抄録
A superconductor is an ideal material for shield, giving excellent attenuation of electric/magnetic fields from DC to very high frequency. It is particularly useful for low frequency region shields because there is no effective material which gives effective shielding performance. In this paper, superconducting shielding design technologies are discussed on the basis of analytical methods and experimental results. Superconductors are excellent material for shield, however, external fields penetrate through the superconductor. The following two cases are discussed: 1. Field penetration when the external field is so strong that the shielding current exceeds the critical current of the superconductor. 2. A weak intrinsic field penetration due to kinetic inductance of the supercurrent. A superconducting hollow cylinder is an adequate shielding construction because the magnetic field decays rapidly along the depth from an open end. However, if we require a field attenuation of 10-8, the length of superconducting cylinder must be 5 times its diameter. Such a length is too long to be of pratical use when we need a shielded space as large as 1m in diameter. Therefore, design concept is discussed to shorten the length while maintaining the attenuation at 10-8 by coupling with a ferromagnet. When we attain a very high attenuation by the superconducting shield, there may still be some noises of internal origin. This paper discussed the internal noises of: 1. Thermal driven noise from well conductive materials, 2. Flux relaxation noise of the superconductor, 3. Vibration noise.
