Application of GMR Based Probe – for Eddy Current in Flaw Testing System

In this research, we have investigated an application of eddy current probe-based on the GMR spin-valve for the flaw testing system. The eddy current probe consists of a GMR spin-valve sensor and a square modulation coil. The sensing direction is performed perpendicular to the modulation field generated by a modulation coil. The GMR spin-valve used in this work is a model GF708 from Sensitec Inc with a bare-die version. The scanning length is 80 mm for six cracks with a different depth on the surface of a metal specimen. The gap between the cracks to each other is about 14.5 mm. The experimental results are obtained by scanning the probe over six cracks of a specimen. The crack positions on the surface of a specimen are determined by the peak or valley values of in-phase and quadrature-phase differential defect field. Similarly, the depth of the cracks is estimated by the phase of the differential defect field.