Magnetic Field Quantities Research Articles

Consideration of the spatial orientation of magnetic field quantities and tensile mechanical stress in the Finite Element Analysis of electrical machines

Consideration of the spatial orientation of magnetic field quantities and tensile mechanical stress in the Finite Element Analysis of electrical machines

Observation of Exceptional Points in Thermal Atomic Ensembles.

Exceptional points (EPs) in non-Hermitian systems have recently attracted wide interest and spawned intriguing prospects for enhanced sensing. However, EPs have not yet been realized in thermal atomic ensembles, which is one of the most important platforms for quantum sensing. Here we experimentally observe EPs in multilevel thermal atomic ensembles and realize enhanced sensing of the magnetic field for 1 order of magnitude. We take advantage of the rich energy levels of atoms and construct effective decays for selected energy levels by employing laser coupling with the excited state, yielding unbalanced decay rates for different energy levels, which finally results in the existence of EPs. Furthermore, we propose the optical polarization rotation measurement scheme to detect the splitting of the resonance peaks, which makes use of both the absorption and dispersion properties and shows an advantage with enhanced splitting compared with the conventional transmission measurement scheme. Additionally, in our system both the effective coupling strength and decay rates are flexibly adjustable, and thus the position of the EPs are tunable, which expands the measurement range. Our Letter not only provides a new controllable platform for studying EPs and non-Hermitian physics, but also provide new ideas for the design of EP-enhanced sensors and opens up realistic opportunities for practical applications in the high-precision sensing of magnetic field and other physical quantities.

Distorted-toroidal Flux Rope Model

The 3D characterization of magnetic flux ropes observed in the heliosphere has been a challenging task for decades. This is mainly due to the limitations on inferring the 3D global topology and physical properties from the 1D time series from any spacecraft. To advance our understanding of magnetic flux ropes whose configuration departs from the typical stiff geometries, here we present an analytical solution for a 3D flux rope model with an arbitrary cross section and a toroidal global shape. This constitutes the next level of complexity following the elliptic-cylindrical (EC) geometry. The mathematical framework was established by Nieves-Chinchilla et al. with the EC flux rope model, which describes a magnetic topology with an elliptical cross section as a first approach to changes in the cross section. In the distorted-toroidal flux rope model, the cross section is described by a general function. The model is completely described by a nonorthogonal geometry and the Maxwell equations can be consistently solved to obtain the magnetic field and relevant physical quantities. As a proof of concept, this model is generalized in terms of the radial dependence of current density components. The last part of this paper is dedicated to a specific function, , to illustrate possibilities of the model. This model paves the way toward the investigation of complex distortions of magnetic structures in the solar wind. Future investigations will explore these distortions in depth by analyzing specific events; studying implications for physical quantities, such as magnetic fluxes, helicity, or energy; and evaluating the force balance with the ambient solar wind that allows such distortions.

Mathematical Study of the Perturbation of Magnetic Fields Caused by Erythrocytes.

The purpose of this chapter is the mathematical study of the perturbation of a homogeneous static magnetic field caused by the embedding of a red blood cell. Analytical expressions for the magnetic potential and the magnetic strength vector are derived. From the obtained results, it emerges that the magnetic field inside the red blood cell is not uniform and the magnitude depends on the orientation of the erythrocyte. The expressions for the magnetic field quantities are significant in applications such as the magnetic resonance imaging and in the magnetic resonance spectroscopy.

Quantitative Determination of Local Density of Iron Oxide Nanoparticles Used for Drug Targeting Employing Inverse Magnetomotive Ultrasound.

Numerous medical applications make use of magnetic nanoparticles, which increase the demand for imaging procedures that are capable of visualizing this kind of particle. Magnetomotive ultrasound (MMUS) is an ultrasound-based imaging modality that can detect tissue, which is permeated by magnetic nanoparticles. However, currently, MMUS can only provide a qualitative mapping of the particle density in the particle-loaded tissue. In this contribution, we present an enhanced MMUS procedure, which enables an estimation of the quantitative level of the local nanoparticle concentration in tissue. The introduced modality involves an adjustment of simulated data to measurement data. To generate these simulated data, the physical processes that arise during the MMUS imaging procedure have to be emulated which can be a computing-intensive proceeding. Since this considerable calculation effort may handicap clinical applications, we further present an efficient approach to calculate the decisive physical quantities and a suitable way to adjust these simulated quantities to the measurement data with only moderate computational effort. For this purpose, we use the result data of a conventional MMUS measurement and the knowledge on the magnetic field quantities and on the mechanical parameters describing the biological tissue, namely, the density, the longitudinal wave velocity, and the shear wave velocity. Experiments on tissue-mimicking phantoms demonstrate that the presented technique can indeed be utilized to determine the local nanoparticle concentration in tissue quantitatively in the correct order of magnitude. By investigating test phantoms of simple geometry, the mean particle concentration of the particle-laden area could be determined with less than 22% deviation to the nominal value.

Finite element formulation for implicit magnetostrictive constitutive relations

Magnetostrictive materials that couple mechanical and magnetic domains have been widely explored for use in sensors and actuators. These materials often exhibit a nonlinear material response under applied magnetic fields, which limits the use of linear constitutive models. Furthermore, the nonlinear constitutive relations tend to be implicit in nature. Hence, a finite element scheme that can handle the implicit relationship between the mechanical (stresses and strains) and magnetic (magnetic flux density and magnetic field) quantities is proposed in order to arrive at solutions to boundary value problems. In the proposed scheme, while the physical requirements of equilibrium and strain–displacement relation are satisfied point-wise, the constitutive relations hold in a weak integral sense. A fully coupled magnetostrictive plane stress rectangular element is developed based on the proposed scheme and its efficacy in arriving at solutions to coupled field boundary value problems is illustrated by subjecting the element to standard loading conditions.

Modeling and Classification of Stator Inter-Turn Fault and Demagnetization Effects in BLDC Motor Using Rotor Back-EMF and Radial Magnetic Flux Analysis

This paper shall carry out unique study and investigation on the individual and combined effect of Stator Inter-turn Fault (SITF) and rotor demagnetization effects in a Surface Mounted Permanent Magnet (SPM)-type Brushless Direct Current (BLDC) motor. Comprehensive modeling of fault is accomplished using the well-established fault modeling techniques such as Electrical Equivalent Circuit (EEC), Magnetic Equivalent Circuit (MEC), Numerical Methods (NMs) and hybrid modeling-based approaches. The extensive study of SITF conditions using an Improved Winding Function Theory (IWFT) gives better analysis to winding inductance $L_{S}$ , under fault conditions, while modeling the demagnetization effects using MEC and NM based approaches gives more realistic magnetic field quantities. The outcomes obtained are further remodeled in the developed hybrid model of a BLDC motor to study the steady state performance of a machine in terms of rotor back-EMF, $E_{B}$ and radial magnetic flux density $B_{g}$ . The characteristic performance accomplished through the hybrid model system possess better accuracy with less computational time and therefore finds suitability among efficient and fast diagnosis technique feasible for industrial applications. The significant detectable changes in $E_{B}$ and $B_{g}$ under subjected fault conditions, assist in detection, identification and classification of faults in BLDC motor. By obtaining the similar outcome experimentally and under the load conditions, the proposed study on the classification of fault is validated.

Evolution of Coronal Mass Ejection Properties in the Inner Heliosphere: Prediction for the Solar Orbiter and Parker Solar Probe

Abstract The evolution of the magnetic field and plasma quantities inside a coronal mass ejection (CME) with distance are known from statistical studies using data from 1 au monitors, planetary missions, Helios, and Ulysses. This does not cover the innermost heliosphere, below 0.29 au, where no data are yet publicly available. Here, we describe the evolution of the properties of simulated CMEs in the inner heliosphere using two different initiation mechanisms. We compare the radial evolution of these properties with that found from statistical studies based on observations in the inner heliosphere by Helios and MESSENGER. We find that the evolution of the radial size and magnetic field strength is nearly indistinguishable for twisted flux rope from that of writhed CMEs. The evolution of these properties is also consistent with past studies, primarily with recent statistical studies using in situ measurements and with studies using remote observations of CMEs.

Validation of a Harmonic Model for Eddy Currents in Slitted Conducting Plates

The paper describes a 3D semi-analytical harmonic modeling technique that is capable of modeling eddy current distributions in segmented conducting structures, such as slitted conducting plates, and the associated magnetic fields. The spatially varying conductivity of a conducting region is incorporated into the solutions of magnetic-field quantities and the induced current density. The harmonic model is compared to results obtained with finite element analysis. An experimental setup is used to measure the field distribution above differently slitted conducting plates, in which eddy currents are induced by a coil. The measurement results are compared to simulation results, and the perturbations are analyzed.

Developments of a multi-wavelength spectro-polarimeter on the Domeless Solar Telescope at Hida Observatory

Abstract To obtain full Stokes spectra in multi-wavelength windows simultaneously, we developed a new spectro-polarimeter on the Domeless Solar Telescope at Hida Observatory. The new polarimeter consists of a 60 cm aperture vacuum telescope on an altazimuth mounting, an image rotator, a high-dispersion spectrograph, and a polarization modulator and an analyzer composed of a continuously rotating waveplate with a retardation that is nearly constant at around 127° in 500–1100 nm. There are also a polarizing beam splitter located close behind the focus of the telescope, fast and large format CMOS cameras, and an infrared camera. A slit spectrograph allows us to obtain spectra in as many wavelength windows as the number of cameras. We characterized the instrumental polarization of the entire system and established a polarization calibration procedure. The cross-talks among the Stokes Q, U, and V have been evaluated to be about 0.06%–1.2%, depending on the degree of the intrinsic polarizations. In a typical observing setup, a sensitivity of 0.03% can be achieved in 20–60 seconds for 500–1100 nm. The new polarimeter is expected to provide a powerful tool for diagnosing the 3D magnetic field and other vector physical quantities in the solar atmosphere.

Analytical Calculation of Back EMF Waveform for Linear PM Motors in Slotted and Slotless Structures

This paper presents the analytical calculation of back electromotive force (EMF) waveform for linear permanent magnet motors in either slotted or slotless structures. The predictions are based on the analysis of the 2-D magnetic field distributions and the 3-D end effects. In the slotted structure, the relative permeance function obtained by the Schwarz-Christoffel conformal mapping is used to take into account the effects of slotting and to calculate the air-gap flux density. Subsequently, to evaluate the leakage components resulting from the slot opening, slot opening factor is introduced to reflect the elements which do not follow the intended path to produce the back EMF. In the slotless structure, the effective values of the magnetic field quantities, together with the extended theory of winding factors, are employed to evaluate the back EMF waveform. For the analysis of the axial end effects, the 3-D leakage factor is incorporated into the analytical solutions by adding the end leakage permeance to the entire magnetic circuit models. The validity of the analytical results for each topology is confirmed by 2-D finite element and experimental results.

Magnetization of Linear Arrays of Two Ferromagnetic Spheres in a Uniform Magnetic Field

The main objective of this paper is to explore the exact analytical solutions of the magnetization of linear arrays of two ideal ferromagnetic spheres in the presence of external magnetic fields. First, the total scalar magnetic potential outside the spheres, related to the magnetic field intensity, which satisfies the Laplace equation, is obtained by the superposition of the potentials due to all spheres and the potential corresponding to the external field. The translational addition theorems for scalar Laplacian functions in spherical coordinates are then used to translate the two coordinates systems into one coordinates system. Then, the exact boundary conditions were used to solve the magnetic field quantities outside the system. On the other hand, the scalar magnetic potential inside each sphere, related to the magnetic flux density, also satisfies the Laplace equation, which is solved by imposing the boundary conditions known from the solution of the outside quantities. Finally, the expressions derived are used to generate numerical results of controllable accuracy for various field quantities.

3-D MNL-FDTD Formulation in General Orthogonal Grids

In this letter, the implicit Newmark-Beta formulation is partially and magnetically introduced into the explicit leapfrog scheme of Yee’s finite-difference time-domain (Yee-FDTD) method in general orthogonal grids. We describe a partially implicit three-dimensional (3-D) FDTD formulation with directionally implicit time updating only for magnetic field and the conventional explicit time updating for electric field. The time discrete electric and magnetic field quantities are updated in a slightly modified leapfrog manner. Interestingly, the resulting 3-D scheme can be reduced to the conventional Yee-FDTD scheme when the Newmark parameter is chosen as zero. Its stability condition is more relaxed than the Courant–Friedrichs–Lewy stability condition of the Yee-FDTD, and the spatial mesh size in a specific direction on general orthogonal grids can be eliminated. This feature allows us to efficiently analyze electromagnetic field problems with fine structures in one spatial direction on general orthogonal grids. In order to validate the presented formulation, its applications to 3-D simulations of canonical cavity resonator problems with cylindrical and spherical grids are demonstrated.

Thermomagnetism with external and internal magnetic field quantities

In magnetism literature, usually the applied or external field H0 is taken to present the results of an investigation. But for certain purposes, it is advantageous to work with the internal magnetic field H that occurs inside a magnetic body. It is well-known that the susceptibility of the material and the demagnetization effect, given by the geometry of a body, link the two usually different fields under consideration. If a probe is a long needle with the external magnetic field and the magnetization in the probe parallel to the axis of the slender body, the two fields are identical. But when building thermomagnetic machines, other demands may require also other shapes (porous materials, particle beds, wavy structures, etc.) of the magnetized material and then a correct distinction of these fields becomes important and in some cases also laborious if one of them must be theoretically determined from the other. This article shows how—from a theoretical point of view—the most important physical properties of thermomagnetism/magnetocalorics, namely, the adiabatic entropy change, the effective specific heat capacity, and the adiabatic temperature change must be transformed. Furthermore, this theory reveals the invariants of magnetocalorics, which are combinations of these three most important properties.

A High Torque Magnetorheological Brake with Three Effective Areas

A new structure magnetorheological brake with three effective areas was designed, two end surfaces and the cylindrical surface of the rotor work as effective areas, then the effective area was increased with the same volume of the rotor. Depending on the characteristics of the magnetorheological brake structure, the finite element model of the magnetorheological brake was built, the electromagnetic field analysis was performed, then magnetic field quantities of the brake model were got. With the results of the magnetic analysis and the relation between the yield stress and the magnetic field strength of the magnetorheological fluid, the performance simulation of the magnetorheological brake was realized. On these bases, the magnetorheological brake and the mechanical performance test system were developed, the mechanical performance of the brake was researched used the test system, the brake’s properties: torque vs. speed and yield torque vs. current were obtained.

A High Torque Magnetorheological Brake for Gait Rehabilitation Robot

A new structure magnetorheological brake (MR brake) with three effective areas was designed, two end surfaces and the cylindrical surface of the rotor work as effective areas, then the effective area was increased with the same volume of the rotor. Finite element model of the MR brake was built, the electromagnetic field analysis was performed, then magnetic field quantities of the damper model were got. With the results of the magnetic analysis and the relation between the yield stress and the magnetic field strength of the magnetorheological fluid (MR fluid), the performance simulation of the magnetorheological damper was realized. According to the requirements of the gait rehabilitation robot to the yield torque of the MR brake, the current driver was designed. On these bases, the mechanical performance test system of the MR brake were developed, the mechanical performance of the brake was researched used the test system, the brake’s properties: torque vs. speed and yield torque vs. current were obtained.

An assessment of the pulsar outer gap model – I. Assumptions, uncertainties, and implications on the gap size and the accelerating field

The popular outer gap model of magnetospheric emission from pulsars has been widely applied to explain the properties observed in $\gamma$-rays. However, its quantitative predictions rely on a number of approximations and assumptions that are usually overlooked. Here we examine them, reviewing the main ingredients entering in the model, evaluating their range of uncertainties. Usually, in the quantitative applications of the model, key parameters like the radius of curvature and the energies of the interacting photons are taken to be a fixed, single value. Instead, here we explore their realistic ranges, and the impact of these on the consistency of the model itself. We conclude that the popular evaluation of the trans-field size of the gap as a function of period and period derivative, is unreliable and affected by a huge dispersion. Last, the exploration of the possible values for the radius of curvature, the local magnetic field and other quantities deserve more attention for quantitative applications of the outer gap model, like the calculation of $\gamma$-ray spectra, which is the subject of an accompanying paper.

A Complex-Valued Rotating Magnetic Property Model and Its Application to Iron Core Loss Calculation

This paper presents a complex-valued model when considering rotational magnetic properties of an electrical steel sheet from the viewpoint of improving the computation efficiency. The effective magnetic reluctivity and magnetic hysteresis coefficients in this model were interpolated from measured data based on a 2-D rotational magnetic property measurement system, in which the effect of higher harmonic terms of magnetic field intensity after saturation was considered. To reduce the computation error to some extent resulted from complex approximation of magnetic field quantities, the effective magnetic coefficients were expressed as the function of magnitude and direction of magnetic flux density. Considering transformer and three-phase induction motor core models as examples, the magnetic field distribution and core loss were calculated and the effectiveness of the proposed model was verified with the experimental results.

Efficient Iterative Integral Technique for Computation of Fields in Electric Machines with Rotor Eccentricity

To analyze the effects of small variations of the electric machine airgaps due to rotor eccentricity it is necessary to compute the magnetic field highly accurately. An efficient iterative integral technique is proposed, where the material nonlinearity is treated by the polarization method, with the magnetic field determined at each iteration by superposing the contributions of the given electric currents and the polarizations. This computation technique has great advantages over the finite element based procedures, namely, the change in the rotor position does not require the construction of a new discretization mesh, very small airgaps can be taken into consideration without increasing the amount of computation, and the calculated magnetic field in the air is divergenceless and curlless, thus eliminating the introduction of spurious forces. As well, the phase voltages and the magnetic forces are easily calculated from the magnetic field quantities.

Experimental Study of Electromagnetic Environment in the Vicinity of High Voltage Lines

Problem statement: Several studies have investigated the impact of electromagnetic field generated by high voltage power lines on environment. The evaluation of electric and magnetic field quantities are of paramount interest in the characterization of electromagnetic environment of the proposed line. The purpose of this study was to analyze the behavior of electromagnetic fields generated by power lines in an area of strong population. Approach: The method applied in this study was gradual; examined the effects of different couplings between the different neighboring lines on behavior of electric and magnetic fields. Later, these lines will be used as a source of disturbance applied to the auditory implants EMC. Results: The implications of experimental results were also compared and discussed with new standard. Conclusion: The maximum intensities of electric and magnetic fields measured for the circuit of three lines close to each other, within the El-HADJAR substation were significantly lower than the ICNIRP reference levels for occupational and no occupational exposures.