Giant magnetoresistance based eddy current probes for nondestructive testing

Detection of deeply buried cracks and of small cracks initiating at edges of metallic parts and structures are among the challenges encountered by the nondestructive testing industry. Solid-state magnetic sensors based on Giant Magneto-Resistance (GMR) and Spin-Dependent Tunneling (SDT) effects have been integrated in eddy current probes that are capable of addressing these difficult problems. Because of their superior sensitivity, small dimensions and low cost, these sensors have been proved effective for detection of deeply buried cracks (up to 25 mm below the surface) using eddy current methods. A problem of great interest in airplane industry that has been successfully addressed in this work is the detection of deep corner cracks around fastener holes in multi-layered aluminum structures. Significant advances in high-resolution metallic profile imaging and corrosion monitoring using the new generation of eddy current probes are reported in this work. Spatial resolution in the range of 100 micrometers has been obtained by using these probes.