The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
M V Romalis - One of the best experts on this subject based on the ideXlab platform.
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multi channel atomic Magnetometer for magnetoencephalography a configuration study
NeuroImage, 2014Co-Authors: Kiwoong Kim, Samo Begus, H Xia, Seungkyun Lee, Vojko Jazbinsek, Zvonko Trontelj, M V RomalisAbstract:Atomic Magnetometers are emerging as an alternative to SQUID Magnetometers for detection of biological magnetic fields. They have been used to measure both the magnetocardiography (MCG) and magnetoencephalography (MEG) signals. One of the virtues of the atomic Magnetometers is their ability to operate as a multi-channel detector while using many common elements. Here we study two configurations of such a multi-channel atomic Magnetometer optimized for MEG detection. We describe measurements of auditory evoked fields (AEF) from a human brain as well as localization of dipolar phantoms and auditory evoked fields. A clear N100m peak in AEF was observed with a signal-to-noise ratio of higher than 10 after averaging of 250 stimuli. Currently the intrinsic magnetic noise level is 4fTHz(-1/2) at 10Hz. We compare the performance of the two systems in regards to current source localization and discuss future development of atomic MEG systems.
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subfemtotesla scalar atomic magnetometry using multipass cells
Physical Review Letters, 2013Co-Authors: Dong Sheng, Shuguang Li, Nezih Dural, M V RomalisAbstract:: Scalar atomic Magnetometers have many attractive features but their sensitivity has been relatively poor. We describe a Rb scalar gradiometer using two multipass optical cells. We use a pump-probe measurement scheme to suppress spin-exchange relaxation and two probe pulses to find the spin precession zero crossing times with a resolution of 1 psec. We realize a magnetic field sensitivity of 0.54 fT/Hz(1/2), which improves by an order of magnitude the best scalar Magnetometer sensitivity and exceeds, for example, the quantum limit set by the spin-exchange collisions for a scalar Magnetometer with the same measurement volume operating in a continuous regime.
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spin exchange relaxation free magnetometry using elliptically polarized light
arXiv: Atomic Physics, 2009Co-Authors: V Shah, M V RomalisAbstract:Spin-exchange relaxation free alkali-metal Magnetometers typically operate in the regime of high optical density, presenting challenges for simple and efficient optical pumping and detection. We describe a high-sensitivity Rb Magnetometer using a single elliptically-polarized off-resonant laser beam. Circular component of the light creates relatively uniform spin polarization while the linear component is used to measure optical rotation generated by the atoms. Modulation of the atomic spin direction with an oscillating magnetic field shifts the detected signal to high frequencies. Using a fiber-coupled DFB laser we achieve magnetic field sensitivity of 7 fT/$\sqrt{% \mathrm{Hz}}$ with a miniature $5\times5\times5$ mm Rb vapor cell.
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spin exchange relaxation free magnetometry with cs vapor
Physical Review A, 2008Co-Authors: M P Ledbetter, Dmitry Budker, Igor Savukov, Victor M Acosta, M V RomalisAbstract:We describe a Cs atomic Magnetometer operating in the spin-exchange-relaxation-free (SERF) regime. With a vapor cell temperature of $103\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ we achieve intrinsic magnetic resonance widths $\ensuremath{\Delta}B=17\text{ }\ensuremath{\mu}\text{G}$ corresponding to an electron spin-relaxation rate of $300\text{ }{\text{s}}^{\ensuremath{-}1}$ when the spin-exchange rate is ${\ensuremath{\Gamma}}_{\text{SE}}=14\text{ }000\text{ }{\text{s}}^{\ensuremath{-}1}$. We also observe an interesting narrowing effect due to diffusion. Signal-to-noise measurements yield a sensitivity of about $400\text{ }\text{pG}/\sqrt{\text{Hz}}$. Based on photon shot noise, we project a sensitivity of $40\text{ }\text{pG}/\sqrt{\text{Hz}}$. A theoretical optimization of the Magnetometer indicates sensitivities on the order of $2\text{ }\text{pG}/\sqrt{\text{Hz}}$ should be achievable in a $1\text{ }{\text{cm}}^{3}$ volume. Because Cs has a higher saturated vapor pressure than other alkali metals, SERF Magnetometers using Cs atoms are particularly attractive in applications requiring lower temperatures.
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A subfemtotesla multichannel atomic Magnetometer
Nature, 2003Co-Authors: I. K. Kominis, T W Kornack, J. C. Allred, M V RomalisAbstract:The magnetic field is one of the most fundamental and ubiquitous physical observables, carrying information about all electromagnetic phenomena. For the past 30 years, superconducting quantum interference devices (SQUIDs) operating at 4 K have been unchallenged as ultrahigh-sensitivity magnetic field detectors^ 1 , with a sensitivity reaching down to 1 fT Hz^-1/2 (1 fT = 10^-15 T). They have enabled, for example, mapping of the magnetic fields produced by the brain, and localization of the underlying electrical activity (magnetoencephalography). Atomic Magnetometers, based on detection of Larmor spin precession of optically pumped atoms, have approached similar levels of sensitivity using large measurement volumes^ 2 , 3 , but have much lower sensitivity in the more compact designs required for magnetic imaging applications^ 4 . Higher sensitivity and spatial resolution combined with non-cryogenic operation of atomic Magnetometers would enable new applications, including the possibility of mapping non-invasively the cortical modules in the brain. Here we describe a new spin-exchange relaxation-free (SERF) atomic Magnetometer, and demonstrate magnetic field sensitivity of 0.54 fT Hz^-1/2 with a measurement volume of only 0.3 cm^3. Theoretical analysis shows that fundamental sensitivity limits of this device are below 0.01 fT Hz^-1/2. We also demonstrate simple multichannel operation of the Magnetometer, and localization of magnetic field sources with a resolution of 2 mm.
A. Koval - One of the best experts on this subject based on the ideXlab platform.
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a merged search coil and fluxgate Magnetometer data product for parker solar probe fields
Journal of Geophysical Research, 2020Co-Authors: Trevor A Bowen, Guillaume Jannet, J W Bonnell, K Goetz, K Goodrich, J Gruesbeck, P Harvey, A. Koval, Stuart D. BaleAbstract:NASA's Parker Solar Probe (PSP) mission is currently investigating the local plasma environment of the inner-heliosphere ($< $0.25$R_\odot$) using both {\em{in-situ}} and remote sensing instrumentation. Connecting signatures of microphysical particle heating and acceleration processes to macro-scale heliospheric structure requires sensitive measurements of electromagnetic fields over a large range of physical scales. The FIELDS instrument, which provides PSP with {\em{in-situ}} measurements of electromagnetic fields of the inner heliosphere and corona, includes a set of three vector Magnetometers: two fluxgate Magnetometers (MAGs), and a single inductively coupled search-coil Magnetometer (SCM). Together, the three FIELDS Magnetometers enable measurements of the local magnetic field with a bandwidth ranging from DC to 1 MHz. This manuscript reports on the development of a merged data set combining SCM and MAG (SCaM) measurements, enabling the highest fidelity data product with an optimal signal to noise ratio. On-ground characterization tests of complex instrumental responses and noise floors are discussed as well as application to the in-flight calibration of FIELDS data. The algorithm used on PSP/FIELDS to merge waveform observations from multiple sensors with optimal signal to noise characteristics is presented. In-flight analysis of calibrations and merging algorithm performance demonstrates a timing accuracy to well within the survey rate sample period of $\sim340 \mu s$.
V Shah - One of the best experts on this subject based on the ideXlab platform.
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spin exchange relaxation free magnetometry using elliptically polarized light
arXiv: Atomic Physics, 2009Co-Authors: V Shah, M V RomalisAbstract:Spin-exchange relaxation free alkali-metal Magnetometers typically operate in the regime of high optical density, presenting challenges for simple and efficient optical pumping and detection. We describe a high-sensitivity Rb Magnetometer using a single elliptically-polarized off-resonant laser beam. Circular component of the light creates relatively uniform spin polarization while the linear component is used to measure optical rotation generated by the atoms. Modulation of the atomic spin direction with an oscillating magnetic field shifts the detected signal to high frequencies. Using a fiber-coupled DFB laser we achieve magnetic field sensitivity of 7 fT/$\sqrt{% \mathrm{Hz}}$ with a miniature $5\times5\times5$ mm Rb vapor cell.
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subpicotesla atomic magnetometry with a microfabricated vapour cell
Nature Photonics, 2007Co-Authors: V Shah, Susanne Knappe, Peter D D Schwindt, John KitchingAbstract:Highly sensitive Magnetometers capable of measuring magnetic fields below 1 pT have an impact on areas as diverse as geophysical surveying1, the detection of unexploded ordinance2, space science3, nuclear magnetic resonance4,5, health care6 and perimeter and remote monitoring. Recently, it has been shown that laboratory optical Magnetometers7,8, based on the precession of the spins of alkali atoms in the vapour phase, could achieve sensitivities in the femtotesla range, comparable to9,10,11,12, or even exceeding13, those of superconducting quantum interference devices6. We demonstrate here an atomic Magnetometer based on a millimetre-scale microfabricated alkali vapour cell with sensitivity below 70 fT Hz−1/2. Additionally, we use a simplified optical configuration that requires only a single low-power laser. This result suggests that millimetre-scale, low-power femtotesla Magnetometers are feasible, and we support this proposition with a simple sensitivity scaling analysis. Such an instrument would greatly expand the range of applications in which atomic Magnetometers could be used.
José M.g. Merayo - One of the best experts on this subject based on the ideXlab platform.
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The Juno Magnetic Field Investigation
Space Science Reviews, 2017Co-Authors: John E. P. Connerney, J. B. Bjarno, P. S. Jorgensen, A. Malinnikova, J. Espley, Mathias Benn, Peter Lawton, Troelz Denver, J.l. Jorgensen, José M.g. MerayoAbstract:The Juno Magnetic Field investigation (MAG) characterizes Jupiter’s planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent Magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to ∼20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long Magnetometer boom affixed to the outer end of one of ’s three solar array assemblies. The Magnetometer sensors are controlled by independent and functionally identical electronics boards within the Magnetometer electronics package mounted inside Juno’s massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each Magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = 1.6×106 nT$1.6 \times 10^{6}\mbox{ nT}$ per axis) with a resolution of ∼0.05 nT in the most sensitive dynamic range (±1600 nT per axis). Both Magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of view and also provides a continuous record of radiation exposure. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors, and residual spacecraft fields and/or sensor offsets are monitored in flight taking advantage of Juno’s spin (nominally 2 rpm) to separate environmental fields from those that rotate with the spacecraft.
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Digitalization of highly precise fluxgate Magnetometers
Sensors and Actuators A-physical, 2005Co-Authors: Ales Cerman, A. Kuna, Pavel Ripka, José M.g. MerayoAbstract:Abstract This paper describes the theory behind all three known ways of digitalizing the fluxgate Magnetometers: analogue Magnetometers with digitalized output using high resolution ADC, application of the delta–sigma modulation to the sensor feedback loop and fully digital signal detection. At present time the Δ–Σ ADCs are mostly used for the digitalization of the highly precise fluxgate Magnetometers. The relevant part of the paper demonstrates some pitfalls of their application studied during the design of the Magnetometer for the new Czech scientific satellite MIMOSA. The part discussing the application of the Δ–Σ modulation to the sensor feedback loop theoretically derives the main advantage of this method—increasing of the modulation order and shows its real potential compared to the analog Magnetometer with consequential digitalization. The comparison is realized on the modular Magnetometer allowing configurations with modulator inside and outside the feedback loop. The last principle is demonstrated on the project of the fully digital fluxgate Magnetometer based on the digital signal processor (DSP). The results of the presented projects are compared with recently published competitive projects. The main objective of the paper is then to discuss the potential, real advantages and weakness of each concept and to examine their convenience for future implementations.
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Calibration of the Ørsted vector Magnetometer
Earth Planets and Space, 2003Co-Authors: Nils Olsen, José M.g. Merayo, Peter Brauer, Fritz Primdahl, Otto V Nielsen, Lars Tøffner-clausen, Terence J. Sabaka, John L. Jørgensen, J. M. Léger, Torben RisboAbstract:The vector fluxgate Magnetometer of the Ørsted satellite is routinely calibrated by comparing its output with measurements of the absolute magnetic intensity from the Overhauser instrument, which is the second Magnetometer of the satellite. We describe the method used for and the result obtained in that calibration. Using three years of data the agreement between the two Magnetometers after calibration is 0.33 nT rms (corresponding to better than ± 1 nT for 98% of the data, and better than ± 2 nT for 99.94% of the data). We also report on the determination of the transformation between the Magnetometer coordinate system and the reference system of the star imager. This is done by comparing the magnetic and attitude measurements with a model of Earth’s magnetic field. The Euler angles describing this rotation are determined in this way with an accuracy of better than 4 arcsec.
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Scalar calibration of vector Magnetometers
Measurement Science and Technology, 2000Co-Authors: José M.g. Merayo, Peter Brauer, Fritz Primdahl, Jan Raagaard Petersen, Otto V NielsenAbstract:The calibration parameters of a vector Magnetometer are estimated only by the use of a scalar reference Magnetometer. The method presented in this paper differs from those previously reported in its linearized parametrization. This allows the determination of three offsets or signals in the absence of a magnetic field, three scale factors for normalization of the axes and three non-orthogonality angles which build up an orthogonal system intrinsically in the sensor. The advantage of this method compared with others lies in its linear least squares estimator, which finds independently and uniquely the parameters for a given data set. Therefore, a Magnetometer may be characterized inexpensively in the Earth's magnetic-field environment. This procedure has been used successfully in the pre-flight calibration of the state-of-the-art Magnetometers on board the magnetic mapping satellites Orsted, Astrid-2, CHAMP and SAC-C. By using this method, full-Earth-field-range Magnetometers (± 65536.0 nT) can be characterized down to an absolute precision of 0.5 nT, non-orthogonality of only 2 arcsec and a resolution of 0.2 nT.
E. Shoemaker - One of the best experts on this subject based on the ideXlab platform.
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The GOES-16 Spacecraft Science Magnetometer
Space Science Reviews, 2019Co-Authors: T. M. Loto’aniu, R. J. Redmon, S. Califf, H. J. Singer, W. Rowland, S. Macintyre, C. Chastain, R. Dence, R. Bailey, E. ShoemakerAbstract:Since their inception in the 1970s, the NOAA Geostationary Operational Environmental Satellite (GOES) system has monitored the sources of space weather on the sun and the effects of space weather at Earth. These observations are important for providing forecasts, warnings and alerts to many customers, including satellite operators, the power utilities, and NASA’s human activities in space. The GOES Magnetometer provides observations of the geomagnetic field, which can be the first indication that significant space weather has reached Earth. In addition, the magnetic field observations are used to identify and forecast the severity of the space weather activity. This paper reviews the capabilities of the GOES-16 Magnetometer (MAG) and presents initial post-launch calibration/validation results including issues found in the data. The GOES-16 MAG requirements and capabilities are similar to those for previously flown instruments, measuring three components of the geomagnetic field but with an improved sampling rate of 10 samples/second. The MAG data are low-pass filtered with a 2.5 Hz cutoff compared to the 0.5 Hz cutoff of previous GOES Magnetometers. The MAG is composed of two Magnetometers, an inboard (closer to spacecraft bus) and outboard (on tip of boom) Magnetometer. Presented are the science and instrument requirements, ground and initial on-orbit instrument calibration and data validation. The on-orbit analysis found magnetic contamination along with temperature dependency effects that resulted in unexpected instrument noise and decreased accuracy, with the issues generally more significant on the inboard Magnetometer. The outboard sensor was used for initial analysis of MAG performance. Preliminary comparison, excluding arcjet firing periods, between the outboard Magnetometer and the GOES-14 Magnetometer found a statistical difference of 5 nT at 3 σ $3\sigma $ for the total field. This comparison does not consider inaccuracies in the GOES-14 Magnetometer. Future studies will focus on optimizing the outboard sensor performance.
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The GOES-16 Spacecraft Science Magnetometer
Space Science Reviews, 2019Co-Authors: T. M. Loto’aniu, R. J. Redmon, S. Califf, H. J. Singer, W. Rowland, S. Macintyre, C. Chastain, R. Dence, R. Bailey, E. ShoemakerAbstract:Since their inception in the 1970s, the NOAA Geostationary Operational Environmental Satellite (GOES) system has monitored the sources of space weather on the sun and the effects of space weather at Earth. These observations are important for providing forecasts, warnings and alerts to many customers, including satellite operators, the power utilities, and NASA’s human activities in space. The GOES Magnetometer provides observations of the geomagnetic field, which can be the first indication that significant space weather has reached Earth. In addition, the magnetic field observations are used to identify and forecast the severity of the space weather activity. This paper reviews the capabilities of the GOES-16 Magnetometer (MAG) and presents initial post-launch calibration/validation results including issues found in the data. The GOES-16 MAG requirements and capabilities are similar to those for previously flown instruments, measuring three components of the geomagnetic field but with an improved sampling rate of 10 samples/second. The MAG data are low-pass filtered with a 2.5 Hz cutoff compared to the 0.5 Hz cutoff of previous GOES Magnetometers. The MAG is composed of two Magnetometers, an inboard (closer to spacecraft bus) and outboard (on tip of boom) Magnetometer. Presented are the science and instrument requirements, ground and initial on-orbit instrument calibration and data validation. The on-orbit analysis found magnetic contamination along with temperature dependency effects that resulted in unexpected instrument noise and decreased accuracy, with the issues generally more significant on the inboard Magnetometer. The outboard sensor was used for initial analysis of MAG performance. Preliminary comparison, excluding arcjet firing periods, between the outboard Magnetometer and the GOES-14 Magnetometer found a statistical difference of 5 nT at 3 σ $3\sigma $ for the total field. This comparison does not consider inaccuracies in the GOES-14 Magnetometer. Future studies will focus on optimizing the outboard sensor performance.
