Browsing by Author "Akram, Rizwan"

Now showing 1 - 3 of 3

Front-End Assembly Optimization for High-Tcrf Based Magnetic Field Imaging Systems
(IOP Publishing Ltd., 2006-06) Akram, Rizwan; Fardmanesh, M.; Schubert, J.; Zander, W.; Banzet, Marko; Lomparski, Dieter; Schmidt, M.; Krause, Hans J.
We have investigated the rf-SQUID and its coupling to the tank circuit configurations to achieve an optimal front-end assembly for sensitive and high spatial resolution magnetic imaging systems. The investigation on the YBCO rf-SQUID coupling to the conventional LC tank circuits revealed that the 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 0.4mm for LaAlO3 resulting in an increase of SQUID flux-voltage transfer function signal, Vspp, of 1.5 times, and 0.5 mm for SrTiO3 with an increase of Vspp of 1.62 times compared to that of direct face to face couplings. For the rf-coupling with co-planar resonator, CPR, it has been found that the best configuration, in which a resonator is sandwiched between the SQUID substrate and resonator substrate, provides a Vspp about 3.4 times higher than the worse case where the resonator and the SQUID are coupled back to back. It has also been observed that the noise level does not depend considerably on whether a conventional LC tank circuit or a CPR is used. Though the use of resonator leads to a limitation of the achievable spatial resolution due to its flux-focusing characteristics. This resulted in favouring the use of the conventional tank circuits when considering the desired high spatial resolution. 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, in order to reduce the SQUID effective area to increase the spatial resolution and also to study the effect of the coupling of various types of the transformers to the SQUIDs. It is revealed that there is no 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.
Citation - WoS: 3
Citation - Scopus: 2
Signal Enhancement Techniques for Rf Squid Based Magnetic Imaging Systems
(IOP Publishing Ltd., 2006-08) Akram, Rizwan; Fardmanesh, Mehdi; Schubert, Juergen; Zander, Willi; Banzet, Marko; Lomparski, Dieter; Schmidt, Miak; Krause, H. J.; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
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.
Citation - WoS: 2
Citation - Scopus: 4
Signal Performance of Dc-Squids With Respect To Ybco Thin Film Deposition Rate
(Elsevier Ltd., 2009-06) Avcı, İlbeyi; Algül, Berrin Pınar; Akram, Rizwan; Bozbey, Ali; Tepe, Mustafa; Abukay, Doğan; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
The signal performances of YBa2Cu3O7-δ (YBCO) direct current superconducting quantum interference devices (DC-SQUIDs) have been investigated as a function of the thin film structure affected by the growth process. YBCO thin films of 200 nm thicknesses were deposited by DC magnetron sputtering using different deposition rates between 1.0 nm/min and 2.0 nm/min onto 24° bicrystal SrTiO3 (STO) substrates. The thin film samples were subsequently analyzed by XRD and AFM in order to determine their crystalline structures and surface morphologies respectively. The 67 pH directly coupled DC-SQUIDs with 4 μm-wide bicrystal Josephson junctions were fabricated, and characterized with respect to their device performances. The variations in the critical current (Ic), the voltage modulation depth (ΔV) and the noise performance of DC-SQUIDs were reported. The SQUIDs having relatively low deposition rate of 1.0 nm/min was observed to have larger voltage modulation depth as well as higher critical current than that of the samples having larger rate of 2.0 nm/min. The better noise performances were observed as the film deposition rate decreases. The results were associated with the thin film structure and the SQUID characteristics.