Some particularities of EC crack detection in aluminum using an asymmetrical GMR-coil configuration

This paper presents experimental results related to an asymmetrical coil ? GMR configuration for the detection of surface cracks using eddy currents. The system is evaluated for three different excitation frequencies and the relationship between the extracted parameter (DV) from the GMR output voltage and the crack's dimension is validated. The analysis of the presence of the intermediate peak in the output voltage of the GMR sensor is performed. The stability of the excitation current source is presented and it is demonstrated that the presence of the intermediate peak does not have a significant influence on the relationship of DV with the depth of the crack. The intermediate peak could help on deciding if the crack depth is smaller than 2 mm or if the width is thinner than 0.6 mm. It is studied the behavior of the intermediate peak and its relationship with the width of the defects and with the penetration depth of the eddy currents.