A giant magnetoresistive flux focusing eddy current device effectively detects
deep flaws in thick multilayer conductive materials. The probe uses an excitation
coil to induce eddy currents in conducting material perpendicularly oriented to
the coil's longitudinal axis. A giant magnetoresistive (GMR) sensor, surrounded
by the excitation coil, is used to detect generated fields. Between the excitation
coil and GMR sensor is a highly permeable flux focusing lens which magnetically
separates the GMR sensor and excitation coil and produces high flux density at
the outer edge of the GMR sensor. The use of feedback inside the flux focusing
lens enables complete cancellation of the leakage fields at the GMR sensor location
and biasing of the GMR sensor to a location of high magnetic field sensitivity.
In an alternate embodiment, a permanent magnet is positioned adjacent to the GMR
sensor to accomplish the biasing. Experimental results have demonstrated identification
of flaws up to 1 cm deep in aluminum alloy structures. To detect deep flaws about
circular fasteners or inhomogeneities in thick multilayer conductive materials,
the device is mounted in a hand-held rotating probe assembly that is connected
to a computer for system control, data acquisition, processing and storage.
