GMR stands for giant magnetoresistance but the overall effective sensing size is around 1 mm in diameter. It represents the latest solid state thin-film magnetic sensor technology for detecting minute magnetic field perturbation, both DC and AC field, originating from materials under test. With wider frequency response of DC to megahertz range, it's ideally suited for nondestructive evaluation (NDE) applications involving detection of both DC field and AC field. To detect AC eddy current-to-flaw perturbation field, a separate excitation field is required to introduce eddy currents in a test sample.

EPRI has been evaluating the application of GMR-sensor based eddy current technology to power plant components made of stainless steel and Alloy 600 since 2005. The GMR-based eddy current instrument was successfully developed and fabricated along with several different probe types, which were tested on welded plate samples made of Inconel 182 materials. The fabricated GMR test instrument incorporated the use of unique probe design that would rely on the AC component of the sensor for flaw characterization and the DC component for material characterization.