Magnetic Rotation Research Articles

A comprehensive study on MnZn ferrite materials with high saturation magnetic induction intensity and high permeability for magnetic field energy harvesting

Manganese-zinc (MnZn) ferrites have important applications in energy conversion, transmission, and harvesting. MnZn ferrite for magnetic field energy harvesting is expected to enhance the saturation magnetic induction (Bs), initial permeability (μi), and Curie temperature (Tc) aspects simultaneously, which is beneficial to the energy harvesting efficiency and safety of the device. In this paper, various formulations of MnZn ferrite samples were prepared by the conventional oxide ceramic process. The cation distribution was determined through Rietveld refinement of XRD patterns Based on this, the M–T curves were fitted by combining Néel molecular field theory with Brillouin functions. The greatest influence on the Curie temperature was found to be the molecular field coefficient between the A and B sites. The magnetization mechanism of MnZn ferrite was comprehensively analyzed by fitting the complex permeability spectrum, magnetocrystalline anisotropy constant, and magnetostriction coefficient. The ratio of domain wall displacement magnetization to domain rotation magnetization shows an increasing and then decreasing trend with Fe content, while |K1| shows an opposite trend. Finally, MnZn ferrite materials with excellent overall performance (Bs = 505mT, μi = 9016, Tc = 447 K) were prepared by investigating the magnetization mechanism.

Characteristics of the Starter–Alternator with Incorporated Permanent Magnets Made of a Dual-Phase Magnetic Material Rotor

Characteristics of the Starter–Alternator with Incorporated Permanent Magnets Made of a Dual-Phase Magnetic Material Rotor

Numerical Analysis of Williamson-Micropolar Ternary Nanofluid Flow Through Porous Rotatory Surface

This research introduces an advanced nanofluid model for optimizing the rate of heat transmission. The trihybrid nanofluid is constructed by suspending three distinct nanoparticles in a base fluid with diverse physical and chemical affinities. This study confronts the heat transfer characteristics of TiO2, Al2O3, and SiO2 boundary layer flow involving thermal radiation and slip scenarios. The controlling boundary layer equations are modified through an array of ordinary differential equations employing suitable similarity transformations, which have been solved by using bvp4c algorithm in MATLAB. As of yet, no prior investigation has ever been conducted on the flow of tri-hybrid nanofluid TiO2, Al2O3, and SiO2/H2O via rotatory surface. As a result, the current investigation has been undertaken to fill this gap, and the primary objectives of this work is to look into the aspects that optimise the heat transfer of base fluid (H2O) dissolved with tri-hybrid nanoparticles (TiO2, Al2O3, and SiO2) past a rotatory surface with slip conditions. The figures indicate that the presence of distinct nondimensional parameters in this analysis has a tremendous impact on the fluid motion inside the boundary layer. The plots obtained reveal that the diminution in particle movement is addressed simply by raising the Williamson parameter, magnetic parameter, and Forchheimer parameter. While the temperature profiles of the magnetic parameter, rotation parameter, and Williamson parameter demonstrate a reverse pattern. The findings are visualized in graphical format, and it is predicted that the tri-hybrid nanofluid has a greater thermal conductivity than the hybrid nanofluid and traditional fluid.

Effect of Magnetic Field on the Instability of Jeffrey Nanofluid (CuO + Blood and Cu + Blood) Filled in Hele-Shaw Cell with Rotation

There are so many works present in the literature with Hele-Shaw cell, Jeffrey nanofluid, magnetic field, and rotation individually, but here we carried out the combined study of these and it is important because there are so many applications of these in engineering, it may be used in energy absorption in the solar panel, because of Hele-Shaw cell is approximately similar to the solar panel. The main goal of the article is to analyse the instability of Jeffrey nanofluid filled in Hele-Shaw cell in the presence of the magnetic field and rotation. During the investigation, we obtained that the rotation parameter directly affects the behaviour of the Hele-Shaw number and magnetic Chandrasekhar number. Here we also analyze the behaviour of two different types of nanofluids (CuO + Blood and Cu + Blood) on the onset of convection and found that the onset of convection gets delayed in (Cu + Blood). Heat/mass transfer in the system has been analyzed by Mathematica NDSolve and Runge-Kutta-Fehlberg method (RKF-45) and found that the rate of heat/mass transfer is exactly the same by both methods. The Taylor number directly affects the behaviour of heat transfer and also found that the onset of convection gets advanced in Jeffrey fluid.

Nonlinear dynamics of large-amplitude, small-scale Alfvén waves

We study large-amplitude, very oblique Alfvén waves at low β, with small gradient length scales, comparable to the ion inertial scale di. Such waves have large density fluctuations and slight dispersion from finite-frequency and finite-ion sound radius effects. We derive a weakly nonlinear evolution equation governing the behavior of the waves in one dimension and categorize the different solitons appearing in different regimes: the regular solitons involve full rotations of the transverse magnetic field similar to modified Korteweg–de Vries (mKdV) solitons (our nonlinear equation reduces to the mKdV equation in the long-wavelength limit). However, for sufficiently small soliton widths, some become singular, small-amplitude solitons with density discontinuities and, are, thus expected to become strongly dissipative in a real plasma. These solutions may be useful in explaining some aspects of the sharp, ion-scale magnetic field rotations (switchbacks) observed in the near-Sun solar wind by Parker Solar Probe.

Slot-pole structure investigation for radial flux permanent magnet generator

Recently, Radial Flux Permanent Magnet Generator (RF-PMG) has been applied in various applications of generator. The configuration of the radial flux permanent magnet is the magnetic rotor arranged in a circle rotation while the inner core attached to the rotor’s center. However, various sizes and structure of RF-PMG can produce different output power levels, cogging torque and generator’s flux regulation capability. By investigating the output voltage and cogging torque value, this paper showed the suitable slot-pole combinations that can influence the output performance of the generator by using 2D-Finite Element Analysis. This investigation shows the comparison of the slot-pole that resulting the least cogging torque value and high output voltage, 0.1739Nm and 180.81V respectively. Hence, 36slots-30poles indicates as the best slot-pole combinations.

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We study the dissociation effect of J/Ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J/\\Psi $$\\end{document} in magnetized, rotating QGP matter at finite temperature and chemical potential using gauge/gravity duality. By incorporating angular velocity into the holographic magnetic catalysis model, we analyze the influence of temperature, chemical potential, magnetic field, and angular velocity on the properties of J/Ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J/\\Psi $$\\end{document} meson. The results reveal that temperature, chemical potential, and rotation enhance the dissociation effect and increase the effective mass in the QGP phase. However, the magnetic field suppresses dissociation, and its effect on the effective mass is non-trivial. Additionally, we explore the interplay between magnetic field and rotation, identifying a critical angular velocity that determines the dominant effect. As a parallel study, we also examine the rotation effect in the holographic inverse magnetic catalysis model, although the magnetic field exhibits distinctly different behaviors in these two models, the impact of rotation on the dissociation effect of J/Ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J/\\Psi $$\\end{document} is similar. Finally, we investigate the influence of electric field and demonstrate that it also speeds up the J/Ψ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J/\\Psi $$\\end{document} dissociation.

A wearing orientation-independent electromagnetic self-powered sensor for human activity recognition based on biomechanical energy scavenging

Self-powered human activity recognition (HAR) using vibration energy harvesters attracts broad interest in wearable electronics. To address the challenge of making such sensors adaptive to human motions, we design a novel electromagnetic self-powered HAR sensor with an eccentric-rotor-based vibration pick-up structure. Its adaptability to the low-dominant-frequency (<5 Hz) and volatile-direction wrist movement is realized by the low resonant frequency and in-plane rotary responses of this magnetic rotor, promoting the biomechanical motion pick-up. Particularly, its capability of providing repeatable and human-activity-related voltage signals is revealed and proved wearing orientation-independent. On this basis, walking, jogging, and running at 2–8 km/h are recognized precisely by multi-feature-based signal representation and random forest models, achieving comparable classification accuracies over 97% with different wearing orientations. The practicality of this sensor is also enhanced by its light weight and small volume. The proposed sensor and signal analyzing method offer a promising and versatile solution to convenient HAR.

Probing the strongly correlated magnetic state of Co2C nanoparticles at low temperatures using μSR

Co2C nanoparticles (NPs) are amongst transition metal carbides whose magnetic properties have not been well explored. An earlier study (Roy et al 2021 J. Phys.: Condens. Matter 33 375804) showed that a pellet made from Co2C NPs exhibits exchange bias (EB) effect below a temperature, T EB = 50 K and a spin glass (SG) feature emerges below T SG = 5 K. In the current study we use magnetic, electrical transport, specific heat, and muon spin rotation (μSR) measurements to explore further the magnetic properties of a pellet made with 40 nm diameter pure Co2C NPs. We uncover the onset of Kondo localization at Kondo temperature T K (= 40.1 K), which is close to the onset temperature (T EB) of the EB effect. A crossover from the Kondo-screened scenario to the Ruderman–Kittel–Kasuya–Yosida interaction-dominated regime is also observed for T < T K. Temperature-dependent specific heat measurement further supports the Kondo localization scenario in the pellet and shows the heavy fermionic nature of the strongly correlated electronic state in Co2C. The zero field μSR asymmetry spectra in the low-temperature regime are characterized by two distinct fast and slow relaxation rates. The spectra show the absence of long-range magnetic order in the sample. However, our analysis suggests the NPs-pellet shows the presence of a dominant magnetically disordered fraction and a smaller fraction with short-range order. Muons in the disordered fraction exhibit a slower relaxation rate, while muons in the smaller fraction with short-range order exhibit a faster relaxation rate. We observe an increase in this fast relaxation rate between T EB and T SG. This increase below T EB ∼ 50 K suggests a slowing down of the fluctuating local magnetic environment around muons. Transverse field-μSR asymmetry spectra show the emergence of a stable, multi-peaked local magnetic field distribution in the pellet below T EB. Longitudinal field μSR spectra shows distinct changes in the dynamics of fluctuations suggesting the presence of a frozen glassy like state below 6 K. Based on our results, we suggest that below T EB, the pellet of Co2C NPs develops a magnetic interface that separates the two magnetic fractions; one is a disordered fraction, and the other is a fraction with short-range order. The exchange interaction that sets in below T EB at the interface couples the two fractions, leading to a suppression of the fluctuations. With the suppression of magnetic fluctuations below T EB, strong correlation effects in the electronic state of Co2C lead to Kondo localization.

Temperature dependent behavior of a kA-class superconducting flux pump with a continuous cylindrical stator

A high temperature superconducting (HTS) dynamo is a type of device known as a “flux pump” that can inject DC into a closed superconducting circuit. Here, we report experimental results from a variable-temperature dynamo-type HTS flux pump operated within a cryo-cooled chamber. This device employs a “continuous stator” topology, whereby an HTS “coated conductor” is wrapped to form a cylinder around a mechanical rotor such that applied flux from the rotor magnet must always penetrate the stator. This leads to a high current device that can inject &amp;gt;1 kA into a series-connected HTS coil at 53 K. The open-circuit DC output voltage (Voc) from this HTS dynamo has been studied at stator temperatures between 35 and 95 K and attained a maxima at a temperature ∼5 K lower than the stator Tc. At lower temperatures, Voc decreases and falls to zero below ∼40 K. This non-intuitive effect is found to be due to flux-screening by critical currents flowing with the HTS stator, which increase with decreasing temperature. These shielding currents prevent flux from penetrating the HTS stator and, hence, reduce the magnitude of locally induced emf (and thus DC output) within the HTS film. A key implication of these results is that all magnetically driven HTS flux pumps should be operated at temperatures well above their flux-screening point, and this consideration must be taken into account for future designs of multi-kA class HTS flux pumps.

Solution of MHD-stokes flow in an L-shaped cavity with a local RBF-supported finite difference

One of the popular meshless methods for solving governing equations in applied sciences is a local radial basis function-finite difference (RBF-FD). In this paper, we proposed a new idea for an L- shaped (or like T- and Z-shaped) domain based on the domain decomposition. RBF-FD formulation is used at the interface points to get a better solution, while the classical FD is applied to all sub-regions. We use the algorithm based on the Gaussian-RBF (RBF-GA) in the stable calculation of the weights to avoid choosing optimal shape parameters. Stencil size is considered the nearest n-points (9,12,15) and benchmark results are presented for divided-lid driven cavity. Further, Navier–Stokes equations adding the Lorentz force term with Stokes approximation for a single-lid L-shaped cavity exposed to inclined magnetic field are solved by the devised numerical method. The flow structure is analyzed in aspect of streamline topology under the various magnetic field rotation (0∘≤α≤90∘ ) and its strength (M=10,30,50,100 ).

Magnetic properties and crystallization behavior of Fe-based nanocrystalline strips fabricated by twin-roll casting

In this study, the Fe78.4B12.3Si7.6C1Cu0.7 MG strip with a thickness of 157 µm was produced via twin-roll casting. The increased thickness resulted in a lower colling rate, lower energy state, and smaller free volume content. Moreover, the tremendous squeezing force applied during casting caused significant residual stress. Dense atomic stacking with high stress residual suppressed the magnetic domain rotation and domain-wall movement, producing a great coercivity (Hc). Two-pass rapid annealing(TPRA) was explored to improve the soft magnetic properties. Low-temperature annealing eliminated the residual stress, reducing the stress anisotropy and magnetic domain pinning of strips. A co-existing structure of residual amorphous and α-Fe(Si) phase was produced after high-temperature annealing. Fine α-Fe(Si) grain size of 24 nm decreased the magnetocrystalline anisotropy, and a great volume fraction of 71.3 % reduced the magnetostriction coefficient from 30 to 4.33 ppm. Finally, the Hc decreased from 27.4 to 6.4 A·m−1 after TPRA.

Research on Rotor Loss and Rotor Structure Optimization of Rare Earth Permanent Magnet Synchronous Motors in the Weak Field Area

The rotor loss of rare earth permanent magnet synchronous motor (PMSM) affects the efficiency and reliability of the motor and is an important research direction of rare earth permanent magnet synchronous motors. In this paper, the influence of rotational speed on the loss of the rotor core and the permanent magnet is analyzed through the analysis of the motor magnetic field and rotor loss calculation. Specifically, with the increase in rotational speed, the weak magnetic current increases, the amplitude of flux density change in the rotor core decreases, and the loss of the rotor core also decreases. The greater the influence of the harmonic current magnetic field on the outside of the rotor, the greater the loss. The core loss on the rotor is mainly distributed on the outside of the rotor. For further engineering applications, this paper analyzes the loss composition of three kinds of motors with different rotor structures and judges the optimal scheme based on the minimum loss. Finally, the correctness of this research is verified by comparing the experimental and simulation results of two kinds of motors with different rotor structures. The research content of this paper can provide a reference for the loss analysis and optimization and rotor structure selection of rare earth permanent magnet synchronous motor rotor design.

Synchronous Vibration Force Suppression of Magnetically Suspended CMG Based on Modified Double SOGI-FLL

The mass imbalance of the rotor will produce the synchronous vibration force that is transmitted to the magnetically suspended control moment gyroscope (MSCMG) through the magnetic levitation stator, which affects the imaging performance of the satellite. The suppression of the synchronous vibration force needs the speed signal. In order to solve the synchronous vibration force of the MSCMG when the speed measurement sensor fails, this paper proposed an modified double second-order generalized integral frequency-locked loop (SOGI-FLL) method, which uses the frequency of the disturbance signal generated through the mass imbalance of the rotor to adaptively estimate the rotor speed and suppress the synchronous vibration force generated by the active magnetic bearing system. The phase compensation is introduced to ensure the stability of the system in full frequency band. The electromagnetic force is directly used as the input signal of the control algorithm to achieve zero magnetic force control. Simulation and experimental are carried out, and the results are given to prove that the algorithm proposed in this paper can accurately estimate the rotation speed and achieve the vibration force suppression in the full rotation speed range. It is of great significance for the high-precision control of the active magnetic bearing rotor system.

Analysis of the Amount of Flux Variation on the HTS Surface by the Oscillation of HTS Magnetic Bearing Rotor

Magnetic bearing is used in flywheel energy storage system and can address energy loss at contact points in rotating because a rotor can be supported without contact points. However, in order to keep a rotor levitating, a control system is required. The HTS magnetic bearing levitates the rotor by pinning force without a control system and of a rotor including permanent magnets and a HTS. The vertical oscillation of the rotor is suppressed because the flux is interlinked to the outside of the HTS. Therefore, the rotor oscillates in the horizontal direction in rotating. This oscillation generates the flux variation on the HTS surface and it decreases the number of revolutions. This paper proposes an analysis of flux variation on the HTS surface by the oscillation of HTS magnetic bearing rotor. The effect of the oscillation of the rotor on the number of revolutions is shown by the analysis of the flux variation of the HTS. In the analysis results, the amount of flux variation increased rapidly because the rotor increases the oscillation. The flux variation causes a decrease the in number of revolutions and the small oscillations cause flux variation on the HTS surface. However, the decrease in the number of revolutions is small because the amount of the flux variation is small.

PARAMETERS OF RADIO PULSARS AT DIFFERENT DISTANCES FROM THE “DEATH LINE”

Calculations of angles \(\beta \) between magnetic moments and rotation axes have been carried out for radio pulsars located at different distances from the “death line”. It is shown that these angles decrease from 36° to 10° when pulsars move to the “death line”. Such values correspond to kinematic ages from 1 to 10 millions of years. It is detected also that for these ages radio luminosities of pulsars decrease. This means that radio pulsars fade out when their age increases.

Nanostructure Effect on Magnetization Processes in FePt Polytwin Crystals.

In FePt polytwin crystals with large magnetocrystalline anisotropy, the boundaries may play a crucial role in the magnetization processes occurring under an external magnetic field. In this study, we employed phase-field modeling and computer simulations to systematically investigate the effect of three types of polytwin boundaries-namely, symmetric (Type I), asymmetric (Type II), and mixed (Type III) boundaries-on magnetization processes as well as coercive fields under an external magnetic field along various directions. Because of the large anisotropy of FePt, the domain wall motion mechanism is usually dominant in the domain switching processes, while the magnetization rotation mechanism only becomes important at the late magnetization stage under a high external magnetic field. Among these three types of polytwin boundaries, the low coercivity is mainly due to the domain wall motion process, which starts from the intersection point at the polytwin boundary. The coercive field for the mixed polytwin boundary (Type III) is always in between the values of Type I and II.

A nonuniform demagnetizing field model for both static and dynamic responses of anisotropic magnetoresistive thin film sensors

In this paper, an anisotropic magnetoresistive (AMR) thin film sensor which can be used for magnetic scale has been prepared, and its output voltage is about 4.7–4.9 mV V−1. On the basis of the Stoner–Wohlfarth model and with considering the non-uniformity of the demagnetizing field along the width direction of the strips, both the static and dynamic responses of the AMR sensors have been calculated. The results have shown that the calculated results are in agreement with the experimental data. The magnetization rotation in the magnetic sensor strongly depends on the nonuniform demagnetizing field along the width direction. The magnetization at the center is easily rotated into the field direction, and the magnetization at the edge is difficult to be rotated. The smaller the width of the magnetoresistive strip is, the larger both the demagnetizing field at the edge and the saturation field of the magnetic sensor are. The results are helpful for understanding the magnetization rotation of magnetic sensors and developing the magnetic sensors with high performance.

Species dependence of the impurity injection induced poloidal flow and magnetic island rotation in a tokamak

Recent experiments have demonstrated the species dependence of the impurity poloidal drift direction along with the magnetic island rotation in the poloidal plane. Our resistive MHD simulations have reproduced such a dependence of the impurity poloidal flow, which is found mainly determined by a local plasmoid formation due to the impurity injection. The synchronized magnetic island rotation is dominantly driven by the electromagnetic torque produced by the impurity radiation primarily through the modification to the axisymmetric components of current density.

Synchronous disturbance suppression of active magnetic bearing rotor systems using variable period adaptive control algorithm

This paper aims to investigate the issue of suppressing synchronous vibration in active magnetic bearing (AMB) systems. The rotor mass imbalance is a challenging problem for the AMB system, which will cause synchronous vibration and severely affect the system stability and safety. However, existing algorithms based on the iterative feed-forward control strategy find it difficult to simultaneously ensure system’s stability and competent convergence performance. They struggle to maintain tolerable robustness within the system operating bandwidth. This paper proposes a variable period adaptive control algorithm to address these challenges. The overall control scheme can achieve current and displacement elimination separately by switching control structures and is applicable to variable speed conditions. This algorithm can adaptively adjust the iteration period based on rotational speed to ensure both splendid convergence performance and system dynamic performance. Furthermore, this work employs the Lyapunov method to analyze the algorithm’s asymptotic stability and provides a lookup table for algorithm parameters. This could significantly enhance the robustness and stability of the algorithm within the system operating bandwidth. Finally, this methodology has proven to be effective and superior in simulations and experiments.