Bi系酸化物超電導体による交流磁場の磁気シールド特性

概要

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One of the applications of high-Tc oxide superconductor is magnetic shielding. For example, it is very important to shield very weak fields produced in the human body from the geomagnetic field or fields generated by the electric instruments in order to detect precisely them. The purpose of this study is to investigate the relation between the shielding efficiency and the superconducting properties. The cylinders made up from Bi2Sr2Ca2Cu3Ox high-Tc superconductors with different critical currents and magnetizations were prepared by changing the sintering condition. The shielding efficiency in the cylinder was measured as functions of the shape factor of L/D of the cylinder and the internal position of the cylinder, where L and D are the lenght and inner diameter of the cylinder, respectively. The shielding efficiency, defined by the ratio of the transverse and applied fields, was logarithmically dependent on the shape factor and increased with the critical current and volume fraction of the superconducting component which is in proportion to the gradient of the initial magnetization curve. The efficiency, however, was independent of the magnitude of the magnetization and the frequency of the external AC magnetic field.
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