scholarly journals Active Magnetic-Field Stabilization with Atomic Magnetometer

Sensors ◽  
2020 ◽  
Vol 20 (15) ◽  
pp. 4241 ◽  
Author(s):  
Rui Zhang ◽  
Yudong Ding ◽  
Yucheng Yang ◽  
Zhaoyu Zheng ◽  
Jingbiao Chen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Natural Environments ◽  
Optically Pumped ◽  
Low Frequencies ◽  
Complementary Method ◽  
Noise Rejection ◽  
Proposed Model ◽  
Field Noise ◽  
General Guidance ◽  
The Magnetic Field

A magnetically-quiet environment is important for detecting faint magnetic-field signals or nonmagnetic spin-dependent interactions. Passive magnetic shielding using layers of large magnetic-permeability materials is widely used to reduce the magnetic-field noise. The magnetic-field noise can also be actively monitored with magnetometers and then compensated, acting as a complementary method to the passive shielding. We present here a general model to quantitatively depict and optimize the performance of active magnetic-field stabilization and experimentally verify our model using optically-pumped atomic magnetometers. We experimentally demonstrate a magnetic-field noise rejection ratio of larger than ∼800 at low frequencies and an environment with a magnetic-field noise floor of ∼40 fT/Hz1/2 in unshielded Earth’s field. The proposed model provides a general guidance on analyzing and improving the performance of active magnetic-field stabilization with magnetometers. This work offers the possibility of sensitive detections of magnetic-field signals in a variety of unshielded natural environments.

scholarly journals Practice and perspectives of using ultrasensitive magnetometers in biomedical research.

2021 ◽  
Author(s):  
Yu.V. Maslennikov ◽  
◽  
◽  
Keyword(s):  
Magnetic Field ◽  
Biomedical Research ◽  
Magnetic Measurements ◽  
Signal To Noise Ratio ◽  
Frequency Range ◽  
Optically Pumped ◽  
Technical Solutions ◽  
Further Development ◽  
The Magnetic Field

There are a large number of sensors for measuring the magnetic field of biological objects. They are characterized by the type of the measured physical parameter (magnetic field strength, magnetic flux, etc.), the level of intrinsic sensitivity, and the frequency range of the recorded signals. The long-term practice of studying biomagnetic signals shows that only SQUID-based magnetometers and optically pumped magnetometers have sensitivity levels sufficient for recording biomagnetic signals with the required signal-to-noise ratio. This chapter reflects the main directions of using such magnetometers and methods of magnetic measurements in biomedical research, gives examples of existing technical solutions, and shows possible ways of their further development.

scholarly journals Recording brain activities in unshielded Earth’s field with optically pumped atomic magnetometers

2020 ◽  
Vol 6 (24) ◽  
pp. eaba8792 ◽  
Author(s):  
Rui Zhang ◽  
Wei Xiao ◽  
Yudong Ding ◽  
Yulong Feng ◽  
Xiang Peng ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Medical Diagnosis ◽  
Alpha Rhythm ◽  
Brain Activity ◽  
High Sensitivity ◽  
Noninvasive Method ◽  
Optically Pumped ◽  
Field Noise ◽  
The Relationship ◽  
The Brain

Understanding the relationship between brain activity and specific mental function is important for medical diagnosis of brain symptoms, such as epilepsy. Magnetoencephalography (MEG), which uses an array of high-sensitivity magnetometers to record magnetic field signals generated from neural currents occurring naturally in the brain, is a noninvasive method for locating the brain activities. The MEG is normally performed in a magnetically shielded room. Here, we introduce an unshielded MEG system based on optically pumped atomic magnetometers. We build an atomic magnetic gradiometer, together with feedback methods, to reduce the environment magnetic field noise. We successfully observe the alpha rhythm signals related to closed eyes and clear auditory evoked field signals in unshielded Earth’s field. Combined with improvements in the miniaturization of the atomic magnetometer, our method is promising to realize a practical wearable and movable unshielded MEG system and bring new insights into medical diagnosis of brain symptoms.

Low-frequency response of a buried object in a lossy ground

1990 ◽  
Vol 68 (1) ◽  
pp. 111-120 ◽  
Author(s):  
A. Helaly ◽  
L. Shafai ◽  
A. Sebak
Keyword(s):  
Magnetic Field ◽  
Integral Equation ◽  
Scattered Field ◽  
Numerical Results ◽  
Low Frequencies ◽  
Impedance Boundary ◽  
Buried Object ◽  
Magnetic Field Integral Equation ◽  
The Magnetic Field ◽  
Field Integral

An approximate method is developed for treating problems of electromagnetic scattering, at low frequencies, from a buried object in a lossy ground and excited by a source located in the air region above. The field incident on the object's surface is calculated using the dyadic Green's functions for a half-space. Neglecting the coupling between the air–Earth interface and the object as a first-order approximation at low frequencies, we formulate the scattering problem in terms of the magnetic-field integral equation in conjunction with the impedance boundary conditions. The method of moments is then used to reduce the magnetic-field integral equation to a matrix one in order to determine the induced surface currents. The total scattered field is separated into two terms. One is the direct scattered field, which acts as if no buried inhomogeneity were present. The other term is the anomalous field, which represents the presence of the inhomogeneity. Solutions have been generated, and the numerical results are examined for a few limiting cases to confirm their accuracy. The formulation is then applied for investigating scattering by buried steel spheres. The numerical results show that the method can be used for detecting buried objects.

scholarly journals On the structure of the magnetic field of sunspots

1968 ◽  
Vol 35 ◽  
pp. 215-229 ◽  
Author(s):  
E. I. Mogilevsky ◽  
L. B. Demkina ◽  
B. A. Ioshpa ◽  
V. N. Obridko
Keyword(s):  
Magnetic Field ◽  
Free Field ◽  
Large Field ◽  
Doppler Velocity ◽  
Small Scale ◽  
High Excitation ◽  
Proposed Model ◽  
Background Magnetic Field ◽  
Definition Of ◽  
The Magnetic Field

The model of the magnetic field of sunspots, taking account of fine structure of magnetic field in solar plasma, is considered. Small-scale subgranules with their own field form magnetic filaments in the external current-free field. The filaments are vertical in the umbra, while in the penumbra they run along the surface with sharp bends. In a number of spot umbra the relation between Doppler velocity and the field is established on polarized spectrograms. The π-component splitting in umbra is interpreted as a result of a weak background magnetic-field existence together with a large field of magnetic filaments. Spectrographic definition of the magnetic field in spot umbra is accomplished on the effect of magnetic-lines intensification and directly on spectrograms of low-excitation (Fe I, Ti I) and high-excitation (Fe II) lines. Magnetic field measured in low-excitation lines exceeds twice the field value obtained in high-excitation lines. This result has been considered in the light of the proposed model of sunspot field.

Non‐oriented cesium sensors for airborne magnetometry and gradiometry

Geophysics ◽  
1984 ◽  
Vol 49 (11) ◽  
pp. 2024-2031 ◽  
Author(s):  
C. D. Hardwick
Keyword(s):  
Magnetic Field ◽  
National Research Council ◽  
Larmor Frequency ◽  
High Sensitivity ◽  
Field Vector ◽  
Error Characteristic ◽  
Optically Pumped ◽  
Optimal Angle ◽  
Multiple Sensor ◽  
The Magnetic Field

Optically pumped magnetometers are characterized by an optimal angle between their optical axes and the direction of the magnetic field they are sensing. Departure from the optimal angle causes a shift in the Larmor frequency with a corresponding error in the scalar value of the magnetic field being measured. To minimize this error, magnetometers are conventionally either mounted in multiple sensor clusters such that the errors tend to cancel, or they are mechanically oriented to maintain the optimal angle with respect to the magnetic field vector. Recent cesium vapor magnetometers using a split‐beam technique have a sufficiently flat error characteristic that they can be flown in a non‐oriented or “strap‐down” configuration. This configuration has advantages with respect to conventional methods in terms of reduced size and weight and of greatly reduced cost. This paper describes two fixed orientations for a particular split‐beam magnetometer and calculates the allowable maneuver envelope for all dip angles from 0 to 90 degrees. It is shown that the residual orientation errors can best be handled by the conventional type of magnetic interference compensation model that must, in any case, be implemented in digital form for high‐sensitivity magnetometry or for any type of gradiometry. The National Aeronautical Establishment (NAE) of the National Research Council of Canada has flown strap‐down magnetometers in a three‐axis gradiometer array in a Convair 580 for several years. Results for the entire normal maneuver envelope of the aircraft, including 30 degree bank turns, have equalled or surpassed those obtained with oriented magnetometers. Several typical maneuver compensation results are presented that gave root‐mean‐square (rms) (one‐sigma) residual errors as low as 0.03 gammas (γ) for total field and 3.5 mgammas/m (mγ/m) for lateral gradient.

INVESTIGATING THE TIME DEPENDENCE OF THE MR EFFECT

2007 ◽  
Vol 21 (28n29) ◽  
pp. 4832-4840 ◽  
Author(s):  
FERNANDO D. GONCALVES ◽  
J. DAVID CARLSON
Keyword(s):  
Magnetic Field ◽  
Experimental Data ◽  
Response Time ◽  
Time Dependence ◽  
Dwell Time ◽  
High Shear ◽  
Proposed Model ◽  
Mr Effect ◽  
The Magnetic Field ◽  
Field Strengths

Magnetorheological fluids are known to respond in a matter of milliseconds to the application of a magnetic field. To date, however, very little work has been done to study the time dependence of the MR response. The purpose of this study is to investigate the response time of the fluid. Experiments were conducted on a high shear rate rheometer capable of fluid speeds in excess of 35 m/s. With an MR valve length of 6.35 mm, the resulting dwell times were as low as 0.18 ms. For each of three magnetic field strengths, a reduction in yield stress is observed as dwell time decreases. A model is proposed to represent the time response of the fluid to the application of the magnetic field. The experimental data and the proposed model are used to identify the response time of the fluid for each field strength. Results indicate that as the magnetic field increases, the response time of the MR fluid decreases. For the range of magnetic field strengths considered in this study the response time of the fluid ranged from 0.24 ms to 0.19 ms.

scholarly journals Study on the deep conductive geologic structure by magnetovariational method

2015 ◽  
Vol 18 (3) ◽  
pp. 10-18
Author(s):  
Van Thanh Nguyen ◽  
Lieu Nguyen Nhu Vo
Keyword(s):  
Magnetic Field ◽  
Data Interpretation ◽  
Response Functions ◽  
Low Frequencies ◽  
Linear Relations ◽  
Electric And Magnetic Fields ◽  
The Matrix ◽  
Magnetotelluric Method ◽  
Two Parameters ◽  
The Magnetic Field

In the magnetotelluric method, along with the magnetotelluric response functions originating from linear relations between components of the electric and magnetic fields we can determine the magnetovariational response functions derived from linear relations between components of the magnetic field Hx, Hy, Hz. This consideration may significantly enhance the capabilities of the magnetotellurics, since at low frequencies the magnetic field becomes free of nearsurface distortions and shines a nondeceptive light on the deep geoelectric structures. The components of the magnetic field are represented by Wiese–Parkinson matrix 𝑊 . From the matrix, we use the transformations to construct Vozoff tipper 𝑉 , tipper phase ψ, and tipper ellipticity of magnetic field H   to study the electrical heterogeneity. We obtain more information than previous methods because V gives two parameters: direction and amplitude, |V| > |ReW| and |V| > |ImW|; therefore data interpretation has many advantages over previous methods. The results allow us to give meaningful conclusions about the geology, such as mapping some deep conductive geologic structures of the crust.

scholarly journals Magnetic Field Mapping and Correction for Moving OP-MEG

2021 ◽  
Author(s):  
Stephanie J Mellor ◽  
Tim M Tierney ◽  
George C O'Neill ◽  
Nicholas Alexander ◽  
Robert A Seymour ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Brain Activity ◽  
Low Frequency ◽  
Optically Pumped ◽  
Magnetic Field Mapping ◽  
Modelling Method ◽  
Movement Artefact ◽  
Power Spectral ◽  
Background Magnetic Field ◽  
The Magnetic Field

Background: Optically pumped magnetometers (OPMs) have made moving, wearable magnetoencephalography (MEG) possible. The OPMs typically used for MEG require a low background magnetic field to operate, which is achieved using both passive and active magnetic shielding. However, the background magnetic field is never truly zero Tesla, and so the field at each of the OPMs changes as the participant moves. This leads to position and orientation dependent changes in the measurements, which manifest as low frequency artefacts in MEG data. Objective: We modelled the spatial variation in the magnetic field and used the model to predict the movement artefact found in a dataset. Methods: We demonstrate a method for modelling this field with a triaxial magnetometer, then showed that we can use the same technique to predict the movement artefact in a real OPM-based MEG (OP-MEG) dataset. Results: Using an 86-channel OP-MEG system, we found that this modelling method maximally reduced the power spectral density of the data by 26.2 ± 0.6 dB at 0 Hz, when applied over 5 s non-overlapping windows. Conclusion: The magnetic field inside our state-of-the art magnetically shielded room can be well described by low-order spherical harmonic functions. We achieved a large reduction in movement noise when we applied this model to OP-MEG data. Significance: Real-time implementation of this method could reduce passive shielding requirements for OP-MEG recording and allow the measurement of low-frequency brain activity during natural participant movement.

scholarly journals Muscle fatigue revisited - Insights from optically pumped magnetometers

2021 ◽  
Author(s):  
Davide Sometti ◽  
Lorenzo Semeia ◽  
Hui Chen ◽  
Juergen Dax ◽  
Cornelius Kronlage ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Muscle Fatigue ◽  
Isometric Contraction ◽  
Muscle Fibers ◽  
Muscular Activity ◽  
Rectus Femoris ◽  
Optically Pumped ◽  
Rectus Femoris Muscle ◽  
The Magnetic Field ◽  
Femoris Muscle

Muscle fatigue is well characterized electromyographically, nevertheless only information about summed potential differences is detectable. In contrast, recently developed quantum sensors optically pumped magnetometers (OPMs) offer the advantage of recording both the electrical current propagation in the muscle as well as its geometry, by measuring the magnetic field generated by the muscular action potentials. Magnetomyographic investigation of muscle fatigue is still lacking and it is an open question whether fatigue is characterized similarly in magnetomyography (MMG) compared to electromyography (EMG). Herein, we investigated the muscle fatigue during a 3x1-min strong isometric contraction of the rectus femoris muscle of 12 healthy subjects using simultaneous EMG-MMG (4-channel surface EMG and 4 OPM along the rectus femoris muscle). Both EMG and MMG showed the characteristic frequency decrease in the signal magnitude during isometric contraction, which is typical for muscle fatigue. In addition, it was shown that the main part of this frequency decrease seems to occur in the circular component of the magnetic field around the muscle fibers and less longitudinally along the muscle fibers. Overall, these results show not only that magnetomyography is capable of reproducing the electromyographic standards in identifying muscular fatigue, but it also adds relevant information about the spatial characterization of the signal. Therefore, OPM-MMG offers new insights for the study of muscular activity and might serve as a new, supplementary neurophysiological method.

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