Frequency Effect on Shielding Quality of Closed Superconducting Magnetic Shields Made of Superconducting Tapes

Magnetic fields can be effectively shielded with superconducting tapes. They can be used either to attenuate a magnetic field or to improve its homogeneity. In this paper, magnetic field changes, due to the presence of a superconducting shield, are investigated. Both experimental and model results are shown. Specimens were subjected to a low-frequency ac magnetic field (up to 45 Hz). Attenuation of the field inside a shielded cavity was observed. The dependence of the shielding effect on the magnetic field strength and frequency was analyzed. A computer model of a shield has been developed. The additional increase of the shielding effect was observed above a certain threshold frequency depending on the geometry and material properties of a screen. The size and limits of this increase were investigated. It was observed to be linear in some frequency intervals. The interval of magnetic field amplitude, in which magnetic field attenuation is constant, becomes thinner at higher frequencies. Analyzed shields may find multiple applications in devices where dc and low-frequency magnetic fields are present. Their construction is uncomplicated, and they are relatively cheap. Medicine and science can greatly benefit from this simple and reliable method of magnetic field attenuation.