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Millimeter wave components, such as circulators and isolators, frequently use magnetic fields to break symmetry of the signal propagation and provide unidirectional signal transmission. While effective, these components have not seen the level of miniaturization of other millimeter wave components, primarily due to the discrete nature of the magnets used in the components. Using circulators in the 40-50 GHz range as a motivating application, requirements arise for the deposited films, namely immunity to eddy currents, sufficient magnetization to act as self-biasing magnets, and out-of-plane orientation of the self-biasing field. Based on these required properties, hexaferrite materials are selected for their strong magnetocrystalline anisotropy (MCA) and low conductance. The difficulty of integrating these components monolithically with monolithic microwave integrated circuits (MMIC) originates from the incompatibility of crystal structure with standard semiconductor materials and process conditions. Additive manufacturing using a composite of strontium hexaferrite (SrFe12O19) particles and photoresist has been chosen as a method to overcome the difficulties of integrating hexaferrite material to semiconductor substrates. Due to their large internal anisotropy field, the particles of strontium hexaferrite tend to rotate to the field direction instead of changing magnetization direction under application of an external magnetic field (less than the anisotropy field). We have developed a method for 3D printing composites of high strontium hexaferrite concentration (up to 20% by volume) in a liquid photoresist, SU8. Rotation of hexaferrite particles in polymer matrix and thus magnetic anisotropy has been demonstrated in the composite, which is subsequently cured to hold the physical position and orientation of the particles. The anisotropy of the self-biasing field provided by the films has been experimentally characterized, and a ferromagnetic resonance (FMR) frequency ~43 GHz has been observed. We have also characterized the viscosity of the particle-laden polymer at different particle concentrations. 3D printing of this composite with poling will make it possible to directly print magnetic components that require out-of-plane anisotropic magnetization.

This paper proposes a novel approach to the modelling of HTS transformer-rectifier flux pumps that can charge HTS magnet-ic loads without the need for bulky current leads or expensive cryogenic requirements. The model was built in MATLAB/Simulink for a flux pump with 2 HTS switches, an HTS transformer with a primary inductance of 15 mH, second-ary inductance of 50 H and an HTS magnetic load with an in-ductance of 2 mH. With a 5 A pk-pk triangular current wave-form at 2 Hz the system can load the HTS load to 34.63 A in 5 s. This incremental addition of flux to the load demonstrates the advantage of flux pumps as they can charge high-field magnets without the need for large power sources. The speed of flux pumping is improved by increasing the system frequency, the magnitude of the dynamic voltage developed in the HTS switches and by increasing the primary inductance of the trans-former. This has widespread industrial applicability in fields such as the charging of high-field magnets for MRI systems.

Analytical modeling (AM) of the magnetic field for axial-flux switched reluctance motors (AFSRMs), considering three-dimensional (3-D) features and nonlinear saturation effects, remains to be a knotty problem. This paper proposes a quasi-3-D nonlinear AM method to predict magnetic field distributions and electromagnetic performances of an AFSRM. Firstly, the harmonic modeling technique is applied to obtain the spatiotemporal distribution characteristics of the axial and tangential magnetic flux density at the mean radius. Secondly, the nonlinearity of the soft magnetic material in teeth is considered by an adaptive convergence rate algorithm. Finally, a radial dependence function is formulated to extend the solution of the annular section to any point in the 3-D space of the AFSRM. To confirm the accuracy of the proposed method, the analytical solutions of magnetic flux density and electromagnetic torque have been compared with FEM simulation results. Meanwhile, an additional validation has been done for the stability of this nonlinear AM method under severe saturation conditions. At last, the reasonable selection of the harmonic truncation order number has been discussed to reach a good balance between the accuracy and time cost. The quasi-3-D nonlinear AM method can consider the curvature and edge effect as well as the saturation effect effectively, which is suitable for performance predictions and parametric studies of AFSRMs.

Robustness and reliability of modern synchronous motors require an accurate design of the permanent magnets (PM) while accounting for the motor operating conditions (demagnetizing field, temperature). In this paper, the important attribute of a PM non-linear demagnetization model within a finite element method (FEM) simulation environment is clearly emphasized. To do so, starting from experimental measurement achieved on a NdFeB PM, a toolbox baptized “PM-Demag” has been developed. This toolbox manages the PM history and updates the PM B(H) characteristics depending on the temperature and the PM working point. Finally, a relatively straightforward coupling is implemented with a FEM software and applied to a simple study case. Results show local magnetization loss in the PM due to the combination of both the temperature and the demagnetizing field.

This work investigates the effect of design parameters of permanent magnet (PM) and flux barriers (FBs) in the rotor on the anti-demagnetization ability (ADA) of fractional slot concentrated windings interior permanent magnet (IPM) motors for electric scooters. A 2.5 kW IPM motor (12 slots and 8 poles) is designed for a wide speed range, and its ADA associated with different PM and FB arrangements is studied under high temperature and high current density operations. The analysis shows the relationship between the ADA and characteristic current (Ich, defined as the ratio of PM flux linkage to d-axis inductance). It is also found that proper designs of flux barriers can significantly improve the ADA of the IPM motor without much affecting Ich. Thus, the motor ADA and performance can be simultaneously improved. Finite element analysis is used for evaluation, and experiments are conducted to validate the analysis.

Hybrid excited synchronous machines (HESM) combine permanent-magnet (PM) excitation and wound field (WF) excitation. The goal of hybrid excitation is to combine the advantages of PM excited machines and wound field synchronous machines. HESM have been identified as one of the emerging technologies for modern energy conversion systems. They have been the subject of many review papers. The principle of hybrid excitation allows solving many drawbacks related to permanent magnet electric machines operation: flux weakening, energy efficiency, and permanent magnets price fluctuation. It helps to introduce an additional degree of freedom in the design of synchronous machines, and allows therefore an easier adaptation of PM synchronous machines to a wider applications scope. To this additional degree corresponds the possibility of adjusting the contribution of the two magnetic field sources, PM and WF. The use of this technology for electric traction has been the subject of many scientific and technical contributions. In this contribution, the emphasis will be put on the use of these machines as generators in transportation applications and renewable energy applications. The design and operation of three particular structures will be presented. Two of them have been designed as generators for transportation applications, and the third one has been designed as generator for renewable energy conversion. All of them are flux switching hybrid excited synchronous structures (FSHESM).

In this paper, two novel dual stator machines with different biased permanent magnet (PM) configurations are developed and comparatively studied. For the proposed machines, the PMs are only located in the inner stator, but with different configurations, i.e., surface-mounted PM (SPM) and interior PM (IPM), respectively. The machine topologies and operating principle are introduced first. Then, the electromagnetic characteristics, including open-circuit performance, torque characteristics, field weakening capability, loss and efficiency are comprehensively analyzed and compared by finite element method (FEM). The experimental validation are conducted to verify the FEM analyses.

Due to the bidirectional field modulated effect, the dual-permanent-magnet-excited (DPME) machine relies on the countless airgap flux density harmonics with specific pole-pair numbers (PPNs) to produce stable torque or effective back-EMF. Regarding the generation of back-EMF, there is no doubt that the flux density harmonics which make a negative contribution will reduce the performance of DPME machine. However, to the best of our knowledge, there is very little research on the identification of field harmonics which play a negative role in the generation of back-EMF. In this paper, the partial-analytical-method (PAM) is proposed to quantitatively identify the field harmonics. Firstly, the PAM is described in detail, and the ratio of contribution (RoC) is defined to assess the contribution of field harmonics to back-EMF. Then the PAM is applied to a 12/10 DPME machine. The identification results show that two of the five types of field harmonics, i.e., Type-II and Type-V, make a negative contribution to back-EMF, the RoCs of which are -2.94% and -4.32%, respectively. In these two types of harmonics, the ones with PPN=22 are mainly responsible for the negative contribution to back-EMF, which needs attention at the outset of the design.

MnBi-LTP has excellent magnetic intrinsic properties and attractive characteristics as a permanent magnet material. It is necessary to synthesize fine particles of MnBi-LTP with a size close to that of its single magnetic domain (. 500 nm) to improve the magnetic anisotropic characteristics. Although the room-temperature ball milling process has been reported as a common method to reduce MnBi particle size, it has an inevitable limitation in reducing the powder size due to the low milling energy as well as the powder agglomeration by cold welding phenomenon. In this study, we synthesized fine particles of MnBi-LTP by the cryo-milling process at a temperature of 77 K. Phase analysis and magnetic properties were examined as a function of the amount of stearic acid for the cryo-milled powders. As a result, it was found that stearic acid as a surfactant plays an important role in suppressing the decomposition of the magnetic phase that occurs during the cryo-milling process. Consequently, high-purity fine MnBi-LTP particles, with (BH)max of 9.25 MGOe, were obtained through this method. Thus, this indicates that the cryo-milling process has the potential to synthesize fine MnBi-LTP particles with superior magnetic properties.

This paper overviews novel magnetic-field-shifting techniques for enhancing the torque in a new class of asymmetric rotor pole interior permanent magnet (AIPM) machines. The principle for torque enhancement is introduced firstly. AIPM topologies are then categorized in terms of asymmetries and symmetricities of PM configuration and rotor core geometry. Subsequently, the merits and demerits of various AIPM rotor topologies in each category are analyzed and compared. Finally, torque capabilities of selected AIPM machines are compared.

Stator and rotor cores of interior permanent magnet (IPM) motors are usually saturated, and the saturation distribution and saturation depth vary with the stator current. Also, their rotor structures are complex; hence the saturation cannot be accurately reflected by a saturation factor. These considerations lead to existing equivalent air-gap length models of induction motors and inset permanent magnet (PM) motors no longer suitable for IPM motors. Therefore, based on the consideration of stator and rotor saturation, this paper proposes the equivalent air-gap length model of IPM motors expressed by magnetic potentials on the stator inner surface and the rotor outer surface. The proposed equivalent air-gap length model can accurately reflect the influences of complex structure and severe saturation of IPM motors. Compared with existing models, the proposed one is no longer uniquely determined by motor structure parameters; it is also a function of stator current and rotor position. Furthermore, the obtained equivalent air-gap length model is combined with the winding function and the modified winding function to solve the inductances under different stator currents and different rotor eccentricity states. Finally, the proposed method is verified by both finite element analysis (FEA) and experiments.

In this paper, the balanced bidirectional-magnetization effect of a newly developed hybrid-magnet-circuit variable flux memory machine (HMC-VFMM) is revealed and investigated. Firstly, the machine topology and variable flux principle of the HMC-VFMM are described, respectively. In addition, the balanced bidirectional-magnetization effect is analytically unveiled by using a Fourier-series based hysteresis model of low coercive force (LCF) magnet. The PM magnetization characteristics are then investigated by a coupled solution, which is employed to identify the mismatch between the LCF magnet movement trajectories subject to either continuous one-way or bidirectional alternate current pulses. Finally, a prototype is manufactured and tested to verify the theoretical analyses.

Aiming at the problem of excessive eddy current loss of permanent magnets in fractional slot concentrated winding permanent magnet synchronous motors (FSCW-PMSM) at high speed, a new PMSM with hybrid rotor structure for electric vehicles (EV) is proposed in the paper, the key is to introduce additional ferrite magnets in d and q axis magnetic flux paths, respectively. Furthermore, slotting on the rotor surface and genetic algorithm (GA) optimization are adopted to compensate for the side effects caused by the introduction of ferrite magnets and to obtain optimal parameters of the new motor. Compared with the traditional all-Nd-Fe-B structure, the proposed hybrid rotor structure can not only curb the magnet loss at high speed, but also present a cost-effective design approach for IPMSM for EV applications with less usage of expensive Nd-Fe-B magnets as well as enhanced reluctance torque capability.

The magnetic printing onto energy-assisted magnetic recording (EAMR) media by utilizing double magnet master (DMM) media has been demonstrated. The double magnet master media is effective for improving printing characteristics by enhancing recording field with two different magnetic patterns which consists of high coercivity and low coercivity magnets. The magnetization distributions and printing performances for magnetic printing onto EAMR media were evaluated by the micromagnetic simulation. The DMM can clearly print the L/S and checkerboard patterns onto EAMR media, and the DMM printing performance was superior to that of the conventional master media. The DMM printing could write the servo-signals onto the EAMR media with the coercivity of up to 30 kOe. The narrower switching distributions of grains in EAMR media enhances the printing characteristics. The potential of magnetic printing with DMM media was revealed for writing the servo-signals onto the EAMR media.

A novel hot extrusion method to fabricate anisotropic nanocrystalline SmCo5 magnet was investigated. The results indicate that the hot-extruded (HE) SmCo5 magnet obtains a strong c-axis texture in perpendicular to the extrusion direction, but the texture strength is clearly different in different regions. The deformation degree plays a key role in the formation of c-axis crystallographic texture and magnetic anisotropy. In surface region of the HE magnet, the deformation degree of grains is the biggest, and the c-axis texture and remanence are the strongest. Furthermore, deformation mechanism of the HE SmCo5 magnet was preliminarily discussed.

Offshore wind turbines are the key enabling technology to increase the green energy penetration in the electricity market. Increasing the power generation per tower and reducing the levelized cost of energy are the two significant problems faced by wind turbine manufacturers. Traditional turbine manufacturers use rare-earth permanent magnets (PMs) to increase the air-gap flux density and maximize the machine outer diameter to increase the torque output. Since the air-gap flux density achievable with available PM is limited, increasing the power output of a traditional generator invariably leads to a significant increase in the volume and mass on top of the turbine tower and associated manufacturing, transportation, and installation costs. Superconducting (SC) wind turbine generators offer 5 to 10 times the air-gap flux density of a PM generator, and a corresponding increase in specific power and power density. Previous MW scale SC wind turbines designs used heavy back iron in the design, iron saturation limits the achievable air-gap flux density in the designs and resulted in bulky generators and moderate efficiency. In this paper a hybrid design approach is proposed to reach an ultra high field (5 to 10 times of PM air-gap flux density) and high efficiency (>98turbine for offshore wind turbine. An additional stray field limitation is introduced for safety concerns and shielding techniques are explored. Electromagnetic, mechanical, and cooling designs are provided to support the feasibility of proposed SC wind turbines. A nacelle integration inside a commercially available 6-MW wind turbine is shown to demonstrate the size comparison of the proposed generator.

Objective: Ironless, permanent magnet, synchronous linear (IPMSL) motors are applied widely in precision servo control for the nonexistence of cogging forces and comparatively small fluctuations in thrust and speed. Method: The air and water cooling structures are designed by assuming the heat loss in the motor operations is the source for the distribution of the temperature field in the analysis under natural cooling. Conclusion: The temperature fields of the linear motor under the two cooling modes are compared and analyzed, which helps monitor the temperature of linear motors during development and operations.

This paper employs grain-oriented (GO) silicon steel in an axial-flux permanent magnet (AFPM) machine to improve its torque and efficiency. Rolling direction of the GO material have been studied to ensure the machine’s main magnetic flux passes through the easy magnetization direction. Based on the study of the electromagnetic characteristics of AFPM machine, GO silicon steel is laminated to form a stator according to a certain lamination direction. The torque and efficiency of the proposed machine with GO material shows an increase in comparison with that of the conventional non-oriented (NO) silicon steel machine under identical conditions. In addition, an equivalent magnetic circuit model is established to illustrate little difference of electromagnetic property under no-load condition for the yokeless stator AFPM using two kinds of silicon steel sheet. Furthermore, a AFPM machine with stator yoke is also established to highlight the superiority of GO in the application of the AFPM machine with yokeless stator.

Hypothesis Solid lipid nanoparticles (SLNs), co-encapsulating superparamagnetic iron oxide nanoparticles and sorafenib, have been exploited for magnetic-guided drug delivery to the liver. Two different magnetic configurations, both comprising two small magnets, were under-skin implanted to investigate the effect of the magnetic field topology on the magnetic SLNP accumulation in liver tissues. A preliminary simulation analysis was performed to predict the magnetic field topography for each tested configuration. Experiments SLNs were prepared using a hot homogenization approach and characterized using complementary techniques. Their in vitro biological behavior was assessed in HepG-2 liver cancer cells; wild-type mice were used for the in vivo study. The magnet configuration that resulted in a higher magnetic targeting efficiency was investigated by evaluating the iron content in homogenated murine liver tissues. Findings SLNs, characterized by an average size smaller than 200 nm, retained their superparamagnetic behavior and relevant molecular resonance imaging properties as negative contrast agents. The evaluation of iron accumulation in the liver tissues was consistent with the magnetic induction profile of each magnet configuration, concurring with the results predicted by simulation analysis and obtained by measurements in living mice.

In this paper, a novel winding switching control strategy is proposed to extend the speed range of a consequent-pole ferrite-PM hybrid-excited machine (CPFPM-HEM) for electric vehicle application. The key is that in low-speed range, the AC armature winding and DC field winding are connected in series to achieve large starting torque, while in high-speed range, DC field winding are injected with adjustable DC currents to realize variable speed constant voltage of AC armature winding. Furthermore, consequent-pole rotor is used to reduce the usage of the permanent magnet (PM). In the meantime, ferrite PMs are used to replace rare-earth PMs to reduce the cost with the shortage of rare earth resources. In this paper, the machine configuration, operation principle with dual excitation sources, flux modulation principle and winding switching strategy are illustrated in detail. Then, the electromagnetic performance of the CPFPM-HEM in different speed ranges is investigated. Finally, the speed range extension with winding switching strategy is verified by the Maxwell/Simplorer co-simulation.

With the rapid development of vehicle information systems, liquid crystal displays (LCDs) have been widely used to enhance information experience. A linear vibration motor is usually placed behind the LCD to provide sufficient haptic feedback. A linear vibration motor with a large permanent magnet causes massive flux leakage around the display. As a result, it may cause unpredictable harm to people with implanted medical devices. Therefore, in this paper, a novel magnetic circuit design of a slim-width type linear vibration motor is introduced to reduce the static magnetic flux leakage. The haptic performance of the slim-width type linear vibration motor was analyzed using the electromagnetic-mechanical coupling method. Three types of experimental results were obtained to verify the analysis results. In conclusion, compared to the prototype motor, the slim-width type linear vibration motor proposed in this paper exhibits significant flux leakage reduction of 94.01% and 96.34% at the measuring positions. Furthermore, the slim-width type linear vibration motor exhibits an acceleration similar to that of the prototype motor.

In this paper, the split-tooth stator-slot permanent-magnet (ST-SSPM) machines with different PM arrangements are comprehensively analyzed. Four types of ST-SSPM machines are first introduced and classified by the positions and polarities of PMs. Then, the operation principles are elaborated and the slot-pole combinations are derived from the view of field modulation theory. Besides, four types of ST-SSPM machines with different slots and rotor poles are globally optimized to achieve maximum torque and minimum torque ripple. Furthermore, the electromagnetic performances of the optimal designs are thoroughly analyzed by using the finite-element analysis (FEA), including the cogging torque, back-EMF, steady torque, PM utilization ratio, loss, efficiency, and PM demagnetization. Finally, some conclusions are drawn based on the optimal designs and analyzed results.

This paper proposes and implements a compact wireless motor drive using orthogonal bipolar coils for the coordinated operation of robotic arms. The key is to orthogonally integrate two bipolar coils to form a compact magnetic coupler (CMC), while each CMC serves as the transmitting coil and receiving coil, respectively. Instead of adopting the one-to-many coil structure and operating at multiple frequencies, in this paper, two bipolar coils in the CMC are mutually decoupled and separately energized to drive two permanent magnet DC (PMDC) motors. As such, the wireless and selective motor drives can be achieved via the shared power-transfer channel at a single resonant frequency. All controls and switches are concentrated at the transmitter so that the receiver is entirely sealable. Accordingly, the coordinated operation of robotic arms can be realized with the high integration and no electrocution. Theoretical calculations and experimental results are given to validate the flexibility and feasibility of the proposed system.

In this paper, a new consequent-pole segmented dual-stator permanent magnet (CPSDSPM) machine, which is used for some high-torque & low-speed applications, is proposed. This proposed machine adopts two stators, in which the external stator is segmented into three parts. The intermediate rotor is sandwiched between the internal stator and the external stator. Due to a particular coupling effect between the internal stator and the external stator, the CPSDSPM machine can inherently exhibit excellent flux-enhancing ability and output capability. The configuration of this proposed machine is introduced. The working mechanism especially the coupling effect is discussed by analytical models. The electromagnetic properties, such as the no-load back electromotive force (back-EMF), the cogging torque, the output capability and the torque ripple, are all calculated and analyzed by the finite element (FE) method. It can be seen that the simulating results can verify the correctness of the theoretical analysis and the superiority of the proposed CPSDSPM machine. A prototype machine is fabricated and tested to validate the results of the FE analysis.

In this paper, a robust optimization design method considering magnet material uncertainties is proposed for permanent magnet (PM) machines. The key of this method is to improve the machine design robustness to resist the uncertainties influence from PM material, including material diversity, manufacture error, and assembly accuracy. To verify the proposed optimization method, a double permanent magnet machine is selected as an example. During the implementation of optimization design, firstly, the robust optimization model is constructed based on the analysis of PM uncertainties. Then, the Kriging surrogate model and non-dominated sorting genetic algorithm II (NSGA-II) are adopted to solve the optimization model. Finally, to verify the effectiveness of the method, the machine performance and corresponding reliability are evaluated, and a prototype is manufactured and tested. Both simulation and experimental results indicate that the proposed robust optimization method can effectively reduce the influence of magnet material uncertainties on PM machine performance.

In this paper, a flux-controllable permanent magnet (FC-PM) motor has been designed and optimized to achieve the optimal torque component distribution under different flux leakage conditions. The FC-PM motor can realize the flexible adjustment and control of air-gap magnetic field by reasonable flux bridge design, which further broadens the speed range of the motor effectively. The focus of the research is to analyze and optimize the torque characteristics in combination with typical operation conditions. Firstly, a motor topology is proposed, the mechanism of flux leakage and the distribution of torque characteristics are studied. Then, according to different flux leakage operation conditions, an optimization method considering the torque component distribution is newly proposed. Based on the proposed optimization method, the optimal motor can be obtained. Finally, the performance of the optimal motor is analyzed and compared with the initial motor. The comparison results indicate that, based on the proposed optimization method, the torque output capability is improved effectively while the desired leakage flux adjustment range is maintained.

This paper attempts to present a quasi-3D finite element method technique for modeling and analyzing tubular linear permanent magnet machines (TLPM) with translator eccentricity. Normal tubular linear machines can be modeled effectively using 2D axisymmetric models, but with the introduction of the eccentricity factor into the geometry the axis symmetry is no longer valid, and hence 3D modeling techniques become the only way for studying the machine. However, sometimes 3D modeling can become time-consuming and requires a huge amount of resources especially for non-linear problems, so the interest in modeling techniques that can represent the problem at hand with less computation time and relatively accurate results is high. A quasi-3D technique was specifically developed to be able to represent the eccentricity in TLPMs. The finite element method (FEM) was used for modeling. Eccentricity analysis has been carried on two different TLPM structures using the proposed quasi-3D, and the results from the quasi-3D model were compared to those obtained using the 3D FEM model. Both the open circuit and the on-load operating conditions were studied with the magnetic saturation taken into account. The behavior and the accuracy of the proposed model varied between the two studied structures and for the different operating conditions, and with very low computation time and cost the results obtained from the quasi-3D model were satisfactory in general except for certain cases.

Direct drive wave energy conversion (DD-WEC) is a typical low-speed long-stroke application. Harvesting wave energy presents enormous challenges, because wave energy naturally exists in the form of extremely low speed, high force, or torque motion. However, the frequency of flux linkage in field-modulated machine can be increased by the magnetic gear effect, and the output voltage and power density can also be effectively enhanced. In this paper, based on the field modulated principle, a field-modulated transverse flux linear generator (FM-TFLG) is proposed. Different combinations of permanent magnet number, slot number and translator number are selected and their performances are compared and analyzed. Results show that the electric frequency is enhanced as the modulation ratio increases. Compared with 18/12/17 (permanent magnet number/slot number/translator number) topology, 12/12/11 FM-TFLG has advantages of lower thrust ripple and total harmonic distortion (THD) of back-EMF, higher thrust/power density and efficiency. The proposed 12/12/11 FM-TFLG is a good candidate for DD-WEC.

Over the past four years, the magnetism of 2D magnets has been extensively studied by the full arsenal of probing techniques. 2D magnets can be incorporated to form heterostructures with clean and sharp interfaces, which gives rise to exotic phenomena as a result of the interfacial proximity effect. Here we report a detailed study of the spin (ms) and orbital (ml) moments of an epitaxial (CrSb/Fe3GeTe2)6 superlattice. The synchrotron-radiation based x-ray magnetic circular dichroism (XMCD) technique was performed to probe the microscopic magnetic properties of the superlattices in an elemental resolved manner. We unambiguously obtained a bulk-like moment of Fe3GeTe2 i.e., ms = 1.58 ± 0.2 μB/Fe and ml = 0.22 ± 0.02 μB/Fe. Future works to explore the tuning of the spin polarized band structure of 2D ferromagnetic superlattices will be of great interest and can have strong implications for both fundamental physics and the emerging spintronics technology.

Permanent magnet (PM) synchronous motors have become excellent alternatives for traditional induction and DC motors in numerous applications in recent years. Therefore, torque density and efficiency improvements in development of PM synchronous motors has become a significant issue. In this study, various PM synchronous motor alternatives are proposed with both non-oriented (NO) and grain-oriented (GO) silicon steel material in the same stator in order to increase the power density and the efficiency. Detailed performance comparison using 2D/3D FEA is completed and a feasible stator design is manufactured. The proposed design with GO material is also compared with a conventional PM motor with a NO stator steel. As a result of the investigations, it is observed that the proposed motor with GO material in the stator have higher torque density and efficiency as opposed to the conventional PM motor.

Advances in additive manufacturing have been paving the way for unconventional topologies in electromechanical systems. As such, topology optimization can be employed to uncover topologies that were once considered impractical. This paper investigates enhancing the shear stress of the reluctance trans-rotary magnetic gear (TROMAG) by optimizing the topology of the gear’s variable reluctance component. Reluctance TROMAG is a strong contender for force-intensive linear motion applications where a long stroke is required. Topology optimization is performed on the reluctance TROMAG with radially-magnetized permanent magnet (PM) configuration as well as with quasi-Halbach magnetized configuration. Results show that the use of elliptical iron teeth backed by non-ferromagnetic core can make 40% increase compared to the shear stress of the conventional (rectangular teeth) reluctance TROMAG with radial magnetization. The Halbach-magnetized TROMAG with elliptical iron teeth backed by non-ferromagnetic core achieves the same shear stress as the conventional reluctance TROMAG with Halbach magnetization, and the use of light weight non-ferromagnetic material for the variable reluctance component can make significant reductions in the total gear weight.

Multiphysics field coupling analysis requires that the electromagnetic and thermal performance be analyzed simultaneously. In this paper, electromagnetic field and thermal field based on lumped parameter thermal network(LPTN) are coupled. This method can give a more accurate evaluation of electromagnetic and thermal performance at the design stage. Take a 7500 rpm, 4.5 kW permanent magnet rectifier generator as an example: after designing the electromagnetic model by FEM and the LPTN model respectively, the electromagnetic field and thermal field are coupled by temperature-dependent material properties. Experiment shows that the error of simulated temperature and electromagnetic performance is within 5%. Moreover, this method reduces calculation time of thermal analysis dramatically, which can be applied to analyze and optimize a PM rectifier generator, as well as other typed motors.

In this paper, a high-speed permanent magnet synchronous machine (PMSM), which is rated at 15kW, 120krpm for a gas compressor, is designed and optimized. According to the design specifications, two design schemes of different rotor topologies are presented and compared by the finite element method (FEM) to determine the preliminary scheme of the original machine. The performance of the original machine is obtained by FEM. Meanwhile, the losses of the original machine are analyzed and calculated for the optimization. Especially, the conductor diameter of the winding is selected to reduce the copper loss of the machine. Finally, in order to reduce wind friction loss and increase power density, the dimensions of stator core and the thickness of permanent magnet (PM) are optimized. Compared with the original model, the wind friction loss is reduced by 17.2%, and the power density is increased by 6.64% in the optimized machine.

This paper proposes a new axial dual-stator flux-switching permanent magnet (FSPM) machine for high-speed applications. The machine adopts a fractional slot distributed winding, which has a higher winding factor, efficiency and torque density. Firstly, the high-speed FSPM machine topology and operating principle are introduced. By employing the winding complementarity principle, the unfavorable even harmonics of a single stator in the FSPM machine can be counteracted, resulting in an essentially sinusoidal PM flux-linkage as well as effectively reduced cogging torque and torque ripple. Secondly, based on the three-dimensional (3D) finite element method (FEM), both the no-load and on-load electromagnetic performances are obtained. Compared with the other three FSPM machines, the advantages of the proposed machine are highlighted. Finally, a high-speed FSPM prototype is manufactured and a test platform is built to measure the no-load and on-load performances, which verifies the theoretical analysis and simulated results.

In this paper, based on a 6-stator-coil/17-rotor-tooth (6/17) conventional concentrated-winding multi-tooth flux-switching permanent magnet (C-MFSPM) machine, a novel full-pitch multi-tooth FSPM (FP-MFSPM) machine is proposed by changing winding configurations. Then, the electromagnetic performance of six FP-MFSPM topologies sharing the same 6-stator-coil but with different rotor teeth combinations, namely 6/13, 6/15, 6/17, 6/19, 6/21, and 6/23, is compared by using finite element analysis (FEA). The results show that 6/17 and 6/19 are the optimal stator-coil/rotor-tooth combinations for FP-MFSPM machines, which exhibit better electromagnetic performance, such as more enormous torque and smaller torque ripple. Thereafter, the existing C-MFSPM and the proposed FP-MFSPM machines with 6/17 and 6/19 structures are quantitatively compared in terms of no-load back electro-motive force (back-EMF), air-gap flux density, cogging torque, electromagnetic torque, torque ripple, etc. The FEA-predicted results validate that the proposed FP-MFSPM machines have more sinusoidal back EMF, larger torque output, and smaller torque ripple, which are superior to the C-MFSPM topologies.

The motor in high power electric vehicle (EV) easily reached at voltage limit because of its large magnetic flux. Therefore, the motor should be designed so that the voltage is controlled at the limit. To achieve well voltage control condition, the interior permanent-magnet synchronous motor (IPMSM) is controlled by the field-weakening control method after the constant torque region. This is conducted by canceling the magnetic flux from the permanent magnet with the magnetic flux of the stator winding. However, this method generates many harmonics. In this paper, a design that effectively controls the voltage by reducing the harmonics generated in the field-weakening control is proposed. To reduce the harmonics in the field-weakening region, change stator and rotor design parameters, and the reason for using v-type permanent magnet arrangement for high-speed operation will be elucidated.

The demand for low-speed and high-torque electrical machines is increasing in different applications. Previous research showed that dual-stator magnetically geared machines, such as Vernier pseudo-direct-drive machines (VPDD) can have a high torque density as well as a high power factor. However, the size of their end-winding can affect heavily their torque density. Based on a distributed winding VPDD, we propose a concentrated-winding split-teeth VPDD (ST-VPDD), which can reduce the size of end-winding and output higher torque density. In this research, a model of the end-winding volume is given. Through preliminary design and finite element model FEM analysis, the torque density optimization has been performed to maximize the torque density. Taking the end-winding into account, there is a 93.8% improvement for the torque density, compared to the VPDD, to reach 78.1 Nm/L. After adding a sleeve for mechanical stability, the ST-VPDD still gives a 68.7% improvement compared to the VPDD.

This paper presents a method to reduce cogging torque in permanent magnet (PM) machines from dynamic control based on harmonic torque counteract (HTC). We find the possibility of dynamic cancellation of cogging torque and harmonic torque by studying their generation mechanism and period characteristics, and further study the current harmonic injection scheme for cogging torque reduction. Further, two case studies of a integer slot PM machine and a fractional slot PM machine based on finite element analysis well validate the proposed method. Among them, the cogging torque of a 6-slot/2-pole PM synchronous machine is weakened from 932.0mN.m to 56.2mN.m, with a weakening ratio of 94.0%, and the cogging torque of the other with 6-slot/4-pole is weakened from 1.23N.m to 44.21mN.m, with a weakening ratio of 96.4%. The theory of this paper can be extended to PM machines with other different pole/slot combinations and topologies.

A permanent magnet synchronous reluctance machine (PMSynRM) is studied in this paper. It has a stack of surface-mounted permanent magnet (SPM) rotor and a stack of synchronous reluctance (SynR) rotor, which are axially combined on the shaft. Unlike the traditional PM-assisted SynR machine (PMASynRM), the magnets are not located in the flux barriers of the SynR rotor, therefore, the magnets and flux barriers have no more geometric confliction between them. The two rotor stacks can be circumferentially shifted to any relative angle. Clearly, the shifting angle and the axial length ratio between the two rotor stacks, together with the phase angle of the armature current vector, influence the motor performance, and their optimal design is detailed in this paper. Analysis of the prototypes shows that the studied PMSynRM evidently exhibits higher torque density than the conventional PMASynRM.

High temperature superconducting (HTS) tapes could be introduced into large scale electrical machines in order to improve the power density. However, the alternating current (AC) loss of HTS tapes will cause the reduction of efficiency. On the basis of analytical and numerical model calculations, this paper presents an optimal design of the HTS armature winding aiming at lower AC loss. The main contribution of this work is that the relationship between the installation parameters and the AC loss of such HTS armature windings has been figured out based on the analysis of the shape feature of the HTS tape and the external magnetic field. When the tape is placed along a particular direction where the perpendicular component of external magnetic field has the lowest amplitude, the AC loss is the smallest. The modified installation location and angle are found based on the proposed generator. These results are verified using finite element method (FEM).

To solve the problem of complex operating device and permanent magnets (PMs) demagnetization at high temperature, a new type of permanent magnet fluxed-switching coupler (PMC) with synchronous rotating adjuster is proposed. Its torque can be adjusted by rotating a switched flux angle between the adjuster and PMs along the circumferential direction. The structural feature and working principle of the PMC are introduced. The analytical model of the novel PMC was established. The torque curves are calculated in transient field by using the three-dimensional finite element method (3-D FEM). The temperature distribution of the novel PMC under rated condition is calculated by 3-D FEM, and the temperature distribution of the PM is compared with that of the conventional PMC. The simulation and test results show that the maximum temperature of copper disc and PM of the novel PMC are 100 °C and 48 °C respectively. The novel PMC can work stably for a long time under the maximum load condition.

Various technologies have ever been developed to minimize the detent force of linear motors. Although the traditional modular structure can effectively reduce the detent force, the width of the flux barrier and the number of units severely limit its application. To solve these, this paper proposes a new modular type of tubular permanent magnet synchronous linear motor (TPMSLM), which consists of two identical unit motors. For simplification, a subdomain analytical method of the unit motor is firstly established, and its accuracy is verified by a comparison with that of the finite element method. Using the two approaches, the important parameters of the motor are analyzed. A modified two-unit modular TPMSLM is also proposed through the star vectograms of the electromotive force, which achieves thrust performance similar to the traditional three-unit modular TPMSLM with a smaller axial size. Moreover, to make full use of the volume of the flux barrier, end teeth are added at both ends of the unit motors. The simulation results indicate that a reasonable end tooth structure can not only reduce the magnetic leakage phenomenon of the end but also effectively improve the thrust of the motor.