Eddy-current phasography

Phasography shows excellent potential for high resolution imaging of flaws using eddy current data. The process is an eddy current equivalent to acoustic holography. Phase multiplication of the detected coherent signal is used to simulate a test wavelength one to two orders of magnitude smaller than the actual wavelength, permitting the use of image reconstruction techniques. Since this process is performed on the detected data, the eddy current penetration depth remains unchanged. It is also possible to apply this phase multiplication technique to low frequency acoustic holography, resulting in a test which combines excellent penetration of difficult materials with high resolution images. Preliminary experimental results graphically illustrate this unique imaging technique. Eddy current phasograms and their reconstructed images of small internal simulated defects in 1 mm thick stainless steel plates are presented.