The 50 most-cited articles in IEEE Transactions on Magnetics, 2022

Magnonics addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operation in the GHz-to-THz frequency range, utilization of nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a few of many advantages offered by magnons. Although magnonics is still primarily positioned in the academic domain, the scientific and technological challenges of the field are being extensively investigated, and many proof-of-concept prototypes have already been realized in laboratories. This roadmap is a product of the collective work of many authors, which covers versatile spin-wave computing approaches, conceptual building blocks, and underlying physical phenomena. In particular, the roadmap discusses the computation operations with the Boolean digital data, unconventional approaches, such as neuromorphic computing, and the progress toward magnon-based quantum computing. This article is organized as a collection of sub-sections grouped into seven large thematic sections. Each sub-section is prepared by one or…

This work presents an approach to detect the inter-turn short-circuit (ITSC) faults in permanent magnet synchronous motors (PMSMs) using machine learning. PMSMs possess many attractive advantages such as high efficiency and high power density. However, with their widespread applications, preventive fault diagnosis to secure safe operations and reduce maintenance costs becomes increasingly critical. To achieve this objective, in this article, machine learning is employed for fault diagnosis, wherewith minor ITSC faults can be detected in a preventive manner. Therefore, the faulty motors can be replaced early to ensure system healthy operations. Moreover, machine learning is also utilized here to classify fault levels (e.g., minor, moderate, serious faults) for reference to appropriate maintenance actions. The proposed method adopts support vector machines (SVMs) and convolutional neural networks (CNNs) for training the diagnosis model with experimental data collected from tests in the laboratory. In the SVM, appropriate features required for training are selected through analysis…

Deep learning has achieved remarkable success in diverse applications; however, its use in solving partial differential equations (PDEs) has emerged only recently. Here, we present a feasibility study of applying physics-informed deep learning methods for solving PDEs related to the physical laws of electromagnetics. The methodology uses automatic differentiation, and the loss function is formulated based on the underlying PDE and boundary conditions. The feasibility of the method is shown using three electromagnetic problems of varying complexity and the results show close agreement with the ground truth from a finite-element analysis solver. The application of transfer learning is also explored and results in faster training. Furthermore, a hybrid approach involving physics-based governing equations and labeled data is also introduced to improve the accuracy of the results.

In current engineering, the skewing slots approach is commonly used for permanent magnet synchronous motor (PMSM) to reduce torque ripple and electromagnetic vibration. However, this approach may limit the axial length of the motor and increase the manufacturing cost. This article studies a segmented rotor with different pole widths approach to mitigate torque ripple and electromagnetic vibration for PMSM, which has a lower implementation cost and facilitates mechanized production. The mapping relationship between geometric dimensions and torque performance is obtained, and the optimal dimensions are determined. An 8-pole/48-slot V-shaped PMSM is taken as the original motor, and the influence of engineering error on the torque performance of the presented approach is discussed. The electromagnetic performances and vibration responses of the motor with the presented approach are compared with that of the skewing slot motor to verify the effectiveness of the presented approach. Finally, prototypes are built, and intensive experimental tests are carried out to verify the analysis and…

The magnetic nanoferrites (Fe3O4, CoFe2O4, and NiFe2O4) were synthesized via hydrothermal method using an aloe vera plant extract solution. Magnetic nanoferrites were characterized using X-ray powder diffraction (XRD), vibrating sample magnetometer (VSM), field emission electron microscope (FESEM), transmission electron microscopy (TEM), and X-ray photon spectroscopy (XPS). Cytotoxicity was obtained using the water-soluble tetrazolium salt (WST) assay. X-ray diffraction analysis also demonstrated that the size range of the nanoferrites exhibited average diameters of 6–28 nm and also exhibited high crystallinity. Results showed that all the metallic nanoparticles (NPs) are magnetic with saturation values of Fe = 52 emu/g, Co = 33 emu/g, and Ni = 20.43 emu/g. The magnetic nanoferrites exhibited a high cell viability rate at high concentrations and as shown from the optical images of the cells signifies their nontoxic and biocompatibility property. From SEM and TEM, the spherical structure was noticeable and the particle size is also in accordance with XRD. The chemical states for each…

A review of advanced Fe-based amorphous and nanocrystalline soft magnetic alloys that are currently being used in the market and their primary industrial applications is discussed as well as emerging trends. The high-efficiency distribution transformer market continues to be the largest segment by volume for Fe-based amorphous foil. The industry has been shifting toward higher induction levels (1.63 T) with increased stacking factor (>90%) to minimize the transformer size and reduce costs. New magnetic domain refined grades of amorphous foil are now commercially available which show a reduction of ~25% in core losses compared to the standard amorphous material. Nanocrystalline soft magnetic alloys have become the standard material for many applications including low-loss electrical components, magnetic shielding, electronic filtering, medium frequency transformer cores, and a variety of others. The nanocrystalline alloys are commonly cast fully amorphous and devitrified through controlled heat treatments. New nanocrystalline alloy compositions and processing methods have enhanced…

The original loss separation formula introduced by Bertotti has long been utilized mainly for low-frequency sinusoidal applications. In this article, the traditional method is improved to fit into the core loss calculation under higher frequency sinusoidal and nonsinusoidal excitations, verified by the measured data of nanocrystalline material that is often used in medium-frequency transformers (MFTs). For high-frequency sinusoidal waveform, it is proposed that the exponent of the excess loss needs to be reidentified, and it is necessary to consider the skin effect for hysteresis and eddy current loss calculation under broader frequency scope. When the core is supplied with nonsinusoidal excitation (square and rectangular waveform), a new empirical method is derived based on the concept of effective frequency and the loss separation results, with which the estimation accuracy is greatly guaranteed compared to empirical methods originated from the Steinmetz equation such as improved generalized Steinmetz equation (iGSE). Due to clear separation of loss components, the new method has…

Fractional-slot concentrated-windings (FSCWs) interior permanent magnet (IPM) synchronous machines (IPMSMs) provide several advantages compared with other types of electric machines and have promising applications in electric vehicles (EVs). Minimizing the cogging torque and torque ripple of this type of motors is essential for improving output torque and driving stability. This article proposes a method for optimizing the torque performance of IPMSM with single-layer FSCW. At first, the theoretical analysis of cogging torque and torque ripple is conducted as the research basis for the optimization. The key point of this method is to describe the structure of the rotor notch as determined by seven design parameters. Then, the response surface methodology (RSM) is adopted to analyze the relationships between torque performance and design parameters. For the multiobjective optimization process, the seagull optimization algorithm (SOA) is introduced to obtain the optimal solution. After the optimization, the torque ripple of the motor achieves a significant reduction and the output…

As an intelligent collection of power electronics, automated guided vehicles (AGVs) tend to involve more and more devices. Thus, it is necessary to develop a versatile charger with different double outputs for AGVs. This article investigates a dual-receiver inductive charging system. Through a well-organized magnetic coupling structure, relatively load-independent outputs can be realized simultaneously by these two receivers. Specifically, the first receiver ($R_{\mathrm {X}}$#1) can realize constant current (CC) output, whereas the second one ($R_{\mathrm {X}}$#2) can achieve constant voltage (CV) output. By utilizing such a passive coupling structure, complex control methods and additional decoupling circuits can be avoided, facilitating a compact and light on-board part. Moreover, this system can realize zero phase angle (ZPA) to lower the volt-ampere rating and improve the overall efficiency. Overall, a scaled-down experimental prototype with 2 A charging current and 12 V charging voltage is constructed to validate the feasibility of such a system. Experimental results…

In this article, a magnetic-field probe with improved common-mode rejection ratio (CMRR) is proposed, fabricated, and calibrated. The magnetic-field probe consists of a differential dual loop (DDL) and an integrated balun. The advantage of this integrated design is to sense more magnetic flux and convert the differential signal into a single port signal, which makes the test easier. The CMRR of the proposed probe is more than 35 dB from 0.8 to 2.5 GHz under the condition that the loop size is 4.7 mm$\times4.6$mm. The probe is verified through the simulation, the comparisons with reference probes and the near-field measurement of a U-shaped microstrip line.

Turn-to-turn short-circuit (TTSC) faults, which are among the most common and potentially threatening faults inside large-capacity converter transformers, can lead to catastrophic accidents and causalities. Due to the lack of a proper model, the reproduction and analysis of actual TTSC faults remain difficult challenges. In this article, converter transformer TTSC faults are numerically investigated by directly coupling an internal finite-element (FE) model with a model of the external electric circuit. In every calculation step, data are automatically transferred between the FE and circuit domains, and the simulations for the winding magnetic leakage flux and fault current are executed simultaneously. Furthermore, the Hochrainer arc model is used to simulate the nonlinear conductance of the low-impedance arc shorting adjacent turns; this model is directly integrated into the short-circuit loop by means of user-defined code. A realistic 405.2-MVA/500-kV single-phase three-core-limb converter transformer within an ultrahigh voltage (UHV) converter system is modeled as a simulation…

When an external short circuit occurs, the axial electromagnetic force increases dozens of times. Under the effect of the axial short-circuit electromagnetic force, the transformer windings vibrate violently. The spatial distribution of the disks is constantly changing during vibration, which can change the temporal and spatial distributions of the leakage magnetic field and the axial electromagnetic force. This process is called the strong coupling phenomenon of the structural field and the leakage magnetic field. In this article, a strong coupled magnetic-structural model is proposed by using the analysis method. The strong coupling equations, where the independent variables are the axial position of the disks, are obtained. The vibration process with strong coupling phenomenon considered can be obtained. The accuracy of the strong coupling model is verified by the iterative method. By comparing the results calculated by the strong coupling model with those calculated by the weak coupling model, the influence of the strong coupling phenomenononthe vibration process is obtained.…

Conventional magneto-static finite element (FE) analysis of electrical machine design is time-consuming and computationally expensive. Since each machine topology has a distinct set of parameters, design optimization is commonly performed independently. This article presents a novel method for predicting key performance indicators (KPIs) of differently parameterized electrical machine topologies at the same time by mapping a high-dimensional integrated design parameters in a lower-dimensional latent space using a variational autoencoder (VAE). After training, via a latent space, the decoder and multi-layer neural network will function as meta-models for sampling new designs and predicting associated KPIs, respectively. This enables parameter-based concurrent multi-topology optimization.

This article serves as an overview of existing models of permanent magnets (PMs) for electrical machines. The review study starts with the linear recoil model, which is commonly used to describe the reversible part of the demagnetizing curve. It is a simple model, especially useful for representing materials with high anisotropy, such as ferrite, NdFeB, and SmCo. The model is harder to apply for nonlinear materials, such as Alnico, but still possible since their recoil curves are linear. The study shows how the linear recoil model could be extended to include irreversible demagnetization, temperature dependence, and angular dependence. All such models have their advantages and disadvantages, which will be discussed further. Both the magnetization and the risk of demagnetization are temperature-dependent. It could be noted that NdFeB has an increased risk of demagnetization at high temperatures, while ferrite has it at very low temperatures. The temperature dependence is described and compared for several materials, also including simplifying models. There are different methods to…

In this article, a novel magnetic field calculation approach that considers the static inclined eccentricity of axial flux permanent magnet (AFPM) machine is presented. The equivalent remanence of permanent magnet (PM) is introduced and calculated, in which the air-gap length can be regarded as uniform. Then, the analytical model based on harmonic subdomain technology can be used directly. The magnetic field distribution (MFD) and electromagnetic performance under eccentric state are calculated and compared. The effectiveness of the proposed method is verified both by the finite element (FE) model and experimental results. The main contribution of this article is to provide a simple and accurate method for the calculation of the eccentric magnetic field of the PM motor, not limited to the AFPM.

In this study, we propose a fast topology optimization (TO) method based on a deep neural network (DNN) that predicts the current-dependent motor torque characteristics using its cross-sectional image. The trained DNN is shown to provide the current condition that provides the maximum torque under the assumed motor control method. The proposed method helps perform TO with a reduced number of field computations while maintaining a high search capability.

Vibration and acoustic noise are essential in electrical equipment. Amorphous alloy is widely used in the medium- to high-frequency transformer due to its low loss, but its significant vibration and noise cannot be ignored, which will even reduce the reliability of the equipment. Ultra-thin grain-oriented silicon steel (≤0.2 mm) is expected to design medium- to high-frequency transformers due to its high magnetic permeability, high saturation magnetic flux density, and high stability. In this article, the loss characteristic, three-dimensional vibration acceleration, and noise level of three C-type core samples made of ultra-thin grain-oriented silicon steels (GT-050, GT-100) and amorphous alloy CACC30 are measured and analyzed under sinusoidal and rectangular excitations. The mathematic analysis predicts that the vibration acceleration increases with duty cycle decrease under rectangular excitation, which is consistent with the experimental results. The ultra-thin grain-oriented silicon steel has lower vibration and noise under medium- to high-frequency excitation compared with…

This article presents a fast population-based multi-objective optimization of electromagnetic devices using an adaptive neural network (NN) surrogate model. The proposed method does not require any training data or construction of a surrogate model before the optimization phase. Instead, the NN surrogate model is built from the initial population in the optimization process, and then it is sequentially updated with high-ranking individuals. All individuals were evaluated using the surrogate model. Based on this evaluation, high-ranking individuals are reevaluated using high-fidelity electromagnetic field computation. The suppression of the execution of expensive field computations effectively reduces the computing costs. It is shown that the proposed method works two to four times faster, maintaining optimization performance than the original method that does not use surrogate models.

The laser beam melting (LBM) additive manufacturing (AM) technology is used for processing a high silicon steel (Fe 6.5%wtSi). The effects of LBM machine parameters over microstructure and magnetic properties are studied. Particular attention is dedicated to determining the influence of a normalized energy density over the material density, the grain size, and the crystallographic texture and their impact on the magnetic properties: magnetic flux density and coercivity.

Post-fault modeling for dual three-phase permanent magnet synchronous motors (DTP-PMSMs) under the open-phase fault is presented in this article. By using the positive and negative sequence components for the dual three-phase system, the stator currents under the open-phase fault can be treated as a combination of the positive and negative sequence currents. By artfully constructing the negative sequence components in terms of the different initial angles and amplitudes, the single-phase open-circuit fault and certain dual-phase open-circuit fault can be represented. Based on the conventional and modified vector space decomposition (VSD), only the positive sequence components are projected into the$\alpha \beta $subspace, namely, the torque-producing subspace, and the negative sequence components are transformed into the harmonic subspace. With the conventional proportional–integral (PI) current regulators, the dc components of the positive and negative sequence currents can be readily controlled under the open-phase fault. Experiments based on a DTP-PMSM prototype verify the…

To reduce the switching delay, area overhead, and power consumption in the magnetic tunnel junction (MTJ)-based memories, this article presents a double data rate magnetic random access memory (DDR-MRAM), which can store information at both clock levels. The proposed memory structure is such that any MTJ type (perpendicular or in-plane) and any switching method can be used as needed. The post-layout simulations based on 40 nm TSMC CMOS technology show that the proposed DDR-MRAM has at least 52% lower write PDP and at least 32% less area-to-maximum input frequency ratio than the conventional MRAMs. Monte–Carlo simulations also confirm the correct and robust operation of the proposed memory in the presence of the inevitable process variation. Moreover, based on the designed DDR-MRAM cell, three architectures are proposed to design$m\times n$DDR-MRAM arrays. These architectures are designed and optimized for a specific application, including artificial intelligence (AI) hardware accelerators, high-capacity memory banks, and high-speed cache memories. The simulation results of the…

This article proposes and implements an advanced pulse frequency modulation (PFM) scheme to adjust the output power of the parity-time (PT) symmetric wireless power transfer (WPT) system. The key is to utilize PFM to adjust the duty ratio of the self-excited oscillating inverter for the PT-symmetric WPT system, hence transferring more power than that of the conventional forced oscillating inverter under the same input voltage and duty ratio. Besides, the transmission efficiency can maintain high when the coupling coefficient is larger than the critical value. With a proper signal processing circuit, the phase of the inverter output voltage can lead to that of the primary-side current, which can help reduce the switching loss. Therefore, the system efficiency of this self-excited oscillation scheme for WPT can keep high, while the output power can be larger than that of using the conventional forced oscillation scheme. Theoretical analysis and simulation results are given to verify the feasibility of the proposed scheme.

Flux-modulated-type magnetic gears are expected to be applied as a step-up gear for wind-power generation because of their advantages, including high torque density and maintenance-free operation. Furthermore, the flux-modulated-type magnetic gears with an axial-flux structure have attracted great attention recently since they have a smaller axial length and are relatively easy to assemble. In some cases, magnetic gears are required to have an integer gear ratio based on the design requirements of the entire system, which results in larger cogging torque in the high-speed (H-speed) rotor that causes vibration, acoustic noise, and startup error. A skewed rotor structure is well known to be capable of reducing the cogging torque; however, it is complicated and poor in assembling, especially in a large-scale axial-flux magnetic gear (AFMG) used for the wind-power generation. To resolve the above problem, this article presents two new types of pole pieces for reducing the cogging torque: one is an unequal-space type, and the other is an unequal-width type. The validity of the two newly…

In this article, a novel fault-tolerant design process of the spoke-type interior permanent magnet (IPM) motor is proposed to prevent the increase of cogging torque and torque ripple due to partial demagnetization fault and to minimize the motor size. First, unlike other research papers on the irreversible partial irreversible demagnetization of permanent magnet (PM), in this article, the effect of partial irreversible demagnetization faults on the cogging torque and torque ripple for the fault cases is investigated. Then, a novel fault-tolerant design process is proposed to solve the problem of partial demagnetization faults that increase the cogging torque and torque ripple. In the novel fault-tolerant design process, first, to solve the problem of increasing cogging torque and torque ripple due to the partial demagnetization fault, a process for implementing a uniform irreversible PM demagnetization is proposed. Second, to compensate for the motor torque constant decreased by degraded PM, which is caused by irreversible demagnetization of PM, a torque compensation coefficient is…

With the advent of the digital age, real-time monitoring, diagnosis, and control become essential demands in the life-cycle management of electrical equipment. The methods for behavior modeling that allows accurate and real-time physical simulation gain increasing attention in recent years. Construction of the behavior model in a parametric space needs a large amount of simulation data based on the physics model which is very time-consuming. This work proposes a methodology by using the model order reduction (MOR) technique based on the proper orthogonal decomposition (POD) to build compact behavior model of rotating electric motors. With the help of the reduced-order model, the computation time to generate simulation data in a parametric space is largely reduced. The association of the behavior models with the mechanical rotation equation leads to twin models of the motors that can reflect accurately their physical state in real time. Results show that the twin models can provide an accurate time-domain response of the motor (including the speed, the torque, as well as the power…

In this article, a method for topology optimization (TO) of a synchronous reluctance motor (SynRM) is proposed using deep reinforcement learning (RL). Due to the need for simulating a large number of finite-element models in a traditional TO task, incorporating a study involving a different problem formulation (such as a varying design domain) can be an overwhelming task. A neural network (NN)-based agent trained using an RL formulation is able to extend the knowledge from one TO design problem to other similar TO tasks. The applicability of such learning is performed using a sequence-based TO environment. It is observed that such an approach not only reduces the computation required for TO, but also introduces the capability to generalize RL to unseen TO scenarios. The proposed optimization method reduces computation time by 70%–90% when compared to a genetic algorithm-based implementation.

In today’s ever-developing electronic world, tremendous efforts are being made to develop highly efficient microwave absorbing materials with thin thickness and broad bandwidth while maintaining a simple manufacturing procedure. Since so much study is devoted to structural and component designing of microwave absorbers, the mechanism of microwave absorption still has potential for improvement. It is critical to have fundamental mechanistic knowledge of microwave absorption by absorbing materials with diverse types of geometries and components. It is also important to explore the influence of different physical/chemical characteristics of absorbing materials on microwave absorption performance. The methodical and thorough examination of these issues may provide internal information on the interaction of the microwave absorber’s components and subsequent structural design. Therefore, in this article, by taking cobalt (Co) as the base material, an attempt has been made to comprehend the microwave absorption mechanism of Co milled at various times, which results in changes in particle…

A novel automatic design method for permanent magnet (PM) motors using a Monte Carlo tree search is presented. The optimal motor structures are determined through a tree search, in which the motors with different numbers of poles, current phase angles, PM configurations, and numbers of PMs are simultaneously considered. At the leaf nodes, parameter and topology optimizations are performed to obtain the optimal material shape and distribution. The proposed method was applied to the optimization of a 24-slot motor. It was shown to be effective in finding the optimal motor structure and geometry to maximize the average torque while considering iron loss. The proposed method can be applied not only to the design of PM motors but also to many types of electric apparatus and other systems.

The electrical conductivity and dielectric constant of seawater are quite different from those of air, so it is necessary to explore the differences between wireless power transmission characteristics in the air and seawater. The equivalent circuit model of the magnetic coupling mechanism is of great significance to the analysis of the transmission characteristics. In this article, a more accurate model analyzing the wireless power transmission in seawater environment is proposed, in which all parameters of the model can be obtained by specific expressions. First, by establishing the electromagnetic field analysis model in the seawater environment, the distribution laws of underwater electric field intensity and magnetic induction intensity are obtained. Then, the equivalent self- and mutual resistances of eddy current loss are introduced based on electromagnetic field model, and the analytical solutions of them are given. The lumped parameter equivalent circuit model of the underwater magnetic coupling mechanism is further derived, and the influencing factors of eddy current loss…

The sizing process is necessary to analyze the electromagnetic characteristics according to the major shape parameters during the early design stage of permanent magnet synchronous motors (PMSMs). However, predicting the performance of PMSMs with 2-D finite element analysis (FEA) has errors due to axial leakage flux. Therefore, the axial leakage flux should be considered in the sizing process. The most accurate way to consider the axial leakage flux is to perform 3-D FEA, but it has a disadvantage of high computational cost. In this view, we propose a deep transfer learning-based surrogate modeling method to reduce the computational cost for calculating 3-D FEA-based motor parameters. The transfer learning is conducted using a large amount of 2-D FEA-based and small amount of 3-D FEA-based motor parameters. Using the proposed process, it is possible to accurately predict the motor characteristics according to size-related variables that satisfy the required specifications with small amount of 3-D FEA-based motor parameters. The proposed method was verified through 3-D FEA and…

Considerable progress has been achieved in motor design and control and related material technologies. Motor driving systems are increasingly being incorporated in various applications, such as transportation machines, including hybrid/electric vehicles, and industrial machines, including robot, crane, rolling mill machine, and home appliances. However, various motors used in such applications consume the majority of electric energy generation. Increasing electric energy generation through the expansion of a power generation system is time-consuming and requires considerable money and time. Therefore, a high-efficiency motor should be designed. Domestic and foreign standard agencies are implementing policies and standards to grade energy efficiency based on the electric energy used by motors. A study was conducted on improving motor efficiency for home appliances. When designing a high-efficiency motor for home appliances, a design plan that maximizes the magnetic flux density of the air gap and reduces various losses was first considered. In this study, a spoke-type structure was…

In this article, based on flux modulation theory, torque characteristics improvement method is proposed for double-stator vernier permanent magnet (DS-VPM) motor. Also, the detailed torque production mechanism of DS-VPM motor is derived. Based on theoretical analysis results, key design parameters which possess significant influence on motor torque characteristics are selected to be further optimized purposefully. Non-dominated sorting genetic algorithm is then adopted to obtain increased output torque and reduced torque ripple of inner, outer, and total DS-VPM motor. Besides, based on finite-element analysis, motor performances before and after optimization are compared in detail. Finally, a prototype motor is built and corresponding experiments are carried out. Both theoretical analysis and experimental results verify the effectiveness of the proposed torque characteristics improvement method, which provides a potential research path for the design optimization of high-performance VPM motors.

In this article, a clear analytical model for predicting the performance of permanent magnet (PM) eddy current couplers is proposed. The interaction of the reaction magnetic fields between adjacent eddy current rings was considered for the first time. Based on a magnetic equivalent circuit (MEC) and the Ampere circuital theorem, the accurate distribution of the air gap magnetic field under different slip velocities was deduced in a 2-D model, and the analytical expression of the transmission torque was obtained. 3-D effects were also taken into account to calibrate the model. The validity of the analytical model was verified by comparison with results from the 3-D finite element method (FEM). The comparison shows that the analytical model can accurately predict the magnetic field distribution and transmission torque over a wide range of slip velocity variations. This model can greatly reduce the number of calculations required and save time, and it is suitable for the preliminary design and optimization of PM eddy current couplers.

A global sensitivity analysis (SA) method enhanced with a kriging surrogate model is considered in this work. To decide on the importance of many model parameters in the case of a functional output, the Sobol’ sensitivity indices—being functions of an independent variable—are to be calculated over a domain of interest. Since for expensive-to-evaluate models obtaining such a sensitivity map is highly computationally demanding, the number of required samples is reduced by a kriging approximation combined with an adaptive sampling strategy that exploits the probability information provided by the kriging model. The advantages of the approach are demonstrated through the example of an electromagnetic interference (EMI) filter.

The application of surrogate models in engineering design is becoming popular due to their mimicking capabilities. In the design of electric motor drives for example, where a control-drive circuit is connected directly to the electric motor, the finite element simulations of the integrated motor drive system can be time-consuming. A complete motor simulation can run into several hours, if not days. Therefore, the main contribution of this article resides in the effort to address the computational burden associated with the design process by replacing the finite element models with surrogate models to achieve a faster design process. Briefly, the procedure involves filling the design space with multiple motor geometries created from an 8-pole 12-slot surface-mounted permanent magnet (SPM) synchronous motor. Then, a multiphysics performance evaluation is performed over the design space for different switching frequencies over a range of dc bus voltages. The design variables of the motor, the inverter, and the calculated performance objectives are used to train a collection of…

Inspired by the superconducting electrodynamic suspension (EDS) system in Japan, a new permanent magnet (PM) EDS system combining PM and 8-shaped null-flux coils has emerged in recent years. In general, the structure of a single PM was used as the onboard magnet. This single magnet structure is difficult to further optimize the core magnetic field resource of the EDS system. Facing this issue, we proposed a PM EDS system combining a Halbach PM array (HPMA) with good magnetic collecting capability and the 8-shaped null-flux coils. Furthermore, we established a numerical model for this new HPMA EDS system. The core of the calculation method is to discretize each PM in the HPMA into a coil group. By calculating the mutual inductance between the equivalent coil groups and the null-flux coils, the interaction electromagnetic force is obtained. In order to verify the correctness of our numerical model, the calculation results of the finite-element method (FEM) simulation model are compared with those of the numerical model. The results of two models are basically consistent. It shows that…

The permanent magnet electrodynamic wheel system is a competitive alternative for the implementation of maglev car due to its levitation–propulsion integration ability. However, the temperature rise of conductive plate may deteriorate the operational performance even result in suspension failure, which underlines the importance of thermal analysis. In this article, the thermal-force coupling analysis is conducted by experiment combined with the co-simulation method. First, the heat resource generated by power loss in the conductive plate is obtained and verified by analytical model, simulation, and experiment, and the lumped thermal model is presented. Additionally, a knowledge of the transient temperature distribution and the variation of electromagnetic forces under different speeds are studied. Eventually, a proof-of-concept prototype of maglev car with its auxiliaries was manufactured and used for further thermal analysis. Temperature management is considered by increasing the volume of conductive plate and cooling the conductive plate via water medium, and a good heat…

Zeroth-mode vibration is the dominant noise source in permanent magnet synchronous machines (PMSMs). In conventional approaches, the zeroth-mode vibration is reduced by lowering the amplitudes of concentrated forces. Different from conventional approaches, this article proposes a zeroth-mode vibration suppression method through adjustment on phase difference of concentrated forces. First, the characteristics of concentrated forces are analyzed considering the effect of slotted structure on air-gap electromagnetic force wave (EMFW), and the relationship between phase difference of concentrated force harmonics (CFHs) and the mode of vibration is obtained. Subsequently, the effects of both permanent magnet (PM) and harmonic currents on air-gap EMFW are analyzed. It is found that the phase differences of CFHs can be adjusted by combining PM shape optimization and harmonic current injection. Finally, a 12-pole 36-slot PMSM and a 16-pole 48-slot PMSM are carried out to calculate the concentrated forces and vibrations by finite element method (FEM). It is proven that the proposed method…

The development of an efficient microwave absorbing structure (MAS) for the concealment of electromagnetic (EM) waves is a consistent puzzling errand. In this regard, a new kind of lightweight broadband multilayer honeycomb (HC)-MAS is developed, by coating aramid HC with Fe/SiC polymeric paint optimized using effective medium approximations. An environment-friendly, cost-effective, and easily accessible procedure is embraced for the preparation of microwave absorbing paint and diverse coatings at X-band. The multi-objective Jaya’s algorithm is envisioned for the optimum design of multilayered and hybrid HC-MASs. A multi-objective fitness function is integrated into the optimization algorithm to resolve the issue of the thickness-bandwidth (BW) tradeoff. As a result, optimized single layer HC-MAS with thickness 2.1 mm attains a reflection coefficient (RC) of −12.0 dB at 10.3 GHz with a BW of 3.2 GHz below the −10 dB threshold. The intriguing results are obtained by doing a dual-mode analysis, i.e., multilayer HC-MAS and multilayer hybrid HC-MAS. Hybrid HC-MAS achieves anRCof −31 dB…

This article proposes an improved analytical model of slotted linear permanent magnet synchronous machines (LPMSMs) to fast and accurately obtain the magnetic field distribution and detent force. Considering the secondary end effect can optimize the thrust performance in terms of machine control, while there are few research works focusing on this study. Combined with the periodic extension method, both the primary and secondary end effects are taken into consideration, which is the major contribution of this article. The analytical model containing seven subdomains (SDs) is conducted in Cartesian coordinates. The magnetic distributions in air-gap, slots, and end regions are obtained by solving Maxwell equations with various interface conditions. The thrust and normal forces are subsequently calculated based on the Maxwell stress tensor. The corresponding finite element (FE) model produces numerical results to validate the analytical results. A prototype is manufactured and tested. The experimental results show that the improved analytical model is accurate and efficient in no-load…

Halbach arrays have been widely implemented in magnetic levitation systems. They concentrate the magnetic field over one side, and their magnetic flux density in the central region can be modeled. This article proposes a novel lookup table-free data-driven method to model the force and torque on a 2-D Halbach array when the magnet array is above a stationary coil. One critical contribution of this article is the rapid and accurate force and torque modeling when the coil is located near the edge of the 2-D magnet array. First, the area under the 2-D Halbach array is divided into a central region, edge regions, and corner regions. Then, nonlinear force and torque components are identified and modeled with a modified third-order Fourier series for force and torque modeling. The proposed model is implemented on an industrial server, and the average computation time is measured to be$2.3 ~\mu \text{s}$. This model is universal for symmetric coils, verified through experimental measurements with circular and square coils of different sizes. The measurement result agrees well with the…

In this article, we address the problem of synthesized magnetic field focusing (SMF) of the pulsed eddy-current (PEC) technology for the non-destructive testing (NDT) of oil and gas well casing pipes. The electromagnetic response excited by multiple transmitters was derived using the signal model of downhole PEC system. The magnetic field was shown to be adjustable by modifying the currents of the multiple transmitting array. Based on this property, magnetic fields were synthesized with the mean squared error (MMSE) criterion to be focused on the center of the transmitting array, and a weighted MMSE (WMMSE)-based SMF was also proposed to achieve an optimal synthetic magnetic field. Furthermore, the primal-dual interior-point method was used to solve the WMMSE optimization problem with the total and single transmit power constraints for the practical application. Simulations and experimental results showed that the SMF with the PEC array effectively focuses the eddy-current field on the center of the transmitting array.

This article presents an improved dynamic hysteresis model to predict magnetic hysteresis properties under high-frequency sinusoidal excitations. A new expression of magnetic field strength related to classical loss is derived and proposed to consider the effect of skin effect on the iron loss. The permeability related to statistical parameter is presented to establish the relationship between classical loss and excess loss. The introduction of shape factor provides a possibility for accurate prediction of dynamic loops at high frequency over a broad induction range. The accuracy of the proposed dynamic hysteresis model is verified by comparing the predicted results with the measured ones. In addition, the variation of loss components with frequency and peaked induction is analyzed.

It is important to explore better alternatives to CMOS to sustain Moore’s law far in the future. One option is to integrate non-volatile spin devices, such as magnetic tunnel junction (MTJ), with the existing CMOS technology to augment its capability. This article presents five approximate 1 bit full adders for applications where accuracy can be traded for energy, speed, and area. The application of an approximate adder is demonstrated in image processing for smoothening an image. Three of these adders are fully non-volatile, one is partially volatile, and one is fully volatile. All the adders use SRAM-based sense amplifier (SA) to reduce sensing energy and hardware count. To reduce the delay, some of the adders utilize the parallel connection of logic devices (MTJ or MOSFET) in the logic tree. All the adders are simulated using 45 nm CMOS predictive technology model (PTM) and perpendicular magnetic anisotropy (PMA) CoFeB/MgO/CoFeB MTJ model with HSPICE simulator. After performing simulations, results show that the proposed fully non-volatile approximate adder (AXFA4) performs…

An efficient method is proposed to predict eddy current loss of Litz wire coils, or completely transposed multi-strand coils, in transient finite element analysis (FEA). The method is based on analytical solutions of eddy current loss in a solid wire due to skin effects and proximity effects. The bundle of Litz or solid wires is homogenized by introducing a fill factor to describe the conducting area ratio. The analytical solutions in the frequency domain for round, square, and rectangular wires are further expanded to those in the time domain. The wire length direction in each 3-D mesh is automatically detected so that the flux density vector in each mesh can be correctly decomposed to the orthogonal and tangential components for anisotropic proximity effect loss computation. The method is applied to calculating eddy current loss of a gapped inductor in both 2-D and 3-D, and the results are compared with that using real solid wires.

This article presents the design of a superconducting (SC) rotor with a spoke supported structure that minimizes the heat loss and enables the motor to be cooled by one cryocooler. The main challenge with the SC machines is the need to maintain the SC coils at cryogenic temperatures. Though usually placed in the vacuum, the cryogenic coils still receive a large amount of heat through the conduction of the torque tube which connects to the ambient temperature. The heat flown into the system exceeds the cooling capacity of a cryocooler and requires the boiling of cryogen, which comes with a more complicated and bulky hardware system. The SC rotor proposed in this article uses a spoke system to support the cryogenic windings. Connecting the windings to the shaft, the flexible spokes with low thermal conductivities transfer the torque from the windings to the shaft. The spoke system has much lower thermal conductivity than a traditional torque tube. Preliminary results show that with the ambient temperature 298 K and the cryogenic temperature at 40 K, the total heat transfer rate from…

Energy efficient computing hardware has played an instrumental role in enabling novel abundant data applications and transformative new user experiences. As we look forward, many emerging nonvolatile memory technologies have been proposed to further improve the energy efficiency of tomorrow’s computing systems. Spin–orbit torque magnetoresistive random access memory (SOT-MRAM) and its variants are one class of emerging nonvolatile memory technology, which promises static random access memory (SRAM)-like performance at a higher bit-cell density. In this article, we discuss high-density, field-free spin-transfer torque (STT)-assisted SOT-MRAM (SAS-MRAM) as an emerging nonvolatile memory technology, which could drastically improve the energy efficiency of future computing systems. Such benefits are enabled by sharing the SOT line between one or many magnetic tunnel junctions (MTJs), thereby amortizing the areal and energy costs of the SOT drive transistor across multiple bits.

Topology optimization (TO) has been formulated as a quadratic unconstrained binary optimization (QUBO) problem that can be solved by Digital Annealer (DA) and quantum computers, which can realize massive parallelization. It is shown that the 3-D TO of a permanent magnet (PM), with 600 unknowns, is successfully performed by the DA with the aid of the finite element method (FEM) for field computations. Moreover, it is shown to perform TO of a magnetic core, with 758 unknowns, in such a way that the QUBO and field problems are iteratively solved to determine the optimal solution in which the magnetic field and optimal core structure are self-consistent.

This article presents a new analytical approach for the calculation of mutual inductance based on magnetic vector potential (MVP). To demonstrate the proposed mutual inductance calculation method, planar spiral coils of polygonal shape with an arbitrary number of sides are discussed. The coils considered in this work are coaxial and assumed to be composed of concentric filaments. The flux produced by the primary and linking the secondary is calculated by the line integral of the MVP. In order to simplify the calculation strategy, the MVP contribution of only one side of each single-turn filament of the primary is considered due to the symmetry of the coils’ shapes. Accordingly, coupling flux across the surface surrounded by each turn of the secondary is calculated by the line integral of the MVP over half path of the filament’s turn. The accuracy of the new analytical approach is confirmed by examining coil systems with a different primary and secondary in terms of the number of sides, the number of turns, and size. Results of the new approach are compared with those obtained from…

This work couples a magnetic multi-stable mechanism to a pendulum vibration energy harvester so as to widen its bandwidth, especially in low-frequency operation. Multiple stable points are formed by a movable permanent magnet installed on the pendulum and two fixed permanent magnets installed symmetrically on the base of the energy harvester. Thus, the pendulum can swing between the stable points at two sides, which causes large motion amplitude and power generation. In designing the prototype of the energy harvester, dynamical modeling and potential energy analysis are carried out to achieve a low threshold for snap through. An experimental setup is developed and a series of comparative experiments are implemented to investigate prototype performance. It is shown that the energy harvester with the fixed magnets can generate a noticeable normalized induced voltage at 0.7 Hz, while the energy harvester without the fixed magnets requires the excitation frequency of 1.0 Hz to reach a similar level. The electrical outputs varying with vibration acceleration and load resistance are also…