Magnitude Of Magnetic Field Research Articles

Electron Rolling-pin Distribution Inside Magnetic Hole

Abstract Magnetic holes (MHs), characterized by depressions in the magnetic field magnitude, are transient magnetic structures ubiquitous in space plasmas. The electron pitch-angle distribution inside the MHs is key to diagnosing the MH properties and has been suggested to mainly exhibit a pancake-type distribution showing pitch angles near 90°. Here, we present the first observation of electron rolling-pin distribution—showing electron pitch angles mainly at 0°, 90°, and 180°—within an electron-scale MH, by using Magnetospheric Multiscale mission high-resolution measurements. With a second-order Taylor expansion method, the magnetic field topology of the MH is reconstructed, and the characteristics of the rolling-pin distribution inside the MH are investigated. We find that the rolling-pin distribution primarily appears near the MH center and at energies ranging from 110 to 1200 eV. We interpret the rolling-pin formation as a consequence of the combination of local-scale electron trapping and global-scale Fermi acceleration. These results can improve current understanding of electron dynamics in the MHs.

Magnetoplasmon-Polaritons in a Two-Dimensional Electron System with a Back Gate

Magnetoplasmon-polariton excitations in a two-dimensional (2D) electron system with a back gate are theoretically studied. The back gate is a metal layer that is parallel to the layer of 2D electrons and is separated from them by a dielectric substrate serving as a waveguide. In the absence of a magnetic field, the interaction of 2D plasmons with the modes of the waveguide limited by the gate from one side results in the formation of a family of waveguide plasmon-polariton modes. The two lowest of these modes are TM modes and have a gapless dispersion relation. As known, a static magnetic field B perpendicular to the plane of the system hybridizes different modes. The spectra and magnetodispersion of the found 2D modes are determined. The classification of all modes as longitudinal and transverse (ТМ–ТЕ classification), which is usually valid only in the absence of B, is recovered in the limit of high fields B. The magnetic field dependence of the cutoff frequencies of the considered modes significantly affects the results. Even a low magnetic field opens a frequency gap proportional to the magnetic field magnitude B in the spectrum of one of the lowest magnetoplasmon-polariton modes. As the magnetic field increases, the gap is saturated and the mode becomes waveguide.

Spectral Properties of the N Component of the Heliospheric Magnetic Field from IMP and ACE Observations for 1973–2020

Abstract We analyze the normal (N) component of the heliospheric magnetic field observed by the Interplanetary Monitoring Platform and the Advanced Composition Explorer spacecraft for the period 1973–2020. Parameters characterizing the frequency spectrum are calculated with a novel technique, which is based on calculating variances at incremental lags to yield the integral of a turbulence spectrum. We compare this technique with the standard second-order structure function to show their similarity in the inertial range, and use the latter to calculate correlation functions. We find that the yearly average for magnetic field magnitude and the variance attained their lowest values since spacecraft observations began for the period that includes the 2020 solar minimum, 4.2 nT and 3.3 nT2, respectively. The ratio of the magnitude of fluctuations of the N component to the field magnitude shows little variation, with an average value of 0.43 ± 0.04. The average value of the spectral index of the energy range for the whole data set is −1.0 ± 0.1, and shows some solar-cycle dependence. The average value for the inertial range is an almost constant −1.69 ± 0.04. While the break between the energy and the inertial range is difficult to determine accurately to search for a solar-cycle dependence, an indirect indication of such a dependence follows when the ratio of spectral levels in the energy and in the inertial range is calculated. The e-folding correlation length has an average value of 1.1 ± 0.3 Mkm, with a clear solar-cycle dependence.

Mechanical frequency control in inductively coupled electromechanical systems

Nano-electromechanical systems implement the opto-mechanical interaction combining electromagnetic circuits and mechanical elements. We investigate an inductively coupled nano-electromechanical system, where a superconducting quantum interference device (SQUID) realizes the coupling. We show that the resonance frequency of the mechanically compliant string embedded into the SQUID loop can be controlled in two different ways: (1) the bias magnetic flux applied perpendicular to the SQUID loop, (2) the magnitude of the in-plane bias magnetic field contributing to the nano-electromechanical coupling. These findings are quantitatively explained by the inductive interaction contributing to the effective spring constant of the mechanical resonator. In addition, we observe a residual field dependent shift of the mechanical resonance frequency, which we attribute to the finite flux pinning of vortices trapped in the magnetic field biased nanostring.

Temperature-dependent dynamic properties of magnetorheological gel composite: experiment and modeling

Of all the smart materials that can vary with a change in external excitation, magnetorheological gel (MRG) is one of the most pre-eminent composites, having controllable and reversible responses according to the magnitude of the external magnetic field. Temperature has been identified as another important driver that can alter the dynamic properties of a MRG, and so far this has not been studied systematically. The temperature-dependent dynamic properties of a MRG under different magnetic field strengths were investigated by three kinds of experiments—strain amplitude, frequency and magnetic field sweep tests. The experimental results demonstrate that the storage and loss moduli of MRGs display a temperature-induced stiffening effect with a magnetic field but a temperature-induced softening effect in the absence of a magnetic field. The storage modulus improves with magnetic field strength, whereas the loss modulus first shows rapid growth and then a gradual reduction with increasing magnetic field strength. This temperature dependence of dynamic properties is also interpreted through different mechanisms related to the transformation of the MRG microstructure. Furthermore, a modified magnetic dipole model which could predict the relationship between storage modulus and magnetic field strength is combined with the classical Arrhenius equation expressing the effect of temperature on viscosity to describe the temperature dependence of the storage modulus of a MRG under different magnetic field strengths. This paper may provide some useful guidance for designing a magnetorheological device.

Experimental and numerical analysis of vibration-based hybrid energy harvesting from non-classical beam structures

It is known that the displacement and stress on beams will directly affect the energy harvesting performance. For this purpose, structural changes are made on the beam elements. Behaviours of these beam structures are investigated by designing different non-classical beam geometries. This study examines vibration-based electromagnetic and piezoelectric energy harvesting from the non-classical beam structures under various conditions. Before analysing the non-classical beam structure, studies are performed for a classical beam for electromagnetic and piezoelectric energy harvesting studies. In the electromagnetic energy harvesting analysis, the effects of magnitude of magnetic field and the distance between the coil and the permanent magnet on the harvesting performance are studied by free vibration experiments. In this regard, a neodymium permanent magnet is attached to the vibrating aluminium beam endpoint. During the free vibration period, the coil and the magnet interact closely. As a result, a voltage output is obtained by inducing an electric field on the coil side. Secondly, voltage outputs of piezoelectric energy harvesting structures are experimentally evaluated for a classical beam and used for the verification of numerical simulations. Using the verified numerical simulations, new types of beam structures so-called non-classical beams are designed to obtain higher voltage outputs. Finally, by introducing the phenomenon of continuous vibration with the effect of air, the hybrid energy performance is analyzed for the proposed structure. The continuous vibration is created by the air-flow on the square galloping geometry.

Graphene-Based Plasmonic Sensor at THz Frequency with Photonic Spin Hall Effect Assisted by Magneto-optic Phenomenon.

Graphene monolayer of sub-nanometer thickness shows strong metallic and plasmonic behavior in terahertz (THz) frequency range. This plasmonic effect varies considerably when graphene layer is placed under a magnetic field of appropriate strength. The strong adsorption characteristic of graphene layer is another advantage. In this work, a photonic spin Hall effect (PSHE)-based plasmonic sensor consisting of germanium prism, organic dielectric layer, and graphene monolayer is simulated and analyzed in THz aiming at highly sensitive and reliable sensing under variable magnetic field. Modified Otto configuration and magneto-optic effect in graphene are considered. The sensor’s performance is examined in terms of sensitivity, limit of detection (LOD), and figure of merit (FOM). The analysis indicates that LOD of the order of 10−5 RIU for gas sensing is achievable, which is finer than recently reported gas sensors based on different techniques. Further, the FOM improves when a larger magnitude of magnetic field is applied. The FOM is even greater for rarer gaseous media, which can make the sensor extremely useful in early detection of airborne viruses such as SARS-Cov-2 (while using appropriate specificity method) and to measure the concentration of a particular gas in a given gaseous mixture. The results further indicate that the same sensor design can be used for magnetic field detection while the FOM of magnetic field detection is significantly greater for rarer gaseous medium (e.g., air), which may enable the probe to be used in early detection of radiation leakage in nuclear reactors. For larger magnitudes of magnetic field, the corresponding LOD becomes finer.

Viscous flow of two-component electron fluid in magnetic field

In pure conductors with a low density of defects, frequent electron-electron collisions can lead to the formation of a viscous fluid consisting of conduction electrons. In this work, is studied magnetotransport in a viscous fluid consisting of two types of electrons, for which some of their parameters are different. The difference between such system and the one-component electron fluid is as follows. The scattering of electrons with their transitions from one component to another can lead to an imbalance in flows and concentrations, which affects the flow as a whole. In this work, the balance transport equations for such a system are constructed and solved for the case of a long sample with rough edges. The equation for the flow of the unbalance value towards the edges contains the bulk viscosity term. It is shown that in sufficiently wide samples, the transformation of particles into each other during scattering leads to the formation of a single viscous fluid flowing as a whole, while in narrow samples the two components flow as two independent fluids. The width of the sample at which this transition occurs is determined by the internal parameters of the fluid and the magnitude of magnetic field. The distributions of the flow of the fluid components over a sample cross section and the magnetoresistance of a sample are calculated. The latter turns out to be positive and saturating, corresponding to the transition with increasing of magnetic field from independent Poiseuille flows of the two components to the Poiseuille flow of a uniform fluid. Keywords: electron fluid, viscosity, two-component system, nanostructures, magnetoresistance.

Вязкое течение двухкомпонентной электронной жидкости в магнитном поле

Viscous flow of two-component electron fluid in a magnetic field P. S. Alekseev Ioffe Institute, Politekhnicheskaya 26, 194021, St. Petersburg, Russia Abstract In pure conductors with a low density of defects, frequent electron-electron collisions can lead to the formation of a viscous fluid consisting of conduction electrons. In this work, is studied magnetotransport in a viscous fluid consisting of two types of electrons, for which some of their parameters are different. The difference between such system and the one-component electron fluid is as follows. The scattering of electrons with their transitions from one component to another can lead to an imbalance in flows and concentrations, which affects the flow as a whole. In this work, the balance transport equations for such a system are constructed and solved for the case of a long sample with rough edges. The equation for the flow of the unbalance value towards the edges contains the bulk viscosity term. It is shown that in sufficiently wide samples, the transformation of particles into each other during scattering leads to the formation of a single viscous fluid flowing as a whole, while in narrow samples the two components flow as two independent fluids. The width of the sample at which this transition occurs is determined by the internal parameters of the fluid and the magnitude of magnetic field. The distributions of the flow of the fluid components over a sample cross section and the magnetoresistance of a sample are calculated. The latter turns out to be positive and saturating, corresponding to the transition with increasing of magnetic field from independent Poiseuille flows of the two components to the Poiseuille flow of a uniform fluid.

Electromagnetic Non-Contacting Position Estimation of a Centimetre-Scale Robot

This paper develops an electromagnet-based position estimation system for a cm-scale robot with two degrees of freedom. The orientation of an external electromagnet is actively controlled in realtime to maximize the magnetic field magnitude at the robot. This results in a monotonic relationship between the magnetic field magnitude and radial distance leading to a simple and robust position estimation system. The radial distance is then estimated using an asymptotically stable nonlinear observer designed using a linear matrix inequality. The analytical principles of the estimation system are first presented using key technical lemmas and proofs. Experimental results are then presented on the verification of the analytical principles and on the performance of the position estimation system.

Влияние упругих деформаций на спектр дипольных спиновых волн в латеральной системе магнонных кристаллов с пьезоэлектрическим слоем

In this work, we will reveal the regularities in the control of the dipole spin-wava spectra of in lateral heterostructures formed from two magnonic crystals with a piezoelectric layer placed on one of them. The electric field control of the spatial and transfer characteristics of dipole spin waves in lateral heterostructures is shown. Based on the finite element method, the influence of distributed elastic deformations on the magnitudes of internal magnetic fields in magnonic crystals is evaluated. Based on the results of numerical simulations, a physical interpretation of the transformation of the eigenmode spectrum of coupled magnon crystals is given.

Influence of elastic strains on the dipole spin wave spectrum in the lateral system of magnonic crystals with a piezoelectric layer

In this work, we will reveal the regularities in the control of the dipole spin-wava spectra of in lateral heterostructures formed from two magnonic crystals with a piezoelectric layer placed on one of them. The electric field control of the spatial and transfer characteristics of dipole spin waves in lateral heterostructures is shown. Based on the finite element method, the influence of distributed elastic deformations on the magnitudes of internal magnetic fields in magnonic crystals is evaluated. Based on the results of numerical simulations, a physical interpretation of the transformation of the eigenmode spectrum of coupled magnon crystals is given. Keywords: spin waves, magnonics, straintronics, lateral structures.

Surface Magnetic-Field Enhancement Technology With a Double-Polarization Coil for Urban Hydrology Quantitative Survey

Electromagnetic geophysical methods are widely applied in urban shallow exploration, considering their convenience and noninvasiveness. As one of the emerging techniques, polarizing surface nuclear magnetic resonance (SNMR) shows significant potential for water-based target detections. However, problems involving weak signal response and strong noise interference are challenging to avoid. Therefore, numerous studies focused on suppressing the electromagnetic interference and improving the effective electromagnetic control accuracy to achieve high-precision shallow imaging. On this basis, we proposed a new magnetic-field enhancement technology that explored double-polarization coils, instead of the single loop, to improve the applications of polarizing SNMR. By controlling the current for double-polarization coils, the magnetic field, which is twice as strong as the single coil, could be provided. As a result, the sensitivities and signal responses for subsurface detection sensitive areas with the same power consumption were further enhanced. Considering the SNMR research, we also identified that this new configuration with double-polarization coil can effectively improve the resolution of the shallow depth because it compensates for the magnitude of the static magnetic field in the center. Based on the theoretical analysis, we developed the instrument and, for the first time, realized the accurate interpretation of the real ground soil in an urban environment, verifying the effectiveness of the proposed configuration and the reliability of the system.

Magnetic Field-Responsive Pulsatile Drug Release Using A Magnetic Fluid.

Ferrofluids are colloidal liquids with fine magnetic particles. They change shape and fluidity depending on the magnitude and direction of the external magnetic field. The magnetic field-responsive pulsatile release of a model drug, lidocaine hydrochloride (LID·HCl), was determined using a depot-type injection containing white petrolatum and/or hydrophilic cream with a magnetic fluid in various proportions. Drug release was confirmed using a self-made diffusion cell and the application of a moving magnet at the bottom of the preparation. Magnetic field-responsive LID release was observed only when using the white petrolatum preparation and depended on the concentration of the magnetic fluid. Magnetic field responsiveness was not observed in the preparation with only the hydrophilic cream. A greater magnetic field-responsive release was observed with a combination of white petrolatum and hydrophilic cream than with white petrolatum alone. These results may lead to the development of an injectable formulation that enables pulsatile administration of macromolecular drugs.

Intermittent Magnetic Field Monitoring System Based on Passive RFID Sensor Tags

The monitoring of magnetic fields is extremely important in many industrial environments, e.g., power grids. Despite of its importance, the existing monitoring methods either are large in size, require high power consumptions and manual observation, or although integrated in small wireless devices, need the use of batteries, increasing maintenance costs. This paper proposes an intermittent magnetic field monitoring system based on passive ultra-high frequency (UHF) radio frequency identification (RFID) technology. A magnetic field magnitude sensor has been integrated into a micro-controller unit (MCU) based tag, and the standard RFID communication protocol ISO/IEC 18000-6 Type C has been partially modified to allow faster sensed data transfer, especially for multiple tag situations rarely considered in the open literature. Static or 50 Hz magnetic field sensing accuracy lower than 3% have been experimentally measured with reasonable tag charging times and read distances, making possible for example to monitor magnetic fields on more than 10 locations simultaneously with a 60 s of updating time with a tag read range of 3 m.

Influence of Anisotropy on Thermosolutal Convection in Porous Media with Magnetic Field Effect

In the present study, both anisotropy and magnetic field effects on bi-diffusive natural convection in a rectangular cavity filled with a porous medium saturated by a binary fluid are investigated analytically for fully developed flow regime. The cavity is heated isothermally by the sides and its horizontal walls are thermally insulated or conducted. The porous medium is anisotropic in permeability whose principal axes are oriented in a direction that is arbitrary to the gravity field. On the basis of the generalized Brinkman-extended Darcy model of newtonian fluids on steady flow through porous media, analytical expressions were obtained for the flow and thermal fields, the concentration of speaces, the average Nusselt and Sherwood numbers in terms of the Darcy number, the anisotropic permeability ratio, the orientation angle of the principal axes and the Hartmann number. The limiting case corresponding to pure porous media (<i>Da</i>→0) and pure fluid media (<i>Da</i>→∞) for the thermal conditions mentioned on the cavity completed these results in order to compare them to those obtained in the literature. It is found that, Nusselt and Sherwood numbers increase by increasing anisotropic parameters of the porous medium while increasing magnetic field magnitude greatly reduces the intensity of the flow and thus affects significantly heat and mass transfer.

The effects of magnetic-field direction and magnitude on forced convection of aluminum oxide–water nanofluid over a circular cylinder

In this paper, the forced convection of Al2O3-water nanofluid over a circular cylinder inside a magnetic field is simulated and studied. The Navier-Stokes and energy equations are discretized using the finite element method. The nanoparticles and base fluid are aluminum oxide and water. An experimental model as a function of the temperature, nanoparticle diameter, and volume fraction of the nanofluid is utilized to calculate the nanofluid's viscosity and conductivity coefficient. In addition, some cases are compared with the analytical model of Brinkman-Maxwell that is a function of the volume fraction of the nanofluid. The ranges of the main parameters, including the Reynolds numbers, Hartman numbers, angles of magnetic field, and volume fractions of the nanofluid, are 40≤Re≤200, 0≤Ha≤100, 0≤γ≤90 and 0≤φ≤0.06, respectively. The results for local and average Nusselt numbers, drag and lift coefficients, and streamlines are presented and discussed. The findings show that the model of the nanofluids is important, and the values of the Nusselt numbers in the experimental model are different than the Brinkman-Maxwell analytical one. The value of the Nusselt number is increased with increasing of the Reynolds number and the angle of the magnetic field. In addition, the change in the Nusselt number with the Hartmann number depends on the angle of the magnetic field. The variation of the Nusselt number with the volume fraction of the nanofluid is almost increasable; however, the rate of that is dependent on the Reynolds number, the Hartmann number, and the angle of the magnetic field.

A Solar Source of Alfvénic Magnetic Field Switchbacks: In Situ Remnants of Magnetic Funnels on Supergranulation Scales

Abstract One of the striking observations from the Parker Solar Probe (PSP) spacecraft is the prevalence in the inner heliosphere of large amplitude, Alfvénic magnetic field reversals termed switchbacks. These δ B R / B ∼  ( 1 ) fluctuations occur over a range of timescales and in patches separated by intervals of quiet, radial magnetic field. We use measurements from PSP to demonstrate that patches of switchbacks are localized within the extensions of plasma structures originating at the base of the corona. These structures are characterized by an increase in alpha particle abundance, Mach number, plasma β and pressure, and by depletions in the magnetic field magnitude and electron temperature. These intervals are in pressure balance, implying stationary spatial structure, and the field depressions are consistent with overexpanded flux tubes. The structures are asymmetric in Carrington longitude with a steeper leading edge and a small (∼1°) edge of hotter plasma and enhanced magnetic field fluctuations. Some structures contain suprathermal ions to ∼85 keV that we argue are the energetic tail of the solar wind alpha population. The structures are separated in longitude by angular scales associated with supergranulation. This suggests that these switchbacks originate near the leading edge of the diverging magnetic field funnels associated with the network magnetic field—the primary wind sources. We propose an origin of the magnetic field switchbacks, hot plasma and suprathermals, alpha particles in interchange reconnection events just above the solar transition region and our measurements represent the extended regions of a turbulent outflow exhaust.

Domains of Magnetic Pressure Balance in Parker Solar Probe Observations of the Solar Wind

Abstract The Parker Solar Probe (PSP) spacecraft is performing the first in situ exploration of the solar wind within 0.2 au of the Sun. Initial observations confirmed the Alfvénic nature of aligned fluctuations of the magnetic field B and velocity V in solar wind plasma close to the Sun, in domains of nearly constant magnetic field magnitude ∣ B ∣, i.e., approximate magnetic pressure balance. Such domains are interrupted by particularly strong fluctuations, including but not limited to radial field (polarity) reversals, known as switchbacks. It has been proposed that nonlinear Kelvin–Helmholtz instabilities form near magnetic boundaries in the nascent solar wind leading to extensive shear-driven dynamics, strong turbulent fluctuations including switchbacks, and mixing layers that involve domains of approximate magnetic pressure balance. In this work we identify and analyze various aspects of such domains using data from the first five PSP solar encounters. The filling fraction of domains, a measure of Alfvénicity, varies from median values of 90% within 0.2 au to 38% outside 0.9 au, with strong fluctuations. We find an inverse association between the mean domain duration and plasma β. We examine whether the mean domain duration is also related to the crossing time of spatial structures frozen into the solar wind flow for extreme cases of the aspect ratio. Our results are inconsistent with long, thin domains aligned along the radial or Parker spiral direction, and compatible with isotropic domains, which is consistent with prior observations of isotropic density fluctuations or flocculae in the solar wind.

A new type of magnetic field arrangement to suppress meniscus fluctuation in slab casting: Numerical simulation and experiment

This research aimed at proposing a new type of magnetic field arrangement to suppress the meniscus fluctuation in slab continuous casting. The work was conducted by three dimensional (3D) numerical simulation and followed by an experiment validation. The results indicated that the maximum height of meniscus was decreased and the meniscus fluctuation was decreased significantly whilst the applied magnetic field was increased from 0 to 0.05 T. The surface velocity was not sensitive to the applied magnetic field magnitude to 0.05 T. The results obtained from the designed experiment had a good agreement with the simulation results: this is an indication of the effectiveness of the proposed magnetic field arrangement.