In this paper we use the eddy current testing (ECT) method to determine the depth of superficial cracks by measurement of the secondary magnetic field perturbation when an excitation current with surface uniform density is launched perpendicularly to the crack orientation. The secondary magnetic field is measured using giant magneto-resistor (GMR) detectors.
The experimental part of this work was performed by inspection of the secondary field obtained by scanning a large number of slits machined on aluminum plates. The field component represented in the figure was obtained with sinusoidal excitation and was measured on the direction of the linear slits. The measured component presents a single maximum on the center of each one of the seven defects.