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Zhao B, Tang J, Li L, Zhang Y, Cao L, Liu Y, Zhai Y. In-situ measurement and cancellation of the light-shift in fiber-coupled atomic magnetometers. OPTICS EXPRESS 2022; 30:44309-44320. [PMID: 36523109 DOI: 10.1364/oe.476113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2022] [Accepted: 11/03/2022] [Indexed: 06/17/2023]
Abstract
In optical atomic magnetometers (AMs), the light-shift caused by the circularly polarized pumping beam have a significant impact on the response and is also one of the non-negligible sources of the noise. In this paper, we develop a novel method whereby utilizing the symmetry of the frequency response in an AM to measure and cancel the light-shift. Furthermore, we theoretically analyze and experimentally verify a rapid method of magnetic field compensation and the approach is convenient to measure and cancel of the light-shift. Moreover, the influence of intensity and frequency of the pumping beam is also investigated. The proposed method of in - situ measurement and cancellation of light-shift will be particularly profitable to other optical systems based on AMs.
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Rea M, Holmes N, Hill RM, Boto E, Leggett J, Edwards LJ, Woolger D, Dawson E, Shah V, Osborne J, Bowtell R, Brookes MJ. Precision magnetic field modelling and control for wearable magnetoencephalography. Neuroimage 2021; 241:118401. [PMID: 34273527 PMCID: PMC9248349 DOI: 10.1016/j.neuroimage.2021.118401] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 06/30/2021] [Accepted: 07/13/2021] [Indexed: 11/27/2022] Open
Abstract
Optically-pumped magnetometers (OPMs) are highly sensitive, compact magnetic field sensors, which offer a viable alternative to cryogenic sensors (superconducting quantum interference devices – SQUIDs) for magnetoencephalography (MEG). With the promise of a wearable system that offers lifespan compliance, enables movement during scanning, and provides higher quality data, OPMs could drive a step change in MEG instrumentation. However, this potential can only be realised if background magnetic fields are appropriately controlled, via a combination of optimised passive magnetic screening (i.e. enclosing the system in layers of high-permeability materials), and electromagnetic coils to further null the remnant magnetic field. In this work, we show that even in an OPM-optimised passive shield with extremely low (<2 nT) remnant magnetic field, head movement generates significant artefacts in MEG data that manifest as low-frequency interference. To counter this effect we introduce a magnetic field mapping technique, in which the participant moves their head to sample the background magnetic field using a wearable sensor array; resulting data are compared to a model to derive coefficients representing three uniform magnetic field components and five magnetic field gradient components inside the passive shield. We show that this technique accurately reconstructs the magnitude of known magnetic fields. Moreover, by feeding the obtained coefficients into a bi-planar electromagnetic coil system, we were able to reduce the uniform magnetic field experienced by the array from a magnitude of 1.3 ± 0.3 nT to 0.29 ± 0.07 nT. Most importantly, we show that this field compensation generates a five-fold reduction in motion artefact at 0–2 Hz, in a visual steady-state evoked response experiment using 6 Hz stimulation. We suggest that this technique could be used in future OPM-MEG experiments to improve the quality of data, especially in paradigms seeking to measure low-frequency oscillations, or in experiments where head movement is encouraged.
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Affiliation(s)
- Molly Rea
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
| | - Niall Holmes
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
| | - Ryan M Hill
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
| | - Elena Boto
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
| | - James Leggett
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
| | - Lucy J Edwards
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
| | - David Woolger
- Magnetic Shields Limited, Headcorn Road, Staplehurst, Tonbridge, Kent, TN12 0DS, UK
| | - Eliot Dawson
- Magnetic Shields Limited, Headcorn Road, Staplehurst, Tonbridge, Kent, TN12 0DS, UK
| | - Vishal Shah
- QuSpin Inc., 331 South 104th Street, Suite 130, Louisville, 80027, Colorado, USA
| | - James Osborne
- QuSpin Inc., 331 South 104th Street, Suite 130, Louisville, 80027, Colorado, USA
| | - Richard Bowtell
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
| | - Matthew J Brookes
- Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
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Jaufenthaler A, Kornack T, Lebedev V, Limes ME, Körber R, Liebl M, Baumgarten D. Pulsed Optically Pumped Magnetometers: Addressing Dead Time and Bandwidth for the Unshielded Magnetorelaxometry of Magnetic Nanoparticles. SENSORS (BASEL, SWITZERLAND) 2021; 21:1212. [PMID: 33572285 PMCID: PMC7915455 DOI: 10.3390/s21041212] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Revised: 02/03/2021] [Accepted: 02/05/2021] [Indexed: 01/21/2023]
Abstract
Magnetic nanoparticles (MNP) offer a large variety of promising applications in medicine thanks to their exciting physical properties, e.g., magnetic hyperthermia and magnetic drug targeting. For these applications, it is crucial to quantify the amount of MNP in their specific binding state. This information can be obtained by means of magnetorelaxometry (MRX), where the relaxation of previously aligned magnetic moments of MNP is measured. Current MRX with optically pumped magnetometers (OPM) is limited by OPM recovery time after the shut-off of the external magnetic field for MNP alignment, therewith preventing the detection of fast relaxing MNP. We present a setup for OPM-MRX measurements using a commercially available pulsed free-precession OPM, where the use of a high power pulsed pump laser in the sensor enables a system recovery time in the microsecond range. Besides, magnetometer raw data processing techniques for Larmor frequency analysis are proposed and compared in this paper. Due to the high bandwidth (≥100 kHz) and high dynamic range of our OPM, a software gradiometer in a compact enclosure allows for unshielded MRX measurements in a laboratory environment. When operated in the MRX mode with non-optimal pumping performance, the OPM shows an unshielded gradiometric noise floor of about 600 fT/cm/Hz for a 2.3 cm baseline. The noise floor is flat up to 1 kHz and increases then linearly with the frequency. We demonstrate that quantitative unshielded MRX measurements of fast relaxing, water suspended MNP is possible with the novel OPM-MRX concept, confirmed by the accurately derived iron amount ratios of MNP samples. The detection limit of the current setup is about 1.37 μg of iron for a liquid BNF-MNP-sample (Bionized NanoFerrite) with a volume of 100 μL.
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Affiliation(s)
- Aaron Jaufenthaler
- Institute of Electrical and Biomedical Engineering, UMIT—Private University for Health Sciences, Medical Informatics and Technology, 6060 Hall in Tirol, Austria;
| | - Thomas Kornack
- Twinleaf LLC, Plainsboro Township, NJ 08536, USA; (T.K.); (M.E.L.)
| | - Victor Lebedev
- Department Biosignals, Physikalisch-Technische Bundesanstalt (PTB), 10587 Berlin, Germany; (V.L.); (R.K.); (M.L.)
| | - Mark E. Limes
- Twinleaf LLC, Plainsboro Township, NJ 08536, USA; (T.K.); (M.E.L.)
| | - Rainer Körber
- Department Biosignals, Physikalisch-Technische Bundesanstalt (PTB), 10587 Berlin, Germany; (V.L.); (R.K.); (M.L.)
| | - Maik Liebl
- Department Biosignals, Physikalisch-Technische Bundesanstalt (PTB), 10587 Berlin, Germany; (V.L.); (R.K.); (M.L.)
| | - Daniel Baumgarten
- Institute of Electrical and Biomedical Engineering, UMIT—Private University for Health Sciences, Medical Informatics and Technology, 6060 Hall in Tirol, Austria;
- Institute of Biomedical Engineering and Informatics, Technische Universität Ilmenau, 98693 Ilmenau, Germany
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Gerginov V, Pomponio M, Knappe S. Scalar Magnetometry Below 100 fT/Hz 1/2 in a Microfabricated Cell. IEEE SENSORS JOURNAL 2020; 20:12684-12690. [PMID: 36275194 PMCID: PMC9586184 DOI: 10.1109/jsen.2020.3002193] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Zero-field optically-pumped magnetometers are a room-temperature alternative to traditionally used super-conducting sensors detecting extremely weak magnetic fields. They offer certain advantages such as small size, flexible arrangement, reduced sensitivity in ambient fields offering the possibility for telemetry. Devices based on microfabricated technology are nowadays commercially available. The limited dynamic range and vector nature of the zero-field magnetometers restricts their use to environments heavily shielded against magnetic noise. Total-field (or scalar) magnetometers based on microfabricated cells have demonstrated subpicotesla sensitivities only recently. This work demonstrates a scalar magnetometer based on a single optical axis, 18 (3 × 3 × 2) mm3 microfabricated cell, with a noise floor of 70 fT/Hz1/2. The magnetometer operates in a large static magnetic field range, and and is based on a simple optical and electronic configuration that allows the development of dense sensor arrays. Different methods of magnetometer interrogation are demonstrated. The features of this magnetic field sensor hold promise for applications of miniature sensors in nonzero field environments such as unshielded magnetoencephalography (MEG) and brain-computer interfaces (BCI).
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Affiliation(s)
- Vladislav Gerginov
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309 USA
| | - Marco Pomponio
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309 USA
| | - Svenja Knappe
- Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309 USA
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In-Situ Measurement of Electrical-Heating-Induced Magnetic Field for an Atomic Magnetometer. SENSORS 2020; 20:s20071826. [PMID: 32218349 PMCID: PMC7181036 DOI: 10.3390/s20071826] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 03/20/2020] [Accepted: 03/24/2020] [Indexed: 11/17/2022]
Abstract
Electrical heating elements, which are widely used to heat the vapor cell of ultrasensitive atomic magnetometers, inevitably produce a magnetic field interference. In this paper, we propose a novel measurement method of the amplitude of electrical-heating-induced magnetic field for an atomic magnetometer. In contrast to conventional methods, this method can be implemented in the atomic magnetometer itself without the need for extra magnetometers. It can distinguish between different sources of magnetic fields sensed by the atomic magnetometer, and measure the three-axis components of the magnetic field generated by the electrical heater and the temperature sensor. The experimental results demonstrate that the measurement uncertainty of the heater’s magnetic field is less than 0.2 nT along the x-axis, 1.0 nT along the y-axis, and 0.4 nT along the z-axis. The measurement uncertainty of the temperature sensor’s magnetic field is less than 0.02 nT along all three axes. This method has the advantage of measuring the in-situ magnetic field, so it is especially suitable for miniaturized and chip-scale atomic magnetometers, where the cell is extremely small and in close proximity to the heater and the temperature sensor.
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Murzin D, Mapps DJ, Levada K, Belyaev V, Omelyanchik A, Panina L, Rodionova V. Ultrasensitive Magnetic Field Sensors for Biomedical Applications. SENSORS (BASEL, SWITZERLAND) 2020; 20:E1569. [PMID: 32168981 PMCID: PMC7146409 DOI: 10.3390/s20061569] [Citation(s) in RCA: 61] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Revised: 03/02/2020] [Accepted: 03/06/2020] [Indexed: 12/27/2022]
Abstract
The development of magnetic field sensors for biomedical applications primarily focuses on equivalent magnetic noise reduction or overall design improvement in order to make them smaller and cheaper while keeping the required values of a limit of detection. One of the cutting-edge topics today is the use of magnetic field sensors for applications such as magnetocardiography, magnetotomography, magnetomyography, magnetoneurography, or their application in point-of-care devices. This introductory review focuses on modern magnetic field sensors suitable for biomedicine applications from a physical point of view and provides an overview of recent studies in this field. Types of magnetic field sensors include direct current superconducting quantum interference devices, search coil, fluxgate, magnetoelectric, giant magneto-impedance, anisotropic/giant/tunneling magnetoresistance, optically pumped, cavity optomechanical, Hall effect, magnetoelastic, spin wave interferometry, and those based on the behavior of nitrogen-vacancy centers in the atomic lattice of diamond.
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Affiliation(s)
- Dmitry Murzin
- Institute of Physics, Mathematics and Information Technology, Immanuel Kant Baltic Federal University, 236041 Kaliningrad, Russia; (K.L.); (V.B.); (A.O.); (L.P.); (V.R.)
| | - Desmond J. Mapps
- Faculty of Science and Engineering, University of Plymouth, Plymouth PL4 8AA, UK;
| | - Kateryna Levada
- Institute of Physics, Mathematics and Information Technology, Immanuel Kant Baltic Federal University, 236041 Kaliningrad, Russia; (K.L.); (V.B.); (A.O.); (L.P.); (V.R.)
| | - Victor Belyaev
- Institute of Physics, Mathematics and Information Technology, Immanuel Kant Baltic Federal University, 236041 Kaliningrad, Russia; (K.L.); (V.B.); (A.O.); (L.P.); (V.R.)
| | - Alexander Omelyanchik
- Institute of Physics, Mathematics and Information Technology, Immanuel Kant Baltic Federal University, 236041 Kaliningrad, Russia; (K.L.); (V.B.); (A.O.); (L.P.); (V.R.)
| | - Larissa Panina
- Institute of Physics, Mathematics and Information Technology, Immanuel Kant Baltic Federal University, 236041 Kaliningrad, Russia; (K.L.); (V.B.); (A.O.); (L.P.); (V.R.)
- National University of Science and Technology, MISiS, 119049 Moscow, Russia
| | - Valeria Rodionova
- Institute of Physics, Mathematics and Information Technology, Immanuel Kant Baltic Federal University, 236041 Kaliningrad, Russia; (K.L.); (V.B.); (A.O.); (L.P.); (V.R.)
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