Exact Magnetic Field Research Articles

Exact Analytical Magnetic Field Analysis, Optimization Design and Realization of an Eccentric Magnetic Harmonic Gear

The eccentric magnetic harmonic gear (EMHG) has a high efficiency and high gear ratio capability for large torque transmission. The air gap magnetic field can be calculated using an exact analytical model. The analytical approach is based on the theoretically accurate hyperbolic cotangent transformation method. The relative permeance function, which is derived from the impact of rotor eccentricity, can be used to find the eccentric air gap magnetic field solution. The proposed analytical approach is employed as the basis for a genetic algorithm that is used to develop and optimize the EMHG. The analytical results are in good agreement with the finite element method results, which verifies the correctness and validity of the proposed analytical model. The experimental measurements on the dual-stage EMHG confirm the validity of the analytical prediction.

Use of integration to calculate the magnetic field in a space by using mathematica software for the effective production of nano-particles

One of the challenges is to know the exact value of magnetic field in a three-dimensional space which is unknown so far. In this paper we have used integration formula in a Mathematica software to calculate the exact magnetic field and then set up an experimental method to verify this experimentally by applying a magnetic field with a physical magnet of the diameter of 8.1 cm and height of 6 cm. Finally, a comparison between theoretical and experimental calculations is shown in two-dimensional and three-dimensional graphs.We develop a theoretical model by using Mathematica software to calculate the magnetic field for a one-sided magnet using a single electromagnetic coil and several electromagnetic coils. Similarly, we have developed a method to calculate the magnetic field using Mathematica software when two electromagnets are set on both sides of the arc plasma for a single coil and several coils. In all cases, theoretical data is verified by the experimental value. By comparing the graph for both one-sided and two-sided coils we have found a good agreement between the data with the experimental and theoretical values.

Characterization of the Gamma-ray Emission from the Kepler Supernova Remnant with Fermi-LAT

The Kepler supernova remnant (SNR) had been the only historic SNR that lacked a detection at GeV and TeV energies, which probe particle acceleration. A recent analysis of Fermi-LAT data reported a likely GeV γ-ray candidate in the direction of the SNR. Using approximately the same data set but with an optimized analysis configuration, we confirm the γ-ray candidate to a solid >6σ detection and report a spectral index of 2.14 ± 0.12stat ± 0.15syst for an energy flux above 100 MeV of (3.1 ± 0.6stat ± 0.3syst) × 10−12 erg cm−2 s−1. The γ-ray excess is not significantly extended and is fully compatible with the radio, infrared, and X-ray spatial distribution of the SNR. We successfully characterized this multiwavelength emission with a model in which accelerated particles interact with the dense circumstellar material in the northwest portion of the SNR and radiate GeV γ rays through π° decay. The X-ray synchrotron and inverse-Compton emission mostly stem from the fast shocks in the southern regions with a magnetic field B ~ 100 μG or higher. Depending on the exact magnetic field amplitude, the TeV γ-ray emission could arise from either the south region (inverse-Compton dominated) or the interaction region (π° decay dominated).

3D modeling of electromagnetic levitation coils

Electromagnetic levitation (EML) enables the handling of samples in a containerless manner, facilitating more precise measurements or manipulation of materials. Currently, EML coil design is based on two-dimensional (2D) mathematical models combined with empirical data and experience. We propose that employing a truly 3D model enables a more accurate and rational coil design. This approach shows significant differences in magnetic field, and the resulting lift and heating properties, when comparing a 2D and a 3D coil. A 3D coil, resembling the geometry of a 2D coil, requires more current to generate the same lift. Reversing the situation, a 3D coil producing the exact same magnetic field as a 2D coil has a vastly different design. Furthermore, we show that the assumption that the magnetic field is homogeneous in the axial plane within the sample volume is invalid, even for small samples, in the upper and lower regions of the coil. Using a 3D model, we design a coil capable of levitating and melting an iridium sphere with a diameter of 6 mm.

Pressure and Temperature Effects on the Magnetic Properties of Donor Impurities in a GaAs/AlGaAs Quantum Heterostructure Subjected to a Magnetic Field

Abstract: The exact diagonalization method has been used to solve the effective-mass Hamiltonian of a single electron confined parabolically in the GaAs/AlGaAs quantum heterostructure, in the presence of a donor impurity and under the effect of an applied uniform magnetic field. The donor impurity is located at distance (d) along the growth direction which is perpendicular to the motion of the electron in a two-dimensional heterostructure layer. We have investigated the dependence of the magnetization (M) and magnetic susceptibility (χ) of a GaAs/AlGaAs quantum heterostructure nanomaterial on the magnetic field strength (ω_c), confining frequency (ω_o), donor impurity position (d), pressure (P) and temperature (T). Keywords: Exact diagonalization, Donor impurity, Magnetic field, Magnetization, Magnetic susceptibility, Pressure and temperature.

Analytical Calculation of Magnetic Field in Fractional-Slot Windings Linear Phase-Shifting Transformer Based on Exact Subdomain Model

Fractional-slot windings linear phase-shifting transformers (FW-LPSTs) are a new type of transformer that can be used as an important component of multi-rectifier and multi-inverter systems. The FW-LPSTs are proposed for the first time, and few scholars have studied their magnetic field. However, accurate calculation of magnetic field distribution of the FW-LPSTs is the premise of the optimal design of the ontology, and the establishment of an accurate analytical model which remains a challenging task is the key to solving the magnetic field distribution. In view of the limitation of traditional analytical theory in solving the magnetic field, the FW-LPST model based on the exact subdomain method is proposed to obtain the exact magnetic field distribution. Considering the influences of the permeability and the structural parameters of the slot subdomain and the interaction of all slots on the distribution of the magnetic field, the governing equations of the air gap and slot subdomains are established using magnetic vector potential as the variable. According to the boundary conditions of each subdomain, all equations of the boundary condition are listed based on the Fourier series method. Finally, the vector magnetic potential and open-circuit magnetic flux density distribution of each subdomain are solved. The model accurately analyzes the influence of the cogging effect on the magnetic field distribution. The inductances of the primary side and the induced potentials of the secondary side are solved using the magnetic flux linkage method. The accuracy of the proposed analytical model is verified by comparison of the results obtained with those obtained by the finite element method.

Conducting-Coil Assembly for Producing Three-Dimensional Magnetic Null Points

Three-dimensional magnetic null points (3D nulls) are sites of dynamic activity and particle acceleration in astrophysical environments. Future laboratory infrastructures to validate theoretical models of observed plasma dynamics about 3D nulls will benefit from an experimental infrastructure that closely reproduces these analytical potential magnetic fields. As such, a conducting-coil assembly is presented that closely matches the theoretical form of a 3D null within an interior volume. Exact magnetic field solutions are attained for a spherical aggregation of circular current-carrying coils with finite cross sections that create a central magnetic null point of vanishing magnetic energy density. This configuration is shown to replicate the fan-plane--spine-axis topology of 3D nulls to a high order within the central volume close to the null. Finally, numerical analyses demonstrate that the investigated architecture is scalable over wide size and energy ranges. Applications of the presented conducting-coil assembly include sophisticated next-generation plasma experiments and particle accelerators.

Effects of Coronal Magnetic Field Structures on the Transport of Solar Energetic Particles

Abstract This Letter presents a model calculation of solar energetic particle (SEP) transport to test the sensitivity of the distribution of escaped SEPs in interplanetary space and dependence upon the details of the magnetic field structure in the corona. It is applied to a circumsolar event on 2011 November 3, in which SEPs are observed promptly after the solar event eruption by three spacecraft (the twin Solar TErrestrial RElations Observatories (STEREO-A and STEREO-B) and ACE) separated by more than 100° in longitude from each other. The corona magnetic field reconstructed from photosphseric field measurements using the PFSS method changes substantially before and after the solar eruption, especially around the active region. The locations of open field regions, separatrix surfaces including the heliospheric current sheet, and footpoints of magnetic field lines connected to the spacecraft location have shifted substantially. We inject 100 keV energetic electrons on the open field lines at 1.5 R s within the size of observed coronal mass ejections (CMEs) and follow their propagation in the corona and the interplanetary space. We find that with a perpendicular diffusion due to field line random walk equal to 10% of the supergranular diffusion rate, the overall distribution of escaped SEPs does not change much even though the region of open field lines from SEPs has changed. The result suggests that detailed small-scale coronal magnetic field structures and the exact magnetic field connection are not crucially important for observing SEPs in the interplanetary space.

Design of a low cogging torque Axial Flux Multilayer Permanent Magnet Synchronous Machine for wind turbines applications

In wind turbine generating systems, Axial Flux Permanent Magnet Synchronous Generators (AFPMSG) are becoming increasingly popular due to the many advantages they offer. Nevertheless, these machines suffer from the so-called cogging torque that affects the self-start ability and causes noise and mechanical vibration. Therefore, minimizing its effect is a major design concern for a reliable and smooth operation of small wind turbines. This paper presents a new method for reducing cogging torque based on stacking and shifting rotor magnets in the normal direction. First, the exact magnetic field distribution is computed using Maxwell's equations in magnetostatics. This analytical model takes into account the armature slotting effect and the multilayer permanent magnets configuration. Then, the cogging torque is computed by means of Maxwell's stress tensor. The accuracy of the proposed model is validated by FEA. Simulation results show that a peak magnitude reduction of 80% can be achieved

Large-signal field analysis of a linear beam travelling wave tube amplifier for the anisotropically conducting tape helix slow-wave structure supported by dielectric rods

The large-signal behavior of traveling wave tube amplifier for a linear beam dielectric loaded anisotropically conducting tape helix slow wave structure (SWS) is realized through a swift and reliable field analysis. Using Green’s function sequence, the field components in the SWS are designated as nonlinear functionals of electron arrival time. The electron arrival time in the beam region is formulated into a nonlinear operator in the Banach space mapping form by substituting the axial electric field component into the electron ballistic equation. The nonlinear beam–wave interaction is then obtained by determining the electron arrival time through extensive successive approximations, and thus exact electric and magnetic field components in the tape helix SWS are attained. The numerical computation of the proposed model yields definitive analytical results for the electron exit velocity, induced surface current density, power gain, conversion efficiency, and optimum interaction length.

Magnetic Fiber Integrator and its Application in Precision Noninvasive DC Current Sensor

This paper is concerned with novel method of exact magnetic field sensing and line integration along path required for specific application. One of important applications is the electric current measurement. The sensor based on the presented method can be therefore used as precision dc current sensor. The realized openable flexible current probe based on the magnetic fiber integrator can cover current levels from fraction of A to tens of kA with negligible power and space requirements. Due to the true line integration, the measured current value is independent of areal distribution of the magnetic field, and therefore, the initial laboratory calibration is valid for field applications. The theory is experimentally validated with magnetic integrator for electrical current measurement, but it is not limited to this application only. The method is applicable in variety of instruments exploiting magnetic field evaluation.

Electromagnetic Wave Theory for Calculation of Exact Magnetic Field in Case of BWO

Overall efficiency of high power microwave generating device depends upon input current in the form of electron beam and currents required for electromagnets. In order to increase the efficiency of device, if electromagnets are replaced by permanent magnets, overall efficiency of device shall increase. So, calculation of exact magnetic field is required. In this paper, the exact relation of magnetic field required in high power microwave generation using Backward Wave Oscillator (BWO) is found. BWO interacts with slow waves and is the most promising device to produce high power microwaves. The interaction involves the beams from high current density and the waveguide mode. An exact relation that specifically relates the various parameters of the waveguide like slow wave structures (SWS) dimensions, input beam voltage and operational frequency with axial magnetic field is derived. The derived equation gives calculation of exact values of magnetic field for focusing of beams. Theoretical and simulated work show good agreement with the previously available experimental data. So, with the derived electromagnetic wave relation exact value of magnetic field is calculated for desired frequency and power regime.

Correction to “Closed orbits of a charge in a weakly exact magnetic field”

Correction to “Closed orbits of a charge in a weakly exact magnetic field”

Exact magnetic field control of nitrogen-vacancy center spin for realizing fast quantum logic gates

The negatively charged nitrogen-vacancy (NV) center spin in diamond can be used to realize quantum computation and to sense magnetic fields. Its spin triplet consists of three levels labeled with its spin z-components of +1, 0, and -1. Without external field, the +1 and -1 states are degenerate and higher than the 0 state due to the zero-field splitting. By taking the symmetrical and anti-symmetrical superpositions of the +1 and -1 states as our qubit basis, we obtain exact evolution operator of the NV center spin under time-dependent magnetic field by mapping the three-level system on time-dependent quantum two-level systems with exact analytical solutions. With our exact evolution operator of the NV center spin including three levels, we show that arbitrary qubits can be prepared from the starting 0 state and arbitrary rapid quantum logic gates of these qubits can be realized with magnetic fields. In addition, it is made clear that the typical quantum logic gates can be accomplished within a few nanoseconds and the fidelity can be very high because only magnetic field strength needs to be controlled in this approach. These results should be useful to realizing quantum computing with the NV center spin systems in diamond and exploring other effects and applications.

Effect of sensor positioning error on the accuracy of magnetic field mapping result for NMR/MRI

Nowadays the magnetic field mapping is widely used in the design and analysis of the NMR/MRI magnet system, and the accuracy of mapping result has become more and more important. There are several factors affecting the accuracy of the mapping such as the mapping method, the precision of the sensor, the position of the measurement points, the calculation accuracy, and so on. In this paper the error due to the misalignment of the measurement points was discussed. The magnetic field in the central volume was mapped using an indirect method in an MRI magnet system and the magnetic field was fitted to a polynomial. Considering the misalignment between the original measurement points and the practical measurement points, there must be some errors in the mapping calculation and we called it positioning error. Several comparisons of the positioning error have been presented through the theoretical estimates and the exact magnetic field values. Finally, the allowable positioning errors were suggested to guarantee the accuracy of the magnetic field mapping within a certain degree for an example case.

Catheter Position Tracking System Using Planar Magnetics and Closed Loop Current Control

This paper presents an electromagnetic system for five degrees of freedom position and orientation sensing with application in a virtual bronchoscopy system. Planar magnetic source coils were manufactured on printed circuit boards for reproducibility and low-cost manufacturing. The exact magnetic field of each coil is calculated using a filament-based approach. A constant ac current amplifier is used to drive each coil at an independent frequency and a synchronous demodulator calculates each associated magnetic field component using the current waveform as a reference signal. Commercially available search coil sensors are used and a comparison between shielded and unshielded probes is presented. Extensive testing with two separate methods has shown the accuracy of the system to be between 1 and 2 mm. The use of a novel closed loop coil driver has been found to offer excellent magnetic field stability and significant reduction in crosstalk interference.

Transport properties of two-dimensional electrons through multiple magnetic barriers

Transport properties of 2-dimensional electron system in a varying magnetic flied are investigated theoretically by a transfer matrix technique. The exact magnetic field profiles and the corresponding vector potentials are presented instead of simulated ones. The results show that several transmission domains are formed and each domain contains (N−1)-fold resonance splitting which fully depends on the number of magnetic barriers N. The computed conductance also exhibits rich transfer properties. Three peaks are observed in the low energy range. With the increasing of N, the conductance curves tend to coincide with each other as the tilting angle of magnetization relative to z direction equals to π/2, while the conductance curves shift downwards for other θ. All of our calculations reveal the important features of electron tunneling through multiple magnetic barriers.

Closed orbits of a charge in a weakly exact magnetic field

We prove that for a weakly exact magnetic system on a closed connected Riemannian manifold, almost all energy levels contain a closed orbit. More precisely, we prove the following stronger statements. Let $(M,g)$ denote a closed connected Riemannian manifold and $\sigma$ a weakly exact 2-form. Let $\phi_{t}$ denote the magnetic flow determined by $\sigma$, and let $c$ denote the Mane critical value of the pair $(g,\sigma)$. We prove that if $k>c$, then for every non-trivial free homotopy class of loops on $M$ there exists a closed orbit with energy $k$ whose projection to $M$ belongs to that free homotopy class. We also prove that for almost all $k<c$ there exists a closed orbit with energy $k$ whose projection to $M$ is contractible. In particular, when $c=\infty$ this implies that almost every energy level has a contractible closed orbit. As a corollary we deduce that if $\sigma$ is not exact and $M$ has an amenable fundamental group (which implies $c=\infty$) then there exist contractible closed orbits on almost every energy level.

Analysis of dielectric resonator antenna excited by a slot at the waveguide shorted end

AbstractHemispherical dielectric resonator (HDR) antenna excited with a slot at the short circuited end of waveguide is analyzed theoretically and verified experimentally. The analysis is based on numerical solution of coupled integral equations discretized using the method of moments (MoM). The HDR is modeled using exact magnetic field Green's function because of the equivalent magnetic current in the slot. The field inside the waveguide is expressed in terms of modal vectors and modal functions. For the analysis of HDR antenna part, the modal series is represented as a sum of particular and homogeneous solutions. The particular solution is computed efficiently using spectral domain approach. The scattering parameter for the HDR antenna loaded at the waveguide end slot is calculated and compared with measured and finite element method (FEM) results. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1356–1359, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23382

RECTANGULAR WAVEGUIDE-FED HEMISPHERICAL DIELECTRIC RESONATOR ANTENNA

Hemispherical dielectric resonator (HDR) antenna excited with a thick slot at the short circuited end of waveguide is analyzed theoretically and verified experimentally. The problems are formulated using the Green’s function approach; with unknown slot currents solved using the method of moments (MOM). The HDR is modeled using exact magnetic field Green’s function due to the equivalent magnetic current in the slot. The field inside the waveguide is expressed in terms of model vectors and modal functions. Thickness of the slot is analyzed using cavity approach. For the analysis of HDR antenna part, the modal series is represented as a sum of particular and homogeneous solutions. The particular solution is computed efficiently using spectral domain approach. In order to determine the effects of varying design parameters on bandwidth and matching, sensitivity analysis is carried out using the code developed. Measurements were carried out to verify the theory, and reasonable agreement between them is obtained.