M. A. Johnson, C. Lee, J. Henderkott, Iowa State University, Ames, IA; J. S. Knopp, US Air Force Research Laboratory, Wright-Patterson AFB, OH; J. C. Aldrin, Computational Tools, Gurnee, IL

Summary:

Solid-state magnetic field sensors are thought to be advantageous when making nondestructive evaluation (NDE) measurements at low frequencies or under pulse excitation. The sensitivity of solid state detectors such as Hall devices or GMR (giant magneto-resistive) elements is constant in the low-frequency limit. In contrast, induction coils are sensitive to the rate-of-change of field and are therefore less effective at lower frequencies. However, some studies have shown that induction-coil based systems actually perform better (for the detection of deep corrosion) under pulsed excitation. In order to determine the true optimum configuration (for a given defect type), conventional and pulsed excitation modes have been examined for the case of a standard absolute eddy-current probe and a probe utilizing a Hall-element detector. For some simple flaw geometries, validated finite-element models have been used in conjunction with experimental noise measurements in order to determine detection capabilities for the various configurations.