Evaluation of Airframes with Pulsed Eddy Currents

Use of pulsed eddy currents with superconductive probes offers new technology to image fatigue cracks and corrosion hidden in sublayers of thick sections of airframes, such as wing boxes. A superconductive probe uses a superconductive quantum interference device (SQUID) to achieve unmatched sensitivity and resolution of magnetic flux at frequencies below 100 Hz. It enables deep penetration of aluminum structure. Pulsed eddy currents, at repetition rates below 100 Hz, can provide images of fatigue cracks and corrosion hidden deeply in an airframe from a single scan across a fastener diameter. Pulsed currents enable timing a return to identify depth of a defect and to generate an image from multiple returns. They can give images of defects in a cross section of a structure. To realize the promise of superconducting probes operating with pulsed eddy currents,Phase I develops signal processing algorithms to demonstrate feasibility of achieving high resolution images of small defects hidden deeply in multilayered structure.