Theoretical and experimental investigations of the lateral resolution of eddy current imaging

Analytical, finite element simulation, and experimental methods were used t o investigate the lateral resolution of eddy current microscopy. It was fou nd that the lateral resolution of eddy current imaging is ultimately limite d by the probe coil geometry and dimensions but that both the inspection fr equency and the phase angle can be used to optimize the resolution at the e xpense of some degree of sensitivity. Although eddy current imaging is stil l in its infancy, a direct comparison of 5 MHz eddy current and 40 MHz acou stic microscopic images of the same coarse grained Ti-6Al-4V sample indicat ed that the same features can be observed by both methods at approximately the same resolution level. Electric anisotropy exhibited by noncubic crysta llographic classes of materials such as titanium alloys can play a very sim ilar role in electromagnetic materials characterization of polycrystalline metals to that of elastic anisotropy in ultrasonic materials characterizati on. Our results demonstrate that eddy current microscopy can be enhanced vi a a high resolution, small diameter probe coil which delivers a unique mate rials characterization tool well suited for the evaluation of titanium allo ys.