Spatial Distribution Of Magnetic Field Research Articles

Research on Spatial Magnetic Field Distribution of Magnetic Fluids Based on Microstructure.

This study focuses on the spatial magnetic field distribution of magnetic fluids, an extraordinary class of fluids composed of magnetic nanoparticles (MNPs), employing the Monte Carlo method to simulate the microstructure of magnetic fluids under an external magnetic field. On that basis, a model was established through magnetic dipole theory to delve into the spatial magnetic field distribution of magnetic fluids. The findings reveal that the application of a magnetic field leads to the formation of chain-like structures within the magnetic fluids, resulting in inhomogeneous spatial magnetic field distribution. The size and concentration of MNPs are crucial determinants that significantly affect the microstructure of magnetic fluid and its spatial magnetic field distribution. Furthermore, environmental conditions such as external magnetic field strength or temperature can also regulate the positions of MNPs within magnetic fluids and the spatial magnetic field distribution of the magnetic fluids. These observations enrich the comprehension of the fundamental mechanisms of magnetic fluids and their response to diverse factors, advancing the growing comprehension on the characteristics and applications of these remarkable magnetic fluids.

Anomalous-Chern Steering of Topological Nonreciprocal Guided Waves.

Nonreciprocal topological edge states based on external magnetic bias have been regarded as the last resort for genuine unidirectional wave transport, showing superior robustness over topological states with preserved time-reversal symmetry. However, fast and efficient reconfigurability of their trajectory has remained a formidable challenge due to the difficulty in controlling the spatial distribution of magnetic fields over large areas and short times. Here, thispersistent issue is solved by leveraging the rich topology of unitary scattering networks, and achieve fast steering of nonreciprocal topological transport at an interface between a Chern and an anomalous topological insulator, without having to control a magnetic field. Such interface can be drawn by doping the network with scatterers located at the center of each link, whose level of reflection is electrically tuned. With experiments in the GHz range, the possibility to actively steer the way of unidirectional edge states is demonstrated, switching the transmission path thousands of times per second in a fully-robust topological heterostructure. The approach represents a significant step towards the realization of practical reconfigurable topological meta-devices with broken time-reversal symmetry, and their application to future robust communicationtechnologies.

Scanning ex situ solid-state magnetic resonance imaging on polymeric films using a static magnetic field gradient by an electromagnet.

A new technique for ex situ solid-state nuclear magnetic resonance imaging of polymeric films has been developed. This method uses the static magnetic field gradient generated by a water-cooled copper electromagnet. The imaging process involves scanning the sample in the plane of the film under a static magnetic field gradient. Two-dimensional (2D) 19F MRI measurements are attempted, where the fast Fourier transform (FFT) spectra of the second half of a Hahn echo peak is used for the depth (X-axis) direction, and the sample film is mechanically moved for the Y-axis, which is in-plane with respect to the film surface and normal to the inter-magnetic-pole line (Z-axis). The sample is a poly(tetrafluoroethylene) [PTFE] film with carved stripes on its surface. Furthermore, three-dimensional (3D) measurements of the film surface and thickness orientations were also performed for an analogous PTFE film. For 2D profiling on the film surface, 2D sample-moving was used. For depth profiling, FFT spectrum analysis was undertaken for each voxel situated at a specific (Y, Z) coordinate within the film. As a result, a 3D image of the sample and its corresponding geometry were obtained, although the scanning area was restricted to a part of the sample. Finally, numerical simulations of the spatial distribution of the static magnetic field were performed to confirm the validity of the present method.

Model of self-generated magnetic field generation from relativistic laser interaction with solid targets

Generation of self-generated annular magnetic fields at the rear side of a solid target driven by relativistic laser pulse is investigated by using theoretical analysis and particle-in-cell simulations. The spatial strength distribution of magnetic fields can be accurately predicted by calculating the net flow caused by the superposition of source flow and return flow of hot electrons. The theoretical model established shows good agreement with the simulation results, indicating that the magnetic-field strength scales positively to the temperature of hot electrons. This provides us a way to improve the magnetic-field generation by using a micro-structured plasma grating in front of the solid target. Compared with that for a common flat target, hot electrons can be effectively heated with the well-designed grating size, leading to a stronger magnetic field. The spatial distribution of magnetic fields can be modulated by optimizing the grating period and height as well as the incident angle of the laser pulse.

Patterned magnetophotonic crystal for all-optical magnetization precession generation

A magnetophotonic crystal (MPC) with a locally etched magnetic layer is proposed for all-optical excitation of magnetization precession in the confined area. When the sample is illuminated by circularly polarized monochromatic plane wave, the optical MPC mode and the effective magnetic field excited by the inverse Faraday effect are localized inside the etched area. Therefore, the optical impact on the spin system in a magnetically ordered medium becomes confined in both lateral directions on the order of tens of nanometers and along the film thickness serving as a nanoconfined source of spin waves. The dependence of the spatial distribution of the effective magnetic field and magnetization precession amplitude on the depth and dimensions of the etched area are addressed. A proposed design of the MPC can find its applications in the field of magnetization dynamics generation as a compact and stable source of the spin waves that allows compact arrangement of the sources for some complex spin waves excitations.

Self–dual solutions of a field theory model of two linked rings

In this work the connection established in [7,8] between a model of two linked polymers rings with fixed Gaussian linking number forming a 4-plat and the statistical mechanics of non-relativistic anyon particles is explored. The excluded volume interactions have been switched off and only the interactions of entropic origin arising from the topological constraints are considered. An interpretation from the polymer point of view of the field equations that minimize the energy of the model in the limit in which one of the spatial dimensions of the 4-plat becomes very large is provided. It is shown that the self-dual contributions are responsible for the long-range interactions that are necessary for preserving the global topological properties of the system during the thermal fluctuations. The non self-dual part is also related to the topological constraints, and takes into account the local interactions acting on the monomers in order to prevent the breaking of the polymer lines. It turns out that the energy landscape of the two linked rings is quite complex. Assuming as a rough approximation that the monomer densities of half of the 4-plat are constant, at least two points of energy minimum are found. Classes of non-trivial self-dual solutions of the self-dual field equations are derived. One of these classes is characterized by densities of monomers that are the squared modulus of holomorphic functions. The second class is obtained under some assumptions that allow to reduce the self-dual equations to an analog of the Gouy-Chapman equation for the charge distribution of ions in a double layer capacitor. In the present case, the spatial distribution of the electric potential of the ions is replaced by the spatial distribution of the fictitious magnetic fields associated with the presence of the topological constraints. In the limit in which two of the spatial dimensions are large in comparison with the third one, we provide exact formulas for the conformations of the monomer densities of the 4-plat by using the elliptic, hyperbolic and trigonometric solutions of the sinh-Gordon and cosh-Gordon equations which have been used for instance in the construction of classical string solutions in AdS3 and dS3 [9].

Research on the design of a novel composite solenoid model ship simulation magnetic source based on DTW

In order to study the simulation ability of a solenoid on a ship magnetic field, a new composite model based on a double row magnetic dipole array model with an ellipsoid was designed. The time-domain characteristics, such as magnetic field characteristics, magnetic inclination cosine, magnetic field scalar gradient, and magnetic field spatial distribution characteristics, were extracted. It was verified that the model can accurately simulate the magnetic field characteristics of ships through ship model experiments and simulation analysis. To further quantitatively and accurately analyze the simulation ability of the composite model for ship magnetic fields, a dynamic time wrapping measurement method based on one-dimensional time series was adopted to calculate the similarity of four characteristic quantities: magnetic field vector, magnetic field modulus, magnetic inclination cosine, and magnetic field scalar gradient. The results showed that the composite model has high simulation ability for ship magnetic fields.

Magnetic-assisted preparation and performance control of Fe3O4/PVDF gradient magnetic composites.

In this study, a gradient Fe3O4/PVDF magnetic composite was prepared using magnetic-assisted template filling technology. The purpose of this study was to explore a simple, economical, and scalable method for preparing gradient magnetic composites. The structure and magnetic performance of the composite were studied, and the parameters that influenced the gradient magnetic properties of the material, such as magnetic intensity, magnet spacing, initial content of magnetic particles, and magnet movement speed, were investigated. The results showed that increasing magnetic intensity during the template filling process enhanced the electromagnetic force on the magnetic particles, resulting in a greater magnetic particle content gradient. The variation in magnet spacing affected the spatial magnetic field distribution, and increasing the magnet spacing increased the gradient of the magnetic intensity in the y-direction. The magnetic gradient of the Fe3O4/PVDF composite first decreased and then increased as the magnet spacing increased. Increasing the magnet movement speed enhanced the gradient of the magnetic intensity in the y-component but shortened the duration of the electromagnetic force. By adjusting these parameters, it is possible to regulate the structural and magnetic properties of the Fe3O4/PVDF composite. This work may have implications for research and application in related fields and promote the development and innovation of magnetic materials.

Parameter Optimization of Wireless Power Transfer Based on Machine Learning

Wireless power transfer (WPT) has become a crucial feature in numerous electronic devices, electric appliances, and electric vehicles. However, traditional design methods for WPT suffer from numerous drawbacks, such as time-consuming computations and high error counts due to inaccurate model parameters. As artificial intelligence (AI) continues to gain traction across industries, its ability to provide quick decisions and solutions makes it highly attractive for system optimizations. In this paper, a method for optimizing WPT parameters based on machine learning is proposed. The convolutional neural network is adapted for training and predicting the performance of a pair of coupled coils under a set of input parameters. The performance parameters include the spatial magnetic field distribution map, quality factor, inductance value, and mutual inductance value, which are critical in determining the efficiency and selecting optimal coil parameters such as the number of turns and wire diameter. Moreover, the spatial magnetic field distribution map is also helpful for identifying design compliance with the electromagnetic field safety standards. The training results reveal that the proposed method takes an average of 3.2 ms with a normalized image prediction error of 0.0034 to calculate the results to calculate one set of parameters, compared to an average of 23.74 s via COMSOL. This represents significant computational time savings while still maintaining acceptable computational accuracy.

Effect of transcranial static magnetic stimulation over unilateral or bilateral motor association cortex on performance of simple and choice reaction time tasks.

Transcranial static magnetic stimulation (tSMS) is a non-invasive brain stimulation technique that place a strong neodymium magnet on scalp to reduce cortical excitability. We have recently developed a new tSMS device with three magnets placed close to each other (triple tSMS) and confirmed that this new device can produce a stronger and broader static magnetic field than the conventional single tSMS. The aim of the present study was to investigate the effect of the conventional single tSMS as well as triple tSMS over the unilateral or bilateral motor association cortex (MAC) on simple and choice reaction time (SRT and CRT) task performance. There were two experiments: one involved the conventional tSMS, and the other involved the triple tSMS. In both experiments, right-handed healthy participants received each of the following stimulations for 20 min on different days: tSMS over the unilateral (left) MAC, tSMS over the bilateral MAC, and sham stimulation. The center of the stimulation device was set at the premotor cortex. The participants performed SRT and CRT tasks before, immediately after, and 15 min after the stimulation (Pre, Post 0, and Post 15). We evaluated RT, standard deviation (SD) of RT, and accuracy (error rate). Simulation was also performed to determine the spatial distribution of magnetic field induced by tSMS over the bilateral MAC. The spatial distribution of induced magnetic field was centered around the PMd for both tSMS systems, and the magnetic field reached multiple regions of the MAC as well as the sensorimotor cortices for triple tSMS. SD of CRT was significantly larger at Post 0 as compared to Pre when triple tSMS was applied to the bilateral MAC. No significant findings were noted for the other conditions or variables. We found that single tSMS over the unilateral or bilateral MAC did not affect performance of RT tasks, whereas triple tSMS over the bilateral MAC but not over the unilateral MAC increased variability of CRT. Our finding suggests that RT task performance can be modulated using triple tSMS.

Lattice constant and polarization-independent high transmission in tellurium-based dielectric metasurfaces

High-refractive-index dielectric metasurfaces give rise to unprecedented control of light manipulation, such as control of phase, polarization and amplitude, giving rise to interesting properties, such as directional beam steering, polarization detectors and sensors. Dielectric metasurfaces of sub-wavelength dimensions have tremendous applications in the field of optics, such as negative refractive index, cloaking, perfect absorbers and reflectors. The study of light–matter interactions in such materials has gained impetus due to the formation of novel states, such as anapoles, and transparent states obtained by interference between resonant electric, magnetic and higher-order modes. In this article, we investigate the light–matter interaction of an array of periodic dielectric metasurfaces made from high-refractive-index tellurium in cubic geometries and study its electromagnetic response as a function of the lattice constant, angle of incidence and angle of polarization. More specifically, we observe a non-resonant transparent state at 60.69 THz, which is independent of both the lattice constant and polarization of the input radiation. Moreover, this state shows high transmission for a broad range of incident angles with potential applications as optical filters. It also depends on the incident polarization, thus acting as a perfect polarization detector. Detailed investigations of scattering parameters, the spatial distribution of electric and magnetic fields in the near- and far-field regions and detailed multipole analysis are carried out to analyze the electromagnetic response of the metasurface.

AC magnetic trap for cold paramagnetic molecules

Strong-field-seeking states are the lowest-energy configurations for paramagnetic molecules in the magnetic field. Molecules in strong-field-seeking states cannot be trapped in a magnetostatic field because a magnetostatic maximum in free space is not allowed. In this paper, we propose an AC magnetic trap composed of two pairs of Helmholtz coils. The spatial magnetic field distribution is numerically calculated and the time-sequential control is depicted. We investigate the influence of the switching frequency and the electric current in the coils on the performance of our trap. Variations of the location and phase-space distribution during a whole switching cycle are simulated. Finally, we study the impact of time during which the field is switched off on the number of captured molecules in a switching cycle.

Multi-DOF Lumped-Parameter Modeling of High-Power Giant Magnetostrictive Transducer Coupled With Spatial Distribution of Magnetic Field

Multi-DOF Lumped-Parameter Modeling of High-Power Giant Magnetostrictive Transducer Coupled With Spatial Distribution of Magnetic Field

Full control of electric and magnetic light–matter interactions through a nanomirror on a near-field tip

Light–matter interactions are often considered governed by the electric optical field only, leaving aside the magnetic component of light. However, the magnetic part plays a determining role in many optical processes, from light and chiral-matter interactions and photon-avalanching to forbidden photochemistry, making the manipulation of magnetic processes extremely relevant. Here, by creating a standing wave using a metallic nanomirror, we manipulate the spatial distributions of electric and magnetic fields and their associated local densities of states, allowing selective control of the excitation and emission of electric and magnetic dipolar transitions. This control allows us to image, in 3D, the electric and magnetic nodes and anti-nodes of the fields’ interference patterns. It also enables us to enhance specifically photoluminescence from quantum emitters excited only by the magnetic field, and to manipulate their spontaneous emission by acting on the excitation fields solely, demonstrating full control of magnetic and electric light–matter interactions.

Distributed Poloidal Magnetic Field Measurement in Tokamaks Using Polarization-Sensitive Reflectometric Fiber Optic Sensor.

Determination of the poloidal magnetic field distribution in tokamaks is of prime importance for the successful operation of tokamaks. In this paper, we propose a polarization-sensitive reflectometry-based optical fiber sensor for measuring the spatial distribution of the poloidal magnetic field in tokamaks. The measurement method exploits the Rayleigh backscattering and Faraday magneto-optic effect in optical fibers. The former is an intrinsic property of optical fibers and enables distributed polarization measurements, while the latter arises in the presence of a magnetic field parallel to the optical fiber axis and rotates the polarization state of the light. When an optical fiber is looped around a toroidal section of the vacuum vessel, the local polarization rotation of the light is proportional to the local poloidal magnetic field in the tokamak. The proposed method is discussed theoretically and experimentally using the results from JET. The obtained magnetic field measurement shows a good agreement with that of the internal discrete coils. A potential solution to recover the magnetic field data from the noise-affected region of the optical measurement is proposed and is demonstrated through simulations using the JET magnetic field configuration.

Research on electromagnetic characteristics of traction motor rotary shafts with variable parameter defects based on finite element method

In view of the breakage of the rotary shaft of the traction motor of the locomotive, in order to ensure the reliability and safety of the equipment, this paper studies the magnetic field containing rich information in the space around the rotary shaft, so that the crack defect can be detected and the crack size can be judged in time. In order to study the influence of defect geometric parameters (width, depth and hidden depth) on the spatial magnetic field distribution around the defect in the process of eddy current testing of metal shafts, based on the principle of eddy current testing, a metal rotary shaft detection model with different defect parameters was established by COMSOL software for simulation. The horizontal magnetic induction intensity, vertical magnetic induction intensity and their respective phases are used to analyze the magnetic field distribution around the defect under different parameters. The results show that the magnetic field related parameters can qualitatively and quantitatively evaluate the crack width, qualitatively evaluate the relative size of the crack depth, and qualitatively judge whether there are hidden cracks.

The Attenuation calculation method for the underwater low-frequency magnetic field of finite-length straight wire

Usually, when solving the magnetic field distribution of a finite-length straight wire in a conducting medium, numerical calculation is required. However, this method has some disadvantages, such as complex calculations and not being conducive to engineering implementation. To solve this problem, this paper studied the attenuation calculation method for the underwater low-frequency magnetic field of the finite-length straight wire and then obtained the analytical calculation formula of magnetic field spatial distribution. The simulation results show that, within a certain distance, the analytical method is in good agreement with the numerical calculation results. The method presented in this paper is convenient for calculation and has good engineering practicability.

Estimation of the Spatial and Temporal Distribution of Magnetic Fields around Overhead Power Lines—A Case Study

Due to the growing number, diversity and spreading of magnetic field sources, an increasing need to determine the field levels of human exposure has arisen. Some of the most encountered sources are the overhead power lines (OPL) and the determination of spatial and temporal variation of the magnetic fields produced by OPLs is a challenge. In this paper a hybrid method for the estimation of the temporal and spatial distribution of the magnetic flux density B caused by OPLs, based on experimental measurements and on numerical and analytical simulations, is presented. Thus, using a small number of simultaneous spot measurements correlated with a long-term survey, maps of the magnetic flux density distribution on extended areas are established, for several time instances. The proposed method is verified using two sets of different measurements and the results obtained through simulation. The difference between the estimated and simulated values of B is under 5.5%, which is considered acceptable considering that B spans over a large set of values (724 nT ÷ 1375 nT) in the location of the long-term survey procedure. The possibilities and limitations of the proposed method are discussed.

Small scale magnetic field source detection using recessed atomic vapor cell

With the development of high spatial resolution spin image and magnetic field distribution measurement in atomic vapor cell, one can localize the position and calculate the magnetic moment of the field source around the cell. However, traditional cubic or spherical vapor cell can only measure the magnetic field distribution on one side of the field source, which limits the precision of the field inversion results. Here, we use a recessed atomic vapor cell to obtain field distribution around the source, which is positioned at the center of the cell. The magnetic field distributions around five sides of the field source are measured using movable stages and digital micro-mirror device. We combine the Levenberg–Marquardt algorithm with a genetic algorithm as the magnetic source localization algorithm to realize a quick global search as well as a precise local extreme point search. We obtain a spatial resolution of 219.2 × 387.0 × 451.5 μ m 3 and a magnetic field sensitivity of 0.06 nT / Hz 1 / 2 in a volume pixel of 0.0383 mm 3. The error in the localization of the magnetic source is 1.295 mm in the x direction, 185 μ m in the y direction, and 40 μ m in the z direction. The field distribution measurement method using recessed atomic vapor cell and related inversion algorithm demonstrated here have great potential applications in small scale field source detection of biology and materials science.

Magneto-Optical Indicator Films: Fabrication, Principles of Operation, Calibration, and Applications.

Magneto-optical indicator films (MOIFs) are a very useful tool for direct studies of the spatial distribution of magnetic fields and the magnetization processes in magnetic materials and industrial devices such as magnetic sensors, microelectronic components, micro-electromechanical systems (MEMS), and others. The ease of application and the possibility for direct quantitative measurements in combination with a straightforward calibration approach make them an indispensable tool for a wide spectrum of magnetic measurements. The basic sensor parameters of MOIFs, such as a high spatial resolution down to below 1 μm combined with a large spatial imaging range of up to several cm and a wide dynamic range from 10 μT to over 100 mT, also foster their application in various areas of scientific research and industry. The history of MOIF development totals approximately 30 years, and only recently have the underlying physics been completely described and detailed calibration approaches been developed. The present review first summarizes the history of MOIF development and applications and then presents the recent advances in MOIF measurement techniques, including the theoretical developments and traceable calibration methods. The latter make MOIFs a quantitative tool capable of measuring the complete vectorial value of a stray field. Furthermore, various scientific and industrial application areas of MOIFs are described in detail.