Magnetic Thickness Research Articles

Optimal Number of Flux Modulation Pole in Vernier Permanent Magnet Synchronous Machines

This paper aims to identify the optimal number of flux modulation pole (FMP) in Vernier permanent magnet synchronous machines (VPMSMs) with concentrated tooth-coil windings. First, the influence of number of FMP on machine performance is revealed based on the unified permanent magnet magnetomotive force permeance analytical model. It is found that for a fixed stator slot number, there always exists an optimal number of FMP to maximize the torque, thanks to the enhanced contribution by the fundamental permeance harmonic. Then, the influence of critical dimensional parameters, including the machine diameter, the permanent magnet thickness, and the width of FMP, on the electromagnetic performance of VPMSMs with different numbers of FMP are parametrically analyzed by both analytical and finite element analyses. Results show that the VPMSMs with the optimal number of FMP always have advantages of a higher torque density together with a reduced PM volume, particularly for those with a relatively large diameter. Finally, two VPMSM prototypes with different numbers of FMP are manufactured and tested to validate the analyses.

Evolution of magnetic anisotropy in cobalt film on nanopatterned silicon substrate studied in situ using MOKE

Evolution of magnetization behaviour of cobalt film on nano patterned silicon (1 0 0) substrate, with film thickness, has been studied. In situ magneto-optical Kerr effect measurements during film deposition allowed us to study genuine thickness dependence of magnetization behaviour, all other parameters like surface topography, deposition conditions remaining invariant. The nanopatterned substrate had a 8 nm thick amorphous silicon nitride surface layer. Thus, induced magnetic anisotropy in the Co film is expected to be of purely topographical origin, excluding any effect of the single crystalline Si (1 0 0) surface on magnetic anisotropy film due to possible epitaxy or surface step-induced anisoropy. In conformity with earlier results, the film induces a uniaxial magnetic anisotropy in the film, with its magnitude decreasing with increasing thickness. A magnetically dead layer of 2.6 nm forms at the interface with the substrate. Analysis of the magnetic layer thickness dependence of anisotropy shows that it has contributions from both, i) exchange energy which is volume dependent and, ii) stray dipolar fields at the surface/interface. This suggests that local magnetization follows only partially the topography of the rippled surface. As expected from energy considerations, for small film thickness, the local magnetization closely follows the surface contour of the ripples making the volume term as the dominant contribution. With increasing film thickness, the local magnetization gradually deviates from the local slope and approaches towards a uniform magnetization along the macroscopic film plane making the surface term as the dominant contribution. Significant deviation of the observed stray dipolar field contribution from the anisotropy energy calculated on the basis of Schlomann’s theory is observed, which can be attributed to several factors like, deviation of surface topography from an ideal sinusoidal wave, breaks of continuity along the ripple direction, topological defects like, pattern dislocations, and small film thicknesses compared to the correlation length of surface corrugations.

Surface Study of Fe3O4 Nanoparticles Functionalized With Biocompatible Adsorbed Molecules.

Surfaces of iron oxide of ferrimagnetic magnetite (Fe3O4) nanoparticles (MNPs) prepared by Massart's method and their functionalized form (f-MNPs) with succinic acid, L-arginine, oxalic acid, citric acid, and glutamic acid were studied by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR-S), UV-vis, thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and reflection electron energy loss spectroscopy (REELS). The XPS analysis of elements and their chemical states at the surface of MNPs and f-MNPs revealed differences in chemical bonding of atoms, content of carbon–oxygen groups, iron oxide forms, iron oxide magnetic properties, adsorbed molecules, surface coverage, and overlayer thickness, whereas the Auger parameters (derived from XPS and Auger spectra) and elastic and inelastic scattering probabilities of electrons on atoms and valence band electrons (derived from REELS spectra) indicated modification of surface charge redistribution, electronic, and optical properties. These modified properties of f-MNPs influenced their biological properties. The surfaces biocompatible for L929 cells showed various cytotoxicity for HeLa cells (10.8–5.3% of cell death), the highest for MNPs functionalized with oxalic acid. The samples exhibiting the largest efficiency possessed smaller surface coverage and thickness of adsorbed molecules layers, the highest content of oxygen and carbon–oxygen functionalizing groups, the highest ratio of lattice O2− and OH− to C sp2 hybridizations on MNP surface, the highest ratio of adsorbed O− and OH− to C sp2 hybridizations on adsorbed molecule layers, the closest electronic and optical properties to Fe3O4, and the lowest degree of admolecule polymerization. This high cytotoxicity was attributed to interaction of cells with a surface, where increased content of oxygen groups, adsorbed O−, and OH− may play the role of additional adsorption and catalytic sites and a large content of adsorbed molecule layers of carboxylic groups facilitating Fenton reaction kinetics leading to cell damage.

Science, Medicine, and the Anesthesiologist

Science, Medicine, and the Anesthesiologist

Dynamical mode coexistence and chaos in a nanogap spin Hall nano-oscillator

We utilize microwave spectroscopy to study the auto-oscillation modes in the nanogap spin Hall nano-oscillators based on Permalloy/Pt bilayers. We show that two distinct spin-wave modes appear in such oscillators, regardless of the magnetic film thicknesses or the size of the electrode gap. We identify the primary mode as a nonlinear self-localized bullet soliton localized at the center of the gap between the electrodes, which is excited over a broad range of currents, field magnitudes, and orientations. The secondary high-frequency mode appears at higher currents and coexists with the primary bullet mode. Micromagnetic modeling shows that this mode is stabilized by the dipolar field of the bullet, and its spatial profile exhibits two maxima offset from the center of the gap in two opposite directions collinear with the field. Simulations also suggest chaotic dynamics that emerges at large currents due to the incoherent coupling between the two modes. Our results demonstrate the possibility to induce and control complex nonlinear dynamical phenomena in spin Hall oscillators, which can be utilized in the emergent neuromorphic and reservoir computing applications.

Structural and magnetic properties of single domain CoFe2O4 magnetic nanoparticles dispersed in SiO2 matrix

Uniformly dispersed CoFe2O4 nanoparticles in SiO2 matrix have been synthesized in two-step process by a co-precipitation route at lower temperature (70 °C). Phase purity and average crystallite size of cobalt ferrite (CFO) and CoFe2O4 nanoparticles dispersed in SiO2 matrix (Si-CFO) have been evaluated to be 17.6 nm and 15.2 nm respectively. Bond edges and bond lengths were evaluated from Rietveld refinment confirms the existence of compressed and tensile strain in CFO and Si-CFO nanoparticles. The average particle sizes evaluated from transmission electron microscope (TEM) were found to be 16 and 17.3 nm respectively. Functional groups present in CFO and Si-CFO nanoparticles were investigated from Fourier transform infrared spectra (FTIR). Magnetic properties were investigated by vibrating sample magnetometry (VSM). Lower saturation magnetization (25.6) with enhanced coercivity (977) at room temperature has been observed for Si-CFO nanoparticles and attributed to the increased number of disordered surface spins with reduced effective magnetic anisotropy, enhanced stress and surface anisotropy. Strain in CFO and Si-CFO nanoparticles have been evaluated from magnetic measurements and corroborate well with the strain evaluated from Williamson-Hall-Isotropic strain model (W-H-ISM) and Williamson-Hall-Anisotropic strain model (W-H-ASM). Effect of specific saturation magnetization specific surface area and dead magnetic layer thickness on magnetic properties of pristine CFO and Si-CFO nanoparticles have been investigated. The enhanced specific surface area and dead magnetic layer thickness resulted in increased strain in Si-CFO with reduced saturation magnetization. The dead layer thickness is evaluated to be 1.34 nm and 1.96 nm for CFO and Si-CFO nanoparticles respectively.

Study on propagation properties of electromagnetic waves through a magnetized, collisional and inhomogeneous plasma under oblique incidence

The properties of electromagnetic waves propagation through a collisional, magnetized and inhomogeneous plasma with obliquely incident angles are investigated in this paper. The reflection, transmission, and attenuation ratios are calculated first with the scattering matrix method. Based on the derived formulas, we then analyze the effects of different parameters on the propagation properties under oblique incidence. Simulation results indicate that a larger incident angle causes a longer wave transmission distance in the plasma and is more likely to impede the waves propagation. Under an obliquely incident angle, both the transmission and attenuation ratios are greatly affected by other parameters, such as the effective plasma collisional frequency, background magnetic flux density, plasma thickness and electron density, additionally. These conclusions are of guiding significance to the applications of the interaction between electromagnetic waves and plasma.

Magneto-optical Kerr effect and nuclear resonant scattering study of uni-directional anisotropy in hard-soft magnetic bilayers

The present work reports the unconventional exchange bias (EB) phenomena in an exchange-coupled hard and soft magnetic bilayer system and the tunability of EB. The EB phenomena, i.e., shifting of the hysteresis loop of the soft (Fe) layer is observed when the hard magnetic (L10 FePt) layer is under the remanent state indicating the development of unidirectional anisotropy. The nuclear resonant scattering measurements clearly reveal the development of unidirectional anisotropy in the soft magnetic (Fe) layer, when the hard magnetic layer is under the remanent state. The magnetization reversal process is investigated by measuring two in-plane orthogonal components of magnetization, i.e., parallel (M∥) and perpendicular (M⊥) to the applied field using the magneto-optical Kerr effect (MOKE). When the magnetic field is applied parallel (antiparallel) to the biasing field direction, (HSAT) magnetization reversal is nonuniform, and on the other hand, the rotation of magnetization is observed when the magnetic field is applied away from the HSAT direction. In addition, the sign inversion of the M⊥ component is observed when the magnetic field is applied at the same angle on either side of the HSAT direction, which clearly imply the change in handedness of the chirality of spin structure during the magnetization reversal of the soft layer. Further, it is observed that the EB decreases with the increase of soft magnetic (Fe) layer thickness, demonstrating the tunable nature of EB phenomena even in these unconventional systems.

A magnetic torque optimization method for a hydraulic – magnetic coupling-drive cuttings cleaning tool

During the drilling process, cuttings carrying in the horizontal well section is relatively difficult, and cuttings beds form easily. A new type of hydraulic – magnetic coupling transmission cuttings cleaning tool is proposed, but the magnetic torque transmission influence mechanism, the optimal magnetic circuit structure and the magnet configuration are still yet to be studied. To this end, the finite element numerical simulation method is applied to analyze the influence of magnetic circuit structure and permanent magnet geometry on magnetic torque. The results of numerical simulation and laboratory experiments show that (1) the magnetic torque transmission efficiency can be improved by increasing the air gap flux density, reducing the magnetic reluctance and increasing the magnetostatic energy accumulation; (2) the magnetic torque increases first and then decreases as the number of pole-pair increases. The magnetic torque of 12 pairs of pole pairs reaches the maximum value; (3) by the coupling of the amount of magnets under the constraints of the effective section magnet coverage area percentage and the thickness of the magnet, it is obtained that when the thickness of the permanent magnet is 8.4 mm and the magnet coverage area percentage on the effective section of the tool is 71%, the maximum magnetic torque is generated per unit volume of magnet; (4) the absolute error of the indoor experimental result and the numerical simulation result is less than 17%, which can meet the engineering calculation accuracy requirements. It is concluded that the established numerical simulation model is reasonable and can be used as a technical means for the optimization analysis of the tool structure.

Voltage regulation Rate and THD optimization analysis of coreless axial flux PM synchronous generator for wind power generation

The basic design and characteristic analysis of the coreless axial flux permanent magnet synchronous generator (AFPMSG) for small wind power generation are carried out. The prototype is manufactured and tested to verify the designed generator. In addition, to reduce the voltage regulation rate and harmonic content of the generator, the optimal design is carried out on the basis of the original generator. The voltage regulation rate and THD of a coreless AFPMSG using the Halbach permanent magnet array are studied. The effects of different generator parameters such as pole arc coefficient, air gap length, permanent magnet thickness, and number of turns in series per phase on the voltage regulation rate and THD are analyzed when the generator is loaded with pure resistance. Because the various parameters of the generator are affected each other, the Taguchi algorithm was adopted for multi‐objective optimization. The influence proportion of different generator parameters on the voltage regulation rate and THD was analyzed. According to the results, the parameters are reasonably selected to design the generator and improve the performance of the generator. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Microstructure Characteristics of 2:17 SmCo Commercial Magnets With Different Coercivities

The correlation between microstructure and magnetic properties of 2:17 SmCo commercial magnets 32 H and 32 L is studied. The 32 H magnet with high coercivity has an excellent (00l) orientation texture, and its magnetic properties are (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 29.47 MGOe, B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 11.20 kG, and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> = 29.45 kOe. The magnetic properties of the 32 L magnet with low coercivity are (BH) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 29.28 MGOe, B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 11.40 kG, and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> = 9.829 kOe. The electron probe microanalysis results show that a Cu-lean grain boundary region is obvious in the 32 H magnet, which affects the squareness of the demagnetization curve. The transmission electron microscope result shows that the cell size and cell boundary thickness of high and low coercivity magnets are 129.32 and 9.83, and 90.94 and 7.87 nm, respectively. But the cell structure of the 32 H magnet is more complete and clearer than that of the 32 L magnet. The difference of the Cu concentration between the cell boundary phase and cell phase in the 32 H magnet is bigger than that of the 32 L magnet, which is really responsible for the high coercivity.

Parametric Design and Optimization of Magnetic Gears With Differential Evolution Method

Recently, magnetic gears have drawn wide attention due to their inherent merits, such as noncontact operation, high torque density, and intrinsic overload protection. In this paper, an analytical calculation based on magnet magnetomotive force permeance theory is adopted to analyze the modulation effect in a magnetic gear. After that, the effects of some key parameters on magnetic gear performance are investigated, including the air-slot-opening-to-pole-pitch ratio $c_0$ , the magnet-arc-to-permanent-magnet-pole-pitch ratio $\alpha$ , and the permanent magnet thickness $h_m$ . In particular, three types of steel pole pieces are considered: radial slots, parallel teeth, and parallel slots. A global optimization design is then carried out by using the differential evolution algorithm, and some useful suggestions are derived from the optimal Pareto range. Finally, the determination of outer rotor yoke thickness is discussed considering the iron saturation, and the iron loss distribution is investigated. This paper will be helpful for the design and optimization of a coaxial magnetic gear.

Effects of Design Parameters on the Multiphysics Performance of High-Speed Permanent Magnet Machines

In the design of high-speed permanent magnet machines (HSPMMs), comprehensive effects of design parameters on the various properties of electromagnetic loss, rotor stress, rotor critical speed, and temperature distribution must be analyzed to obtain the optimal design. The aim of this paper is to examine the effects of design parameters, such as the pole number, stator slots number, number of conductors per slot, permanent magnet (PM) thickness, PM pole arc coefficient, air gap length, rotor diameter, core length, and sleeve thickness, on multiphysics performance based on a high-power HSPMM. A reasonable design is determined according to the above-mentioned analysis that satisfies all specified multiphysics constraints. The theoretical results are confirmed by the experimental results on a prototype in terms of electromagnetic, mechanical, and thermal characteristics such as back electromotive force, no-load loss, full-load current, overspeed experiment, and temperature distribution.

Performance Analysis of Conical Permanent Magnet Couplings for Underwater Propulsion

Permanent magnet couplings (PMCs) are widely used in underwater propulsion because it can solve the deep-sea sealing problem effectively. In this paper, a new type of conical permanent magnet coupling (CPMC) is proposed, which is able to match the tail shape of the underwater vehicle and make full use of the tail space to increase pull-out torque capability. Based on the three-dimensional finite element method (3D-FEM), the electromagnetic characteristics of an initial model for CPMC are analyzed. In order to facilitate the design and optimization of CPMC, an equivalent three-dimensional (3D) analytical method for the pull-out torque calculation is presented, and its accuracy is verified by comparison with the 3D finite element results. Finally, the influence of design parameters such as half-cone angle, pole pair, pole arc coefficient and permanent magnet thickness on maximum pull-out torque and torque density of CPMC is analyzed, and a preliminary optimization model is obtained.

Constraining the geotherm beneath the British Isles from Bayesian inversion of Curie depth: integrated modelling of magnetic, geothermal, and seismic data

Abstract. Curie depth offers a valuable constraint on the thermal structure of the lithosphere, based on its interpretation as the depth to 580 ∘C, but current methods underestimate the range of uncertainty. We formulate the estimation of Curie depth within a Bayesian framework to quantify its uncertainty across the British Isles. Uncertainty increases exponentially with Curie depth but this can be moderated by increasing the size of the spatial window taken from the magnetic anomaly. The choice of window size needed to resolve the magnetic thickness is often ambiguous but, based on our chosen spectral method, we determine that significant gains in precision can be obtained with window sizes 15–30 times larger than the deepest magnetic source. Our Curie depth map of the British Isles includes a combination of window sizes: smaller windows are used where the magnetic base is shallow to resolve small-scale features, and larger window sizes are used where the magnetic base is deep in order to improve precision. On average, the Curie depth increases from Laurentian crust (22.2±5.3 km) to Avalonian crust (31.2±9.2 km). The temperature distribution in the crust, and associated uncertainty, was simulated from the ensemble of Curie depth realizations assigned to a lower thermal boundary condition of a crustal model (sedimentary thickness, Moho depth, heat production, thermal conductivity), constructed from various geophysical and geochemical datasets. The uncertainty in the simulated heat flow field substantially increases from ±10 mW m−2 for shallow Curie depths at ∼15 km to ±80 mW m−2 for Curie depths &gt;40 km. Surface heat flow observations are concordant with the simulated heat flow field except in regions that contain igneous bodies. Heat flow data within large batholiths in the British Isles exceed the simulated heat flow by ∼25 mW m−2 as a result of their high rates of heat production (4–6 µW m−3). Conversely, heat refraction around thermally resistive mafic volcanics and thick sedimentary layers induce a negative heat flow misfit of a similar magnitude. A northward thinning of the lithosphere is supported by shallower Curie depths on the northern side of the Iapetus Suture, which separates Laurentian and Avalonian terranes. Cenozoic volcanism in Northern Britain and Ireland has previously been attributed to a lateral branch of the proto-Icelandic mantle plume. Our results show that high surface heat flow (&gt;90 mW m−2) and shallow Curie depth (∼15 km) occur within the same region, which supports the hypothesis that lithospheric thinning occurred due to the influence of a mantle plume. The fact that the uncertainty is only ±3–8 km in this region demonstrates that Curie depths are more reliable in hotter regions of the crust where the magnetic base is shallow.

Optimization of surface-mounted permanent magnet brushless AC motor using analytical model and differential evolution algorithm

Abstract This paper discusses the optimization of surface-mounted permanent magnet brushless AC (PMBLAC) motor using Analytical Sub-domain model with Differential Evolution Algorithm (ASDEA). Only two regions were considered in this analytical sub-domain model, ie magnet and airgap regions, with assistance of Complex Relative Permeance Function (CRPF) to account for the stator slotting effect. Five machine parameters were chosen to be optimized, namely the magnet arc-pole-pitch ratio, slot opening width, magnet thickness, airgap length and stator inner radius. The optimization process has four objectives, ie minimum torque ripple, low cogging torque, high efficiency, and high output torque. The results from the optimized ASDEA were compared with the Analytical Sub-domain Genetic Algorithm (ASGA) and further validated against 2-D finite element model (FEM). Results show a good agreement between analytically optimized models and finite element model. The ASDEA has faster computational time compared to ASGA, and this provides benefit in terms of reducing the machine design parameterization time and less redundancy work required to achieve motor design specifications.

Calculation of PM Vernier Motors Using an Improved Air-Gap Permeance Function

This paper proposes a more convenient and more accurate air-gap permeance function for the calculation of the air-gap flux density of flux modulation machines with permanent magnets (PMs). First, we review the previous air-gap permeance obtained from the approximated linear model and explain the problem that the accuracy of calculation becomes worse as the magnet thickness becomes larger. To solve this problem, we introduce an equivalent model that reflects the actual cylindrical structure of the machine with slots and, then, derives the air-gap function that is easy to be converted into the Fourier series, and finally propose the new air-gap permeance function. Using the proposed permeance function, the working harmonic components in the air-gap flux density of the surface magnet vernier motor are easily predicted, and then additional characteristics as well as flux density are compared with the finite-element simulation results to check the validity of the proposed method.

Structural design and analysis of a new axial magnetic suction planetary gear train

By analyzing the working principle of magnetic gear in the axial magnetic field, the design method of the active wheel and the driven wheel structure of the magnetic gear reducer in axial magnetic field is proposed. The influence of the magnetic tooth thickness on the transmission performance for the axial magnetic field coupled magnetic gear is theoretically explained. The gear reducer permanent magnet adopts a block structure, and the tooth increase coefficient is obtained by establishing a mathematical model. The finite element simulation analysis method is used to verify the rationality and feasibility of the design method, and the data is analyzed by the experimental method to verify the correctness of the simulation method

Study on permanent magnet thickness of high-speed permanent magnet generator

The permanent magnet thickness (PMT) is an important parameter in the design of the permanent magnet machine, and it directly affects the air-gap magnetic field and performance of generator. In this paper, a 117-kW, 60,000-rpm, high-speed permanent magnet generator (HSPMG) is taken as an example, and a two-dimensional finite element model (FEM) is established. By comparing calculation result and test data, the accuracy of the model is verified. The air-gap flux density waveform is obtained by the FEM, and the waveform is decomposed by the Fourier transform principle. The nonlinear variation law of harmonic content with the increase in PMT is obtained, and the nonlinear variation mechanism of air-gap flux density is revealed. On this basis, the variation law of voltage and voltage regulation with the increase in PMT is given, and the PMT is optimized. In addition, the nonlinear variation law of the loss is determined. The research shows that the purpose of optimizing performance of HSPMG can be achieved by adjusting the PMT. The PMT is finally determined when the generator performance is optimal. The conclusions provide some reference for the research of HSPMG.

Performance optimization of permanent magnet synchronous motor by cogging torque reduction

Abstract The development of the robotics and the automation and the need for the motors that can work in the applications that require high speed, precision and increased efficiency have led to the increased use of permanent magnet synchronous motors and their continuous development in terms of improving their performance. Cogging torque is one of the features of these types of the motors that deteriorate motor performance especially at low speeds. Therefore, in this paper the method of genetic algorithms (GA) is applied as an optimization tool, for minimizing the cogging torque without changing the other important operating parameters like output power, torque or current. Even more, the optimized motor model has improved efficiency compared to the starting model and has the decreased weight of the permanent magnets. The optimization is done by changing the rotor design in terms of the magnet thickness, pole span and shape of the magnets. Finite elements (FE) models of the optimized and the basic motor were derived and from them the flux density distribution in the motor cross section and in the air gap was calculated. In addition, the improvement of the motor operation is observed from the torque characteristics calculated by the FE models.