Multifrequency eddy current signal analysis

This thesis presents a novel procedure for representing and processing multifrequency eddy current signals. Multifrequency eddy current NDE methods are used extensively for the inspection of steam generator tubes in nuclear power plants. Existing methods utilize computationally expensive time domain procedures to process the data. The procedure outlined in the thesis uses frequency domain methods to minimize the computational effort significantly. Two different approaches are evaluated. The first method uses the Fourier descriptor to represent the signal. The Fourier coefficients are utilized to obtain the rotation, scaling and translation parameters required for mixing. The second approach uses the cosine transform. The mixing parameters are derived from the transform coefficients. Fast algorithms can be used to compute the transform. A spin-off of the approach is the ability to obtain rotation, translation and scale invariant parameters from the coefficients directly. Experimental results supporting the validity of the approach are presented.