| 摘要 |
<p>PURPOSE:To prevent a magnetic recording medium stored in a case from being damaged by magnetism by a method wherein a case is composed of a material coated with a superconducting film and superconductivity is maintained with the superconducting film as a complete diamagnetic material. CONSTITUTION:A card case 4 consists of sheets 1, 2 and a superconducting film 3 which is composed of ceramics having a monocrystal or polycrystal structure adhered on the inner surface of the sheet 1 by sputtering, etc. The three sheets are cut in approximately the same size and folded together with the three sides joined, and the card case 4 is made transportable in a pocket. A user of a magnetic card inserts the magnetic card between the sheets 1 and 2 to store it. The superconducting film 3 is in the superconducting state and becomes a complete diamagnetic material when its external temperature and magnetic field are kept at the critical temperature and the critical magnetic field, respectively. Therefore, the flux density in a case one of whose sides is covered with the superconducting film 3 is approximately zero, preventing the magnetic card stored in the case 4 from being damaged even if there is a considerably strong external magnetic field.</p> |
