Defect detection in aluminium with an eddy currents sensor

The purpose of this paper is to present an eddy current testing technique for surface defect detection in conducting materials using a giant magnetoresistive (GMR) sensor. A flat coil is used to produce an alternate magnetic field, which gives rise to eddy currents in the material under test. The GMR sensor with the coil placed on top of it is mounted in a holder, which is moved over the surface of the metal plate using an XY table. Three aluminium plates were used with defects having nominals depths of 2, 4, 6, and 8 mm and widths of 0.6, 1 and 1.4 mm, respectively. The defects were scanned with the sensing axis perpendicular to the defect length. The GMR output voltage depends on the width and depth of the defects. Two parameters extracted from the GMR output voltage signal are obtained and a simple correlation between the defects dimensions and the GMR output voltage is proposed.