GMR based eddy current sensing probe for weld zone testing

The detection of flaws in the weld zone of conductive plates is an important issue and, in this field, different solutions using eddy current probes are mentioned in the literature. However, when eddy current pancake probes are used, it is difficult to detect the flaws or the welding non-uniformities due to the lift-off effects. Thus, in the present work we present a novel uniform eddy current probe architecture based on a tangential excitation coil with a rectangular geometry and highly sensitive giant magnetoresistances (GMR). The induced magnetic field is measured using a GMR sensor fixed on the axis midpoint inside the coil. The sensor sensitive axis is perpendicular to the excitation coil axis in order to measure only the induced magnetic fields caused by the presence of flaws. We developed an automatic testing system to characterize the sensor and to perform tests on aluminum plate specimens with flaws included in the weld zone.