Multifrequency eddy current image processing techniques for nondestructive evaluation

This paper describes a new technique for processing eddy current images as used in nondestructive evaluation of materials. A simple description of the image formation physics is given followed by a description of the current state of the art in image processing. Eddy current testing in 2-D results in a sequence of complex valued images that can be linearly combined to enhance the signal-to-noise ratio (SNR) of features of interest. A new approach that selects weights for a linear combination of the images based on SNR maximization is presented. Results on experimental data show SNR improvements up to 1100 percent over traditional two-frequency techniques. The new algorithm presented is general to any number of frequencies, and results of four-frequency processing are given