Development of Very Low Frequency Self-nulling Probe for Inspection of Thick Layered Aluminum Structures

Nondestructive evaluation technologies have recently been challenged to inspect thick, layered, conducting materials for fatigue and corrosion damage. Structures that fall into this class, such as airframe wings, pose significant difficulties for conventional inspection techniques. Reflections of ultrasound at layer boundaries cause serious problems for the application of ultrasonic inspection methods. Conventional eddy-current inspection techniques are also compromised due to the exponential decay of electromagnetic energy with depth into a conductor.