Low Magnetic Flux Research Articles

A generalized inverse Preisach dynamic hysteresis model of Fe-based amorphous magnetic materials

Fe-based amorphous magnetic materials are attracting more and more attentions in the application of low and medium frequency transformers due to their favorable properties of low core loss and high saturation magnetic flux density. Accurate modelling of their static and dynamic characteristics is required for analysis and design optimization of low and medium frequency transformers. In particular, for numerical analysis using the vectorial magnetic potential, an inverse magnetic hysteresis model is needed to predict the magnetic field strength from the magnetic flux density. When the excitation varies with time, the magnetic hysteresis model must be able to predict the dynamic hysteresis characteristics. This paper presents a generalized inverse Preisach dynamic hysteresis model for dynamic characterization of Fe-based magnetic materials. This model incorporates the reversible magnetization and magnetization dependent hysteresis, as well as all core loss components, including the hysteresis, eddy current, and excess losses. The proposed model can predict accurately the magnetic field strength from the magnetic flux density and hence accurate core losses. The predicted results are verified by experimental measurements.

3kW급 풍력발전기용 페라이트 스포크 회전자 형상 특성비교

Most of the generators and electric motors developed in recent years are synchronous machines using permanent magnets of rare earth. As the name suggests, rare earth permanent magnets are expensive because they have a small amount distributed on the earth. In addition, the price fluctuation is large because it is concentrated and mined in a specific region. Therefore, in recent years, research has been actively conducted on developing a generator using a low cost ferrite permanent magnet for stable supply and reduction of the price of the generator. Ferrite magnet has a low magnetic flux density compared to a rare earth permanent magnet, so a large amount of permanent magnet must be used. In particular, the generator rotor is made in the form of a spoke to insert a large amount of permanent magnets. There are three typical spoke type types. This paper compare three types of characteristics at the same size and the same output.

Kinetics modeling for austenite transformation in AISI 1045 steel during rapid heating under high frequency electromagnetic field

To investigate the effect of alternating magnetic field on austenite transformation process in the case of rapid heating, the austenite kinetics model of AISI 1045 steel was built for spot continual induction hardening (SCIH) process. The results shows that the effect of alternating magnetic field on austenite transformation fraction reaches the maximum (about 3%) when heating rate is the lowest. Relatively low magnetic flux density still has a certain effect on the austenite transformation process during the SCIH process. Concave surface structure can reduce the influence scope of alternating magnetic field on surface in all cases and the minimum influence scope appears when the feed path of inductor is longitudinal. Convex surface structure can minimize the influence scope of alternating magnetic field in depth when the feed path of inductor is longitudinal. The austenite distribution of transitional region on surface for horizontal movement is more uniform than that for longitudinal movement. The austenite distribution of transitional region in depth for longitudinal movement is more uniform than that for horizontal movement. The simulated results are consistent with the experimental results and the austenite transformation kinetics model developed for SCIH process is valid.

The Effects of Tilt on the Images of Black Hole Accretion Flows

Abstract We analyze two 3D general-relativistic magnetohydrodynamic accretion simulations in the context of how they would manifest in Event Horizon Telescope (EHT) observations of supermassive black holes. The two simulations differ only in whether the initial angular momentum of the plasma is aligned with the rapid (a = 0.9) spin of the black hole. Both have low net magnetic flux. Ray tracing is employed to generate resolved images of the synchrotron emission. When using parameters appropriate for Sgr A* and assuming a viewing angle aligned with the black hole spin, we find the most prominent difference is that the central shadow in the image is noticeably eccentric in tilted models, with the ring of emission relatively unchanged. Applying this procedure to M87 with a viewing angle based on the large-scale jet, we find that adding tilt increases the angular size of the ring for fixed black hole mass and distance, while at the same time increasing the number of bright spots in the image. Our findings illustrate observable features that can distinguish tilted from aligned flows. They also show that tilted models can be viable for M87, and that not accounting for tilt can bias inferences of physical parameters. Future modeling of horizon-scale observations should account for potential angular momentum misalignment, which is likely generic at the low accretion rates appropriate for EHT targets.

Bistable permanent magnet actuator based on double wing magnetic flux

This letter presents a bistable permanent magnet actuator, based on double wing magnetic flux (DWMF) formed by the structure of welding sleeve and slotted armature. The double wing magnetic flux consist of high wing magnetic flux (HWMF) and low wing magnetic flux (LWMF), resulting in bistable performance under differentiating control. Parameters improvement around DWMF is analyzed based on modeling, and optimized results for a prototype actuator are obtained. The experimental and simulation results agree well, and show that the prototype actuator can realize bistable performance under the DC step voltage drive, with the holding force of 8.2 N (without current) and the restoring force of −31.7 N (with negative current), the dynamic results show that the displacement response time within 8 mm is 28 ms, of which the actuation time is 16.5 ms, the transient maximum power consumption of the restoring period is 18 W.

Structural and cryogenic magnetic properties of rare earth rich RE11Co4In9 (RE = Gd, Dy and Ho) intermetallic compounds.

The crystal structure, magnetic properties and magnetocaloric performances of rare earth rich RE11Co4In9 (RE = Gd, Dy and Ho) intermetallic compounds are investigated systematically in this work. All compounds in this system crystallize in the orthorhombic Nd11Pd4In9-type structure with the Cmmm space group. The stacks of alternate RE and Co/In atomic layers with z = 0, 1 and z = 1/2 along the z-axis constitute the crystal structure. These compounds belong to the REx+yM2yXx family with x = 9 and y = 2, and the ratio of the AlB2-type and CsCl-type fragments in a unit cell is y : x, i.e. 2 : 9. The characteristic of multiple magnetic phase transition is revealed with a low magnetic flux density μ0H of 0.1 T for the present compounds. The ferromagnetic (FM) to paramagnetic (PM) phase transitions of the present compounds around their respective Curie temperatures (TC) are all second order phase transitions (SOPTs). Around the TC of 86, 37 and 20 K for Gd11Co4In9, Dy11Co4In9, and Ho11Co4In9 with a magnetic flux density change Δμ0H of 0-7 T, the values of the maximum magnetic entropy change (-ΔS) and temperature averaged entropy change (TEC) with 3 K span are 10.95 and 10.93 J kg-1 K-1 for Gd11Co4In9, 4.66 and 4.64 J kg-1 K-1 for Dy11Co4In9, and 12.29 and 12.09 J kg-1 K-1 for Ho11Co4In9, respectively. The corresponding values of relative cooling power (RCP) and refrigerant capacity (RC) are 538.1 and 405.9 J kg-1 for Gd11Co4In9, 213.9 and 165.9 J kg-1 for Dy11Co4In9, and 475.2 and 357.4 J kg-1 for Ho11Co4In9, respectively.

Hofstadter butterfly in a cavity-induced dynamic synthetic magnetic field

Energy bands of electrons in a square lattice potential threaded by a uniform magnetic field exhibit a fractal structure known as the Hofstadter butterfly. Here we study a Fermi gas in a 2D optical lattice within a linear cavity with a tilt along the cavity axis. The hopping along the cavity axis is only induced by resonant Raman scattering of transverse pump light into a standing wave cavity mode. Choosing a suitable pump geometry allows to realize the Hofstadter-Harper model with a cavity-induced dynamical synthetic magnetic field, which appears at the onset of the superradiant phase transition. The dynamical nature of this cavity-induced synthetic magnetic field arises from the delicate interplay between collective superradiant scattering and the underlying fractal band structure. Using a sixth-order expansion of the free energy as function of the order parameter and by numerical simulations we show that at low magnetic fluxes the superradiant ordering phase transition is first order, while it becomes second order for higher flux. The dynamic nature of the magnetic field induces a non-trivial deformation of the Hofstadter butterfly in the superradiant phase. At strong pump far above the self-ordering threshold we recover the Hofstadter butterfly one would obtain in a static magnetic field.

Flux pinning mechanisms and a vortex phase diagram of tin-based inverse opals

Three-dimensional periodic tin structures were synthesized by filling pores in silicon opals with a sphere diameter of 194 nm (Sn190) and 310 nm (Sn300). The samples were examined by the ultra-small-angle x-ray diffraction method, energy dispersive x-ray microanalysis and scanning electron microscopy. It was found that the inverse opal structure consists of tin nanoparticles inscribed in octahedral and tetrahedral pores with diameters of 128 nm and 70 nm for the sample Sn300, and 80 nm and 42 nm for the sample Sn190. The study of the magnetic properties of the samples by SQUID magnetometry showed that magnetization reversal curves exhibit hysteretic behavior. The mechanisms of magnetic flux pinning in the samples depend on the size of the tin nanoparticles. Tin nanoparticles in Sn300 behave like a classical type-I superconductor. The hysteretic behavior of the magnetization reversal curves at low magnetic fields is due to the formation of a network of superconducting contours in Sn300. These superconducting contours effectively trap the magnetic flux. The octahedral tin nanoparticles in Sn190 remain type-I superconductors, but smaller tetrahedral particles behave like type-II superconductors. Type-I and II superconducting particles in Sn190 lead to the coexistence of different mechanisms of flux pinning. These are flux trapping by superconducting contours at low magnetic fields and flux pinning by tetrahedral particles due to the surface barrier at high magnetic fields.

Influence of hot rolling reduction rate on the microstructure, texture and magnetic properties of a strip-cast Fe-6.5 wt% Si grain-oriented electrical steel

Grain-oriented electrical steel containing 6.5 wt% Si is a promising soft magnetic material with very low iron losses for high-frequency applications. However, due to the ordered phases formed in the microstructure, the room-temperature ductility (formability) of this material is extremely low. It is essentially not possible to process this steel by conventional cold rolling. In this study, an Fe-6.5 wt% Si grain-oriented electrical steel was processed through strip casting (also known as twin-roll casting), hot rolling, warm rolling, cold rolling, primary and secondary annealing. The effect of hot rolling reduction rate (12–40%) on the microstructure, crystallographic texture and magnetic properties of the final steel sheets was investigated. The results showed that hot rolling increased the area fraction of the Goss ({1 1 0}〈0 0 1〉) grains, reduced the grain size, and promoted the precipitation of fine second-phase particles. After warm rolling, cold rolling and primary annealing, the recrystallized microstructure was the finest if the hot-rolling reduction rate was the highest (40%). After secondary annealing, the steel with the largest hot rolling reduction rate (40%) showed the most apparent abnormal grain growth, leading to the formation of the Goss texture. As a result, the magnetic flux density and the magnetic Barkhausen noise (MBN) also showed the largest values among all the samples. On the other hand, those with lower hot-rolling reduction rates (12–32%) showed no or less abnormal grain growth during secondary recrystallization, which resulted in lower magnetic flux density and weaker magnetic Barkhausen noise. Increasing the amount of hot rolling reduction was thus able to promote abnormal grain growth during secondary recrystallization, and optimize the magnetic properties of the steel.

Comparison between NIST Graphene and AIST GaAs Quantized Hall Devices.

Several graphene quantized Hall resistance (QHR) devices manufactured at the National Institute of Standards and Technology (NIST) were compared to GaAs QHR devices and a 100 Ω standard resistor at the National Institute for Advanced Industrial Science and Technology (AIST). Measurements of the 100 Ω resistor with the graphene QHR devices agreed within 5 nΩ/Ω of the values for the 100 Ω resistor obtained through GaAs measurements. The electron density of the graphene devices was adjusted at AIST to restore device properties such that operation was possible at low magnetic flux densities of 4 T to 6 T. This adjustment was accomplished with a functionalization method utilized at NIST, allowing for consistent tunability of the graphene QHR devices with simple annealing. Such a method replaces older and less predictable methods for adjusting graphene for metrological suitability. The milestone results demonstrate the ease with which graphene can be used to make resistance comparison measurements among many National Metrology Institutes.

Influence of static magnetic field intensity on the separation and migration of Fe-rich bulks in an immiscible (Fe–C)–Cu alloy

ABSTRACTIn this study, we solidified an immiscible pseudo-binary (Fe–C)–50mass%Cu alloy in a static magnetic field and observed macro morphologies as a function of the magnetic flux density. The experimental result shows that the Fe-rich phase exhibits a single bulk when the alloy is solidified at a low magnetic flux density, while it is separated in to two smaller bulks at high magnetic flux densities and the distance between the bulks becomes larger with the increase of the magnetic flux density. The possible reason for the separation of the Fe-rich phase was simply proposed. As far as the migration of separated Fe-rich phase bulks is concerned, the thermoelectric effect between the Fe-rich and Cu-rich metals was considered, from which the thermoelectric body force could be exerted upon the Fe-rich droplets. The higher the body force is produced, the larger the distance will be covered due to the migration of the droplets. Further analysis reveals that the convection attributed to the thermoelectric effect may contribute to the migration of the Fe-rich droplets at a low magnetic field and become negligible at high magnetic flux densities.

Optimization Design of a New Type of Interior Permanent Magnet Generator for Electric Vehicle Range Extender

Aiming at the disadvantages of large leakage flux and low magnetic flux density of radial magnetic circuit and tangential magnetic circuit, a new type of permanent magnet (PM) rotor with parallel tangential and radial magnetic circuits is proposed. Based on Ohm’s law and Kirchhoff’s law of magnetic circuits, equivalent magnetic circuits for rotor poles are developed. The structure parameters of the generator are preliminarily determined. At the same time, by means of the Taguchi method and employing finite element analysis, the rotor poles of generator are optimized to improve air gap magnetic density, the cogging torque, and the distortion of back-EMF waveform. Finally, the validity of proposed design methods is validated by the analytical and experimental results.

The effects of extremely low-frequency electromagnetic fields on c-Maf, STAT6, and RORα expressions in spleen and thymus of rat

ABSTRACTThe study investigated the effect of extremely low-frequency electromagnetic fields (ELF-EMFs) exposure at different magnetic flux densities on genes expression of transcription factor Maf (c-Maf), signal transducer and activator of transcription 6 (STAT6), and retinoid-related orphan receptor alpha (RORα) in the spleen and thymus of rats. Eighty adult male rats were separated into four ELF-EMFs exposed and were exposed to magnetic flux densities of 1, 100, 500, and 2000 µT at a frequency of 50 Hz for 2 h daily for up to 60 d. All rats were intraperitoneally immunized on d 31, 44, and 58 of exposure. The experimental results showed that the expression levels of c-Maf, STAT6, and RORα in the thymus were not significantly changed at different magnetic flux densities. The expression levels of RORα and c-Maf were significantly downregulated at the densities of 1 and 100 µT, while the expression of STAT6 was only significantly decreased at the density of 100 µT. In conclusion, low magnetic flux densities of ELF-EMFs may reduce the expression levels of c-Maf, STAT6, and RORα genes in the spleen.

Surface Spiral Parallel and Antiparallel Winding Designs for High Efficiency, Low Spatial Voltage Stress, and Inductive Wireless Power Transfer Systems

Surface spiral winding (SSW) has been demonstrated to achieve low skin and proximity effects copper losses, and low air-gap magnetic flux density in MHz, kW level inductive wireless power transfer systems. The dielectric losses are still the limiting factor to further improve the coil-to-coil efficiency. In addition, high spatial voltage stress between the first turn and the end turn limits the maximum transferable power due to the voltage breakdown. This paper develops alternative coil configurations to reduce the copper loss, the dielectric losses, and the spatial voltage stress. Through emulating SSW using copper tubing, the dielectric losses and the spatial electric field between adjacent turns are reduced simultaneously. Two surface spiral parallel winding designs are proposed to reduce the equivalent series resistance and improve the coil-to-coil transfer efficiency. A surface spiral antiparallel winding design is proposed to equalize dynamic voltage stress between adjacent turns and improve power scalability while maintaining high coil-to-coil transfer efficiency.

Particle assembling induced by non-homogeneous magnetic field at transformer oil-based ferrofluid/silicon crystal interface by neutron reflectometry

The effect of magnetic nanoparticle assembly formation at a planar interface between a transformer oil-based ferrofluid and single-crystal silicon under non-homogeneous magnetic fields was studied by specular neutron reflectometry. The ferrofluid probed represents a stable suspension of dispersed iron oxide nanoparticles (characteristic size about 10 nm) coated with oleic acid in a low-polarity liquid carrier (transformer oil). It was shown that the reflectivity curves are sensitive to the application of a non-homogeneous external magnetic field. In particular, at a low magnetic flux density (<35 mT) they are well described in terms of the simplest model of a strict boundary between two semi-infinite homogeneous media. Nevertheless, slight concentrating of the ferrofluid bulk at the interface was detected. At a high magnetic flux density (35–75 mT), the analysis gives a three-layered structure of in-depth profiles of the scattering length density, thus showing the formation of two effective adsorption layers with different content of magnetic nanoparticles in them.

A Fanless Operating Trans-Linked Interleaved 5 kW Inverter Using SiC MOSFETs to Achieve 99% Power Conversion Efficiency

A trans-linked interleaved inverter using silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) achieves a power conversion efficiency $(\eta)$ of 99% at 5 kW and an optimum η of 99.4% at 2 kW. Its trans-linked part is composed of two combined reactors: a first reactor, made of a low saturation magnetic flux density $(B_{{\rm{s}}})$ material, has a rectangular ring shape to cancel magnetic fluxes flowing therein; a second reactor, which strides in the hole of the ring to collect the fluxes to form the leakage inductance, acts as the smoothing reactor in the inverter and accordingly possesses a high $B_{{\rm{s}}}$ to increase the output current. This circuit topology along with the high-frequency switching capability of SiC MOSFETs leads to a lower inductance of the smoothing reactor, thereby sufficiently reducing the number of winding turns in the reactor so as to cut off the copper loss of the reactor to decrease total power loss.

Achieving Low Magnetic Flux Density and Low Electric Field Intensity for a Loosely Coupled Inductive Wireless Power Transfer System

In most loosely coupled inductive wireless power transfer systems, the air-gap magnetic flux density between coils is still far above the safety limit, which is a potential threat to human beings and animals. In addition, less attention is paid to the air-gap electric field intensity, which increases significantly as the operating frequency and the number of turns increase. In this paper, a multi-kW loosely coupled inductive wireless power transfer system general design methodology that can inherently achieve low air-gap center plane magnetic flux density and electric field intensity is proposed. The coil-to-coil efficiency, magnetic and electric field distributions of different winding configurations are compared. The effects of coil radius, number of turns, interturn distance, transfer distance, and operating frequency on transfer efficiency, and magnetic and electric field distributions are investigated. The proposed methodology is evaluated with a 3 kW, 30 cm distance wireless power transfer design example by finite element analysis (FEA) and experiment tests.

Electromagnetic Field Analysis of Low-Magnitude High-Frequency Vibrator with Multiple Plungers.

Low-magnitude high-frequency (LMHF) of vibrational stimulation has been accepted as an effective method to enhance bone remolding. However, the electromagnetic field (EMF) generated by the vibrator could also be an influence factor in the vibrational experiments. This phenomenon underlies the bone remodeling effect caused by vibrational stimulation is disrupted to be investigated. This paper presents a design of LMHF vibrator with multiple plungers to generate vibrational stimulation with ultra low magnetic flux density to minimize the biological effect caused by the EMF. The EMF is analyzed in finite element method (FEM) using COMSOL.

Extended interaction oversized coaxial relativistic klystron amplifier with gigawatt-level output at Ka band

In this paper, an extended interaction oversized coaxial relativistic klystron amplifier (EIOC-RKA) with Gigawatt-level output at Ka band is proposed. We introduce the oversized coaxial and multi-gap resonant cavities to increase the power capacity and investigate a non-uniform extended interaction output cavity to improve the electronic efficiency of the EIOC-RKA. We develop a high order mode gap in the input and output cavities to easily design and fabricate the input and output couplers. Meanwhile, we design the EIOC-RKA by using the particle-in-cell simulation. In the simulations, we use an electron beam with a current of 6 kA and a voltage of 525 kV, which is focused by a low focusing magnetic flux intensity of 0.5 T. The simulation results demonstrate that the saturated output power is 1.17 GW, the electronic efficiency is 37.1%, and the saturated gain is 57 dB at 30 GHz. The self-oscillation is suppressed by adopting the absorbing materials. The proposed EIOC-RKA has plenty of advantages such as large power capacity, high electronic efficiency, low focusing magnetic, high gain, and simple structure.

The Effect of the Magnetic Grids and Arc Runner on the Arc Plasma Column in the Contact System of a Molded Case Circuit Breaker

This paper examined the extent of the dependence of the interrupting capability on the shape of the contact system in a molded case circuit breaker (MCCB). Thus, a simple analysis method was suggested for estimating the interrupting capability and used to investigate the magnetic flux density distribution in a contact system caused by a short-circuit current. However, the MCCB produced by a joint-research company turned out to have the poor interrupting capability and a low magnetic flux density distribution for driving arc plasma between two contacts in the contact system. To build up additional interrupting capability without making many changes, a new arc runner was devised to prevent arc plasma from returning to its original position in the contact system. The arc voltage characteristics were tested with a simplified synthetic testing facility using an LC resonant circuit. The result showed that the new MCCB had a much higher arc voltage than the existing MCCB. This implies that investigating the arc voltage is fairly comparable to predicting the arc plasma extinction and the interrupting capability.