| 1. |
- Chukharkin Leonidovich, Maxim, 1980, et al.
(författare)
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Improvement of Ultra-Low Field Magnetic Resonance Recordings With a Multilayer Flux-Transformer-Based High-T-C SQUID Magnetometer
- 2013
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Ingår i: Ieee Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1051-8223 .- 1558-2515. ; 23:3
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a multilayer flux-transformer-based high-T-C SQUID (flip-chip) magnetometer that improves signal-to-noise-ratios (SNR) in ultra-low field magnetic resonance (ulf-MR) recordings of protons in water. Direct ulf-MR-based benchmarking of the flip-chip versus a standard planar high-T-C SQUID magnetometer resulted in improvement of the SNR by a factor of 2. This gain is attributable to the improved transformation coefficient (1.9 vs 5.3 nT/Phi(0)) that increased the signal available to the flip-chip sensor and to the lower noise at the measurement frequency (15 vs 25 fT/Hz(1/2) at 4 kHz). The improved SNR can lead to better spectroscopic resolution, lower imaging times, and higher resolution in ulf-MR imaging systems based on high-T-C SQUID technology. The experimental details of the sensors, calibration, and ulf-MR benchmarking are presented in this report.
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| 2. |
- Chukharkin Leonidovich, Maxim, 1980, et al.
(författare)
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Novel HTS DC squid solutions for NMR applications
- 2014
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Ingår i: NATO Science for Peace and Security Series B: Physics and Biophysics. - Dordrecht : Springer Netherlands. - 1874-6500. - 9789400772649 ; 2014, s. 151-159
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a multilayer flux-transformer-based high-TC SQUID (flip-chip) magnetometer that improves signal-to-noise-ratios (SNR) in ultra-low field magnetic resonance (ulf-MR) recordings of protons in water. Direct ulf-MR-based benchmarking of the flip-chip versus a standard planar high-T C SQUID magnetometer resulted in improvement of the SNR by a factor of 2. This gain is attributable to the improved transformation coefficient (1.9 vs 5.3 nT/Φ0) that increased the signal available to the flip-chip sensor and to the lower noise at the measurement frequency (15 vs 25 fT/Hz1/2 at 4 kHz). The improved SNR can lead to better spectroscopic resolution, lower imaging times, and higher resolution in ulf-MR imaging systems based on high-T C SQUID technology. The experimental details of the sensors, calibration, and ulf-MR benchmarking are presented in this report.
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| 3. |
- Chang, S, et al.
(författare)
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An electrowetting-based microfluidic platform for magnetic bioassays
- 2010
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Ingår i: The 14th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2010, 3-7 Oktober, Groningen, Neterlands. - 9781618390622 ; 2, s. 1331-1333
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Konferensbidrag (refereegranskat)abstract
- Here we present our recent work on a droplet-based microfluidic device for manipulating microliter-sized droplets. By replacing the formerly used common dielectric SiO2 with Si3N4 and applying a 33 nm thick Teflon top layer to create a hydrophobic surface, we successfully lowered the actuation voltage from 450 V to 50 Vdc/40 Vac. Sputtered HfO2 with high dielectric constant was also investigated as an insulator, which could reproducibly yield thin defect-free insulation layers and lower the actuation voltage to less than 40 V.
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| 4. |
- Chukharkin Leonidovich, Maxim, 1980, et al.
(författare)
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Noise properties of high-T-c superconducting flux transformers fabricated using chemical-mechanical polishing
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:4, s. Article Number: 042602 -
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Tidskriftsartikel (refereegranskat)abstract
- Reproducible high-temperature superconducting multilayer flux transformers were fabricated using chemical mechanical polishing. The measured magnetic field noise of the flip-chip magnetometer based on one such flux transformer with a 9 x 9 mm(2) pickup loop coupled to a bicrystal dc SQUID was 15 fT/Hz(1/2) above 2 kHz. We present an investigation of excess 1/f noise observed at low frequencies and its relationship with the microstructure of the interlayer connections within the flux transformer. The developed high-T-c SQUID magnetometers may be advantageous in ultra-low field magnetic resonance imaging and, with improved low frequency noise, magnetoencephalography applications.
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| 5. |
- Chukharkin Leonidovich, Maxim, 1980, et al.
(författare)
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Noise properties of HTS flux transformers fabricated by chemical-mechanical polishing
- 2011
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Ingår i: European conference on applied superconductivity.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present on fabrication and noise properties of high-temperature superconducting (HTS) thin-film integrated multilayer flux transformers fabricated using planarization of YBCO films by chemical-mechanical polishing (CMP). The polishing allows fabrication of very shallow slope edges (less than 5°) in the YBa2Cu3O7, that makes it possible to avoid formation of grain boundary junctions in crossovers and obtain very high critical current densities in the top electrode of about 2•106 A/cm2. The same planarization process is used to create interconnections between top and bottom superconducting electrodes through the SrTiO3/PrBa2Cu3O7/SrTiO3 insulating layer. HTS multilayer flip-chip flux transformer with 8x8 mm2 pickup loop and 20-turn input coil was fabricated and coupled to a bicrystal dc SQUID in a flip-chip configuration. We measured magnetic field gain of 1.2 nT/Ф0 and magnetic flux noise of the magnetometer 10 µФ0/√Hz at 1 kHz, which corresponds to magnetic field noise of 12 ft/√Hz. FLUX NOISE AT LOW FREQUENCIES! The work is supported by European FP7 project "MEGMRI" under contract number 200859.
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| 6. |
- Schaller, Vincent, 1979, et al.
(författare)
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Development of an electrowetting-based microfluidic platform for magnetic immunoassays
- 2009
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Ingår i: 13th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2009; Jeju; South Korea; 1 November 2009 through 5 November 2009. - 9780979806421 ; , s. 85-87
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Konferensbidrag (refereegranskat)abstract
- We report the transport of magnetic nanoparticles (MNPs) in suspension in a 2 μl de-ionized water droplet (DIWD) using ElectroWetting-On-Dielectic (EWOD) actuation, and the detection of the MNPs by magnetic AC-susceptibility measurements using a highly sensitive high-Tc dc Superconducting Quantum Interference Device (SQUID) gradiometer. These results constitute the first development step towards a MNP-based magnetic immunoassay platform with SQUID-readout and sample droplet handling.
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| 7. |
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| 8. |
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| 9. |
- Schaller, Vincent, 1979, et al.
(författare)
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Towards an electrowetting-based digital microfluidic platform for magnetic immunoassays
- 2009
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Ingår i: Lab on a Chip - Miniaturisation for Chemistry and Biology. - : Royal Society of Chemistry (RSC). - 1473-0189 .- 1473-0197. ; 9:23, s. 3433-3436
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate ElectroWetting-On-Dielectric (EWOD) transport and SQUID gradiometer detection of magnetic nanoparticles (MNPs) suspended in a 2 mu l de-ionized water droplet. This proof-of-concept methodology constitutes the first development step towards a highly sensitive magnetic immunoassay platform with SQUID readout and droplet-based sample handling. Magnetic AC-susceptibility measurements were performed on MNPs with a hydrodynamic diameter of 100 nm using a high-Tc dc Superconducting Quantum Interference Device (SQUID) gradiometer as detector. We observed that the signal amplitude per unit volume is 2.5 times higher for a 2 ml sample droplet compared to a 30 ml sample volume.
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| 10. |
- Zevenhoven, Koos C J, et al.
(författare)
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Conductive shield for ultra-low-field magnetic resonance imaging: Theory and measurements of eddy currents
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 115:10, s. 12-
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Tidskriftsartikel (refereegranskat)abstract
- Eddy currents induced by applied magnetic-field pulses have been a common issue in ultra-low-field magnetic resonance imaging. In particular, a relatively large prepolarizing field-applied before each signal acquisition sequence to increase the signal-induces currents in the walls of the surrounding conductive shielded room. The magnetic-field transient generated by the eddy currents may cause severe image distortions and signal loss, especially with the large prepolarizing coils designed for in vivo imaging. We derive a theory of eddy currents in thin conducting structures and enclosures to provide intuitive understanding and efficient computations. We present detailed measurements of the eddy-current patterns and their time evolution in a previous-generation shielded room. The analysis led to the design and construction of a new shielded room with symmetrically placed 1.6-mm-thick aluminum sheets that were weakly coupled electrically. The currents flowing around the entire room were heavily damped, resulting in a decay time constant of about 6ms for both the measured and computed field transients. The measured eddy-current vector maps were in excellent agreement with predictions based on the theory, suggesting that both the experimental methods and the theory were successful and could be applied to a wide variety of thin conducting structures. (C) 2014 AIP Publishing LLC.
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