High Magnetic Flux Research Articles

Unprecedented heat resistance of Fe-based soft magnetic composites realized with tunable double insulation layer: Synergy of MgO diffusion barrier and void-filling SiO2 layer

Soft magnetic composites (SMCs) comprising surface-insulated Fe powders have attracted significant attention owing to their capability of producing innovative three-dimensional cores with high magnetic flux density and their potential utilization in various electrical machinery fields. The aim of this study is to fabricate SMCs with an inorganic double insulating layer, which can substantially enhance heat resistance and enable enhanced magnetic and mechanical performance through high-temperature annealing. Herein, SMCs with different inorganic coating materials (single layers of SiO2, MgO, and PO4 and double-layers of MgO and SiO2) were prepared by a sol–gel method and powder compaction. In particular, a certain double-layered SMC core (Fe@MgO@SiO2) exhibited retention of internal insulation matrix even after annealing at 900 °C and a significantly suppressed core loss owing to synergistic effects of a diffusion barrier in the primary layer and an electrical insulator in the secondary layer. As anticipated, high-temperature heat treatment at > 700 °C reduced coercivity, which enhances permeability and hysteresis loss of SMCs. The double-layered SMCs also showed an increase in flexural strength of 280% when the annealing temperature was increased from 600 to 900 °C.

An experimental study on mechanical properties of a magnetorheological fluid under slow compression

Mechanical properties of magnetorheological (MR) fluids have been investigated in slow compression under different magnetic fields. The compressive stress of the MR fluid has been deduced by assuming that it was a continuous shear flow in Bingham model and has been calculated. The compressive stress has also measured in different magnetic fields and initial gap distances. The compressive stress of the MR fluid in a high magnetic flux density and/or a small initial gap distance was much higher than that predicted by the traditional continuous media theory. Compressive experimental results were also compared with the continuous media theory by a normalized logarithmic form. The achieved experimental result seems to deviate from the prediction by the continuous media theory at a high magnetic flux density and a small initial gap distance. The MR fluid had a high compressive modulus when the compressive strain was lower than 0.042. The compressive modulus had an exponential relationship with the compressive strain higher than 0.042. Frictions between particles, which contribute to the high structure factor, were thought to play an important role in the large deviations in squeeze mode.

Iron Losses Comparison of Two Kinds of Permendurs under Rotating Magnetic Flux Density Conditions

Vector magnetic properties of permendurs have been investigated by using a vector magnetic property measurement apparatus to select a magnetic material suitable as a motor core material. When a motor is rotated at high speed by high-frequency excitation to increase power of a motor, a magnetic material with a high saturation magnetic flux density and a low iron loss is useful for a motor core. However, iron loss versus frequency characteristics under rotating magnetic flux density conditions of permendurs have not been sufficiently investigated. Moreover, the magnetic characteristics of permendurs made by different manufacturers have not been compared. Therefore, in this paper, the vector magnetic properties under rotating magnetic flux density conditions of two kinds of permendur made by different manufacturers are measured and compared for iron losses.

Effects of strong fringing magnetic fields on turbulent thermal convection

We study the influence of fringing magnetic fields on turbulent thermal convection in a horizontally extended rectangular domain. The magnetic field is created in the gap between two semi-infinite planar magnetic poles, with the convection layer located near the edge of the gap. We employ direct numerical simulations in this set-up for fixed Rayleigh and small Prandtl numbers, but vary the fringe width by controlling the gap between the magnetic poles and the convection cell. The magnetic field generated by the magnets is strong enough to cease the flow in the high magnetic flux region of the convection cell. We observe that as the local vertical magnetic field strength increases, the large-scale structures become thinner and align themselves perpendicular to the longitudinal sidewalls. We determine the local Nusselt and Reynolds numbers as functions of the local Hartmann number (based on the vertical component of the magnetic field), and estimate the global heat and momentum transport. We show that the global heat transport decreases with increasing fringe width for strong magnetic fields but increases with increasing fringe width for weak magnetic fields. In the regions of large vertical magnetic fields, the convective motion becomes confined to the vicinity of the sidewalls. The amplitudes of these wall modes show a non-monotonic dependence on the fringe width.

Preparation Methods and Properties of CNT/CF/G Carbon-Based Nano-Conductive Silicone Rubber

Carbon-based nano-conductive silicone rubber is a kind of composite conductive polymer material that has good electrical and thermal conductivities and high magnetic flux. It has good application prospects for replacing most traditional conductive materials, but its mechanical and tensile strengths are poor, which limit its applications. In this study, carbon fiber (CF), graphene (G) and carbon nanotubes (CNT) are used as fillers to prepare carbon-based nano-conductive silicone rubber via solution blending, and the preparation methods and properties are analyzed. The results show that when the carbon fiber content is 7.5 wt%, the volume resistivity of carbon fiber conductive silicone rubber is 9.5 × 104 Ω·cm, the surface resistance is 2.88 × 105 Ω, and the tensile strength reaches 2.12 Mpa. When the graphene content is 5.5 wt%, the volume resistivity of graphene conductive silicone rubber is 8.7 × 104 Ω·cm, and the surface resistance is 2.4 × 106 Ω. When the carbon nanotube content is 1.25 wt%, the volume resistivity of carbon nanotube conductive silicone rubber is 1.34 × 104 Ω·cm, and the surface resistance is 1.0 × 106 Ω. The three conductive nano-fillers in the blended carbon nano-conductive silicone rubber form a stable three-dimensional composite conductive network, which enhances the conductivity and stability. When the tensile rate is 520%, the resistance of the blended rubber increases from 2.69 × 103 to 9.66 × 104 Ω, and the rubber maintains good resilience and tensile sensitivity under repeated stretching. The results show that the proposed blended carbon nano-conductive silicone rubber has good properties and great application prospects, verifying the employed research method and showing the credibility of the research results.

Design and Characteristic Analysis of an Axial Flux High-Temperature Superconducting Motor for Aircraft Propulsion.

In line with global environmental regulations, the demand for eco-friendly and highly efficient aircraft propulsion systems is increasing. The combination of axial flux motors and superconductors could be a key technology used to address these needs. In this paper, an axial flux high temperature superconducting (HTS) motor for aircraft propulsion was designed and its characteristics were analyzed. A 2G HTS wire with high magnetic flux characteristic was used for the field winding of the 120 kW axial flux HTS motor, and the rotational speed and rated voltage of the motor were 2000 rpm and 220 V, respectively. The axial flux HTS motor implements a revolving armature type for solid cooling of the HTS field coil. The electromagnetic and thermal features of the motor were analyzed and designed utilizing a 3D finite element method program. The HTS coil was maintained at the target temperature by effectively designing the current lead and cooling system to minimize heat loss. These results can be effectively used in the design of propulsion systems for large commercial aircraft in the future as well as for the design of small aircraft with less than 4 seats.

New viewpoints of magnetic-field influence on photocatalysis via 2-propanol oxidation

Magnetic-field effect on heterogenous photocatalysis was investigated on Pt/TiO2 by photocatalytic oxidation of 2-propanol. Two-level factorial design of dissolved oxygen concentration (DO), temperature, and magnetic flux density was applied for the first time. The high magnetic flux density with high DO significantly enhanced 22% 2-propanol oxidation. The singlet-triplet intersystem crossing of radicals, as well as the Lorentz force suppressing the recombination of photogenerated electrons and holes, enabled such an extraordinary magnetic effect. Moreover, paramagnetic oxygen and platinum on TiO2 reinforced the intersystem crossing, which contributed to the significant improvement of photocatalytic oxidation of 2-propanol under magnetic field.

Development of Rotor Core with High Magnetic Flux by Partial Non-Magnetic Improvement of Silicon Steel

Flux leakage in the rotor core bridges is a problem specific to interior permanent magnet motors and has been unsolved till date. It is widely known that if the bridges are partially non-magnetically improved with low magnetic polarization, the leakage flux will be smaller, and the rotor will have a higher magnetic flux. We proposed that the portion of the silicon steel sheets that becomes the bridge after pressing can be non-magnetized and laminated to fabricate the rotor core. Partially non-magnetic material with a polarization of almost zero was obtained by melting and mixing Ni–Cr alloy powder with the silicon steel sheets. This non-magnetic improvement treatment was applied to the bridge in the rotor core sheet, in which the non-magnetic area width was 1.45 mm, and the prototype rotor core was fabricated by laminating 60 rotor core sheets. Upon measurement, the rotor core showed approximately 35% higher magnetic flux than a conventional one, with the actual value nearly identical to that obtained from the magnetic field analysis.

Experimental study and numerical simulation of permanent magnet stirring on solidification of IN718 superalloy under different rotation speeds

A novel permanent magnet stirring (PMS) characterized by low power dissipation and high magnetic flux density provides an alternative method for producing IN718 superalloy with uniform microstructure during solidification. In the present work, the electromagnetic force and the molten superalloy flow of PMS under different rotation speeds (0, 75, 150, and 300 rpm) were calculated based on the multi-physics field analysis software Comsol and the flow field software Fluent. The calculated results were validated using the measured magnetic flux densities under different rotation speeds. It was found that the calculated maximum electromagnetic force enhanced from 2.73 to 10.78 kN/m3, and the maximum tangential velocity increased from 0.13 to 0.46 m/s in a diameter of 50 mm molten IN718 ingot when the rotation speeds increased from 75 to 300 rpm. Moreover, the experimental results revealed that the regions of solidification dendrites were broken under the impact of PMS, which were a source of refinement grains and attributed to the uniform distribution of Laves phase (average size decreased from 74.86 to 38.83 µm in the edge) during solidification. In addition, grain refinement and a random distribution of grains decreased texture intensity with the maximum value from 6.124 to 3.828.

Generation of multiply charged ions in accordance with geometry and magnetic field in Hall thruster plasmas

The production of multiply charged ions in Hall effect plasmas has been investigated. The factors that significantly affect plasma characteristics, such as geometry, magnetic field configuration, and magnetic mirror ratio, were analyzed. Among the co-current and counter-current configurations of a cylindrical Hall thruster (CHT) and an annular Hall thruster (AHT), the co-current configuration of the CHT shows the largest fractions of multiply charged ions. In particular, for the CHT, the region with high magnetic flux density had a significant influence on the fraction of multiply charged ions, but the fraction of multiply charged ions was not significantly different depending on magnetic mirror ratios. In addition, the configuration having a similar magnetic field in the CHT demonstrated comparable fractions of multiply charged ions and thrust even with different channel lengths. Hence, the broad region with the high magnetic flux density could enhance the probability of further ionization inside the discharge channel.

Convolutional neural network guided prediction of saturation magnetic flux density of Fe-based metallic glasses

Fe-based metallic glasses (FeMGs) have recently garnered considerable research attention due to their unique characteristics, such as low core loss and high saturation magnetic flux density (Bs). They also have promising applications in modern electrical machines, such as inductors, motors, and transformers. For FeMGs with high Bs, a trial-and-error approach using various metalloid elements as constituents has been intensively carried out to consider satisfactory thermal stability. However, this approach is time-consuming and expensive because it requires a huge compositional space and results in a lack of understanding of metalloid effects on magnetic properties and thermal stability. In this study, we established a deep learning model using a convolutional neural network (CNN) based only on compositional descriptors of FeMG constituent elements to predict Bs as the representative magnetic property. In addition, an artificial neural network was applied with the same compositional descriptors for comparison, resulting in a lower prediction performance than that of the CNN model. The CNN model demonstrated high-performance metrics that included a determination coefficient (R2) of 0.960 and a low root-mean-square error of 0.067 T, indicating that the material composition-to-property map is well-defined. We further applied the CNN model to unseen datasets for Bs prediction and compared it with results reported in the existing literature. The predicted Bs values are in excellent agreement with the reported experimental results.

Effects of Gradient Magnetic Field on Electrical Tree Growth Characteristics in Silicone Rubber

In this article, the positive and inverse gradient symmetric magnetic field and the asymmetric magnetic field with different angles are constructed. The influence of the magnetic field distribution on the electrical tree characteristics is investigated. The experimental results show that both the positive and the inverse gradient magnetic fields can promote the deterioration of the electrical trees. Under the symmetrical <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta 1.5$ </tex-math></inline-formula> T gradient magnetic field, the tree initiation probability increases from 55% to 100%, and the breakdown time decreases by 67.5%. Under the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula> -1.5 T, the tree initiation probability increases from 55% to 75%, and the breakdown time declines by 57.5%. The morphology of the electrical trees is largely affected by the distribution of the magnetic field. The dispersion of the degradation channels increases with the enhancement of the magnetic field. Under the asymmetric magnetic field, the deterioration process is also accelerated, with the increase of the magnetic field. More importantly, the growth direction of the electric trees shifts to the side with the higher magnetic flux density. The magnetic field enhances the local electric field and promotes the occurrence of partial discharge by exerting a deflection force on the charges. Consequently, the growth rate and morphology of electrical trees are affected.

Relationship between blanking performance and microstructure of annealed Fe–Si–B–Cr amorphous alloy sheets

The high saturation magnetic flux density, low coercivity, and high permeability of iron-based amorphous alloys make them excellent magnetic core materials for electrical devices. Their local embrittlement and high fracture strength, however, make them difficult to machine. To overcome these difficulties, we have developed a new machining method with optimized heat treatment to improve the machinability of amorphous alloys. We conducted a series of blanking tests on melt-spun and post-annealed Fe–Si–B–Cr amorphous alloys with as-quenched, relaxed, partially or fully crystallized, and grain-grown microstructures. SEM examinations of the fractured surfaces of the blanked specimens and TEM observations revealed that the blanking resistance and overall machining performance correlated with these microstructures. The as-quenched sample showed the largest blanking resistance, and the fracture surface exhibited a drooped top edge, vertical marks, and the formation of horizontal voids, suggesting that plastic deformation occurred. For the samples annealed up to 763 K, the blanking resistance decreased and fractographic examination indicated that the blanking occurred in a brittle manner. Annealing at higher temperatures (773–873 K) increased the blanking resistance and changed the fracture morphology, exhibiting intragranular and intergranular fractures of crystalline precipitates. After complete crystallization, several burrs appeared at the bottom of the sample. Annealing at 1073 K led to a further decrease in blanking resistance related to the intergranular fracture of large grains. The plastic deformation of the sheet deteriorated the blanking quality. Based on these findings, the optimum microstructure and post-treatment of the amorphous alloy for ideal blanking performance are proposed.

Viscoelastic Effects on the Nonlinear Oscillations of Hard-Magnetic Soft Actuators

AbstractThe hard-magnetic soft materials (HMSMs) belong to the magnetoactive category of smart polymers that undergo large actuation strain under an externally applied magnetic field and can sustain a high residual magnetic flux density. Because of these remarkable characteristics, HMSMs are promising candidates for the remotely controlled actuators. The magnetic actuation behavior of the hard-magnetic soft actuators (HMSAs) is considerably affected by the viscoelastic material behavior of HMSMs. In this article, we aim at developing an analytical dynamic model of a typical planar model of HMSAs concerning the viscoelasticity of HMSMs. A Zener rheological model in conjunction with an incompressible neo-Hookean model of hyperelasticity and Rayleigh dissipation function is employed for defining the constitutive behavior of the viscoelastic HMSA. The governing equations of dynamic motion are deduced by implementing the nonconservative form of the Euler–Lagrange equation. The established dynamic model is utilized for providing preliminary insights pertaining to the effect of the viscoelasticity on the nonlinear oscillations of the actuator. The phase–plane portraits, Poincaré maps, and the time–history response are plotted to investigate the stability, resonant behavior, and periodicity of the actuator. The results and inferences reported here should provide the initial step toward the design and the development of modern actuators for diverse futuristic applications in the medical and engineering fields.

Development of novel FeCo based amorphous FeCoBPSiCr alloy with high Bs of 1.71 T and high corrosion resistance

Metallic ribbons of different compositions were prepared using a single-roller melt-spinning method. The (Fe0.8Co0.2)83B11P4Si2 alloy without Cr showed both high saturation magnetic flux (Bs) of 1.78 T and high corrosion resistance, with a corrosion potential of −607 mV and a corrosion current density of 29 μA/cm2 compared to those of a conventional high-Bs Fe79B13.5Si5.5C2 amorphous alloy. The (Fe0.7Co0.3)82B11P4Si2Cr1 alloy with Cr also exhibited a high Bs of 1.71 T and high corrosion resistance at the same level as that of a conventional Fe73B11Si11C3Cr2 amorphous alloy. The (Fe0.7Co0.3)82B11P4Si2Cr1 alloy showed a corrosion potential of −509 mV and a corrosion current density of 18 μA/cm2. Furthermore, the (Fe0.7Co0.3)82B11P4Si2Cr1 alloys exhibited a high amorphous forming ability because of a single amorphous phase in the metallic ribbon at a thickness of &amp;gt;60 μm. Based on these results, the (Fe0.7Co0.3)82B11P4Si2Cr1 amorphous alloy with the possibility of powderization was confirmed to be a suitable material for the magnetic core that is widely used in metallic inductive components.

低炭素社会実現に資する高磁束密度・超低損失軟磁性材料(M alloy)の開発と社会実装

低炭素社会実現に資する高磁束密度・超低損失軟磁性材料(M alloy)の開発と社会実装

Electrical Treeing and Its Suppression Method of SiR in High Magnetic Field

This paper investigates the effects of high magnetic field on electrical treeing of silicone rubber (SiR). Experimental results show that electrical trees are more easily to be initiated and spread further along the direction of electric field under the effects of high magnetic field. When the direction of high magnetic field is perpendicular to that of electric field, magnetic field with higher magnetic flux density also results in larger accumulated damage area. Splitting of energy band structure and changes in polarization characteristics result in a lower interface barrier and more serious partial discharge, thus causing the weakened resistance to electrical treeing in high magnetic field. Based on the insulation degradation mechanism, SiR was modified by adding ferroferric oxide (Fe3O4) nanoparticles to improve its insulation performance in high magnetic field. Moderate addition amount of Fe3O4 nanoparticles is proved to be able to suppress electrical treeing in high magnetic field by forming quantum dots, modifying polarization properties and partial discharge behavior. Excessive addition of Fe3O4 nanoparticles has negative effects on suppressing electrical treeing due to the magnetization of the nanocomposites.

EFFECTS OF RADIATION AND CHEMICAL REACTION ON MHD CASSON NANOFLUID FLOW PAST A POROUS STRETCHING SURFACE

The present investigation aims to study the influence of thermal radiation and chemical reaction on the unsteady magnetized flow of Casson fluid with immersed nanoparticles. The flow is past a permeable stretching surface. The nanofluid heat transmission characteristics are described with the Buongiorno model. The governing system of non-linear partial differential equations (PDEs) is converted into non-linear ordinary differential equations (ODEs) with a similarity group of transformations. The reduced ODEs are numerically solved with an effective shooting strategy along with the standard R-K fourth-order method. The graphical illustration for the immerging parameters on non-dimensional velocity, temperature, and concentration is obtained through bvp4c using MATLAB. The code validation is provided by comparing the numerical outcomes of a few parameters with recently published work. The result shows that the thermal radiation boosts the energy supply in the flow field, and hence, the thermal regime enhances quickly. Due to the rise in chemical activity and Schmidt number, the concentration profile declines. The flow velocity declines with higher magnetic flux.

Ferrofluid drop impacts and Rosensweig peak formation in a non-uniform magnetic field.

Vertical drop impacts of ferrofluids onto glass slides in a non-uniform magnetic field have been studied using high-speed photography. Outcomes have been classified based on the motion of the fluid-surface contact lines, and formation of peaks (Rosensweig instabilities) which affect the height of the spreading drop. The largest peaks are nucleated at the edge of a spreading drop, similarly to crown-rim instabilities in drop impacts with conventional fluids, and remain there for an extended time. Impact Weber numbers ranged from 18.0 to 489, and the vertical component of the B-field was varied between 0 and 0.37 T at the surface by changing the vertical position of a simple disc magnet placed below the surface. The falling drop was aligned with the vertical cylindrical axis of the 25 mm diameter magnet, and the impacts produced Rosensweig instabilities without splashing. At high magnetic flux densities a stationary ring of ferrofluid forms approximately above the outer edge of the magnet.

Crack nucleation and propagation of electromagneto-thermo-mechanical fracture in bulk superconductors during magnetization

Bulk high-temperature superconductors (HTS) like REBCO (RE: rare earth element or Y) have been widely adopted in a variety of engineering applications. With high magnetic flux applied in a short time of milliseconds, significant tensile stresses are induced during pulsed field magnetization by the Lorentz electromagnetic forces and Joule heating thermal expansions. Consequently, potential damage and fracture may occur in bulk HTS, leading to degradation of the capacity in trapping the magnetic field. In this multi-physical problem, due to the complex stress distribution even in the elastic stage and the intensive redistribution once crack nucleation occurs, the resulting fracture pattern is very complicated. Accordingly, it is a challenging issue to model crack nucleation and propagation of such electromagneto-thermo-mechanical fracture involving both the Lorentz electromagnetic forces and the Joule heating. In this work, the mechanical stresses and multi-physical fracture in bulk HTS during magnetization are studied systematically by the phase-field cohesive zone model (PF-CZM). The governing equations and the involved constitutive relations for the electromagnetic, thermal and cracking-mechanical sub-problems are given together with the numerical implementation. The elastic semi-analytical solutions for the Lorentz forces and thermal expansions induced stresses in an infinitely long cylindrical bulk HTS during magnetization are derived for the determination of crack nucleation. Numerical results are then discussed in details regarding the whole fracture process in bulk HTS under isothermal and non-isothermal cases. It is found that the first crack nucleation occurs at a certain interior position along the circumferential direction after which a couple of cracks nucleate and propagate outwards along the radial direction. The effects of Joule heating and cracking on the electromagnetic performances are quantified, and those of the inhomogeneity in the critical current density are also briefly discussed. Moreover, extension of the proposed PF-CZM to more complex cases is straightforward, making it a promising tool in optimizing the fabrication and practical application of bulk HTS.