<title>Superconducting magnetometry: a possible technique for aircraft NDE</title>

Superconducting quantum interference device (SQUID) magnetometers offer promise as multi- mode instruments capable of obtaining high resolution images of extremely low frequency injected currents or eddy currents, and they can be configured to image the magnetic susceptibility of titanium, aluminum, and nonmetallic composites. While high resolution SQUID magnetometers will generally be noisier than conventional SQUIDs, the small coils and reduced coil-to-source spacing more than compensate to provide low-noise, high- resolution images. To explore SQUID NDE, we have developed research facilities that include the high-resolution MicroSQUID magnetometer, a magnetic shield, a scanning stage, and a computer-based control and data acquisition system. Using this instrumentation, we have imaged magnetic fields produced by varied sources. In support of the experimental studies, we have developed analytical and numerical models for the simulation of flaws with several geometries inside thick and thin current-carrying plates and thin-walled tubes, and have demonstrated that two-dimensional magnetic images can be deconvolved into images of current or magnetization by filtering techniques, finite element models, lead field analyses, and maximum entropy methods.