Magnetic Shielding Research Articles

Test-retest reliability of the human connectome: An OPM-MEG study

Abstract Magnetoencephalography with optically pumped magnetometers (OPM-MEG) offers a new way to record electrophysiological brain function, with significant advantages over conventional MEG, including adaptability to head shape/size, free movement during scanning, increased signal amplitude, and no reliance on cryogenics. However, OPM-MEG remains in its infancy, with significant questions to be answered regarding the optimal system design. Here, we present an open-source dataset acquired using a newly constructed OPM-MEG system with a triaxial sensor design, 168 channels, OPM-optimised magnetic shielding, and active background field control. We measure the test-retest reliability of the human connectome, which was computed using amplitude envelope correlation to measure whole-brain (parcellated) functional connectivity, in 10 individuals while they watch a 600 s move clip. Our results show high repeatability between experimental runs at the group level, with a correlation coefficient of 0.81 in the θ, 0.93 in α, and 0.94 in β frequency ranges. At the individual subject level, we found marked differences between individuals, but high within-subject robustness (correlations of 0.56 ± 0.25, 0.72 ± 0.15, and 0.78 ± 0.13 in α, θ, and β respectively). These results compare well to previous findings using conventional MEG and show that OPM-MEG is a viable way to robustly characterise connectivity.

Magnetic shielding simulation for particle detection

Cherenkov-type particle detectors or scintillators use as a fundamental element photomultiplier tubes, whose efficiency decreases when subjected to the Earth’s magnetic field. This work develops a geomagnetic field compensation system based on coils for large scale cylindrical detectors. The effect of different parameters such as the size of the detector, the distance between coils or the magnetic field strength on the compensation using a basic coil system composed of circular and rectangular coils is studied. The addition of coils of very specific geometry and position to the basic configuration is proposed in order to address the compensation in the areas of the detector where it is more difficult to influence, in order to minimize the loss of efficiency. With such improvement, in the considered simulated system, more than 99.5% of the photomultiplier tubes in the detector experience an efficiency loss of less than 1% due to the effect of the magnetic fields.

IMPROVEMENT LIFETIME OF THE HALL THRUSTER THROUGH MAGNETIC SYSTEM OPTIMIZATION

The object of research in this work is electromagnetic processes in the anode of a Hall thruster. The expansion of the requirements for the total impulse of Hall thrusters emphasizes the need to develop high-performance Hall thrusters, the operational life of which is determined by the amount of time during which the thruster can operate before the plasma in the channel damages the magnetic system. After complete erosion of the dielectric output from the discharge channel, the ion plume interacts with the inner and outer magnetic poles and causes progressive erosion of the magnetic conductor. A new magnetic topology called "magnetic shielding" has been described to reduce channel erosion. The purpose of the work is to increase the lifetime of the Hall thrusters by optimizing the parameters and topology of the magnetic field in the thruster.
 The use of modern programs makes it possible to determine the azimuthal distribution and configuration of the magnetic field in the acceleration channel and in the peripheral zone of the thruster, as well as obtain results that are close to real ones. In this regard, in this work, the method of mathematical modeling was chosen as a research method for conducting research on the magnetic field of the Hall thruster. The quantitative relationship between the magnitude and configuration of the magnetic field, thruster operation parameters, length, and the position of the ionization and acceleration layer in the discharge channel of the Hall thruster, which determines the boundaries of the erosion zones of the walls of the discharge chamber, was determined, namely: - it was established that the boundaries of the erosion zones on the outer and inner walls of the discharge chamber from the anode side are at the intersection of one "boundary" line of force of the magnetic field with the walls, the discharge voltage, the shape of the magnetic lens, the amount of induction and the material of the discharge chamber; - the position of this "limit" line of force is determined by the value along the middle line of the discharge chamber.

The role of extreme geomagnetic storms in the Forbush decrease profile observed by neutron monitors

The Forbush decrease (FD) and Geomagnetic storm (GS) are the two distinct space weather events having common causing agents like interplanetary coronal mass ejection (ICME) or corotating interacting region (CIR). Generally, large-amplitude FDs and extreme GSs are caused by ICME. Here, we studied eight ICME induced extreme storms and their effects on respective FD profiles as observed by neutron monitors. We observed the sudden storm commencement of the GS coincides with the FD onset. Interestingly, we also noted a gradual increase in neutron counts during the main and recovery phases of GS. The maximum enhancement in neutron counts coincides with the minimum value of the Sym-H index. The enhancement is visible primarily in all the neutron monitors but significantly pronounced in high-energy neutrons compared to low-energy neutrons. We observed that the enhancement in cosmic ray flux during Forbush decrease as observed by neutron monitors is contributed by magnetospheric disturbance of geomagnetic storm. Thus we conclude that the weakening of Earth’s magnetic shield due to ICME-Magnetosphere interaction allows more cosmic rays to reach the ground. Thus, we conclude that the geomagnetic storm conditions highly influence the FD profile along with the external causing agent. Therefore, it is essential to include the effect of geomagnetic field variation in the models that are used to reproduce the FD profile.

Electrospinning of polymer nanofibers containing carbon nanotubes filled with iron nanowires

This paper reports the formation of ferromagnetic polymer nanofibers using carbon nanotubes (CNTs) filled with iron nanowires (Fe@CNTs) by an electrospinning method. The solution of polymer in which CNTs filled with Fe@CNTs were dispersed was used for the electrospinning of the fibers. Polymer nanofibers that contain Fe@CNTs were successively formed by electrospinning. The polymer nanofibers showed hard ferromagnetic characteristics originating in Fe@CNTs that have ferromagnetic property due to the shape magnetic anisotropy of Fe nanowires with high-aspect-ratio shapes encapsulated in the CNTs. It is expected that the ferromagnetic polymer nanofibers will have various applications, such as magnetic shields, flexible magnets, electronic devices, etc.

Magnetic Coupling Mechanism With Omnidirectional Magnetic Shielding for Wireless Power Transfer

Electromagnetic field is used as medium for wireless power transfer to realize noncontact power transmission, which is hoped to be concentrated in the power transmission channel as much as possible to improve performance and reduce the impact on surrounding environment. A magnetic coupling mechanism (MCM) with omnidirectional magnetic shielding (ODMS) is designed in this article. Ferrite shielding layers are added at the back of power channel to guide more for power transmission and restraint leakage. The reverse-wound magnetic shielding coil and forward-wound power transmitting coil are connected in reverse series to form a bidirectional antiparallel coil, which eliminates the complex control and additional excitation source, and restrict magnetic in the side areas of power channel. Active and passive shielding methods are comprehensively used to improve the magnetic field distribution in the power transmission channel and reduce magnetic in the full space around MCM. The optimal design method of ODMS MCM is summarized, and the experiments are carried out. The results are consistent with the theoretical and simulation analysis. The proposed ODMS MCM can effectively limit magnetic leakage in all directions and improve transmission power and efficiency.

Comparative Study of Thin Layers Modeling in Electromagnetism: Application to Multilayer Magnetic Shielding

Comparative Study of Thin Layers Modeling in Electromagnetism: Application to Multilayer Magnetic Shielding

Design and Test of Magnetic Shielding for Vacuum Circuit Breaker of CRAFT Quench Protection System

Design and Test of Magnetic Shielding for Vacuum Circuit Breaker of CRAFT Quench Protection System

Design of gradient coils based on the target field method in a high-permeability shield considering sidewall apertures

The combination of high-permeability ferrite and coils is often used to nullify ambient magnetic fields and is widely used in applications such as magnetic resonance imaging and high-sensitivity magnetic sensors. We propose the design method of transverse gradient coils based on the target field method in a high-permeability shield considering sidewall apertures (TFM-HPSCSA), which are installed in the ferrite shield to zero the residual magnetic field gradient. TFM-HPSCSA coils enable an innovative combination of magnetic field gradient linearity and structural luminescence. The coil current density distribution is set to avoid the central sidewall apertures. As a result, the contour distribution of the stream function under the optimized weight coefficients is calculated to obtain the wire alignments of the dBy/dx, dBy/dy and dBy/dz gradient coils. The deviations of the experimentally measured values from the finite element simulations of the three types coils are 0.63%, 1.17% and 0.48%, respectively, which verified the validity and the accuracy of the proposed method. In comparison to the traditional saddle gradient coil designed under the free space condition, the proposed dBy/dx coil produces a 30.5% improvement in the percentage range of regions with 5% magnetic field gradient nonlinearity. The increased linear range of the gradient magnetic field contributes to the improvement of the residual field nulling range in magnetic sensors and magnetic shielding systems in practical applications.

Suppression of thermal coupling noise in the SERF atomic co-magnetometer

Heating the alkali metal vapor cell to obtain high atomic density is a prerequisite for realizing the high-precision measurement for spin-exchange relaxation-free (SERF) co-magnetometer. However, the thermo-magnetic and thermo-optical coupling noise caused by the temperature diffusion from the alkali vapor cell is one of the main factors restricting the co-magnetometer performance at present. Here the influence of heating on the SERF co-magnetometer was comprehensively studied, and the thermal error model of the system was established. A novel heat insulation structure for the co-magnetometer was designed, and the effectiveness was verified through monitoring of characteristic temperature points. Compared to the conventional oven support, the average maximum temperature difference within 12 h of the optical path and magnetic shielding systems (OPMSS) decreased by 52%, the bias instability of the co-magnetometer decreased by 24%, and the noise of the co-magnetometer at 1 Hz decreased by 33%. The experimental results demonstrate that this method reduces the temperature fluctuation of the OPMSS, effectively suppresses the thermal coupling noise, and thus improves the performance of the SERF co-magnetometer. Moreover, this method is also applicable to other quantum sensors based on alkali metal vapor cell.

Ferrite-Loaded Inverted Microstrip Line-Based Artificial Magnetic Conductor for the Magnetic Shielding Applications of a Wireless Power Transfer System

In this paper, we propose a ferrite-loaded inverted microstrip line (IML)-based artificial magnetic conductor (AMC) with a novel design that can provide complete magnetic shielding at the backside of the transmitting (Tx) coil while slightly improving the power transfer efficiency (PTE) of a wireless power transfer system (WPTS). The target frequency of the WPTS application is approximately 6.78 MHz. In the proposed design, the AMC is placed behind the Tx coil, and its magnetic shielding capability and PTE performance were verified through simulations and measurements. The size of the proposed AMC is 528 × 528 × 6.6 mm3. The measurement results verified that, compared with the Tx coil without an AMC surface, the proposed ferrite-loaded IML-based AMC can provide complete magnetic shielding while improving the PTE of the WPTS by approximately 8.05%.

Quantum Effects of Hydrogen Nuclei on the Nuclear Magnetic Shielding Tensor of Ice Ih.

Ice is the most fundamental hydrogen-bonded system in which the hydrogen nuclear quantum effect significantly impacts the structure and relevant thermochemical and spectroscopic properties. While ice was experimentally investigated using proton nuclear magnetic resonance spectroscopy more than 40 years ago, the corresponding theoretical investigations have been rarely reported due to the difficulty in evaluating how the proton nuclear quantum effect influences the spectral characteristics of such a condensed material. In this study, we applied a combination of the ONIOM and multicomponent molecular orbital (MC_MO) methods for calculating the anisotropic and isotropic components of the nuclear magnetic shielding tensor of the hexagonal ice crystal to quantify the effects of nuclear quantum fluctuations on the spectroscopic properties of ice. The nuclear magnetic shielding values computed by incorporating the hydrogen nuclear quantum effect reasonably agree with the experimental values. The nuclear quantum effects were found to increase the anisotropic component of the magnetic shielding tensor while decreasing the isotropic component. Such a difference can be explained by their distinct dependence on the electrostatic field and hydrogen-bonding structural parameters.

Mathematical Analysis on Spherical Shell of Permeable Material in NID Space

In this paper, we have studied the magnetic shielding effect of a spherical shell analytically in fractional dimensional space (FDS). The Laplacian equation in fractional space predicts the complex phenomena of physics. This is a boundary value problem that has been solved by the separation variable method mathematically by taking low frequency w = 0. Electric potential is obtained in fractional dimensional space for the three regions, namely outside the spherical shell, between the shell and hollow sphere and inside the sphere. Also, the induced dipole moment has been derived. We obtain a general solution that reduces to the classical results by setting fractional parameter α = 3 which takes its value (2 < α ≤ 3).

Analysis of the calculation method and evaluation of the magnetic acceleration noise of space inertial sensor

Accurately calculating the magnetic acceleration noise is essential to designing the space inertial sensor and constructing its evaluation system. In view of the shortcomings of the magnetic acceleration noise calculation model, which considers the test mass (TM) as an ideal magnetic dipole rather than an entity, the Maxwell stress tensor method (MSTM) and virtual work principle method (VWPM), which consider the influence of the shape and size of the TM into account are adopted in this study. Through comparison, it is concluded that the non-uniformities of the internal magnetic field and magnetization intensity of the TM are the reasons for the calculation error of the model, and when the magnetic susceptibility is <1 × 10−2, the model can satisfy the requirement of the calculation accuracy. Finally, two specific signals of the near-interplanetary magnetic field and the magnetic field of a circuit board were measured in a magnetic shielding room (MSR), and the magnetic acceleration noises induced by the two magnetic environments were calculated. These can act as significant reference values for magnetic acceleration noise experiments in orbit and the layout of electronic devices in satellite engineering.

Coordination of Mercury(II) in Water Promoted over Hydrolysis in Solvated Clusters [Hg(H2O)1-6](aq)2+: Insights from Relativistic Effects and Free Energy Analysis.

Understanding the nature of the interaction between mercury(II) ions, Hg2+, and water molecules is crucial to describe the stability and chemical behavior of structures formed during solvation, as well as the conditions that favor the Hg2+ coordination or inducing water hydrolysis. In our study, we explored exhaustively the potential energy surface of Hg2+ with up to six water molecules. We analyzed electronic and Gibbs free energies, binding, and nuclear magnetic resonance parameters. We used the zeroth-order regular approximation Hamiltonian, including scalar and spin-orbit relativistic corrections for free energy calculations and geometry optimizations to explore the interplay between electron correlation and relativistic effects. We analyzed intermolecular interactions with energy decomposition analysis, quantum theory of atoms in molecules, and natural bond orbital. Additionally, we used the four-component Dirac Hamiltonian to compute solvent effect on the magnetic shielding and J-coupling constants. Our results revealed that the water hydrolysis by Hg2+ requires a minimum of three water molecules. We found that the interaction between Hg2+ and water molecules is an orbital interaction due to relativistic effects and the most stable structures are opened-shape clusters, reducing the number of oxygen-mercury contacts and maximizing the formation of hydrogen bonds among water molecules. In these types of clusters, Hg2+ promotes the water hydrolysis over coordination with oxygen atoms. However, when we considered the change associated with the transfer of a cluster from the ideal gas to a solvated system, our solvation free energy analysis revealed that closed-shape clusters are more favorable, maximizing the number of oxygen-mercury contacts and reducing the formation of hydrogen bonds among water molecules. This finding suggests that, under room conditions, the coordination of Hg2+ is more favorable than hydrolysis. Our results have significant implications for understanding Hg2+ behavior in water, helping to develop targeted strategies for mercury remediation and management, and contributing to advancements in the broader field of environmental chemistry.

A combined magnetic field stabilization system for improving the stability of 40Ca+ optical clock

Future applications of portable 40Ca+ optical clocks require reliable magnetic field stabilization to improve frequency stability, which can be achieved by implementing an active and passive magnetic field noise suppression system. On the one hand, we have optimized the magnetic shielding performance of the portable optical clock by reducing its apertures and optimizing its geometry; on the other hand, we have introduced an active magnetic field noise suppression system to further suppress the magnetic field noise experienced by the ions. These efforts reduced the ambient magnetic field noise by about 10000 times, significantly reduced the linewidth of the clock transition spectrum, improved the stability of the portable 40Ca+ optical clock, and created the conditions for using portable optical clocks in non-laboratory magnetic field environments. This active magnetic field suppression scheme has the advantages of simple installation and wide applicability.

The radical pair mechanism of biological effects on hypomagnetic fields and one method to verify it

The biological effects due to a hypomagnetic field (HMF) is a very important subject not only for aerospace traveling and space station living but also for some magnetic shielding conditions on the ground just like the underground bunkers and etc. However, to my knowledge, the mechanisms which can be related to the biological effects of a HMF remain unclear. In this study, I firstly summary one radical pair mechanism of biological effects on a HMF based on present researches, and then propose how to prove the radical pair mechanism’s truth in biological effects on a HMF through experiments. In the way of how to prove the radical pair mechanism’s truth I give the relation between the singlet yield of the radical pair and the angle describing the orientation of a HMF to the basis of the hyperfine tensor related to the electron spin and the nuclei spin is the possible one radical pair mechanism on one hand, and give the crucial method which is through that angle changed causes the biological effects in vivo or vitro to prove or disprove the mechanism on the other hand, because the biological effects of a HMF can be related with that angle, which is very easy to be controlled in experiments.

Electromagnetic shielding properties of LPBF produced Fe2.9wt.%Si alloy

Ferromagnetic materials are used in various applications such as rotating electrical machines, wind turbines, electromagnetic shielding, transformers, and electromagnets. Compared to hard magnetic materials, their hysteresis cycles are featured by low values of coercive magnetic field and high permeability. The application of additive manufacturing to ferromagnetic materials is gaining more and more attraction. Indeed, thanks to a wider geometrical freedom, new topological optimized shapes for stator/rotor shapes can be addressed to enhance electric machines performances. However, the properties of the laser powder bed fusion (LPBF) processed alloy compared to conventionally produced counterpart must be still addressed. Accordingly, this paper presents for the first time the use of the LPBF for the manufacturing of Fe2.9wt.%Si electromagnetic shields. The process parameter selection material microstructure and the magnetic shielding factor are characterized.

LOW COST DOSIMETER MODULE FOR MVA LUNAR LANDER MISSION

Understanding the lunar radiation environment is crucial for future space exploration missions, as the lack of atmospheric and magnetic shielding allows charged particles of varying energies and origins to penetrate the surface of the moon. In space radiation environments, it is common practice to use radiation dosimeters to measure absorbed dose and dose rate. In this study, the payload will include a radiation dosimeter capable of measuring the radiation intensity at the landing site’s surface. The design concept and implementation of a radiation readout system for the real-time measurement of gamma absorbed dose and dose rate at the surface of the landing area for the MVA mission are based on a photodiode sensor that is commercially available and will be used as a gamma radiation sensor. The module experienced low levels of activity (Cs137, Co60, and Sr90). The performance of the photodiode-based module has been demonstrated by the Giger counter. Due to its low cost and high sensitivity, this radiation module would be clearly advantageous.

Continuous dynamical decoupling of optical 171Yb+ qudits with radiofrequency fields

The use of multilevel quantum information carriers, also known as qudits, has attracted significant interest as a way of further scaling quantum computing devices. However, such multilevel systems usually express shorter coherence time than their two-level counterparts, which limits their computational potential. We thus propose and experimentally demonstrate two approaches for realizing the continuous dynamical decoupling of magnetic-sensitive states with mF = ±1 for qudits encoded in optical transition of trapped 171Yb+ ions. We improve the coherence time of qudit levels by an order of magnitude (more than 9 ms) without any magnetic shielding, revealing the potential advantage of the symmetry of the 171Yb+ ion energy structure for counteracting magnetic field noise. Our results are a step toward realizing qudit-based algorithms using trapped ions.