Eddy-current imaging of buried cracks, by inverting field data

A novel method for imaging flaws, based on the inversion of eddy-current data, has been demonstrated. A thin subsurface slot was manufactured in an aluminum plate. Oscillating current was injected into the plate, and the magnetic field was sampled with a Hall transducer scanned over the blind face. An integral operator defines an analytical relationship between the distribution of electric dipoles excited on the slot faces and the scattered field. The relationship was inverted using singular value decomposition to obtain the dipole density as a representation of the slot in the form of an image. Enhanced spatial information on the flow may be obtained by performing the inversion at several individual frequencies, and constructing a composite image