Abstract
Oxide superconductor is one of the expected and most effective magnetic shielding materials for the diamagnetic property of its own. A large volume, however, is hardly shielded by using the material because of the limited size of the bulk. The authors studied first about the shielding effects of superconductors disposed on constant and alternative magnetic field experimentally. Reduction ratio of about -6.2(dB) is obtained for constant field, and about the same results even for alternating fields. On the contrary, conductors in several sizes show the shielding effects only in higher frequencies and scarcely small in constant field. Feasibility of superconductor is thus clearly shown.
Nevertheless, shielding effect by single layer oxide superconductor is limited because the composition of single layer has the gap between pieces and flux penetrate into the inside of superconductor. Multi-layered composition of superconductor is proposed to improve the shielding effects. The optimum structure of double-layered composition is numerically analyzed with finite element method because quantity and thickness of shielding pieces is the problem. The arrangement of pieces and the distance between single and double layer is investigated. The optimum structure of shielding pieces is obtained for the space distribution of the magnetic field.
