High Temperature SQUID Microprobe for Eddy Current Evaluation of Airframes

Superconductive Quantum Interference Devices (SQUIDs) bring new physics, new technology, and new capability to eddy current nondestructive evaluation (NDE) of materials. A SQUID offers new technology for measurement of magnetic flux at low frequencies with unprecedented sensitivity. Its extreme sensitivity at low frequencies can provide an electromagnetic microscope for eddy current NDE of underlying defects and hidden corrosion in airframes. Our measurements with a prototype SQUID microprobe, using niobium technology at 4 K, show that it reliably finds a 1 mm flaw through 6 mm of aluminum, at 88 Hz and a standoff of 4 mm, as well as material loss less than 1% from corrosion under a 2.29 mm thick aluminum plate. The new capability offered by a SQUID microprobe together with advances in fabricating SQUIDs and pickup coils from high-temperature superconductors provides a technological opportunity for developing a hand-held, electromagnetic microscope for evaluating hidden defects in airframes during flight-line operations. Its development requires the combined skills of experts knowledgeable in (1) eddy current NDE of materials, (2) NDE of military and commercial airframes, (3) fabrication of SQUIDs from high-temperature superconductors, and (4) use of SQUIDs for eddy current NDE. To realize the promise of a new capability for inspecting the aging fleets of both military and commercial aircrafat, we propose to lead a development team comprising IBM, Northrop Corporation, Boeing, and SQM Technology, Inc.