating error (e.g., point intersection) while retrieving thickness, algorithms avoid computation burden integration, which are used as embedded online retrieval lift-offs via each frequency channel. LII determined dimension geometry sensor, thus eliminating need empirical calibration. method validated means experimental measurements with different materials thicknesses ferrous (dual-phase alloy). calculated has been controlled within 3% an extended range up 10 mm.