Multipole Characterization And Detection OfMetallic Bodies

The magnetic field produced by the equivalent magnetic pole density induced on the surface of a metallic target by the known magnetic field of the source coil of a metal detector is expressed in terms of a multipole expansion. The first term of the expansion is numerically evaluated for some odd-shaped objects and the field due this equivalent dipole is compared with that obtained by numerically solving the boundary integral formulation of the problem. Results show that for small targets, i.e., for observation distances greater than a few target diameters, the induced magnetic pole density can be well approximated by an equivalent dipole.