Open magnetic shielding for static and alternating field

To meet the increasing and various demands for low magnetic field measurement, an open magnetic shielding system created using a combination of copper coils and precisely designed superconducting closed coils is proposed. After testing, the prototype system showed a shielding factor of more than 10 000 in the direct current field and most importantly, a shielding factor of at least 100 in the alternating field from frequencies of 0.01-100 Hz in a 5 cm spherical volume. We interestingly found that the magnetic purity of the open system is capable of catching up with the magnetically shielded room with moderate performance. The structure and principle of the system are introduced in this paper. A key factor that makes the system possible is the decoupled interaction between the copper coils and superconducting coils. The limitations of this system and ways to improve its performance are discussed. This novel approach provides a more sophisticated and flexible way to achieve open magnetic shielding.