The 50 most-cited articles in IEEE Transactions on Magnetics, 2018

We demonstrate ultra-fast (down to 400 ps) bipolar magnetization switching of a three-terminal perpendicular Ta/FeCoB/MgO/FeCoB magnetic tunnel junction. The critical current density rises significantly as the current pulse shortens below 10 ns, which translates into a minimum in the write energy in the nanosecond range. Our results show that spin-orbit torque-MRAM allows for fast and low-power write operations, which makes it promising for non-volatile cache memory applications.

A two-level surrogate-assisted optimization algorithm is proposed for electric machine design using 3-D finite-element analysis (FEA). The algorithm achieves the optima with much fewer FEA evaluations than conventional methods. It is composed of interior and exterior levels. The exploration is performed mainly in the interior level, which evaluates hundreds of designs employing affordable kriging models. Then, the most promising designs are evaluated in the exterior loop with expensive 3-D FEA models. The sample pool is constructed in a self-adjustable and dynamic way. A hybrid stopping criterion is used to avoid unnecessary expensive function evaluations.

Due to the advantages such as high energy density, high power density, high cyclic life, and environmentally friendly, the flywheel battery has the potential to solve the problem of energy storage. In order to improve the torque density and suspension performance of bearingless synchronous permanent magnet (PM) synchronous motors (BPMSMs), a novel rotor structure with V-shaped PMs is designed in this paper. Furthermore, the interior BPMSM (IBPMSM) with V-shaped PM which used for flywheel batteries of electric vehicles is researched in detail. Especially, the influence of geometrical parameters of V-shaped PM on suspension force and electromagnetic torque is investigated. Moreover, the corresponding static electrical magnetic characteristics including inductances and electromagnetic torque are also studied. The finite-element method is employed to evaluate the theoretical analysis of the proposed IBPMSM. In addition, the optimized motor is validated to have good suspension performance by some experiments.

An eddy current test (ECT) is a common nondestructive test to detect flaws in metal structures. Many ECTs use both a detection coil and an induction coil. The application of this method to ferromagnetic materials can be challenging because the applied magnetic field is composed of not only the eddy current but also the magnetization signal. Therefore, we developed two types of miniaturized ECT probes, namely, single- and dual-channel tunneling magnetoresistance (TMR) probes, by using a TMR sensor instead of a detection coil. To evaluate the performance of crack detection in steel with regard to the length, width, and depth of cracks, the sensor probe was line-scanned above the crack position. The output signal was detected using a lock-in amplifier and analyzed using the real and imaginary components of a magnetic vector. The detected signal was then divided into the magnetization and eddy current components. The dual TMR sensor probe installed inside the induction coil could yield a stable crack signal without the influence of magnetization fluctuation. The line-scanned…

Magnetic components in power electronic equipment usually suffer from nonsinusoidal excitations. In this paper, a brief description about the existing core loss calculation methods for nonsinusoidal excitations is given. Then calculation formulas of aforementioned methods for two typical excitation waveforms, that is, square and rectangular with variable duty cycle D, are derived. Core loss of nanocrystalline FT-3KS, under above two nonsinusoidal excitations, is measured on an established test setup. The accuracy and applicability of each method are discussed theoretically and verified experimentally, especially in terms of different duty cycles and frequencies. It is found that the waveform coefficient Steinmetz equation (WcSE) is more applicable for the case of relatively small harmonics content of magnetic field intensity H (normal duty cycle region), while the improved generalized Steinmetz equation (IGSE) has better precision where the harmonics count (extreme duty cycle region). In addition, the IGSE can better follow the changing trend of core loss with D and have better…

In this paper, an 18-slot/26-pole vernier permanent magnet synchronous machine (VPMSM) with coil pitch of two slot pitches is proposed based on a nine-slot/18-flux-modulation-pole/26-pole VPMSM with concentrated tooth-coil windings. Compared with the original VPMSM, the number of slots is doubled and the phase winding connection is adjusted to reduce the space harmonic content, the phase inductance, and hence, improve the power factor. This paper shows that the proposed VPMSM increases power factor from 0.73 to 0.95 with better torque and flux-weakening capability. Moreover, a series of VPMSMs with high-power factor is proposed from the same design principle and given design guidelines.

Due to additive operation’s dominated computation and simplified network in binary convolutional neural network (BCNN), it is promising for Internet of Things scenarios which demand ultralow power consumption. By means of fully exploiting the in-memory computing advantages and low current consumption design using multilevel cell (MLC) spin-toque transfer magnetic random access memory (STT-MRAM), this paper proposes an MLC-STT-computing in-memory-based computing in-memory architecture to achieve convolutional operation for BCNN to further reduce the power consumption. Simulation results show that compared with the resistive random access memory (RRAM)- and spin orbit torque-STT-MRAM-based counterparts, the architecture proposed in this paper reduces power consumption by ~$35{\times}$and 59% in Modified National Institute of Standards and Technology data set, respectively.

For accurate computation of core losses, the Jiles-Atherton (J-A) dynamic hysteresis model accounting for hysteresis, eddy current and excess losses is incorporated into the finite-element method (FEM). The J-A dynamic hysteresis model is constructed by combining the traditional J-A hysteresis model with the models of instantaneous eddy current and excess losses. The J-A model parameters and dynamic loss coefficients are determined by fitting the models to the measurement data of a single sheet tester (SST 500) and Epstein frame tester. To find the robust best fit, the particle swarm optimization algorithm is employed. By using the proposed J-A dynamic hysteresis model and FEM, the magnetic characteristics of a magnetic core is simulated and the core loss distribution within the core obtained. The calculated and measured results are compared to show the accuracy and effectiveness of the proposed model.

High-speed permanent magnet synchronous machine (PMSM) can provide high power density and high efficiency, which is often highly desirable in high performance applications. A multi-physics optimization program based on the multi-objective genetic algorithm was developed in this paper, to achieve a tradeoff solution between the electromagnetic, mechanical, and thermal aspects. First, the parametric electromagnetic model was modeled based on the finite-element method, and then a thermal network model and an analytical mechanical model to determine the thickness of the magnet and the sleeve were developed and merged within a design cycle of the machine, in an effort to attain the target performances of 20 kW/kg at 20 000 r/min for a 2 MW PMSM. Optimization results indicated that a final design with eight poles and 48 slots could obtain a comprehensive performance between power density and efficiency, and the performance satisfied all the requirements.

The most significant assumption in the subdomain technique (i.e., based on the formal resolution of Maxwell's equations applied in subdomain) is that the iron parts are considered to be infinitely permeable, so that the saturation effect is neglected. In this paper, we present a novel contribution on improving this 2-D technique in polar coordinates by focusing on the consideration of iron relative permeability. In non-periodic regions, magnetostatic Maxwell's equations are solved considering non-homogeneous Neumann boundary conditions, and the general solution is obtained by applying the interfaces conditions in both directions (i.e., rand θedges ICs). The proposed model is relevant for different types of radial-flux electrical machines with(out) permanent magnets (PMs) supplied by a direct or alternate current (with any waveforms). For example, the semi-analytical model has been implemented for spoke-type PM machines. The magnetic field calculations have been performed for two different values of iron core relative permeability (viz, 100 and 600), and compared with those obtained…

Recent studies in spintronics (STs) have highlighted ultrathin magnetic metallic multilayers as a novel and very promising class of broadband terahertz (THz) radiation sources. Such ST multilayers consist of ferromagnetic (FM) and non-magnetic (NM) thin films. When triggered by ultrafast laser pulses, they generate pulsed THz radiation due to the inverse spin-Hall effect—a mechanism that converts optically driven spin currents from the magnetized FM layer into transient transverse charge currents in the NM layer, resulting in THz emission. As THz emitters, FM/NM multilayers have been intensively investigated so far only at 800 nm excitation wavelength using femtosecond Ti:sapphire lasers. In this paper, we demonstrate that an optimized ST bilayer structure of 2 nm Fe and 3 nm Pt grown on 500$\mu \text{m}$MgO substrate is just as effective as a THz radiation source when excited either at$\lambda = 800$nm or at$\lambda = 1550$nm by ultrafast laser pulses from a femtosecond fiber laser (pulsewidth ~100 fs and repetition rate ~100 MHz). Even with low incident power levels, the Fe/Pt ST…

The proper magnetic design is one of the most difficult and critical phases in developing an inductive power transfer system, especially for electric vehicle charging. In this communication, a fast and an efficient improved Tabu search algorithm coupled with 2-D finite-element analysis (FEA) was used to determine the optimum design parameters of power pads. A two-objective optimization problem was investigated considering the magnetic coupling, misalignment (horizontal, vertical, and rotational), as well as the cost. The double-D power pad structure was considered as a case of study, and the most effective design parameters were obtained. The 2-D FEA was utilized to calculate the coupling factor at different misalignment conditions. For verification purposes, the system coupling performance and cost are analyzed using the optimum design parameters and compared with three other designs presented in the literature. The proposed optimized design shows the best coupling performance with moderate cost. The results proved the validity and advantages of the proposed design methodology.

This paper proposes an all-in-one system for hyperloop that conducts propulsion, levitation, and guidance. Currently demand on high-speed long-distance transportation is increasing, so that hyperloop is getting attention and studied hard globally. Hyperloop is a new innovative transportation in which a levitated subsonic speed train travels through a vacuum cylindrical tube. Hyperloop needs functions of propulsion, levitation, and guidance for its service, and many devices are necessary for those functions. In the tube, a constrained space, many devices make the entire system complicated, and the size of the vehicle and tube are increased. Therefore, the costs of maintenance, manufacture, and construction are increased and control of each device becomes very difficult. But a non-symmetric double-sided linear induction motor (NSDLIM), the subject of this paper, is an all-in-one system that could conduct all functions. In this paper, the concept of NSDLIM was introduced and its possibility was suggested. Requirements of NSDLIM were investigated considering very high acceleration,…

This paper presents a nonlinear hybrid field model to predict the open-circuit magnetic field distribution in surface-mounted permanent-magnet machines. It combines the complex permeance model (CPM) with the magnetic equivalent circuit (MEC). The saturation effect is accounted for in the CPM by considering the magnetic potential distribution on the stator bore, which is calculated by the MEC and can be transformed to the virtual current on the slot. The proposed model significantly improves the calculation accuracy for saturated machines, which is verified by the finite-element analysis and the experimental results.

In this paper, the magnetostrictive orthogonal calculation method is used to simulate the vibration of iron cores of the transformer and shunt reactor models. The two models have the same size except there is a 2 mm air gap in the middle core of the reactor model. The Maxwell stress and total stress on the two cores are quantitatively calculated. The calculated results show that the air gap has a great influence on the vibration of the shunt reactor core. The Maxwell stress is the main reason for the vibration of the reactor core, but the vibration of the transformer core is mainly caused by magnetostriction. Finally, the experimental platform is built to measure the vibration accelerations of the two models and verify the results of the simulation.

One of the main engineering applications of ferrofluids is in magnetic fluid seals, working in rotary motion. An area, which has so far been insufficiently examined, is the mechanism of leaks between seal stages in this type of seal. This is an important issue in order to understand the principle of the seal operation and to properly design this type of seal. This paper presents the results of research into the mechanism of leaks between stages in multi-stage magnetic fluid seals. The tests were conducted when the pressure of the sealing air increased and reached its maximum value. The influence of the magnetic fluid properties, such as saturation magnetization or dynamic viscosity, was taken into account. Studies were performed for different seal temperatures. Experiments allowed models for determining the maximum pressure of the multi-stage seal to be proposed, based on the information about this pressure for a one-stage seal. This paper presents the comparative results of the critical pressure value obtained from experimental studies and calculations based on numerical…

In this paper, we present the design and optimization of a ring-pair permanent magnet array for head imaging in a low-held portable magnetic resonance imaging (MRI) system. The proposed array generates a longitudinal main static magnetic held (B0held) with an average held strength of 169.7 mT and a homogeneity of 24786 ppm in a held of view with a diameter of 200 mm and a thickness of 50 mm. It is a signihcant increase in held homogeneity by 79.7% compared to a traditional ring-pair structure of the same dimension and mass while still maintaining a similar held strength. The optimization was implemented by applying a genetic algorithm and by proposing an efhcient current model for the forward calculation of the magnetic held. The effectiveness of the optimization is validated by realistic simulations using COMSOL Multiphysics. Compared to a Halbach array, where the held is transversal and the existing coil designs cannot be applied directly, the proposed array generates stronger helds. Its magnetic held is longitudinal, which allows the direct application of the advancements in RF…

This paper deals with the optimization design process of an interior-type permanent magnet synchronous motor (IPMSM) for electric compressors of air conditioners applied to electric cars and hybrid vehicles. Based on a prototype IPMSM, we identified the current level for efficiency and cogging torque using finite-element analysis (FEA). The IPMSM's main design variables are optimized to primarily satisfy the target of efficiency and cogging torque. A second optimization design is carried out using the response surface method (RSM) for the main design variables obtained from the Taguchi method analysis. As a result, the optimization design is carried out through a two-step optimization design process using the Taguchi method and RSM. The IPMSMs are analyzed using FEA, and their validity is confirmed by comparing the test results against each step-by-step model. We validate an effective optimization design process using a two-stage design process. We conclude that the proposed approach provides an effective design method for engineers.

In this paper, a quantitative comparison of five new dual-permanent magnet (PM) linear motors with fault-tolerant teeth is presented, which are promising for application to the ropeless elevator propulsion system. The proposed linear motors have PMs on both the mover and stator, leading to a new class of dual-PM linear motors. In addition, they can offer the advantages of high reliability and fault-tolerant capability, owing to the presence of fault-tolerant tooth mover structure. By using JMAG based finite-element analysis, the electromagnetic performances of five proposed machines are analyzed and quantitatively compared. The comparison results show that the double-mover tooth-PM linear machine is most preferable for application to the ropeless elevator propulsion system because of its high force density, low force ripple and small attraction force. Finally, both the analysis results and experimental verification are given to verify the investigation.

A new flux-assisted consequent pole spoke-type permanent magnet (PM) synchronous torque motor is proposed in this paper. The proposed motor has fractional slot structure with a spoke-type rotor geometry and flux-assisted magnets. Initial design, rotor design optimization, detailed 2-D and 3-D finite-element analyses (FEAs), and structural and thermal simulations are all carried out. A prototype motor is built and tested. The optimized design is validated by 2-D/3-D FEA and experiments and compared with the reference conventional surface PM (SPM)-type torque motor. The results indicate that the proposed new motor has higher torque-to-magnet-weight ratio and wider constant power region than the conventional SPM synchronous torque motor.

As technology node scales down below 90 nm, the conventional complementary metal oxide semiconductor (CMOS) logic circuits suffer from various problems such as high standby power due to increase in leakage current. Spintronic devices based on magnetic tunnel junction (MTJ) is one of the most promising technology candidates for the future of the digital circuits. MTJ-based logic circuits can offer nonvolatility, high endurance, high density, low standby power dissipation, and 3-D integration capability with the CMOS technology. In recent years, several full-adder circuits are proposed based on MTJs that are not fully nonvolatile since they use MTJs to store only one of their inputs. This paper proposes a fully nonvolatile magnetic full-adder (MFA) circuit offering the capability of power gating with no loss of data. The proposed circuit stores all the inputs in MTJs using the spin-transfer torque (STT) method assisted by the spin-Hall effect (SHE). Thanks to the SHE assistance, delay and power consumption of the MTJ switching are reduced significantly. Moreover, as a result of lower…

This paper comprehensively studies the electromagnetic performance of flux-reversal permanent-magnet (FRPM) machines with different consequent-pole PM (CPM) topologies. Four CPM topologies are first introduced and classified by different numbers of PM pieces and PM locations on stator teeth. Then, the distribution and working harmonics of air-gap flux density of each CPM topology are analyzed and compared, from which the CPM topology with the highest torque density is identified. The influence of critical design parameters on machine performance is also parametrically investigated. By comparing the torque performance of CPM topologies with their surface-mounted PM counterparts, the advantages of CPM topologies, i.e., torque improvement and magnet volume reduction, are clearly revealed. Four FRPM prototypes are manufactured and tested to verify the analyses.

Deep spiking neural networks (SNNs) have emerged as one of the popular architectures in complex pattern recognition and classification tasks that can be enabled by low-power neuromorphic hardware. However, hardware implementation of such algorithms using conventional CMOS devices is area expensive and energy inefficient. This is owing to the fundamental mismatch between the underlying neuromophic computations and the CMOS transistors along with energy consumption involved in synaptic memory-access operations. Hence, there is a need for novel “neuro-mimetic” devices offering a direct mapping to synaptic and neuronal functionalities together with the possibility of providing in situ synaptic storage. Magnetic skyrmions have recently been proposed as a promising alternative for next-generation information carrier due to remarkably high stability, ultra-low depinning current density, and extremely compact size. In this paper, the design of skyrmion-based devices to emulate biological synapses and neurons is explored, and skyrmionic synapse-based crossbar architectures driving skyrmionic…

This paper investigates the demagnetization characteristic and permanent-magnet (PM) minimization of the less-rare-earth interior PM synchronous machines (LRE-IPMSMs) used for the electric vehicles, which are featured with high power density, high efficiency, and low cost. First, the equivalent magnet circuit (EMC) of the investigated LRE-IPMSM in demagnetization case is established. Then, the effects of the PM width and the thickness on the machine demagnetization characteristic are investigated. After that, the no-load EMC of the investigated LRE-IPMSM is established. Finally, an analytical method is proposed to obtain the minimum PM volume scheme on the premise of providing the targeted no-load flux and taking the machine anti-demagnetization ability into consideration simultaneously.

Electromagnetic performance of three multi-layered interior permanent magnet (IPM) machines are investigated and compared for electric vehicle applications in this paper. The rotor structure, air-gap field distribution, torque density, torque ripple, core loss, magnet eddy-current loss, and output power are studied with finite-element analysis. It is demonstrated that the two-layered rotor structure with magnets buried deeply has the lower torque density and magnet eddy-current loss due to the utilization of magnets and the block effects of the armature-reaction flux is lower. The three-layered IPM machine has the lower torque ripple and core loss than two-layered IPM machines because the harmonics of air-gap density are reduce by the increase of magnet layers. Finally, an IPM machine with three-layered magnets rotor is prototyped to verify the analysis.

This paper presents a comparison of several methods to compute the magnetic forces experienced by the stator teeth of electrical machines. In particular, the comparison focuses on the virtual work principle (VWP)-based nodal forces and the Maxwell tensor (MT) applied on different surfaces. The VWP is set as the reference. The magnetic field is computed either with finite element analysis or with the semi-analytical subdomain method (SDM). First, the magnetic saturation in iron cores is neglected (linear B-H curve). Then, the saturation effect is discussed in a second part. Homogeneous media are considered and all simulations are performed in 2-D. The link between the slot's magnetic flux and the tangential force harmonics is also highlighted. The comparison is performed on the stator of a surface-mounted permanent-magnet synchronous machine. While the different methods disagree on the local distribution of the magnetic forces at the stator surface, they give similar results concerning the integrated forces per tooth, referred as lumped forces. This conclusion is mitigated for…

A rotor structure of Permanent Magnet (PM)-assisted synchronous Reluctance Machine (PMa-synRM) with ferrite PM is presented in this paper, in which the irreversible demagnetization of PM and torque ripple are reduced. The bypass rib is proposed and added to the flux barrier of the rotor. The path for the demagnetizing field of armature windings is provided and the torque ripple can also be reduced by the bypass rib. Based on the 2-D finite-element analysis (FEA), the location and dimensions of the bypass rib are investigated and improved. A PMa-synRM with the proposed rotor structure is designed and compared with that using a conventional rotor. The field distributions for different currents are studied to explain the principle of the bypass rib. The results show that the PMa-synRM with the proposed rotor achieves higher antidemagnetization ability and lower torque ripple.

Advanced manufacturing techniques using composite materials made of magnetic particles and polymers are attracting much interest for new routes of fabrication of more efficient and functional devices with complex shapes. The 3D printing and bonding technologies of a broad range of materials, such as NdFeB, improved ferrites, and Mn-based alloys, show up as alternatives to traditional fabrication techniques for a large range of permanent magnets’ (PMs) applications. This paper focuses on the fabrication of magnetic products based on strontium ferrite and NdFeB by extrusion of magnetic-polymer composite materials. The composites have been extruded using different nozzles and optimizing the extrusion temperature for each of them, obtaining strips and filaments with rectangular and circular cross section, respectively. The morphological characterization of the strips and filaments has revealed that the polymer covers homogeneously the particles, obtaining continuous strips and filaments with a high filling factor. A decrease in the filling factor has been observed for the NdFeB-based…

The hybrid variable-flux permanent-magnet synchronous machine (VF-PMSM) is an alternative candidate for adjustable speed applications. The series magnet and parallel magnet configurations are the two existing topologies for hybrid VF-PMSMs. However, they both have drawbacks that have not been fully resolved. A premium topology with high power density and magnetization regulation using acceptable current pulses is highly desired. This paper proposes a new hybrid VF-PMSM with a quasi-series magnet configuration and a passive flux barrier. After introducing the proposed topology and its operating principles, the results of a comparative study are presented comparing the magnetization characteristics and torque capabilities of the three configurations. The influences of key design variables on the machine's performance are investigated, showing that the proposed machine can achieve a relatively high power density comparable to the series configuration, and the required magnetization current amplitude falls within acceptable limits.

Halbach array-based permanent magnet (PM) brushless machines exhibit attractive features when compared with conventional PM brushless machines with normal segmented magnets, including the flux-concentration effect, essentially sinusoidal air-gap flux density due to PMs, and negligible cogging torque. However, as for a motor/generator used in flywheel, an external rotor composed of Halbach array and rotor back-iron is necessary to increase the inertia of flywheel system, which is different from the conventional external-rotor machines. In this paper, a Halbach array PM motor is studied compared with the radial magnet array. The relationship between the air-gap field distribution and the magnet array is discussed. Finally, the eddy current loss in PMs of the external-rotor ironless brushless dc motor is analyzed between the Halbach PM motor and the conventional PM motor.

This index covers all technical items -papers, correspondence, reviews, etc. -that appeared in this periodical during 2018, and items from previous years that were commented upon or corrected in 2018.Departments and other items may also be covered if they have been judged to have archival value.The Author Index contains the primary entry for each item, listed under the first author's name.The primary entry includes the coauthors' names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and article number.Article numbers are based on specified topic areas and corresponding codes associated with the publication.

The magnetic field sensors based on anisotropic magnetoresistance (AMR) effect have been widely used in data storage, navigation, and medical diagnosis. However, the AMR effect of metal materials is relatively weak with an AMR ratio below 2%, which results in low voltage output. In order to improve the sensitivity of weak magnetic fields, we optimize the structure of the AMR sensor with a specific photolithographic process. We use two different designs of Hall bar and Wheatstone bridge with similar barber pole structures, and investigate the angular dependence as well as magnetic field dependence of AMR ratio and voltage output. With Wheatstone bridge, the magnetoresistance leads to a voltage output without dc components. The NiFe magnetic layer and the Au electrode are patterned into a highly conductive barber poles structure, and a high voltage output ratio of about 80% is obtained. At the same time, we achieve a high sensitivity of about 4.3 Oe−1, which implies potential applications in AMR effect-based magnetic field sensors.

As CMOS technology scales down to the nanoscale, high leakage power consumption becomes one of the major concerns in the design of electronic circuits. To overcome this challenge, nano-emerging technologies and logic-in-memory (LIM) structures are being studied. Magnetic tunnel junction (MTJ) is an emerging spin-based device, which consumes very minimal leakage power in conjunction with CMOS transistors. In this paper, we propose a novel MTJ/CMOS design, which consumes low power and has lower delay than the existing LIM-based MTJ/CMOS designs. The proposed MTJ/CMOS designs have lower power and lower delay by charge sharing the output nodes during the pre-charge phase. The designs are simulated using 45 nm CMOS technology with perpendicular anistropy CoFeB/MgO MTJ model using a Cadence Spectre simulator. From the simulation results, we can see that the proposed MTJ/CMOS OR, AND, XOR, MUX, and full adder designs have 31.35%, 40.15%, 49.17%, 35.86%, and 42.62% lower power-delay-product, respectively, compared with the existing MTJ/CMOS designs. Furthermore, in this paper, we have also…

This paper proposes a methodology for shape optimization of the starting cage of a line start permanent magnet synchronous motor motor with the aim to improve its synchronization performance. The parameters of the machine are established from a field-circuit model, where the magnetic field is simulated using a finite element method (FEM). A strategy for evaluating machine parameters exploiting parallel computing is proposed. To facilitate the use of FEM package, bespoke procedures have been developed and model parameterization applied with the aid of the scripting language Visual Basic. A particle swarm algorithm has been adapted for design optimization purposes. The proposed strategy has been verified via test simulations.

Stator winding inter-turn (SWI) short-circuit fault and broken rotor bar (BRB) fault are two common faulty modes of the squirrel cage induction motors (SCIMs). These faults have various impacts on the motor performance and may be rooted in each other; therefore, they may be presented at the same time in an SCIM. This paper proposes an exact analytical model for the SCIMs, which is able to include the SWI and BRB faults presenting simultaneously or individually with variable severities. Multiple coupled circuit modeling is applied to achieve such analytical model. The magnetic saturation effect is included in the model by applying appropriate air gap function and the rotor bars skew effect is taken into account by using 2-D winding function theory. Simulation results as well as the corresponding experimental results approve the presence of the same harmonics in the stator line currents due to the proposed faults. However, more detailed study gives solution for discrimination of the faults. The attained analytical model can be applied to examine the performance of the related fault…

The authors proposed the iron-based metal composite bulk magnetic core for high efficient and lightweight MHz switching DC-DC converter using SiC/GaN power devices. Although the iron-based metal composite bulk magnetic core exhibited a lower core loss than that of Ni-Zn ferrite in MHz frequency band, its relative permeability was low around 10. In this paper, in order to increase the permeability of such composite magnetic core with low core loss, we investigated an effect of mixing amorphous alloy powder having different particle size distributions. This method estimated increasing volume fraction of amorphous alloy powder and decreasing the demagnetization field of the composite magnetic core. From the experimental results, the composite magnetic core with an optimal mixing ratio of 2.4 μm and 12.8 μm median diameter Fe-based amorphous alloy (Fe-AMO) powders exhibited a relative permeability of 20.5 which was 2.4 times higher than that of composite magnetic core using 2.4 μm median diameter Fe-AMO powders. And its core loss was 555 kW/m3at 1 MHz in frequency and under 20 mT in…

Ferromagnetic materials are widely used in engineering structures. Damages caused during manufacture and the use of ferromagnetic materials may seriously undermine the safety of the engineering structure, and even lead to serious industrial accidents. For the early damage testing problem of ferromagnetic materials, it is imperative to propose and adopt new nondestructive testing methods. The metal magnetic memory (MMM) method, which is also known as the micromagnetic testing method, can achieve the early detection of damages in ferromagnetic materials such as steels. However, due to the lack of the quantitative research, the MMM method is only applicable for damage localization. In this paper, the MMM method is utilized to quantitatively evaluate the stress and crack in ferromagnetic materials. The inverse model including the objective function and optimization parameters is proposed. The reconstruction approach is established based on the conjugate gradient inversion method and the exact line search algorithm. In the theoretical analysis, the effectiveness of the MMM method in…

Yokeless and segmented armature (YASA) axial-flux permanent-magnet machine has high power density and efficiency, which is suitable for electric traction drive, especially for in-wheel or near-wheel direct-drive electric vehicles. This paper investigates and optimizes the cogging torque of the YASA machine with soft magnetic composite (SMC) core. First, the structure of YASA with SMC core is introduced. Then, the influence of magnet pole-arc ratio, magnet skewing, stator shoe width ratio, and stator shoe shifting on cogging torque is analyzed, based on which the cogging torque is optimized by establishing the response surface model and using the genetic algorithm. Finally, the optimization results are verified by the 3-D finite-element method. The results confirm that based on a certain magnet pole-arc ratio, there exists an optimum combination of magnet skew angle, stator shoe width ratio, and stator shoe shift angle for the cogging torque minimization, while the main performances of the machine remain nearly invariable.

In this paper, improvement of torque quality and magnetic losses of a concentrated winding high-speed permanent magnet (PM)-assisted synchronous reluctance motor (PMaSRM) that can operate in the wide speed range are investigated. Optimization studies have been carried out to enhance the torque quality. In addition, ac copper losses in the stator coils and iron losses in laminations at high frequencies have been investigated. Since the PMaSRM can operate in a wide constant power-speed range, the field weakening performance has also been investigated. The motor performance results of the PMaSRM at both no-load and on-load conditions are examined by using Flux 2-D FEA software. A prototype motor based on the simulations has been built and validated in order to show the feasibility of such technology for white good applications.

Permanent-magnet vernier (PMV) machines have been extensively researched in recent years due to their inherently high torque density. In this paper, a spoke-type PMV machine with multiple working harmonics is proposed. Due to the unaligned stator auxiliary teeth arrangement and carefully chosen slot-pole combination, working field harmonic with lower pole pair number is newly produced, which significantly enhances the flux-modulation effect. The proposed machine could achieve over 50% back electromotive force (EMF) and electromagnetic torque increment than its conventional counterpart. Through theoretical analysis and finite-element algorithm, the production of additional working field harmonics and their contributions to back EMF is quantitatively verified. Then, the electromagnetic performance of the proposed machine is further investigated and compared with several existing PMV machine topologies. Finally, the proposed machine is prototyped and verified by the experimental results as a promising PMV machine candidate.

The temperature rise of the rotor caused by harmonic eddy-current loss constrains the performances of high-speed permanent magnet (PM) motors. Excessive temperature rise can even result in irreversible demagnetization in the PM. An analytical model for the rotor harmonic eddy-current loss of high-speed surface-mounted PM motors in consideration of eddy-current reaction fields, harmonic currents, stator slotting, and different rotation states of the rotor is proposed, which can be utilized to reliably calculate and evaluate the rotor harmonic eddy-current loss. The accuracy and effectiveness of this analytical model are validated by using the finite-element method and a proposed experimental method.

Magnetic flux leakage (MFL) detection is frequently used for oil and gas pipeline inspection, especially for evaluation of the integrity of pipelines. The success of the MFL technique depends on many parameters. However, a sensitive magnetic sensor is an important requirement. Therefore, magnetic field sensors based on different mechanisms have been developed and applied to the MFL technique. In this paper, we evidence for the first time the capability of an innovative device based on a planar Hall magnetoresistance sensor devoted to MFL detection. This promising prototype combines all the required qualifications such as high sensitivity, low thermal drift, and bipolar and linear responses to the magnetic field. New achievements are carried out on embedded sensors in a testing platform reflecting pipeline environments. The ultrasensitive magnetic mapping concludes to a convincing technical approach with a high potential application toward MFL inspection, especially for the detection of shallow defects appearing at near side, far side, and sub-surface of a pipe wall.

This paper proposes a design of a surface-mounted permanent magnet (SPM) motor with a magnet surface of a sinusoidal pulsewidth-modulation (SPWM) shape. The fundamental harmonic of the flux density distribution over the SPWM-shaped magnet surface is sinusoidal, which makes the back electromotive force induced in the phase winding close to sinusoidal. Slots can be cut easily into the magnet to form an SPWM-shaped surface, and less rare-earth magnet material is used if the SPWM-shaped permanent magnet (PM) is sintered or bonded in the molds. The optimal SPWM magnet shape on the SPM motor for an electric scooter is designed by maximizing the output torque and efficiency and minimizing the magnet volume and is verified by the finite-element analysis. Prototype motors are fabricated with magnets of various shapes, with or without an SPWM surface. The amount of rare-earth magnet material used in the motor with the SPWM-shaped PMs is 9.4%-13.2% less than that without the SPWM-shaped PMs, while the maximum torque is reduced by only 3%-5.4%.

Leakage inductance and frequency-dependent resistance of windings are the key parameters for the design of magnetic devices. This paper focuses on analytical or semi-analytical calculation techniques to be integrated into a medium frequency transformer optimization process. To this extend, a review of the currently most used method to calculate the inductance and resistance of windings transformer is established. Based on this review, new calculation methods are developed. Magnetic field cartography is evaluated on the basis of 2-D structures thanks to a combination of Ampère's law and the image method. From this magnetic field map, leakage inductance can be calculated. The obtained accuracy with this method is equivalent to 3-D finite-element modeling (FEM). For frequency-dependent resistance evaluation, new methods based on 2-D or 1-D approach are compared to FEM and reviewed models. An analysis of the behavior of each model is done, showing that newly developed models are more suitable in the case of a medium frequency transformer design in terms of accuracy, robustness, and…

This paper deals with an adaptable semi-analytical model to calculate the open-circuit and armature reaction field distributions as well as the electromagnetic performances in many structures of permanent-magnet synchronous machines (PMSMs). It is based on the multi-layer models considering the iron permeability with the convolution theorem (i.e., Cauchy's product theorem) using the harmonic modeling technique (or the Maxwell-Fourier method). The 2-D semi-analytical model can be used for surface-mounted-inset-mounted or spoke-type PMSMs with different permanent-magnet (PM) magnetization patterns, winding structures, internal/external rotors, and slotless or slotted stators without the need to adopt the model equations to a specific PM machine type. For example, this scientific contribution has been applied to three types of PMSM with different topologies, viz.: i) slotted surface-mounted external rotor PMSM; ii) slotted surface-inset internal rotor PMSM; and iii) slotless external rotor spoke-type tangential PMSM. Finally, the results of semi-analytical method are compared with…

This paper is a study on the application position of skew in order to reduce the cogging torque of a magnetic geared synchronous motor (MGM). The cogging torque affects the noise and vibration of the motor, so it should be reduced as much as possible. To solve this problem, a conventional permanent magnet (PM) synchronous motor is skewed to a PM. However, unlike other synchronous motors, the MGM has pole pieces (PPs), and a larger cogging torque is generated due to a larger reluctance difference. There have been few studies on the reduction of cogging torque of MGM, so it is essential to study the skew structure of MGM. Therefore, this paper has derived the optimum skew method by comparing and analyzing three models of MGM skewed to PM, PP, and PM and PP simultaneously.

Ni1-xMgxFe2O4(x = 0.2-0.8) nanoparticles are prepared by hydrothermal synthesis followed by microwave processing. The effect of microwave processing in reducing the required heat treatment is discussed. The samples are characterized by powder X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometer, and LCR bridge. Microwave processing has enhanced the chemical reaction to form ferrites without any stray ferric oxide phases. Microscopic images have confirmed that the particles still retain nanoscale after microwave processing. An appreciably high magnetic moment is noticed. The experimental magnetic moment is used to estimate the cation distribution in tetrahedral and octahedral sites. Temperature and frequency dependence of initial permeability is discussed in the light of magnetic spin canting.

This paper proposes and implements a single-frequency double-layer coil system for all-metal domestic induction heating. Traditional induction heating has been developed to effectively heat a ferromagnetic pan, but is incapable of heating a non-ferromagnetic pan as it will cause high current stress at the power source. Inevitably, this limitation has hampered the popularization of existing induction heating. The proposed system consists of double-layer concentric coils with their compensated capacitors connected in series. The key is to employ the magnetic resonant coupling mechanism to strengthen the magnetic coupling and hence to enhance the power transfer between the coil and the pan. Differing from using a higher frequency to separately heat the non-ferromagnetic pan, the proposed system can employ a single frequency to operate at the high-voltage low-current and low-voltage high-current modes to effectively heat the ferromagnetic and non-ferromagnetic pans, respectively. Moreover, the required high current can be shifted from the primary coil to the resonant coil, hence…

This paper proposes and implements an accurate position detection method in wireless power transfer (WPT) for implant applications. Since the technique of WPT via magnetic resonant coupling makes it possible to non-invasively supply electricity for implants from an external tramsitter, an accurate position detection of an invisible receiver from the external transmitter is highly desirable to enhance the transfer efficiency and reduce the magnetic leakage. The magnetoresistive (MR) sensor has been widely used to detect the magnetic field variation due to its low power consumption and high accuracy. In this paper, the compact-in-size MR sensor array in plane with the transmitter is developed to directly detect the magnetic field variation caused by the coil misalignment. Thus, definite advantages of efficient and compact position detection in WPT for implants can be achieved. Since the computation process is straightforward, the coil-misalignment position can be intuitively and easily determined by analyzing the output amplitude of MR sensors.

The fractional slot concentrated winding consequent pole (CP) permanent magnet (PM) synchronous machines can improve the PM utilization ratio. However, the even-order harmonics exist in phase back electromotive forces (EMFs) for specific slot and pole number combinations, resulting in high torque ripple. Therefore, the multilayer winding is employed in this paper to reduce the torque ripple by suppressing the even-order harmonic back EMFs. The principles of both even-order harmonic back EMFs and torque ripple suppression by the four-layer windings are illustrated. The electromagnetic characteristics of the CP PM machine with four-layer windings are compared with that of PM machines with the traditional and CP rotors by finite-element analysis. It is demonstrated that the four-layer winding can suppress the even-order harmonic back EMFs and torque ripple in the machine with CP rotor. The prototypes of both the traditional rotor and CP rotors with four-layer wingdings are manufactured and tested to verify the theoretical analysis.