Performance measurements of a superconductive microprobe for eddy current evaluation of subsurface flaws

First measurements of the performance of the superconductive microprobe show that its depth of field and resolution are far superior to those of conventional eddy-current probes. It is shown that the superconductive microprobe can detect millimeter-size flaws to depths of 5 mm in 2024 aluminum. It also easily detects a 1.4% loss in material owing to corrosion at the bond line of two 2.29-mm-thick, 7075 aluminum plates. The corrosion patch is 15.9 mm in diameter. The prototype shows three main limitations: standoff distance, electronic noise in the feedback circuitry, and interference from fluctuations in tilt while scanning a test surface. Decreasing the size of the pickup loops and source coil can decrease both the standoff distance and interference from tilt. Using digital circuitry can suppress the noise of feedback circuitry.<>