The Imaging of Cracks using Eddy-currents

Abstract

When eddy-currents flow in a cracked conductor, an oscillating dipole distribution is created on the length of the crack and this gives rise to a scattered magnetic field above the conductor. We have sampled t h i s field with a Hall transducer which has a point-like response function. We show that this magnetic field is then the convolution of the dipole distribution with the material response function, represented by a Green's function. The deconvolution has been performed with a Wiener filter, in corporating a priori knowledge of the plane in which the given crack lay. Since the dipole distribution only resides on the crack, it effectively represents an image of the crack. Examples of images obtainable using this technique are presented in this paper.