Deep flaw detection with giant magnetoresistive (GMR) based self-nulling probe

Wincheski, Buzz; Namkung, Min
May 2000
AIP Conference Proceedings;2000, Vol. 509 Issue 1, p465
Academic Journal
Giant magneto-resistive sensors provide a high sensitivity to low frequency magnetic fields. This, combined with an inherent small size, low cost, and low power consumption, make GMR sensors a good candidate for low frequency eddy current probe development. Previous research has shown that the incorporation of a GMR sensor in the NASA LaRC developed Self-Nulling Eddy Current Probe greatly enhances the low frequency detection capabilities of the device. Experimental results have shown the detection of a 1.4 cm long notch under up to 9 mm of unflawed aluminum. A limiting factor in this work appeared to be the increased background level with decreasing frequency. In order to improve the signal-to-noise ratio several techniques have been incorporated to reduce the background level and increase the signal-to-noise ratio. The incorporation of a gradiometric sensor, active feedback, and improved shielding have led to an enhanced detectability. In addition, image processing techniques have been explored to filter out background variations from the processed data. Finite element modeling results for the newly designed probe are presented along with experimental data for the detection of EDM notches and fatigue cracks in multi-layered aluminum alloy samples. © 2000 American Institute of Physics.


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