scholarly journals Compensation System for Biomagnetic Measurements with Optically Pumped Magnetometers inside a Magnetically Shielded Room

Sensors ◽  
2020 ◽  
Vol 20 (16) ◽  
pp. 4563 ◽  
Author(s):  
Anna Jodko-Władzińska ◽  
Krzysztof Wildner ◽  
Tadeusz Pałko ◽  
Michał Władziński
Keyword(s):  
Magnetic Field ◽  
Quantum Interference ◽  
Spin Exchange ◽  
Initial Conditions ◽  
Sensor Arrays ◽  
Compensation System ◽  
Zero Field ◽  
Optically Pumped ◽  
Ambient Magnetic Field ◽  
Magnetically Shielded Room

Magnetography with superconducting quantum interference device (SQUID) sensor arrays is a well-established technique for measuring subtle magnetic fields generated by physiological phenomena in the human body. Unfortunately, the SQUID-based systems have some limitations related to the need to cool them down with liquid helium. The room-temperature alternatives for SQUIDs are optically pumped magnetometers (OPM) operating in spin exchange relaxation-free (SERF) regime, which require a very low ambient magnetic field. The most common two-layer magnetically shielded rooms (MSR) with residual magnetic field of 50 nT may not be sufficiently magnetically attenuated and additional compensation of external magnetic field is required. A cost-efficient compensation system based on square Helmholtz coils was designed and successfully used for preliminary measurements with commercially available zero-field OPM. The presented setup can reduce the static ambient magnetic field inside a magnetically shielded room, which improves the usability of OPMs by providing a proper environment for them to operate, independent of initial conditions in MSR.

scholarly journals On-scalp MEG system utilizing an actively shielded array of optically-pumped magnetometers

2018 ◽  
Author(s):  
Joonas Iivanainen ◽  
Rasmus Zetter ◽  
Mikael Grön ◽  
Karoliina Hakkarainen ◽  
Lauri Parkkonen
Keyword(s):  
Spin Exchange ◽  
Dynamic Control ◽  
Sensor Arrays ◽  
Low Frequency ◽  
Sensor Calibration ◽  
Optically Pumped ◽  
Magnetic Shields ◽  
Brain Responses ◽  
Shielding Factor ◽  
Magnetically Shielded Room

AbstractThe spatial resolution of magnetoencephalography (MEG) can be increased from that of conventional SQUID-based systems by employing on-scalp sensor arrays of e.g. optically-pumped magnetometers (OPMs). However, OPMs reach sufficient sensitivity for neuromagnetic measurements only when operated in a very low absolute magnetic field of few nanoteslas or less, usually not reached in a typical magnetically shielded room constructed for SQUID-based MEG. Moreover, field drifts affect the calibration of OPMs. Static and dynamic control of the ambient field is thus necessary for good-quality neuromagnetic measurements with OPMs. Here, we describe an on-scalp MEG system that utilizes OPMs and external compensation coils that provide static and dynamic shielding against ambient fields.In a conventional two-layer magnetically shielded room, our coil system reduced the maximum remanent DC-field component within an 8-channel OPM array from 70 to less than 1 nT, enabling the sensors to operate in the sensitive spin exchange relaxation-free regime. When compensating field drifts below 4 Hz, a low-frequency shielding factor of 22 dB was achieved, which reduced the peak-to-peak drift from 1.3 to 0.4 nT and thereby the standard deviation of the sensor calibration from 1.6% to 0.4%. Without band-limiting the field that is compensated, a low-frequency shielding factor of 43 dB was achieved.We validated the system by measuring brain responses to electric stimulation of the median nerve. With dynamic shielding and digital interference suppression methods, single-trial somatosensory evoked responses could be detected. Our results advance the deployment of OPM-based on-scalp MEG in lighter magnetic shields.

scholarly journals Magnetic Field Compensation Coil Design for Magnetoencephalography

2021 ◽  
Author(s):  
Hermann Sonntag ◽  
Christian F. Doeller ◽  
Jens Haueisen ◽  
Burkhard Maess
Keyword(s):  
Magnetic Field ◽  
Head Movements ◽  
Side Length ◽  
Coil Design ◽  
Optically Pumped ◽  
Active Suppression ◽  
Highly Sensitive ◽  
Movement Artifacts ◽  
Operational Range ◽  
Magnetically Shielded Room

Abstract While optically pumped magnetometers (OPMs) can be attached to the head of a person and allow for highly sensitive recordings of the human magnetoencephalogram (MEG), they are mostly limited to an operational range of approximately ±5 nT. Consequently, even inside a magnetically shielded room (MSR), movements in the remnant magnetic field disable the OPMs. Active suppression of the remnant field utilizing compensation coils is therefore essential. We propose 8 compensation coils on 5 sides of a cube with a side length of approximately 2 m which were optimized for operation inside an MSR. Compared to previously built bi-planar compensation coils, the coils proposed in this report are more complex in geometry and achieved 10 times smaller errors for simulated compensation fields. The proposed coils will allow for larger head movements or smaller movement artifacts in future MEG experiments compared to existing coils.

scholarly journals Magnetic field compensation coil design for magnetoencephalography

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hermann Kutschka ◽  
Christian F. Doeller ◽  
Jens Haueisen ◽  
Burkhard Maess
Keyword(s):  
Magnetic Field ◽  
Head Movements ◽  
Side Length ◽  
Coil Design ◽  
Optically Pumped ◽  
Active Suppression ◽  
Highly Sensitive ◽  
Movement Artifacts ◽  
Operational Range ◽  
Magnetically Shielded Room

AbstractWhile optically pumped magnetometers (OPMs) can be attached to the head of a person and allow for highly sensitive recordings of the human magnetoencephalogram (MEG), they are mostly limited to an operational range of approximately 5 nT. Consequently, even inside a magnetically shielded room (MSR), movements in the remnant magnetic field disable the OPMs. Active suppression of the remnant field utilizing compensation coils is therefore essential. We propose 8 compensation coils on 5 sides of a cube with a side length of approximately 2 m which were optimized for operation inside an MSR. Compared to previously built bi-planar compensation coils, the coils proposed in this report are more complex in geometry and achieved smaller errors for simulated compensation fields. The proposed coils will allow for larger head movements or smaller movement artifacts in future MEG experiments compared to existing coils.

scholarly journals Measurement of the Earth’s Magnetic Field Vector Based on Zero Field Finding Algorithm Using Optically Pumped Magnetometers

2020 ◽  
Vol 14 (1) ◽  
pp. 25-30
Author(s):  
Amin Zamani ◽  
Maliheh Ranjbaran ◽  
Mohammad Mehdi Tehranchi ◽  
Seyed Mohammad Hossein Khalkhali ◽  
Seyedeh Mehri Hamidi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Vector ◽  
Magnetic Field Vector ◽  
Zero Field ◽  
Earth’S Magnetic Field ◽  
Optically Pumped ◽  
Earth's Magnetic Field

scholarly journals Nuclear magnetic field measurement of the spin-exchange optically pumped noble gas in a self-compensated atomic comagnetometer

2020 ◽  
Vol 28 (12) ◽  
pp. 17683
Author(s):  
Yan Lu ◽  
Yueyang Zhai ◽  
Wenfeng Fan ◽  
Yong Zhang ◽  
Li Xing ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Measurement ◽  
Spin Exchange ◽  
Noble Gas ◽  
Magnetic Field Measurement ◽  
Optically Pumped ◽  
Nuclear Magnetic

scholarly journals A Non-Modulated Triaxial Magnetic Field Compensation Method for Spin-Exchange Relaxation-Free Magnetometer Based on Zero-Field Resonance

IEEE Access ◽  
2019 ◽  
Vol 7 ◽  
pp. 167557-167565 ◽  
Author(s):  
Junpeng Zhao ◽  
Gang Liu ◽  
Jixi Lu ◽  
Ke Yang ◽  
Danyue Ma ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Spin Exchange ◽  
Compensation Method ◽  
Zero Field

Magnetoencephalography Using Optically Pumped Magnetometers

2020 ◽  
pp. 104-124 ◽  
Author(s):  
Elena Boto ◽  
Niall Holmes ◽  
Tim M. Tierney ◽  
James Leggett ◽  
Ryan Hill ◽  
...  
Keyword(s):  
Quantum Interference ◽  
Optical Pumping ◽  
Spin Exchange ◽  
Dynamic Range ◽  
Cryogenic Cooling ◽  
Local Magnetic Field ◽  
Optically Pumped ◽  
Fundamental Building Block ◽  
Alkali Atoms ◽  
Theoretical Sensitivity

This chapter explores one of the most promising alternatives to superconducting quantum-interference devices (SQUIDs) as the fundamental building block of magnetoencephalography (MEG) systems: optically pumped magnetometers (OPMs). OPMs exploit the spin properties of alkali atoms, using a technique known as optical pumping to prepare a gas of atoms such that its opacity to laser light becomes a sensitive marker of a local magnetic field. The theoretical sensitivity of the OPM surpasses even that of the SQUID, and OPMs operate without cryogenic cooling. Moreover, they are small and lightweight, offering the potential for development of a flexible MEG system, which could be adapted to any head shape and in principle could become wearable such that subjects could move freely during data acquisition. Because the external surface of an OPM is at approximately body temperature, the sensing volume can be placed close to the head, increasing the signal strength. When operated in the spin exchange relaxation-free (SERF) regime, their bandwidth is suited to MEG acquisition, and their dynamic range, although limited, is acceptable.

Investigation of Multiferroic BiFeO3 Nanorods Using 2-MOE(C3H8O2)-Assisted Citrate Sol–Gel Method

2019 ◽  
Vol 18 (05) ◽  
pp. 1850029
Author(s):  
R. V. William ◽  
A. Marikani ◽  
K. Gangatharan
Keyword(s):  
Quantum Interference ◽  
Spin Exchange ◽  
Bismuth Ferrite ◽  
Sol Gel ◽  
Magnetization Measurement ◽  
Ferromagnetic Behavior ◽  
Zero Field ◽  
Secondary Phases ◽  
X Ray Diffraction ◽  
Ferroelectric Hysteresis

Bismuth ferrite (BiFeO[Formula: see text] nanorods have been prepared from 2-methoyethanol (2-MOE)-assisted sol–gel technique. Structure, dielectric, and magnetic properties of BiFeO3 nanorods are briefly discussed in this paper. Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) results suggest that the BiFeO3 peaks calcined at 500∘C exhibit a distorted rhombohedral perovskite structure with the absence of other secondary phases like Bi2Fe4O9. Meanwhile, the BiFeO3 showed excellent photoluminescence (PL) behavior due to the transmission of electrons from conduction band to the valence band. Ferroelectric hysteresis loop of BiFeO3 shows an increase of coercivity from 5.5–6[Formula: see text][Formula: see text]C/cm2 in a frequency range of 6–12[Formula: see text]kHz. The magnetization measurement resulted in a well-saturated ferromagnetic behavior, and in addition, the temperature-dependent magnetization was discussed for BiFeO3 nanorod using superconducting quantum interference device (SQUID) method. The zero-field-cooled (ZFC) and field-cooled (FC) curves reveal spin-glass effect owing to size effects, spin exchange, and anisotropy of material assembly.

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