Integration Issues of Graphoepitaxial High- &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;${\rm T}_{\rm c}$&lt;/tex-math&gt;&lt;/inline-formula&gt; SQUIDs Into Multichannel MEG Systems

Magnetoencephalography (MEG) systems based on a dense array of high critical temperature (high-Tc) superconducting quantum interference devices (SQUIDs) can theoretically outperform a state-of-the-art MEG system. On the way towards building such a multichannel system, we evaluate feedback methods suitable for use in dense high-Tc SQUID arrays where the sensors are in very close proximity to the head (on-scalp MEG). We test on-chip superconducting coils and direct injection of the feedback current into the SQUID loop as alternatives to the wire-wound copper coils commonly used in single-channel high-Tc SQUID-based MEG systems. For the evaluation, we have performed coupling, noise, and crosstalk measurements. We conclude that direct injection is the optimal solution for dense on-scalp MEG as it gives crosstalk below 0.5% even between SQUIDs whose pickup loops are within 0.8 mm of one another. Further, this solution provides sufficient flux coupling without adding additional noise. Finally, it does not compromise the standoff distance, which is important for on-scalp MEG.

Section: Methodsmentioning

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Feedback solutions for low crosstalk in dense arrays of high-T_cSQUIDs for on-scalp MEG

Ruffieux

Xie

Chukharkin

et al. 2017

“…The sensors should be placed in a dense array and located as close as possible to the chest/scalp and to neighboring sensors. Cross-talk measurements [39] have confirmed the possibility of building such closely-packed arrays of high-T c biomagnetometers. Encapsulated high-T c biomagnetometers are sufficiently small that more than 100 sensors can be placed above and around an adult human head in the form of a single helmet-shaped cryostat.…”

Section: Cooling Of High-t C Dc Squid Biomagnetometersmentioning

confidence: 74%

“…Two special compensation signals help to remove the residuals of the current-bias-reversal in the primary winding of the matching transformer and to compensate, e.g., the slight asymmetry in the critical currents of the JJs in a given SQUID. In order to reduce crosstalk between the SQUID biomagnetometers, both the main and the biasreversal modulations and feedback should be applied locally to the SQUID by a coil that has a much smaller outer size when compared to the size of the pickup loop [39]. Direct injection of current into the SQUID loop [51,52] is another possibility for generating a locally applied modulation-feedback signal, which is convenient for single-chip integrated DC SQUID magnetometers.…”

Section: Readout Electronics For High-t C Dc Squid Biomagnetometersmentioning

confidence: 99%

High-T_cSQUID biomagnetometers

Faley

Dammers

Maslennikov

et al. 2017

In this paper, we review the preparation technology, integration in measurement systems and tests of high-Tc superconducting quantum interference devices (SQUIDs) intended for biomagnetic applications. A focus is on developments specific to Forschungszentrum Jülich GmbH, Chalmers University of Technology, MedTech West, and the University of Gothenburg, while placing these results in the perspective of those achieved elsewhere. Sensor fabrication, including the deposition and structuring of epitaxial oxide heterostructures, materials for substrates, epitaxial bilayer buffers, bicrystal and step-edge Josephson junctions, and multilayer flux transformers are detailed. The properties of the epitaxial multilayer high-Tc direct current SQUID sensors, including their integration in measurement systems with special electronics and liquid nitrogen cryostats, are presented in the context of biomagnetic recording. Applications that include magnetic nanoparticle based molecular diagnostics, magnetocardiography, and magnetoencephalography are presented as showcases of high-Tc biomagnetic systems. We conclude by outlining future challenges.

“…Multichannel high-T C SQUID systems have been developed for magnetocardiography and demonstrated high potential in clinical studies [2,3]. Recently, the prospective use of high-T C SQUIDs for magnetoencephalography was demonstrated [4][5][6][7][8]. It was shown that despite higher magnetic field noise, high-T C SQUID magnetometers can have similar or even higher signal-to-noise ratio compared to their low-T C counterparts [5,6,8].…”

Section: Introductionmentioning

confidence: 99%

Operation of a high-T_CSQUID gradiometer with a two-stage MEMS-based Joule–Thomson micro-cooler

Kalabukhov

Hoon²,

Kuit³

et al. 2016

Practical applications of high-TC superconducting quantum interference devices (SQUIDs) require cheap, simple in operation, and cryogen-free cooling. Mechanical cryo-coolers are generally not suitable for operation with SQUIDs due to their inherent magnetic and vibrational noise. In this work, we utilized a commercial Joule–Thomson microfluidic two-stage cooling system with base temperature of 75 K. We achieved successful operation of a bicrystal high-TC SQUID gradiometer in shielded magnetic environment. The micro-cooler head contains neither moving nor magnetic parts, and thus does not affect magnetic flux noise of the SQUID even at low frequencies. Our results demonstrate that such a microfluidic cooling system is a promising technology for cooling of high-TC SQUIDs in practical applications such as magnetic bioassays.