Five-Channel SQUID Based Non-Destructive Evaluation (NDE) Instrument

摘要

A 5-channel SQUID-based NDE instrument has been built and tested. A combinationof first derivative axial and planar concentric gradiometers enable the simultaneous evaluation of magnetic signatures of surface and deep sources. Features of the system include: Liquid Helium dewar to cool the probe with 5 mm coil to external dewar surface distance, superconducting magnet assembly to provide both DC and AC applied fields, noise reduction circuitry to cancel signals generated by applied AC signals coupled to pick up coils, computerized data acquisition and control system, including customized software, to control system, to collect, analyze and display data. Testing includes studies of transformation induced plasticity in steel, defects in non-magnetic metals using AC magnetic fields, defects in metals by applied modulated currents, AC fields applied to magnetic systems, and magnetization changes induced by applied tension. These tests indicate this system can locate and identity defects and sources in a variety of different applications using a number of novel experimental techniques. (AN).