Current around a crack in an aluminum plate under nondestructive evaluation inspection

This paper presents an inversion problem algorithm applied in eddy current inspection using a sinusoidal magnetic field with fixed-amplitude, in a metallic plate sample with machined crack defects. The uniform magnetic field is obtained in a wide area around the probe due to the building technique of the excitation coil. The magnetic sensor in use is a giant magnetoresistance (GMR) with high sensibility. It measures the amplitude and phase of the magnetic field originated from eddy currents. A perturbation occurs in the measured magnetic field in the proximity of a crack defect. The current density is then determined around the crack defect through an inversion problem algorithm. The applied method consists in determining the transformation kernel and applying a Tikhonov regularization algorithm. With this data it is possible to obtain information about the defect geometrical characteristics.