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Description
One of the properties in superconductor is perfect diamagnetism called as Meissner effect. Among superconductors, YBa2Cu3O7-δ (YBCO) polycrystals has high critical temperature (Tc) over 90 K and high critical current density (Jc) of the order of 104 A/cm2 at 77 K in self-magnetic field［1］, so it is expected as a material for shielding magnetic field under liquid nitrogen cooling. Concerning to use it in future electric aircraft, it is desirable to be large size with flexible shape and lightweight material. In this study, we tried to fabricate a magnetic shielding sheet consisted to YBCO powders and resin matrix because the resin is lightweight and flexible material. The diamagnetic performance of the sheet is affected strongly on current density of YBCO powders. Furthermore, no cracks and pores are desirable for the shielding sheet to suppress leaking magnetic field. So, we investigated particle size dependence of shielding rate and microstructure of the sheet. We prepared two types of YBCO powder with different particle size, 3.8 µm and 27 µm. The powders were mixed with resin, separately, and the mixture solutions were coated on substrates. Then, the coated substrate were dried at 135 C by electric hot plates. Magnetic field shielding rate was measured by a hall element device, and microstructure was observed by scanning electron microscope. Shielding rate of the sheet by YBCO powders of 3.8 µm and 27 µm were 16% and 14%, respectively, under external magnetic field of 20 mT. Microstructure observation showed cracks and pores in the sheet by the powder of 27 µm. So, it was considered that the difference of shielding rate was due to the difference of crack formation in the sheet. We succeeded in fabricating magnetic field shielding sheet with flexible shape and lightweight material.
［1］Nakamura Yuichi, Shiohara Yuh, OYOBUTURI, 61, (1992), 456-463 in Japanese
