This paper has highlighted a band of frequencies, outside the conventional operation range, and close to electrical resonance of an eddy current probe, where the magnitude of impedance SNR reaches a peak. The SNR of scans of three slots of varying depth were enhanced by a factor of up to 3.7, from the SNR measured at 1MHz. This is a result of a defect-decoupling resonance-shift effect and is referred to as the near electrical resonance signal enhancement (NERSE) phenomenon. NERSE frequency operation has significant potential for ECT inspection, and opens up a range of investigative possibilities. Within this investigation, only the magnitude of the electrical impedance has been analyzed. An immediate extension of this investigation will be to consider phase information, and determine whether a similar exploitable NERSE effect exists.
