Imaging flaws in magnetically permeable structures using the truncated generalized inverse on leakage fields

In order to image the magnetic source distribution inside a flawed magnetically permeable structure, the truncated generalized inverse and singular value decomposition were used. These techniques were applied to the magnetic flux leakage generated when the structure is magnetized. The leakage field from different flaw shapes was simulated by placing magnetic dipoles at the boundary surfaces, which reduces the flux density in the flawed structure. A criterion to establish the generalized inverse truncation index is proposed, by using the two-dimensional correlation coefficient between the original image and the reconstructed image. Others aspects such as the measurement signal-to-noise ratio, and density of the model source distribution are also discussed. This imaging technique was successfully applied to a number of different model flaw sources. (C) 1997 American Institute of Physics.