SQUIDS FOR NONDESTRUCTIVE EVALUATION

We attempt a comprehensive review of all published research in nondest ructive evaluation (NDE) performed with the superconducting quantum in terference device (SQUID) magnetometer since the first work was report ed in the mid-1980s. The SQUID is the most sensitive detector of magne tic flux known. The energy sensitivity of the SQUID may make it the mo st sensitive detector of any kind. The research on SQUIDs for NDE is b ased on the promise of that sensitivity and on the various other desir able properties developed for SQUID instrumentation in biomagnetism an d other fields. The sensitivity of SQUID instruments down to very low frequencies allows them to function as eddy-current sensors with unpar alleled depth resolution, and to image the static magnetization of par amagnetic materials and the flow of near-de corrosion currents. The wi de dynamic range of the SQUID makes it possible to image defects in st eel structures and to measure the magnetomechanical behaviour of ferro magnetic materials with high sensitivity. In the last decade SQUID ins trumentation designed specifically for NDE has appeared and improved t he spatial resolution of most work to roughly 1 mm, with promise of an other order of magnitude improvement within the next five years. Algor ithms for flaw detection and image deconvolution have begun to flouris h. With many talented, industrious people in the field, the future of SQUID NDE looks bright, provided the crucial first niche can be found.