Evaluation of an Eddy-Current Tape-Head Probe

SRI International is performing basic evaluation and characterization of eddy-current probes that are fabricated using ferrite tape-head technology. Tests conducted during the previous two years using both absolute and differential probes, frequencies of 100 kHz and 1 MHz, and flat-plate samples made of aluminum and titanium demonstrated that such probes exhibit both high sensitivity to surface cracks and high spatial resolution.1,2 To round out this evaluation, during the past year we studied tape-head reflection probes and measured their characteristics over a broad range of frequencies. This paper discusses reflection probes briefly and presents the results of comparative tests that were made using tape-head and coil-type reflection probes in conjunction with a commercial eddy-current instrument