Elimination of 1/ƒ Noise in Gradiometers for SQUID-Based Ultra-Low Field Nuclear Magnetic Resonance

Matlashov, Andrei; Magnelind, Per E.; Volegov, P. L.; Espy, Michelle A.

doi:10.1109/isec.2015.7383455

Cited by 4 publications

(5 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This leads to the conclusion that Pb does not trap flux and therefore renders it a potential alternative. In contrast, Matlashov et al [9] observed significant 1/f -noise after pulsed fields using type-I superconductor Tantalum (Ta) pick-up coils which could be eliminated by thermocycling the Ta coil above it's T c . This can be taken as evidence for rearrangement of trapped flux.…”

Section: Introductionmentioning

confidence: 94%

Ultra-sensitive SQUID Systems for Pulsed Fields—Degaussing Superconducting Pick-Up Coils

Al-Dabbagh

Storm

2018

IEEE Trans. Appl. Supercond.

View full text Add to dashboard Cite

SQUID systems for ultra-low-field magnetic resonance (ULF MR) feature superconducting pick-up coils which must tolerate exposure to pulsed fields of up to 100 mT. Using type-II superconductor niobium (Nb) field distortions due to trapped vortices in the wire result. In addition, their rearrangement after quick removal of the pulsed field leads to excess low frequency noise which limits the signal-to-noise ratio. In contrast, type I superconductors, such as lead (Pb), do not exhibit vortices but form an intermediate state with the coexistence of normal and superconducting domains.We measured the magnetization loops of superconducting wire samples of Nb and Pb together with their noise behavior after pulsed fields. Pb also exhibits significant excess low frequency noise once the wire has been driven into the intermediate state.To avoid this problem, we removed the field not abruptly but in a linearly decaying sinusoidal manner thereby degaussing the wire. After application of 57 mT, we found that Nb can be degaussed within at least 50 ms, the shortest time used in this study. Pb can also be degaussed, albeit within 100 ms and a more complex dependency on the degaussing parameters. After successful degaussing, negligible excess low frequency noise is observed.

show abstract

Section: Introductionmentioning

confidence: 94%

Ultra-sensitive SQUID Systems for Pulsed Fields—Degaussing Superconducting Pick-Up Coils

Al-Dabbagh

Storm

2018

IEEE Trans. Appl. Supercond.

View full text Add to dashboard Cite

show abstract

“…With respect to the noise performance, the application of a large B P has been shown to lead to an excess low-frequency noise due to flux trapping in the superconducting pick-up coil [36]. However, it may be avoided by operation at a sufficiently large Larmor frequency [37], a suitable B P ramp down [38] or rapid thermal cycling of the pick-up coil [39]. Consequently, the noise performance is ultimately limited by Johnson noise of the human body which was recently measured at 55 aT Hz −1/2 [40].…”

Section: Theoretical Sensitivity Limits Of 3d Dcncimentioning

confidence: 99%

Computational and Phantom-Based Feasibility Study of 3D dcNCI With Ultra-Low-Field MRI

et al. 2021

View full text Add to dashboard Cite

The possibility to directly and non-invasively localize neuronal activities in the human brain, as for instance by performing neuronal current imaging (NCI) via magnetic resonance imaging (MRI), would be a breakthrough in neuroscience. In order to assess the feasibility of 3-dimensional (3D) NCI, comprehensive computational and physical phantom experiments using low-noise ultra-low-field (ULF) MRI technology were performed using two different source models within spherical phantoms. The source models, consisting of a single dipole and an extended dipole grid, were calibrated enabling the quantitative emulation of a long-lasting neuronal activity by the application of known current waveforms. The dcNCI experiments were also simulated by solving the Bloch equations using the calculated internal magnetic field distributions of the phantoms and idealized MRI fields. The simulations were then validated by physical phantom experiments using a moderate polarization field of 17 mT. A focal activity with an equivalent current dipole of about 150 nAm and a physiologically relevant depth of 35 mm could be resolved with an isotropic voxel size of 25 mm. The simulation tool enabled the optimization of the imaging parameters for sustained neuronal activities in order to predict maximum sensitivity.

show abstract

“…If during prepolarisation the pick-up-coil wire, usually made of the type-II superconductor niobium (Nb), experiences a field above its lower critical field H c1 , flux will be trapped. During the signal acquisition phase when the prepolarization field is removed, rearrangement of the vortices may cause flux jumps resulting in excess low-frequency noise [21,22]. An example is shown on the right in figure 2.…”

Section: Noise Sources Unique To Ulf Mrimentioning

confidence: 99%

“…There appears to be a large spread in the behavior of different Nb wire samples, indicating an unsolved material issue. A possible alternative might be the use of a type-I superconductor such as lead [24] or thermocycling the gradiometer wire as demonstrated by Matlashov et al [22].…”

Section: Noise Sources Unique To Ulf Mrimentioning

confidence: 99%

“…A superconducting polarizing coil can also be left magnetized by the pulses, which requires further development of in-sequence demagnetization of the coil. Also the SQUID sensors are exposed to the pulsed fields, and their recovery after a pulse is associated with an amount of transient noise that depends on the type of superconducting pickup coil [24,22,62]. The recovery period should be made short compared to tissue relaxation times.…”

Section: Advances In Science and Technology To Meet Challengesmentioning

confidence: 99%

See 1 more Smart Citation

SQUIDs in biomagnetism: a roadmap towards improved healthcare

Körber

Storm

Seton

et al. 2016

Supercond. Sci. Technol.

View full text Add to dashboard Cite

Globally, the demand for improved health care delivery while managing escalating costs is a major challenge. Measuring the biomagnetic fields that emanate from the human brain already impacts the treatment of epilepsy, brain tumours and other brain disorders. This roadmap explores how superconducting technologies are poised to impact health care. Biomagnetism is the study of magnetic fields of biological origin. Biomagnetic fields are typically very weak, often in the femtotesla range, making their measurement challenging. The earliest in vivo human measurements were made with room-temperature coils. In 1963, Baule and McFee (1963 Am. Heart J. 55 95−6) reported the magnetic field produced by electric currents in the heart (‘magnetocardiography’), and in 1968, Cohen (1968 Science 161 784−6) described the magnetic field generated by alpha-rhythm currents in the brain (‘magnetoencephalography’). Subsequently, in 1970, Cohen et al (1970 Appl. Phys. Lett. 16 278–80) reported the recording of a magnetocardiogram using a Superconducting QUantum Interference Device (SQUID). Just two years later, in 1972, Cohen (1972 Science 175 664–6) described the use of a SQUID in magnetoencephalography. These last two papers set the scene for applications of SQUIDs in biomagnetism, the subject of this roadmap. The SQUID is a combination of two fundamental properties of superconductors. The first is flux quantization—the fact that the magnetic flux Φ in a closed superconducting loop is quantized in units of the magnetic flux quantum, Φ0 ≡ h/2e, ≈ 2.07 × 10−15 Tm2 (Deaver and Fairbank 1961 Phys. Rev. Lett. 7 43–6, Doll R and Näbauer M 1961 Phys. Rev. Lett. 7 51–2). Here, h is the Planck constant and e the elementary charge. The second property is the Josephson effect, predicted in 1962 by Josephson (1962 Phys. Lett. 1 251–3) and observed by Anderson and Rowell (1963 Phys. Rev. Lett. 10 230–2) in 1963. The Josephson junction consists of two weakly coupled superconductors separated by a tunnel barrier or other weak link. A tiny electric current is able to flow between the superconductors as a supercurrent, without developing a voltage across them. At currents above the ‘critical current’ (maximum supercurrent), however, a voltage is developed. In 1964, Jaklevic et al (1964 Phys. Rev. Lett. 12 159–60) observed quantum interference between two Josephson junctions connected in series on a superconducting loop, giving birth to the dc SQUID. The essential property of the SQUID is that a steady increase in the magnetic flux threading the loop causes the critical current to oscillate with a period of one flux quantum. In today’s SQUIDs, using conventional semiconductor readout electronics, one can typically detect a change in Φ corresponding to 10−6 Φ0 in one second. Although early practical SQUIDs were usually made from bulk superconductors, for example, niobium or Pb-Sn solder blobs, today’s devices are invariably made from thin superconducting films patterned with photolithography or even electron lithography. An extensive descriptio...

show abstract

Elimination of 1/ƒ Noise in Gradiometers for SQUID-Based Ultra-Low Field Nuclear Magnetic Resonance

Cited by 4 publications

References 6 publications

Ultra-sensitive SQUID Systems for Pulsed Fields—Degaussing Superconducting Pick-Up Coils

Ultra-sensitive SQUID Systems for Pulsed Fields—Degaussing Superconducting Pick-Up Coils

Computational and Phantom-Based Feasibility Study of 3D dcNCI With Ultra-Low-Field MRI

SQUIDs in biomagnetism: a roadmap towards improved healthcare

Contact Info

Product

Resources

About