Richard Oscar Mccary

Eddy-Current Probe Design

This paper describes theoretical and experimental work directed toward finding the optimum probe dimensions and operating frequency for eddy current detection of half-penny surface cracks in nonmagnetic conducting materials. The study applies to probes which excite an approximately uniform spatial field over the length of the crack at the surface of the material. In practical terms, this means that the probe is not smaller than the crack length in any of its critical dimensions.

Eddy Current Probe Evaluation: Experimental Measurements and System Interaction

Eddy current testing is often considered an old and mature technology. However, the state of the art technology cannot meet the new stringent demands that the US Government has imposed on inspection of new aircraft engines under a program called ENSIP (engine structural integrity program). These demands require substantial improvements both in inspection sensitivity and speed — for instance, crack detection capability must improve by a factor of 3 over what is currently possible. In order to meet the new goals, all aspects of an eddy current inspection system must be addressed from probe selection and mechanical scanning noise to system electronics and signal processing. It has previously been shown [1,2] that imaging techniques provide improved flaw detection capability and also may be used to optimize system performance. This paper describes work that combines imaging with probe measurements to analyze eddy current probes and system performance from a practical point of view. Slightly different designs of a specific type of probe have been examined to evaluate differences in the designs and to determine how well the probe construction method is controlled. Parameters were calculated from electric measurements on the probes and plotted in an attempt to explain their significance and to provide a method for selection of probes with superior qualities. The probe/system interaction was also analyzed in order to learn why some probes with good electric properties did not perform well in the eddy current system. Finally, images were created and used to evaluate the impact of different imaging parameters on inspection performance.