A New Approach to Design Flexible Magnetic Active Shielding

The shielding of low-frequency magnetic fields from “sensible” domains (e.g., in hospital areas or in control rooms in industrial environments) is usually achieved using ferromagnetic walls (passive shielding) or suitably designed coils, fed with appropriate currents (active shielding). Anyway, when disturbing fields are not known in advance, and weight or cost issues prevent passive shielding, general-purpose active shielding coils could be used, provided that their design is flexible enough to counteract a large class of fields and an adequate disturbing field detection system is present. This paper proposes a procedure able to perform the active shielding for a large class of disturbing fields. The procedure includes an identification step through a suitable measurement system and a current design step, based on the design of shimming coils specialized to cancel single “eigenfunctions” of the Laplace operator in the sensible domain.