THE MAGNETIC FIELDS OF STEEL DRUMS

Abstract

The concept of apparent susceptibility can be extended to bodies with arbitrary geometry by considering the integrated magnetization or dipole moment associated with the body. This unique characteristic can be easily computed numerically for features of arbitrary shape and susceptibility. Numerical studies reveal that the thin-walled steel drum displays an anisotropic apparent susceptibility with distinct longitudinal and transverse values. While the apparent susceptibility is independent of drum size, it varies with the susceptibility, the wall thickness and with the dimension ratio of the drum. Exact numerical modelling of total field magnetic profiles over a buried steel drum allows the evaluation of a range of approximate modelling techniques. While all reasonably match the form of the measured profile, only the response computed for an equivalent magnetic shell and that using an equivalent magnetic dipole with moment computed from the true drum susceptibilities allow the profile amplitude to be predicted with any accuracy. Of these, the latter technique is the more successful. It also provides a discernable improvement in the shape of the modelled profile.