This paper is concerned with a novel self-compensating Giant Magneto-Resistance (GMR) based eddy current probe for hidden cracks inspection. Instead of a pickup coil commonly used, a GMR sensor is employed in the probe to work as the sensing element to detect magnetic field. In order to obtain the compensating signal, the system identification techniques are used to establish a transfer function model, which quantitatively describes the relationship between the excitation and response of the GMR-based probe. Subsequently the compensating signal is predicted by the developed transfer function model and reproduced by physical circuits via phase shifter and amplitude regulator. Inspection experiments on simulated hidden cracks in thick conductive specimen were carried out. The experimental results show that the newly developed self-compensating GMR-based probe has larger dynamic range as well as higher sensitivity and resolution. The presented new probe is promising for the in-service inspections in many fields such as aircrafts and pipelines evaluation using eddy current testing.
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