Magnetic Field Disturbances Research Articles

MRI on ion exchange resins at different length scales

AbstractIon exchange resins were studied on different length scales by magnetic resonance imaging (MRI) with the focus on their interactions with nanoparticles (NP) and molecular clusters. On the length scale of resin beds (bed diameters <20 mm), the behavior of NP and of molecular clusters was shown to depend on the kind of ion exchange resin and nanoscale moiety. The kinetics of absorption and penetration into the resin beads was quantified on a smaller length scale of a stack of resin beads (sample with an outer diameter of 1.7 mm). Finally, using an MRI μ‐coil (3D spatial resolution ≥8 μm), adsorption of superparamagnetic NP on individual resin beads was observed via the magnetic field disturbance characteristic for magnetic dipoles. As a result, this allows the detection of NP (diameter ≤100 nm) by MRI on much larger length scales of several micrometers.

Monitoring May 2024 solar and geomagnetic storm using broadband seismometers

The abrupt variations in the magnetic field due to the May 2024 geomagnetic storm have been recorded by broadband seismometers distributed around the world for a time interval of more than 55 h. Signals related to magnetic field variations can be identified in seismic data for frequencies below 10 mHz, but are clearer between 1.5 and 5 mHz, the frequency band corresponding to Pc5 magnetic pulsations. The number of seismological stations that detect these signals varies significantly between the various seismic networks analyzed, but in general they do not exceed 50–60%. The origin of these signals appears to be related to the interaction between telluric currents induced by magnetic field disturbances associated with the geomagnetic storm and the detection systems in broadband sensors, which measure the current intensity necessary to keep the mass of the seismometer fixed. Although detailed calibration of each seismometer will be necessary to use the seismic data to model the waveforms and amplitudes of the magnetic pulsations, the analysis of this data provides a significant densification with respect to the magnetic observatory data, as is of interest to analyze the temporal and regional evolution of the magnetics disturbances associated to the May 2024 solar storm.

Strong turbulence and magnetic coherent structures in the interstellar medium

Magnetic turbulence is classified as weak or strong based on the relative amplitude of the magnetic field fluctuations compared to the mean field. These two classes have different energy transport properties. The purpose of this study is to analyze turbulence in the interstellar medium (ISM) based on this classification. Specifically, we examined the ISM of simulated galaxies to detect evidence of strong magnetic turbulence and provide statistics on the associated magnetic coherent structures (MCoSs), such as current sheets, that arise in this context. We analyzed magnetohydrodynamic galaxy simulations with different initial magnetic field structures (either completely ordered or completely random) and recorded statistics on the magnetic field fluctuations ($ B/B_0$) and the MCoSs, which are defined here as regions where the current density surpasses a certain threshold. We also studied the MCoS sizes and kinematics. The magnetic field disturbances in both models follow a log-normal distribution, peaking at values close to unity; this distribution turns into a power law at large values ($ B/B_0 > 1$), which is consistent with strong magnetic turbulence The current densities are widely distributed, with non-power-law deviations from a log-normal at the largest values. These deviating values of the current density define MCoSs. We find that, in both models, MCoSs are fractally distributed in space, with a typical volume-filling factor of about 10 percent, and tend to coincide with peaks of star formation density. Their fractal dimension is close to unity on sub-kiloparsec scales, and between 2 and 3 on larger scales. These values are consistent with MCoSs having a sheet-like or filament-like morphology. Our work challenges the prevailing paradigm of weak magnetic turbulence in the ISM by demonstrating that strong magnetic disturbances can occur even when the initial magnetic field is completely ordered. This strong magnetic turbulence arises self-consistently from differential rotation and supernova feedback. Our findings provide a foundation for a magnetic turbulence description of the galactic ISM that includes strong fluctuations of the magnetic field.

Geomagnetic and ionospheric effects two consecutive strong earthquakes in Morocco on september 08, 2023

The geophysical effects of a strong seismic event in the form of two earthquakes of magnitude 6.8 and 4.9 that occurred on September 08, 2023 in Morocco at close times 22:11 and 22:30 UTC with an epicentral distance between the foci of ~ 4 km are considered. We used data from a number of observatories of the INTERMAGNET network and the results of magnetic registration at the Mikhnevo Geophysical Observatory of IDG RAS. It was shown that in the absence of significant global disturbances of the Earth’s magnetic field, earthquakes were accompanied by a series of three positive bay-shaped geomagnetic variations with maximum amplitudes from ~1 to ~10 nT, following each other after ~60 min. The maxima of the induced magnetic field variations were observed almost synchronously at distances from ~800 to ~10000 km. The delay time of the magnetic effect relative to the main shock of the first earthquake was ~70 min. Taking into account the almost planetary nature and high synchronicity of the magnetic field disturbances caused over a significant range of distances, as well as time delays corresponding in order of magnitude to the travel time of the seismic signal of a distance multiple of the size of the Earth, it is suggested that the magnetic effect of the seismic event in question was caused by a global source, which can serve as an excited geodynamo. The ionospheric effect of the seismic event under consideration is presented in the form of variations of the critical frequency f0F2 calculated from the data of the ground-based sounding station of the del Ebre Observatory.

Zastosowanie Metody Elementów Skończonych do analizy metody określania rozmiaru buta na podstawie pomiarów pola magnetycznego

Paper presents utilization of Finite Element Method (FEM) for analysis of usefulness of shoe size assessment method, based on magnetovision measurements. Measurement method based on disturbances of the uniform magnetic field (e.g. Earth’s magnetic field) is presented. Disturbances are caused by loose material of high magnetic permeability placed inside the tested shoe, which adapts to the insides of the shoe. The disturbed magnetic field is measured by the matrix of magnetometers. The values of magnetic field are an input into inverse transformation algorithm which fits the position of matrix sensors into the reference (obtained by FEM) distribution of magnetic field. Based on the fitted parameters of sensors matrix a ratio between the measured and reference shoe size was determined. A FEM-based forward transformation is presented, which allows for generation of three-dimensional array of magnetic field distribution. Initial tests of inverse transformation were conducted successfully. Next steps consisted of tests of inverse transformation method with an inclusion of the typical measurement noise. A FEM-based forward transformation was conducted of a modified shoe model (including simplified screw model). Inverse transformation was conducted but both influence of measurement noise, as well as the presence of additional high permeability material, resulted that the presented shoe size assessment method is not suitable for practical implementation.

Near-zero magnetic field disturbance suppression method based on adaptive filtering and quasi-proportional resonance control

The cardiac magnetic field used for magnetocardiographic (MCG) imaging must be detected in a stable near-zero magnetic field environment. In the hospital environment, there are mainly two kinds of magnetic field disturbances that affect the signal-to-noise ratio of cardiac magnetic field detection. One is the magnetic field disturbance with high power spectral density at a specific frequency, and the other is the random magnetic field disturbance with low frequency. To suppress magnetic field disturbances, this paper proposed a near-zero magnetic field disturbance suppression method that combined a PI controller with adaptive filtering and quasi-proportional resonance control (PI-APF-QPR). The magnetic field disturbance with high amplitude and specific frequency was extracted by the adaptive filter (APF) and suppressed by the quasi-proportional resonance (QPR) controller. Additionally, the low-frequency random disturbance was suppressed by the PI controller. The experimental results showed that compared with the PI controller, the peak-to-peak value of the magnetic field by the PI-APF-QPR controller was reduced by 39.1%, and the suppression ratio of the magnetic field noise by the PI-APF-QPR controller was improved by 29.5%, which verified the effectiveness of the proposed magnetic field disturbance suppression method.

How the Ionosphere Responds Dynamically to Magnetospheric Forcing

AbstractGround magnetic field variations have been used to investigate ionospheric dynamics for more than a century. They are usually explained in terms of an electric circuit in the ionosphere driven by an electric field, but this is insufficient to explain how magnetic field disturbances are dynamically established. Here we explain and simulate how the ionosphere dynamically responds to magnetospheric forcing and how it leads to magnetic field deformation via Faraday's law. Our approach underscores the causal relationships, treating the magnetic field and velocity as primary variables (the B, v paradigm), whereas the electric field and current are derived, in contrast to the E, j paradigm commonly used in ionospheric physics. The simulation approach presented here could be used as an alternative to existing circuit‐based numerical models of magnetosphere‐ionosphere coupling.

A novel sensor based on the composite mechanism of magnetic flux leakage and magnetic field disturbance for comprehensive inspection of defects with varying angles and widths

Ferromagnetic components are susceptible to various defects after prolonged service. The defects generated in these components are diverse and exhibit irregular orientation, which may impede comprehensive defect examination using a single magnetic testing method. This paper proposes a novel magnetic measurement sensor that integrates the principles of magnetic flux leakage (MFL) and magnetic field disturbance (MFD). The combined theory is analyzed and validated through the utilization of finite element method (FEM) simulations as well as experimental investigations. By comparing simulation results with experimental data, the composite nature of the signal acquired beneath a magnetic bridge is convincingly demonstrated. In comparison to conventional MFL and MFD methods, this innovative sensor exhibits superior defect detection performance for varying angles and widths, while also addressing some inherent limitations associated with MFL and MFD principles.

An optically pumped magnetic gradiometer for the detection of human biomagnetism

We realise an intrinsic optically pumped magnetic gradiometer based on non-linear magneto-optical rotation. We show that our sensor can reach a gradiometric sensitivity of 18 fT cm−1Hz−1 and can reject common mode homogeneous magnetic field noise with up to 30 dB attenuation. We demonstrate that our magnetic field gradiometer is sufficiently sensitive and resilient to be employed in biomagnetic applications. In particular, we are able to record the auditory evoked response of the human brain, and to perform real-time magnetocardiography in the presence of external magnetic field disturbances. Our gradiometer provides complementary capabilities in human biomagnetic sensing to optically pumped magnetometers, and opens new avenues in the detection of human biomagnetism.

Statistical Analysis of Low‐Latitude Boundary of Polar‐Type Medium‐Scale Traveling Ionospheric Disturbances Observed by a 630‐nm Airglow Imager at Nyrölä, Finland

AbstractMedium‐scale traveling ionospheric disturbances (MSTIDs) are one of the ionospheric plasma density structures and are observable through 630‐nm airglow images. Previous studies using airglow images at Tromsø (69.6°N, 19.2°E; magnetic latitude: 66.7°N), Norway, reported high‐latitude MSTIDs (here we call them as polar‐type MSTIDs) whose propagation direction changes associated with auroral brightening and magnetic field disturbances. However, there has been little statistical analysis on the connection of MSTIDs occurring at high and middle latitudes. In this study, we statistically analyzed the MSTIDs observed by an airglow imager at Nyrölä (62.3°N, 25.5°E; magnetic latitude: 59.4°N), Finland, which is located ∼7° south of Tromsø, corresponding to subauroral latitudes. The period analyzed was from 23 January 2017, to 30 September 2021. We found 11 cases of MSTIDs during this period. Eight cases were found to be the polar‐type MSTIDs whose motion changes associated with auroral brightening and magnetic field disturbances. We found that 9 cases of MSTID show the low‐latitude boundary at 61° ± 2°N for geographic latitude and 58° ± 2°N for magnetic latitude, indicating disconnection between high‐ and mid‐latitude MSTIDs. We also derived occurrence probability, velocity, wavelength, period, wave front direction, and propagation direction of these MSTIDs. The occurrence probability of MSTIDs at Nyrölä is 1.9%, which is much lower than those at high (Tromsoe, more than 50%) and middle (Japan, ∼30%) latitudes. We discuss these MSTID characteristics at subauroral latitudes based on possible difference of generation mechanisms of nighttime MSTIDs at high and middle latitudes.

Numerical Simulation for Solitary Waves of the Generalized Zakharov Equation Based on the Lattice Boltzmann Method

The generalized Zakharov equation is a widely used and crucial model in plasma physics, which helps to understand wave particle interactions and nonlinear wave propagation in plasma. The solitary wave solution of this equation provides insights into phenomena such as electron and ion acoustic waves, as well as magnetic field disturbances in plasma. The numerical simulation of solitary wave solutions to the generalized Zakharov equation is an interesting problem worth studying. This is crucial for plasma-based technology, as well as for understanding nonlinear wave propagation in plasma physics and other fields. In this study, a numerical investigation of the generalized Zakharov equation using the lattice Boltzmann method has been conducted. The lattice Boltzmann method is a new modeling and simulating method at the mesoscale. A lattice Boltzmann model was constructed by performing Taylor expansion, Chapman–Enskog expansion, and time multiscale expansion on the lattice Boltzmann equation. By defining the moments of the equilibrium distribution function appropriately, the macroscopic equation can be restored. Furthermore, the numerical experiments for the equation are carried out with the parameter lattice size m=100, time step Δt=0.001, and space step size Δx=0.4. The solitary wave solution of the equation is numerically simulated. Numerical results under different parameter values are compared, and the convergence and effectiveness of the model are numerically verified. It is obtained that the model is convergent in time and space, and the convergence orders are all 2.24881. The effectiveness of our model was also verified by comparing the numerical results of different numerical methods. The lattice Boltzmann method demonstrates advantages in both accuracy and CPU time. The results indicate that the lattice Boltzmann method is a good tool for computing the generalized Zakharov equation.

An Inertia-Based Upper Limb Motion Capture Model for Accurate Position Estimation in Magnetic Field Disturbances

An Inertia-Based Upper Limb Motion Capture Model for Accurate Position Estimation in Magnetic Field Disturbances

Occurrence Probability of Magnetic Field Disturbances Measured With Swarm: Mapping the Dynamic Magnetosphere‐Ionosphere Coupling

AbstractThe exchange of kinetic and electromagnetic energy by precipitation and/or outflow and through field‐aligned currents are two aspects of the ionosphere‐magnetosphere coupling. A thorough investigation of these processes is required to better understand magnetospheric dynamics. Building on our previous study using the Defense Meteorological Satellite Program spectrometer data, here we use Swarm vector field magnetometer data to describe the auroral zone morphology in terms of east‐west magnetic field perturbations. We define a threshold for detecting magnetic fluctuations based on the power spectral density of ΔBEW, and derive the disturbed magnetic field occurrence probability (dBOP) at low [0.1–1 Hz] and high [2.5–5 Hz] frequencies. High‐frequency distributions of dBOP reveal a dayside‐nightside asymmetry, whereas low‐frequency dBOP exhibits a persistent morphological asymmetry between the dawn‐to‐noon and the dusk‐to‐midnight sectors, peaking at dawn. Notably, weak solar wind conditions are associated with an increase in the dBOP asymmetric patterns. At low frequency in particular, while the dBOP seems to be primarily constant at dawn, the dusk dBOP decreases during quiet times, inducing a relatively larger dawn‐dusk asymmetry in such conditions. Furthermore, based on a comparison analysis between low‐frequency dBOP and auroral electron precipitation occurrence probability, we suggest that both types of distribution offer a more comprehensive understanding of the large‐scale auroral zone when considered concurrently. Our interpretation is that the dBOP at low frequencies reflects a quasi‐steady state circulation of energy, while the high‐frequency dBOP reflects the regions of rapid changes in the magnetosphere. The dBOP is therefore a crucial source of information regarding the magnetosphere‐ionosphere coupling.

Changes in the energy density of the Earth's magnetic field at the PIA, Slovenia, observatory during the G5 Geomagnetic Storm on May 11, 2024

Geomagnetic storms are the largest disturbance in the Earth's magnetic field. On May 11, 2024, a geomagnetic storm occurred at the peak of the 25th solar cycle, reaching the highest level (G5) on the planetary scale. On that day, a geomagnetic storm was also measured at the PIA geomagnetic observatory (Piran, Slovenia), reaching the maximum possible value of the geomagnetic index K = 9. Such strong geomagnetic storms occur on average every 40 to 60 years. A geomagnetic storm with an index of K = 9 represents an important reference for all disturbances in the local magnetic field from different sources and different intensities. Therefore, an analysis of accelerations in the energy density of the local magnetic field during the first 150 days in 2024 was made. The identified effects of geomagnetic storms with different K indices will serve to better analyse disturbances in the local magnetic field that have occurred in the past years and will happen in the future.

Magnetic phase transition regulated by an interface coupling effect in CrBr3/electride Ca2N van der Waals heterostructures.

Compared with ferromagnetic (FM) materials, antiferromagnetic (AFM) materials have the advantages of not generating stray fields, resisting magnetic field disturbances, and displaying ultrafast dynamics and are thus considered as ideal candidate materials for next-generation high-speed and high-density magnetic storage. In this study, a new AFM device was constructed based on density functional theory calculations through the formation of a CrBr3/Ca2N van der Waals heterostructure. The FM ground state in CrBr3 undergoes an AFM transition when combining with the electride Ca2N. In such a system, since the metal Ca atoms form the exposed layer in the electride, the heterostructure interface has a high binding energy and a large amount of charge transfer. However, for individual electron doping, the FM ground state in the CrBr3 monolayer is robust. Therefore, the main factor in magnetic phase transition is the interface orbital coupling caused by the strong binding energy. Furthermore, the interface coupling effect was revealed to be a competition between direct exchange and superexchange interactions. Additionally, different pathways of orbital hybridization cause a transition of the magnetic anisotropy from out-of-plane to in-plane. This work not only provides a feasible strategy for changing the ground state of magnetic materials on electride substrates but also brings about more possibilities for the construction and advancement of new AFM devices.

Electromagnetic image recognition of a defect profile on a metal surface with a protective layer based on magnetic disturbance

In order to obtain defect information quickly and effectively and improve the accuracy and evaluation ability of traditional electromagnetic non-destructive testing (NDT), an electromagnetic image recognition method for the defect profile based on magnetic field disturbance is proposed in this paper. The excitation coil structure is designed, the excitation mode of the signal source is optimised and a three-dimensional electromagnetic transient analysis model is established for defect profile identification of a metal surface with an anti-corrosion protective layer. The research shows that the disturbed magnetic field Bz has the characteristics of high-resolution imaging and symmetry. The orientation of the defect on the surface has different effects on the clarity of image recognition. The larger the angle between the defect boundary and the induced current, the more complete and clear the image formed by the disturbed magnetic field Bz . A rectangular square wave is the best excitation signal for defect recognition. Its Bz image at t = 0 can present complete shape and position information about the defect. In addition, the excitation coil structure based on the principle of the disturbed magnetic field must provide a uniform induced current to produce a pronounced disturbed magnetic field. It is concluded that electromagnetic imaging technology based on the disturbed magnetic field Bz can better detect and characterise the shape of metal surface defects without damaging the metal protective layer and has good application potential for NDT and safety evaluation of in-service equipment.

Highly collisional regions determined by interplanetary magnetic field structures

Abstract Submicron debris released in interplanetary collisions gets charged in the solar wind and generates disturbances to the magnetic field environment. The unique magnetic field disturbances, named interplanetary field enhancements (IFEs) are recorded by many spacecraft. In this study, we have developed a novel model to trace the IFEs to their origins. By employing this model, we can pinout regions with highly collision frequencies, thereby identifying regions of intense collisional activity. The model can help constrain interplanetary magnetic disturbances and our results can be used to guide part of the interplanetary-object survey.

A mechanistic computational framework to investigate the hemodynamic fingerprint of the blood oxygenation level-dependent signal.

Blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) is one of the most used imaging techniques to map brain activity or to obtain clinical information about human cortical vasculature, in both healthy and disease conditions. Nevertheless, BOLD fMRI is an indirect measurement of brain functioning triggered by neurovascular coupling. The origin of the BOLD signal is quite complex, and the signal formation thus depends, among other factors, on the topology of the cortical vasculature and the associated hemodynamic changes. To understand the hemodynamic evolution of the BOLD signal response in humans, it is beneficial to have a computational framework available that virtually resembles the human cortical vasculature, and simulates hemodynamic changes and corresponding MRI signal changes via interactions of intrinsic biophysical and magnetic properties of the tissues. To this end, we have developed a mechanistic computational framework that simulates the hemodynamic fingerprint of the BOLD signal based on a statistically defined, three-dimensional, vascular model that approaches the human cortical vascular architecture. The microvasculature is approximated through a Voronoi tessellation method and the macrovasculature is adapted from two-photon microscopy mice data. Using this computational framework, we simulated hemodynamic changes-cerebral blood flow, cerebral blood volume, and blood oxygen saturation-induced by virtual arterial dilation. Then we computed local magnetic field disturbances generated by the vascular topology and the corresponding blood oxygen saturation changes. This mechanistic computational framework also considers the intrinsic biophysical and magnetic properties of nearby tissue, such as water diffusion and relaxation properties, resulting in a dynamic BOLD signal response. The proposed mechanistic computational framework provides an integrated biophysical model that can offer better insights regarding the spatial and temporal properties of the BOLD signal changes.

Investigation of the aberrant record from bus GPS receiver onboard FORMOSAT-7/COSMIC-2 satellite constellation in low Earth orbit

The FORMOSAT-7/COSMIC-2 (F7/C2) satellite constellation, a joint Taiwan-US collaboration mission, was launched on 25 June 2019. Following the FORMOSAT-3/COSMIC, the F7/C2 mission aims to provide global users the next-generation global navigation satellite system (GNSS) radio occultation data. The mission consists of six identical small satellites with an inclination angle of 24°, launched to the parking orbit of 720 km, and then transferred to the mission orbit of 550 km. Each satellite bus is equipped with two commercial off-the-shelf global positioning system receivers manufactured by Surrey Satellite Technology Ltd. for positioning, navigation, and timing functions. This receiver generates “GPS Receiver (bus GPSR) Warm Start Requested (WSR)” messages after commissioning, which could be considered as a kind of single event effect (SEE). More than 7000 WSR events have been recorded in 3 years after launch, providing another opportunity to investigate the SEE with the commercial off-the-shelf bus GPSR. In addition, the F7/C2 mission is the first satellite constellation that allows scientists to investigate the SEE using the same constellation at different altitudes of Low-Earth orbit. This study investigates and discusses the cumulative rate, distribution of WSRs, and their relationships between altitude and geomagnetic field. The statistical method is applied to define a warning area of the high probability occurring the SEE of this kind of component based on the geomagnetic field, whose corresponding strength is around 21,200/20,550 nT and close to the South Atlantic Anomaly area. Moreover, the relationships with space weather, including the disturbance of the Earth's magnetic field (Kp index) and the solar activity (F10.7 index), are also analyzed and reported.

Large-scale structures in the stellar wind of fast-rotating stars spawned by the presence of Earth-like planets

ABSTRACT Forming planets around young, fast-rotating solar-like stars are exposed to an intense X-ray/extreme ultraviolet radiation field and strongly magnetized stellar winds, as a consequence of the high magnetic activity of these stars. Under these conditions, Earth-like exoplanets may experience a rapid loss of their primordial hydrogen atmospheres, resulting in atmosphereless rocky obstacles for the stellar winds. The interaction of stellar winds with those planets leads to the formation of potentially observable structures due to the formation of large-scale magnetic field and density disturbances in the vicinity of these planets, such as bow shocks, induced magnetospheres, and comet-like tails. In this work, we study the interaction between the stellar winds of active, fast-rotating solar-like stars in the superfast-magnetosonic regime with Earth-like, unmagnetized, tenuous atmosphere, planetary obstacles through numerical three-dimensional simulations using the pluto magnetohydrodynamical code. The properties of AB Doradus, a nearby young star with a small rotation period (0.51 d) and a strong flaring activity, have been used to parametrize this early wind state. Bow shock and induced magnetosphere formation are characterized through the Alfvénic Mach number MA of the wind, for different stellar wind configurations. Large bow shocks, up to an extension of ∼7.0 planetary radii, are found for low-MA winds. The general increase of density, temperature, and magnetic field in these large-scale structures formed around planets may result in potentially detectable spectral signatures.