Thin film superconducting shields

To date, magnetic shields utilizing high-temperature
superconductor materials mostly comprise bulk materials, usually
shaped into a cylinder and then heat treated. We analyze the potential
of thin-film technology, whereby a layer of superconductor
is deposited on a substrate, to fabricate magnetic shields. Films
deposited on a curved surface are inevitably granular, leading to
reduced critical current density compared with crystalline films.
This limits the maximum field that can be screened. Granular
films also have an enhanced penetration depth compared with the
bulk value, which determines the maximum possible screening at
applied fields below the maximum.We demonstrate the utility of a
mutual inductancemeasurement to evaluate small flat test samples
of a granular film for their potential as a shielding material in a
more complex geometry. Thismeasurement predicts both themaximum
magnetic field that can be screened and the residual leakage
at fields below the maximum. The tested film was produced by
the Electrophoretic deposition of YBCO on a silver substrate. The
maximum screening field was comparable with that obtained for a
similar film on a cylindrical substrate. We also show comparable
results from a crystalline YBCO film.