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Title: Signal enhancement techniques for rf SQUID based magnetic imaging systems
Authors: Akram, Rizwan
Fardmanesh, Mehdi
Schubert, Juergen
Zander, Willi
Banzet, Marko
Lomparski, Dieter
Schmidt, Miak
Krause, H. J.
Keywords: SQUID
Back coupling
Circuit configuration
Voltage transfer functions
Coplanar resonators
Issue Date: Aug-2006
Publisher: IOP Publishing Ltd.
Source: Akram, R., Fardmanesh, M., Schubert, J., Zander, W., Banzet, M., Lomparski, D., Schmidt, M., and Krause, H. J. (2006). Signal enhancement techniques for rf SQUID based magnetic imaging systems, Superconductor Science and Technology, 19(8), 821-824. doi:10.1088/0953-2048/19/8/023
Abstract: We have investigated the rf SQUID (radio-frequency superconducting quantum interference device) and its coupling to tank circuit configurations to achieve an optimal front-end assembly for sensitive and high spatial resolution magnetic imaging systems. The investigation of the YBCO rf SQUID coupling to the conventional LC tank circuits revealed that coupling from the back of the SQUID substrate enhances the SQUID signal while facilitating the front-end assembly configuration. The optimal thickness of the substrate material between the SQUID and the tank circuit is 0.4 mm for LaAlO3 resulting in an increase of the SQUID flux-voltage transfer function signal, Vspp, of 1.5 times, and 0.5 mm for SrTiO3 with an increase of V spp of 1.62 times compared to that for direct face to face couplings. For rf coupling with a coplanar resonator, it has been found that the best configuration, in which a resonator is sandwiched between the SQUID substrate and the resonator substrate, provides a Vspp about 3.4 times higher than that for the worse case where the resonator and the SQUID are coupled back to back. The use of a resonator leads to a limitation of the achievable spatial resolution due to its flux focusing characteristics. This resulted in a favouring of the use of the conventional tank circuits when considering the desired high spatial resolution. The effect of the YBCO flip chip magnetic shielding of the SQUIDs in the back-coupling with the LC tank circuit configuration has also been investigated, with a view to reducing the SQUID effective area to increase the spatial resolution and also for studying the effect of the coupling of various kinds of transformers to the SQUIDs. It is revealed that there is no very considerable change in the flux-voltage transfer function signal level with respect to the effective shield area, while the lowest working temperature of the SQUIDs was slightly shifted higher by a couple of degrees, depending on the shield area.
ISSN: 0953-2048
Appears in Collections:Physics / Fizik
Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection

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