Magnetic thickness gauge using a Fourier transformed eddy current technique

A Fourier-transformed eddy current (FTEC) technique has been proposed and developed. This technique employs Fourier transformation analysis to analyze pulsed eddy current signals measured by magnetoresistive sensors. The advantage of this technique is that the intrinsic response, Gamp(f)Gamp(f), of a sample material can be extracted without it being affected by the characteristics of the measurement systems. Aluminum plates with an area of 100mm×100mm and various thicknesses were used as test samples. We examined the relationship between the thickness of the sample and the frequency, when Gamp(f)Gamp(f)'s reached 90% of the maximum magnitude. The results indicate that FTEC can be used for non-contact measurements of conductive materials. We also evaluated lift-off effects for Gamp(f)Gamp(f) for 1- and 5-mm-thick samples. The deviations of the frequencies for the 90% response were 453.386±14.37453.386±14.37 and 99.789±4.13Hz for the 1- and 5-mm-thick samples, respectively. This result indicates that the lift-off effect was reduced by the FTEC analysis.