SBIR-STTR Award

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.

Keywords:
FATIGUE CRACKS NONDESTRUCTIVE EVALUATION HIGH-TEMPERATURE SUPERCONDUCTORS CRYOCOOLERS

High-temperature superconductors offer an opportunity to bring superconductive quantum interference devices, SQUIDs, into common use for evaluating underlayers of aging airframes with eddy currents. The millionfold advantage in resolution of magnetic flux of a SQUID at low frequencies enables identification of corrosion and millimeter long fatigue cracks through 15 mm or so of aluminum. SQUIDs alone offer high sensitivity at low frequencies with 1 mm pickup loops, enabling arrays giving images of defects in underlayers with high resolution. Phase II develops a prototype instrument comprising a planar array of sixteen elements coupled to four SQUIDs. The arrays scans electronically along its rows, by exciting source coils of each column sequentially, and moves parallel to its columns. It fits on a fifty millimeter square substrate in a cryogenic battery, which keeps it operating for four to six hours. A built-in miniature cryocooler trickle charges the battery every few hours to give a self-contained unit that both operates without interference from the cryocooler and keeps the array at constant temperature. Phase III produces a hand-held instrument the size of a small flashlight, weighing less than two pounds, and providing an inspection rate exceeding 10cm/min. Its battery operated electronics weigh less than twenty pounds and give readily understood images of defects, with few false calls. Support for product development in Phase III, following successful imaging of a 1 mm crack through 15 mm of aluminum in Phase II, would come from Northrop Corporation and Northwest Airlines, Inc.