The 50 most-cited articles in IEEE Transactions on Magnetics, 2021

Spin-orbit torque (SOT) is an emerging technology that enables the efficient manipulation of spintronic devices. The initial processes of interest in SOTs involved electric fields, spin-orbit coupling, conduction electron spins and magnetization. More recently interest has grown to include a variety of other processes that include phonons, magnons, or heat. Over the past decade, many materials have been explored to achieve a larger SOT efficiency. Recently, holistic design to maximize the performance of SOT devices has extended material research from a nonmagnetic layer to a magnetic layer. The rapid development of SOT has spurred a variety of SOT-based applications. In this Roadmap paper, we first review the theories of SOTs by introducing the various mechanisms thought to generate or control SOTs, such as the spin Hall effect, the Rashba-Edelstein effect, the orbital Hall effect, thermal gradients, magnons, and strain effects. Then, we discuss the materials that enable these effects, including metals, metallic alloys, topological insulators, two-dimensional materials, and complex…

The possibility of tuning the magnetic properties of materials with voltage (converse magnetoelectricity) or generating electric voltage with magnetic fields (direct magnetoelectricity) has opened new avenues in a large variety of technological fields, ranging from information technologies to healthcare devices and including a great number of multifunctional integrated systems, such as mechanical antennas, magnetometers, and radio frequency (RF) tunable inductors, which have been realized due to the strong strain-mediated magnetoelectric (ME) coupling found in ME composites. The development of single-phase multiferroic materials (which exhibit simultaneous ferroelectric and ferromagnetic or antiferromagnetic orders), multiferroic heterostructures, as well as progress in other ME mechanisms, such as electrostatic surface charging or magneto-ionics (voltage-driven ion migration), have a large potential to boost energy efficiency in spintronics and magnetic actuators. This article focuses on existing ME materials and devices and reviews the state of the art in their performance. The…

Many electric traction drive systems (ETDSs) are driven by electric motors primarily composed of high-energy rare-earth (RE) permanent magnets (PMs), such as neodymium-iron-boron (NdFeB) and samarium-cobalt (SmCo). Given the high cost of RE materials, there is a great interest among various industry sectors in searching for breakthrough technologies that reduce the consumption of high-energy RE magnets in their electromechanical energy conversion systems. The reduction of the magnetic volume is typically realized either by replacing a portion of the high-energy RE magnet with the low-energy ferrite magnet (knows as hybrid structure) or by modifying the magnetic arrangement of the machine itself, where a portion of the physical RE magnets is removed and replaced by induced magnets (known as consequent-magnetic pole structure). For this purpose, this article presents a review of the current state-of-the-art motor typologies with less-RE PMs and their key design challenges, followed up by a series of recommended guidelines to overcome related design challenges.

Computational micromagnetics has become an essential tool in academia and industry to support fundamental research and the design and development of devices. Consequently, computational micromagnetics is widely used in the community, and the fraction of time researchers spend performing computational studies is growing. We focus on reducing this time by improving the interface between the numerical simulation and the researcher. We have designed and developed a human-centered research environment called Ubermag. With Ubermag, scientists can control an existing micromagnetic simulation package, such as object oriented micromagnetic framework (OOMMF), from Jupyter notebooks. The complete simulation workflow, including definition, execution, and data analysis of simulation runs, can be performed within the same notebook environment. Numerical libraries, co-developed by the computational and data science community, can immediately be used for micromagnetic data analysis within this Python-based environment. By design, it is possible to extend Ubermag to drive other micromagnetic…

Axial flux permanent magnet synchronous motors (AFPMSMs) have advantages over other motor types in terms of efficiency, vibration, and noise. However, torque ripple is an important problem for axial flux permanent magnet (AFPM) motors. One of the methods recommended as a solution to this problem is the skew operation. The skew can be applied to the magnets or the stator. However, for these motors, this process is mostly applied to magnets because the skew applied to the stator makes it difficult to manufacture. In this article, a solution to the torque ripple of an in-wheel AFPMSM for the electric vehicle is sought. For this purpose, designs, optimization, and 3-D analyzes have been carried out. This solution has been applied to magnets designed by skewing for ease of production. 3-D analyses have been carried out by applying skew of up to 40 degrees with an angle of 5 degrees to the magnets in the rotor. In light of the analysis, the most appropriate skew angle that does not affect motor performance has been determined. As a result of the analysis of the motor model obtained with…

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

This article introduces novel hybridization of parameter optimization (PO) and topology optimization (TO) methods. The proposed method is applied to the optimization of a permanent magnet motor. The magnet shape and topology of the flux barrier of the rotor core are optimized by performing PO and TO simultaneously. In the optimization, automatic mesh generation is adopted to improve the resolution of the shape representation. It is shown that the increase in the average torque resulting from the proposed hybrid optimization is larger than that obtained by the conventional TO in which only the topology of the flux barrier is optimized. The decomposition of the total torque to the magnet and reluctance torques suggests that the reluctance torque is effectively generated in the rotor optimized by the proposed method.

This article reviews the power density and torque density of permanent magnet (PM) motor technology that is currently commercially developed for use in electric aircraft. The review shows that in order to meet the ambitious electrical motor power density goals recently set forth, the power density of a motor needs to more than double. The requirements imposed by the maximum propeller rotor tip speed, as well as the diameter constraints set by the aerodynamic requirements, will further limit the practical electric motor design sizing options. This article advocates for considering using magnetic gearing (MG) and using an integrated contra-rotating motor propeller co-design approach as a way of both increasing propulsive thrust performance and thereby increasing the aircraft’s overall power density.

Cylindrical magnetic nanowires (NWs) feature unique properties, which make them attractive for fundamental research and novel applications. These 1-D structures introduce a pronounced shape anisotropy that together with material selection can strongly affect the magnetic properties and can be tuned by incorporating segments of different materials or diameters along the length. They attract a large interest in the scientific community, ranging from physicists to material scientists to bioengineers. Consequently, these NWs are developed for and used in very diverse applications in medicine, biology, data and energy storage, catalysis, or microwave electronics, among others. In this review, we investigate the most active emerging applications of cylindrical NWs grown in alumina templates by electrochemical deposition. This method has several key features, including low cost and a high level of control over the design. A fundamental property that distinguishes those applications is the operating frequency, which we chose to apply as an underlying structure for this review. With this, we…

Due to the significant advantages of cost savings, low temperature rises and high efficiency, synchronous reluctance machines (SynRMs) have attracted growing interest from academia to industrial applications. Numerous articles have been published to obtain a SynRM with improved performance (i.e., a high torque density and efficiency and a lower torque ripple) using different focusing points at healthy and faulty conditions such as rotor design, magnetic steel grade, stator winding, and fault tolerance control (FTC) strategy. Hence, this article reviews the scientific researches about SynRMs aiming to improve their performance. These scientific researches can be categorized into four sections: 1) optimal rotor design; 2) magnetic steel grade; 3) winding configurations; and 4) FTC strategies.

Fault signal analysis and processing are critical issues in bearing fault diagnosis, and complete ensemble empirical mode decomposition (CEEMD) is an effective means to dispose of fault vibration signals. In this article, a CEEMD optimization method based on the genetic algorithm (GA) is proposed, which suppresses mode mixing by adaptive matching of the Gaussian white noise amplitude. The proposed optimization method utilizes the GA’s global optimality to optimize the white noise amplitude in ensemble empirical mode decomposition (EEMD) and then processes signal by CEEMD with optimized Gaussian white noise. The results of selecting the amplitude of the Gaussian white noise by practical experience are compared. Compared with the empirical method results, this optimization method can adaptively match the appropriate white noise amplitude for different signals, which further suppresses the mode mixing phenomenon, and the fault frequency can be found in the spectrum diagram. It is shown that the proposed optimization method can process different signals adaptively and can be used for…

In order to solve the problems of poor capacity and unsatisfactory efficiency of flux-weakening control for the axial-flux permanent magnet (AFPM) machines with surface-mounted permanent magnet (PM) rotor structure, a new axial-flux hybrid-excitation machine (AFHEM) with double consequent-pole rotors is proposed, which combines the high torque density of the AFPM machine and the flexible flux regulation of the hybrid excitation machine. It meets the stringent requirements of the distributed in-wheel motor electric drive vehicle for high efficiency and high torque density. The topology, principle, and basic electromagnetic properties of the new axial-flux hybrid-excitation in-wheel motor are presented in this article. Based on the complex magnetic circuit of the AFHEM, a 3-D equivalent magnetic network (EMN) model is established. The air-gap flux density, flux linkage, back EMF, torque, and fault tolerance ability of the motor are solved through the EMN model and compared with the 3-D finite element analysis (FEA) to verify its validity and correctness. It is hoped to form a rapid…

This study presents a novel two-step optimization method that incorporates explainable neural networks into topology optimization. The deep neural network (DNN) is trained to infer the torque performance from the input image of the motor cross section. The sensitive region that has a significant influence on the average torque is extracted using gradient-weighted class activation mapping (Grad-CAM) constructed from the DNN. Then, the optimization with respect to the torque ripple is performed only in the incentive region with little influence on the average torque. The proposed method is shown to increase the average torque of an interior permanent magnet (IPM) motor by 14% and reduce the torque ripple by 79% compared with the original model.

Nondestructive testing (NDT) methods are widely used in the rail industry to detect rolling contact damage (RCD) defects to ensure railway safety. With the need of monitoring millions of miles of rail tracks more effectively and efficiently that leads to improved rail safety, reliability, and optimized assets management, the research on high-speed and high-accuracy NDT methods that can obtain high signal-to-noise ratio (SNR) and high sensitivity defect signals at higher speeds is of vital importance. Magnetic flux leakage (MFL) is one of the NDT methods used for high-speed rail inspection, which is suitable for detecting surface and subsurface RCD defects on railhead, but the measured MFL signals are distorted severely by the effect of motion-induced eddy currents (MIEC). However, the fundamental understanding of the mechanism of MIEC generation, distribution, and magnitude is lacking, and the physical interaction between MIEC and MFL measurement during high-speed rail inspection has not been well studied. This article investigates the effect of MIEC on three-axis MFL signals…

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

Electromagnetic performance of high-speed permanent magnet synchronous machines (PMSMs) is studied for electro-hydrostatic actuator (EHA) applications in this article. The electromotive force (EMF) of different magnet pole-arc to pole-pitch ratios is studied. The no-load air-gap density, cogging torque, average torque, torque ripple, core loss, and rotor eddy current losses are investigated by closed slots design. The rotor eddy current losses of different magnetic retaining sleeve materials such as stainless steel, titanium alloy, and carbon fiber are calculated by finite-element analysis (FEA). The results show that, compared with the opening slot structure, the torque ripple and the rotor eddy current losses of closed slot structure are extremely reduced due to the fact that the 11th and 13th harmonics of air-gap flux density are significantly reduced and the slotting effect are effectively weakened. Increase the closed slot height not only reduce the average torque and increase the core loss but also the torque ripple and the rotor eddy current losses reduction effect is slight.…

In this work, a topology optimization procedure is proposed and applied to the TEAM 25 problem, i.e., a model of a die press with an electromagnet for orientation of magnetic powder. The shape of the press is described as a free discretized profile, and its relation to the flux density in the cavity is simulated by finite element analysis (FEA) and learned by a deep neural network (DNN) model. The DNN is used as a surrogate model for optimization, aiming to obtain a desired flux density distribution in the cavity. Results are promising, as better accuracy is obtained with respect to the full FEA-based optimization approach with the reduced time cost. Once trained, the surrogate model can be used to efficiently solve a whole family of problems where a different target field distribution is defined.

Nondestructive testing (NDT) methods are widely used in the rail industry to detect and characterize rolling contact fatigue (RCF) defects in railroads, which is very important for railway inspection and maintenance to prevent catastrophic accidents. Existing NDT methods, e.g., ultrasonic testing (UT), magnetic flux leakage (MFL), and eddy current testing (ECT) have been successfully applied in the rail industry, and the state-of-the-art UT method reported recently achieved a high speed of 40 mi/h with a probability of detection (POD) over 80% under 30% false alarms. However, NDT methods still suffer from a bottleneck in that a higher inspection speed causes lower detection sensitivity due to their physical limits, such as negative velocity effect and long sensing time. One of the leading challenges to the rail NDT community is to develop a high-speed high-sensitivity (HSHS) capability that can provide an improved POD of rail defects in high-speed inspection scenarios over 60 mi/h. This article proposes a horizontal U-shaped magnets-based motion-induced eddy current array (MIECA)…

The nanocrystalline alloys are gradually used as shielding materials in wireless power transfer (WPT) systems with the development of high power density. In this article, the system properties of WPT using ferrite and four types of nanocrystalline cores are simulated by 3-D finite element analysis (FEA). Based on this, a novel shielding pad composed of nanocrystalline alloy and ferrite is designed to improve the WPT system properties. The WPT systems are preliminarily compared with 3-D FEA when the different nanocrystalline alloys are used in the novel shielding pad. The experimental WPT system for 85 kHz and 1.5 kW with a 24 cm air gap between the primary and secondary coils is built to validate the simulation. The results show that significantly greater shielding can be realized for the novel pad at the price of a slight decrease of transmission efficiency than conventional ferrite core.

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

This article proposes an efficient surrogate-assisted design optimization method based on a multicriteria optimal Latin hypercube design (LHD) for multi-objective optimization of a surface-mounted permanent-magnet vernier machine (SPMVM). An improved iterated local search (ILS) method is proposed to optimize the spatial distribution uniformity and orthogonality of LHDs so that the data feature over the wide ranges of optimization variables can be captured more efficiently. Using the optimal LHD, a highly generalizable surrogate model can be trained with fewer samples, thus greatly reducing the required number of finite element analysis (FEA) cases and improving the optimization efficiency. A prototype corresponding to the optimal design is built and measured to validate the proposed method.

There are many space harmonics in the stator magnetomotive force (MMF) of fractional-slot concentrated winding (FSCW). These harmonics will produce high eddy current losses in the permanent magnet (PM), which will reduce motor efficiency and affect motor performance. Aiming at the above problems, the harmonic components of traditional stator MMF are first analyzed in this article, and then, a novel space-shifted unequal-turn winding structure is proposed for dual three-phase fractional-slot permanent magnet synchronous motors (PMSMs). Meanwhile, the sub- and super-harmonics in the stator MMF can be simultaneously eliminated using the proposed winding structure. To verify the effectiveness of the proposed structure, an 18-slot/8-pole motor and a 30-slot/14-pole dual three-phase fractional-slot PMSM with low space harmonic are designed by using the proposed space-shifted unequal-turn winding structure based on the analysis of nine-slot/eight-pole and 15-slot/14-pole motors. Finally, by comparing the finite element analysis (FEA) results, it is verified that the dual three-phase PMSM…

In this article, a special magnetic coupler for three-coil wireless power transfer (WPT) is proposed to eliminate the mutual inductance between the source coil and the receiver coil, which can significantly improve the design freedom. Specifically, unipolar Q coil, mixed QDD coil, and bipolar DD coil are designed for the source coil, the transmitter coil ($\text{T}_{\mathrm {X}}$), and the receiver coil ($\text{R}_{\mathrm {X}}$), respectively. By making use of unipolar coils and bipolar coils, this structure magnetically decouples the receiver coil from the source coil. Meanwhile, under different lateral misalignment conditions, this new coupler facilitates maintaining high efficiency. A laboratory prototype has been constructed to validate the proposed structure, demonstrating that the proposed structure can realize inherent characteristics, enhance misalignment tolerance, and energy transfer. The potential applications are EV systems, but this design can be generalizable to other three-coil systems.

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

This article proposes a scannable leaky-wave antenna (LWA). The antenna consists of a ferrite-blade waveguide with a longitudinal slot on the upper wall, which has a tunable composite right-/left-handed (CRLH) property. The left-handed (LH) behavior of this structure is based on the negative effective permeability of the ferrite material and the negative effective permittivity of the waveguide excited below its cutoff frequency. First, based on the modal analysis and calculated dispersion relation, the unbalanced CRLH response of the ferrite-blade waveguide is investigated. Second, an LWA is presented by using a longitudinal slot on the upper wall of the proposed ferrite-blade waveguide, where the tunable balance CRLH response is achieved and analyzed by the transverse resonance method (TRM). The proposed LWA can provide backward, broadside, and forward radiations by a change in the operation frequency or the magnetic bias, independently. The given results show a +59° to -57° sweep in the radiation beam when the magnetic bias of the ferrite changed from 1400 to 1600 Oe at the…

To accurately and quickly predict the open-circuit air-gap magnetic field in interior permanent magnet synchronous machines (IPMSMs), an analytical model based on magnetic equivalent circuit (MEC) method is proposed. The analytical model can provide radial and tangential components of open-circuit magnetic field in the slotless air gap. The radial component is obtained from the MEC model, and the tangential component is obtained from boundary conditions of macroscopic equations. Then, a complex relative air-gap permeance is applied to take the effect of slots into account. As a result, an accurate solution of both radial and tangential components of the flux density in the slotted air gap is obtained. Additionally, the no-load back electromotive force (EMF) and cogging torque are calculated based on the open-circuit air-gap magnetic field. All the analytical results are verified by the finite element (FE) analysis and they are well matched. In the end, a direct measurement experiment of open-circuit air-gap magnetic field is proposed to verify the validity of both radial and…

This article covers the design methodologies and optimization techniques studied in the performance improvement of line-start permanent magnet synchronous motors (LSPMSMs). LSPMSM performance improvement using design techniques are chiefly limited to either the transient or the steady-state performance improvement, and a focus on only the transient performance improvement may degrade the steady-state performance of the LSPMSM and vice versa. Optimization studies of LSPMSMs can be categorized in terms of optimization aim in three classifications: transient performance improvement, steady-state performance improvement, and simultaneous improvement of both transient and steady-state performances. This study indicates the impact of various variables on the LSPMSM performance improvement. The optimization review shows that starting cage optimization without considering the steady-state characteristics as constraints results in synchronous performance degradation. The steady-state performance optimization with transient characteristics as constraints results in a minor synchronous…

Ultra-high-speed (UHS) surface-mounted permanent-magnet synchronous motors (SPMSMs) are widely used for driving air compressors. UHS SPMSMs can suffer from high stator iron loss and rotor eddy current loss due to their high rotational speed and changes in the magnetic flux density when loading. Since these losses do not have a linear trend but change according to the motor design parameters, mathematical models cannot always predict them. This study aims to design UHS SPMSMs based on a kriging surrogate model that takes into account the stator iron loss and rotor eddy current loss. Since the kriging surrogate model is highly predictive for nonlinear inputs, it is the perfect candidate to take into account the stator iron loss and rotor eddy current loss. The design proposed in this study allowed to minimize the size and losses of a motor that satisfied the power specification.

Core loss prediction is quite complex as the excitation of magnetic materials varies depending on the topology and the operating mode of switched-mode power supplies. In particular, the waveform of the magnetic flux density, including its dc bias, affects core losses. This article presents the results of an extensive core loss study performed on Mn-Zn ferrites. The investigation comprises core excitations with, among others, sinusoidal and triangular shapes of the magnetic flux density with and without dc bias. Based on the obtained core loss data, an empirical core loss model has been derived for the prediction of specific core losses in Mn-Zn ferrites that is valid for arbitrary excitations, including dc bias of the magnetic flux density. Multiplying the quasi-static energy losses depending on the swing and the dc bias of the magnetic flux density by an effective frequency yields the core losses. The proposed model covers a wide frequency range and only requires the quasi-static energy losses at low frequencies and two frequency-independent parameters. These parameters can be…

This article presents a quasi-3-D analytical model for double-sided axial-flux permanent magnet machines (AFPMMs) with coreless structures. A simple, fast, and accurate technique is developed to calculate flux densities in different parts of the AFPMM combining the solution of Maxwell's equations and the magnetic equivalent circuit (MEC). In this technique, Maxwell's equations are used to generate flux sources that are used in the reluctance network of the MEC. After calculating all the reluctances and flux sources, the magnetic flux densities are obtained. This method takes into account the effects of permanent magnet (PM) reluctance, leakage flux between PM-to-PM, PM-to-rotor leakage flux at different PM edges, and the fringing flux effect. By considering these leakage fluxes as a factor called variation function in the design procedure of the machine, the analysis time is dramatically reduced compared to numerical methods while maintained high reliability. It should be noted that since considering saturation phenomenon effects in coreless AFPMM analysis does not give rise to…

This article presents a novel surface-mounted permanent magnet motor (SPMM) with hybrid NdFeB-Alnico magnets to achieve low cost and low torque pulsation. Based on the analysis of the effects of stator magnetomotive force (MMF) on rotor magnets, the Alnico magnets can be properly configured to avoid demagnetization. To reduce torque pulsation, three models with different slot-pole combinations are proposed and compared, with the aid of the finite element method (FEM), and the results show that the torque pulsation of the 27-slot/4-pole model is the lowest, which is selected for further optimization. The multi-objective genetic algorithm (MOGA) is adopted to optimize the usage of Alnico and NdFeB magnets, thereby improving torque performance and reducing the cost. To verify the effectiveness of the optimization, the optimized model with hybrid NdFeB-Alnico magnets is compared with other models with only NdFeB magnets under the same operating conditions. As a result, it shows that the optimized model can significantly reduce the cost of magnets while maintaining excellent torque…

Massive data growth is accelerating the need for storage. Hard disk drive read/write technology continues to advance to support this demand. This Advanced Storage Research Consortium report combines a top-down (system) and bottom-up (micromagnetic) approach to define a reader technology roadmap for 2.4, 4.0, and 6.0 terabits per square inch (Tbpsi) including dimensional and performance targets. We examine the resolution, SNR, stability and manufacturing requirements, challenges, and gaps. We show that the extension of today’s spin valve-based reader designs may enable 4 Tbpsi, but significant gaps must be closed. For higher areal densities, we review future reader designs, challenges, and discuss potential solution paths.

AC magnetic flux leakage (ACMFL) testing is a novel method for the detection of defects of metallic materials. Conventional ACMFL probes excited by a single-frequency (SF) sine signal have limitations in accurately detecting the defect size and identifying the defect orientation. In this article, a multifrequency ACMFL (MF-ACMFL) method is proposed to address these issues. First, we give a thorough analysis of the effects of excitation frequencies on magnetic flux density under different defect sizes and orientations using the finite-element method. The numerical results indicate that the optimal frequencies are 400 and 500 Hz to detect the defect size, and that to identify the defect orientation are approximately 400-500 Hz. Then, we compare the receiver signal under SF and MF excitations and estimate the size of the defect including its length, width, and depth under oblique angles of 0° and 30°, whose results validate the effectiveness of the proposed method. Finally, measuring the depths and orientations of the defect on the thick steel plate verifies the correctness of the…

This article proposes a novel topology optimization method using the Gabor filter, which is widely used in the field of image processing. The proposed method is applied to the optimization of a synchronous reluctance motor; its average torque is maximized, and simultaneously, the torque ripple is minimized. It is shown that the proposed method results in a motor with thin layer-shaped flux barriers, which achieves a better torque performance in comparison with a conventional model and a motor optimized using normalized Gaussian network (NGnet).

Based on thermoelectric analogy method, a thermal network model coupled with electromagnetic loss is presented. According to the actual structure of dry-type transformer windings, an accurate thermal network is established. Considering the distribution characteristics of heat source along the cooling ducts inside the dry-type transformer, the thermal parameters such as heat flux and convective heat transfer coefficients are calculated by finite element method (FEM) analysis and computational fluid dynamics (CFD). Based on the temperature rise experiment, the hottest spot located at the top of the outmost high-voltage (HV) winding is 151.8 °C, which verified the correctness of thermal network model.

Three-phase wireless power transfer (WPT) systems have compact coil structures, canceled triplen harmonics, and less dc -link current ripple, which are suitable for wireless electric vehicle (EV) charging systems. Most three-phase WPT systems are based on two-level inverters. Alternately, three-level (TL) inverters have the potential to further promote the performance of EV chargers by reducing the electromagnetic interference (EMI) and the voltage stress of power switches. However, the unbalance of the neutral point (NP) voltage is a problem for traditional TL inverters. This article proposes a TL three-phase WPT system for EV wireless charging, which is based on a T-type neutral point clamp (TNPC) inverter. The modeling, coil structure, and switching pattern of the proposed system are analyzed in detail. Furthermore, a novel output regulation method based on vector control is proposed for the WPT system. Also, a NP voltage balance strategy is proposed to enhance the reliability of the TL inverter. Both simulations and an experimental prototype based on SIC- MOSFET are given to…

In traditional applications such as machine field excitation, where power transfer from stationary to rotary side is needed, contact slip rings are often adopted. However, this kind of slip ring is easy to wear and needs frequent maintenance. In a contactless power transfer system, mechanical slip rings can be removed which will largely increase the system reliability. In this article, a contactless power transfer device using wireless power transfer (WPT) is designed. Its performances are simulated by finite-element method. To increase the system power rate and efficiency, the device is operated under high frequency. Thus, high-frequency ferromagnetic materials and Litz wires are used. Moreover, compensation circuits are added to improve the coupling between the primary and secondary sides. At last, a prototype is built and tested. From the experimental results, the functions and performances of the device are well verified.

In this article, a novel spoke-type permanent magnet (PM) machine with two types of PM materials is proposed to reduce the cost. In order to improve torque density and reduce torque ripple, the multi-objective optimization combined finite element method (FEM) and genetic algorithm (GA) are used. In addition, the electromagnetic performances of the novel spoke-type PM machine, including no-load air-gap flux density, electromagnetic torque, torque ripple, efficiency, and cost are compared with the conventional spoke-type PM machine. It is demonstrated that the novel spoke-type PM machine obtains a 1.5% lower torque ripple and 36% lower cost, and the torque density is 4.3% lower than the conventional spoke-type PM machine. Meanwhile, the novel spoke-type PM machine has lower core loss and higher efficiency. Finally, a 40 kW spoke-type PM machine is manufactured to verify the analyzing method. Experimental results demonstrate that the proposed machine exhibits high torque density and low cost in the application of electric vehicles (EVs).

The recording performance of a new prototype magnetic tape based on perpendicularly oriented strontium ferrite particles is investigated using a 29 nm wide tunneling magnetoresistive reader. At a linear density of 702 kbpi, a post-detection byte-error rate (BER) of 2.8e-2 is demonstrated based on measured recording data and a software read channel. The read channel uses a 64-state implementation of an extended version of a data-dependent noise-predictive maximum-likelihood detection scheme that tracks the first- and second-order statistics of the data-dependent noise. At the demonstrated post-detection BER, a post-error-correction-coding BER of less than 1e-20 can be achieved using an iterative decoding architecture. To facilitate aggressive track-density scaling, we made multiple advances in the area of track following. First, we developed a new timing-based servo pattern and implemented a novel quad channel averaging scheme. Second, we developed a new field programmable gate array prototyping platform to enable the implementation of quad channel averaging. Third, we enhanced our…

Underwater magnetic signature of sea vessel is an important characteristic in mine threat estimation. Traditionally, the vessel's signal is measured with the help of stationary magnetic range equipped with bottom-mounted magnetic sensors. However, such a range may be unavailable near vessel's operating area. In this work, we investigate a capability of underwater magnetic signature estimation basing on the results of overhead magnetic mapping of the vessel by a portable total field magnetic sensor installed on a light aerial platform. A magnetic model of the vessel is represented by an array of point magnetic dipoles distributed over steel hull and clusters of ferromagnetic equipment. The model parameters are estimated by fitting the calculated magnetic field produced by the model to a measured overhead magnetic anomaly map. Once these parameters are determined, the vector magnetic field produced by the object may be calculated at any point both in “near” and “far”-field zones. To confirm this approach, we built a steel model ship in a scale of around 1:100. Dedicated setup enables…

In this article, an analytical method is presented for modeling the complex air gap field distribution and the magnetic force of a novel permanent magnet (PM) bias hybrid magnetic thrust bearing (HMTB). This bearing has a very compact structure and is proposed to replace the traditional magnetic thrust bearings (MTBs) for high-speed rotor systems. The proposed method introduces the notion of the complicated air gap field, calculated from the Schwarz–Christoffel transformation of the air gap geometry, to take into account the effect of slot fringing and leakage. As a result, accurate solutions of the flux distribution and the bearing force can be obtained, which shows good agreement with the results of the finite-element method (FEM). The prototype of the HMTB is designed, analyzed, and tested. The results of the analytical model are compared with experimental data.

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

It is well known that the slotted motor has higher power and torque ripple than the slotless motor. However, how much the power and torque ripple can increase is rarely reported. In this article, the analytical method is used to compare the torque of the slotless and slotted motor. First, the armature reaction field (ARF) and open-circuit permanent magnets (PMs) field are solved by the subdomain model. Then, the torque is calculated by the Maxwell stress tensor method. Moreover, we also obtain the back electromotive force (back EMF) and cogging torque. Finally, the average torque and the torque ripple of the slotless and slotted motor are compared and discussed. The above analytical model is verified by the 3-D finite element method (FEM) and experiment. Results show that the average torque and torque ripple of the slotted motor have increased 52.6% and 22.5 times compared with that of the slotless motor. This article will provide a useful reference for the design of both the slotted and slotless ultra-high-speed axial flux permanent magnet (AFPM) motors.

In this article, the experimental investigation and analysis of the effect of rheological properties on the starting torque of the magnetic fluid seal are reported. The change of the starting torque with a standing time for perfluoropolyether-based magnetic fluid seal and diester-based magnetic fluid seal, as well as the viscosity of magnetic fluids under the relevant magnetic field and shear rate, were measured. It was observed that the magnetic fluid with higher viscosity correspondingly exhibited higher starting torque. The starting torque of seals with two different magnetic fluids exhibited the same variation tendency. The starting torque was exponentially increased with the standing time and then tended to be a stable state with small scale fluctuation. The average maximum starting torque of PFPE-based ferrofluid seal after standing five days was ten times as large as the value of the initial standing, whereas that of diester-based ferrofluid seal was 3.5 times as large the value of the initial standing. The rheological behavior was the key factor influencing the starting…

We here present a novel deep learning (DL) approach for designing structures of permanent magnets. The challenge for the DL method in this kind of problem is to learn the mapping from a desired magnetic field to a simple magnetic structure, i.e., an inverse design approach. We demonstrate this approach by training six different standard convolutional neural network (CNN) structures previously used in the ImageNet Large Scale Visual Recognition Challenge (ILSVRC) to inversely predict the properties of a single hard magnet (magnetization, size, and location) from a given 2-D magnetic field. We show that the best network, ResNeXt-50, can perform this prediction with an error of 0.22% in the properties of the magnet.

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

Transverse flux permanent magnet motor (TFPM) benefits from the high power density and design freedom but traditional TFPM exhibits some disadvantages-high flux leakage, cogging torque, and low-power factor-which restrict its development. In order to overcome these disadvantages, claw pole TFPM (CTFPM) is developed, but it also be plagued by the demerits of soft magnetic composite (SMC) material. In this article, a novel CTFPM based on hybrid stator core (Hybrid-CTFPM) is proposed to improve the performance of CTFPM. The parameters of claw pole are investigated in this article and are optimized using a new optimization strategy eventually. This article provides a valuable reference for the design and optimization of CTFPM.

Physical unclonable function (PUF) is an emerging hardware security primitive which is increasingly used to authenticate and identify Internet of Things (IoT) devices. Spin-transfer torque magnetoresistive random access memory (STT-MRAM) provides new opportunities for novel PUFs due to inherent randomness sources, such as process variations, stochastic switching, and chaotic magnetization. In this article, we propose a hybrid STT-MRAM/complementary metal-oxide semiconductor (CMOS)-based reconfigurable arbiter PUF (MPUF) with enhanced performance metrics in terms of reliability, uniqueness, and uniformity. This design has a mean intra-hamming distance (HD) of 0.147%, a mean inter-HD of 50.21%, and passes the National Institute of Standards and Technology (NIST) statistical tests. The proposed arbiter MPUF features distinct advantages, such as reconfigurable architecture, challenge-dependent stage delays, and huge challenge-response pair (CRP) space. Moreover, the robustness of the proposed MPUF against machine learning (ML)-based modeling attacks is tested using three ML algorithms,…

In a wireless charging system, non-alignment has been a big problem that affects the transmission efficiency. The uniform magnetic field can ensure the charging power stability and extension of battery life in a multi-load wireless charging system, which also expands the free charging area of the loads. In this article, the array circular coils of wireless power transfer (WPT) with a compensation structure have been proposed, which can be obtained by analyzing the magnetic field trajectory of the elementary unit of the array coils. Larger scale of the uniform magnetic field could be expended by the joint of several elementary units. The correctness and validity of the structure are verified by theoretical derivation and finite element simulation. Besides, the compensation method could be used for any forms of array coils.

Soft magnetic powder cores are attractive because of their loss at medium frequency. However, the performance of electrical equipment is affected by temperature increase by the heat of core losses. In this article, the magnetic properties of nanocrystalline powder core, amorphous powder core, X-Flux (Fe-Si), Sendust (Fe-Si-Al), and ferrite are measured and compared in the range of 25 °C–125 °C from 20 to 100 kHz. The discussed magnetic properties include the temperature-dependent coercive field, initial permeability, inductance factor, saturation flux density, and core loss. The results show that magnetic properties depend on temperature and frequency. In comparison, the nanocrystalline powder core has the best temperature stability and relatively low core loss among the five materials, so it can be well used at broad temperature and medium frequency.