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This paper proposes a coupled analysis method to deal with ion generation and ion drift in the air. Electric discharge is utilized in various products, and it is very important to clarify not only how much ion is generated but also where ion drifts in the air. The proposed method, which modeled interactions between electric field and ion behavior, including ion generation, ion drift, and charging of a dielectric body, has succeeded in calculating charge removal of a metallic target, which was tens of millimeters away from a pin electrode as a source of generated ion. The calculated results show that the amount of generated ion is drastically changed because electric field is affected by electric charge of ion in the air and charging of a dielectric body. This paper also reports a comparison of measured and calculated results of charge removal time of a metallic target, which were found to be in good agreement. [ABSTRACT FROM AUTHOR]

After designing and optimizing an electric machine, efficiency maps are needed to predict a vehicle’s performance in a dynamic simulation. Calculating efficiencies at various torque and speed points, however, requires prior knowledge of the input excitation conditions, such as the current magnitude and advance angle, in an electromagnetic finite-element analysis simulation. Hence, this paper derives and uses nonlinear motor control equations (MTPA, FW, MTPV) in the study of efficiency map calculation while accounting for both saturation and cross-coupling effects. Two synchronous ac motors are considered in this paper, including the 2010 Prius IPM and a PM-assisted synchronous reluctance machine, with all procedure steps outlined in detail. [ABSTRACT FROM AUTHOR]

When solving eddy-current problems containing topologically non-trivial conductors with formulations using the magnetic scalar potential in the insulators, cohomology generators are necessary to obtain a well-defined problem. The Dłotko–Specogna (DS) algorithm is a simple and efficient tool to compute the lazy generators of the first cohomology group of the insulator that can be used in such potential design. This paper introduces an upgrade in the DS algorithm that speeds up the execution for very complicated geometries. Moreover, this paper provides, for the first time, a detailed comparison of computational resources needed for the topological pre-processing by our toolbox and by the tool to compute a standard cohomology basis available in the mesh generator GMSH. In addition, we make our implementation of DS algorithm available for download on request for non-profit use as a Topoprocessor package. [ABSTRACT FROM AUTHOR]

An electrical motor’s inverse thermal model formulates the precision with which its power losses can be predicted from noisy local temperature measurements. This paper proposes constrained linear least square optimization followed by noise smoothing as a method to accurately predict a 37 kW induction motor’s power loss components. The anisotropic heat transfer and complex geometry of the motor are represented well by the motor’s lumped thermal network and 3-D finite element models, which characterize its intrinsic heat-transfer processes. With the inverse solution method, satisfactory temperature to power inverse mapping was achieved for different sets of noisy temperature inputs simulated from analytical and numerical forward solutions. This paper demonstrates that even with measurement noise in input data, if reliable information about the expected response of the system is available, an accurate reconstruction of power losses can be achieved. [ABSTRACT FROM AUTHOR]

An innovative method to reduce electromagnetic interference (EMI) of an electric machine drive has been simulated and experimented in this paper. In this method, matrix converter with wide-bandgap switches is built. This control system not only makes the controlling smooth but also has the capability to reduce the EMI since the switching frequency is high. In this method, finite element model of the permanent magnet synchronous machine is implemented and coupled with the MATLAB simulink simulation. In addition to the modeling, numerical simulation for two different wide-bandgap switches i.e., Si-IGBT and silicon carbide MOSFET (SiC MOSFET) are carried out and results are compared. The results of the proposed system show that ripple in torque and speed response, as well as harmonics in stator current for SiC MOSFET, are less than Si-IGBT. Moreover, the proposed converter is implemented in hardware to verify the simulation results. The practical implication of this paper is that the proposed matrix converter that can replace the conventional one for sensitive applications in which the EMI disturbs the system’s performance. [ABSTRACT FROM AUTHOR]

A semi-high-speed magnetic levitation (maglev) train with a maximum speed of 200 km/h is being developed in Korea. It utilizes linear induction motors for propulsion and adopts electromagnetic suspension for levitation. For high-speed operation, guidance systems should be adopted to stabilize the train especially on curved tracks. For compatibility of the rail with previously developed urban maglev trains, the installation of the guidance electromagnet has to be restricted to be placed near the levitation electromagnet. Owing to the spatial closeness, mutual magnetic flux by the levitation and guidance electromagnets is produced at an overlapping portion of the rail. For stable control of the two systems, the coupling effects must be analyzed, because the levitation and guidance electromagnets are not operated independently. This paper aims to analyze the coupling effects by considering the magnetic field and a magnetic equivalent circuit. This paper suggests levitation and guidance systems for the semi-high-speed maglev train by considering each electromagnetic characteristic depending on the current direction. [ABSTRACT FROM AUTHOR]

This paper proposes a methodology for the assessment of the human exposure to magnetic fields generated by dynamic inductive power transfer systems for automotive applications. Since the magnetic field is pulsed, current safety standards and guidelines require the use of time-domain approaches to evaluate the peak exposure, which has to be limited under the prescribed limits. This paper shows that, for these kind of systems, the peak exposure can be efficiently evaluated by means of a time-harmonic formulation. Furthermore, a methodology to identify the worst case scenario is proposed and applied to a real case. [ABSTRACT FROM AUTHOR]

In this paper, a new finite element Gaussian belief propagation (FGaBP) method is presented for time-domain applications. The unconditionally stable Newmark time-stepping scheme is combined with FGaBP for this purpose. As shown empirically, the method converges for increasing time step sizes without losing stability. The combined FGaBP-time stepping is able to retain the parallel scalability from FGaBP as in previous work. In addition, this paper also shows that lossy material properties can be easily supported by the method with minimal changes to its formulation. [ABSTRACT FROM AUTHOR]

Recently, the layout optimization of the secondary coils for wireless power transfer systems has been developed using the fixed grid (FG) representation. Although this method can effectively and efficiently determine the optimized coil design under the given conditions, a distinct discrepancy exists between the evaluated coil mass (i.e., simulation data) and the physical coil mass (i.e., experiment data). In this paper, the FG-based coil layout optimization is revisited based on the smooth boundary (SB) representation in order to resolve the inherent drawbacks of the FG representation. Induced voltage, electromagnetic field strength, and coil mass, which have been previously derived in the FG representation, are reformulated in terms of design variables (i.e., a reference turn and relative turns in this paper) in the SB representation. Through the layout optimization, the optimized layouts of the secondary coil are determined in order to minimize the coil mass while satisfying the constraints for induced voltage and magnetic field strength; then, they are postprocessed in order to obtain a smooth, elaborate boundary. The experimental validation demonstrates that the proposed SB-based approach outperforms the previous FG-based method in terms of coil mass and boundary representation. [ABSTRACT FROM AUTHOR]

This paper employs an overhang structure for axial flux permanent magnet motor to enhance the torque density. However, the overhang structure requires a computationally expensive 3-D finite-element method (FEM) for analysis, because a quasi-3-D FEM cannot be applied to such a geometry. Thus, in order to reduce the computational cost of above-mentioned topology, this paper adopts a field reconstruction method (FRM). The conventional FRM is applicable only in the case, where the slot pitch to teeth length ratio is the same along radial direction. To address this problem, we introduce a virtual air gap concept so that it can take into account parallel slot effect as well as overhang effect. In this paper, the effectiveness of the proposed method is verified by the 3-D FEM and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a lithium ion cobalt polymer battery cell is modeled using 3-D finite elements (3DFE) for the study of its performance under a wide range of operating scenarios. The electrochemistry is modeled and coupled to an electromagnetic model to forecast the cell voltage overpotential as a result of charging and discharging under six current densities. To study this phenomenon, light ( $C$ /10), medium ( $C$ /2), and high ( $1C$ ) charging and discharging currents are imposed at the battery terminals and compared with experimental results. The electric field inside the electrodes and electrolyte is analyzed at each case highlighting regions where loss occurs. A magnetic field analysis depicts the total electrochemical generation of current densities inside the cell while identifying how the development of gradient currents occur, a mechanism which can shorten the life span of the battery. This paper distinguishes where 3DFE analysis battery models can be useful in studying how lithium ion batteries will behave given a particular loading or a charging profile before placing them in service. [ABSTRACT FROM AUTHOR]

Magnetic nanostructures have potential applications in ultrahigh-density magnetic storage. In this paper, the dynamics of the dual magnetic vortices in elliptical Permalloy nanodisk are investigated using micromagnetic modeling. Under the stimulation of the short-axis ( $y$ -axis) Gaussian field pulse and long-axis ( $x$ -axis) constant field, the equilibrium positions of dual-vortex cores can be driven away from the initial positions. The displacement in the $y$ -direction is proportional to the magnitude of the $x$ -axis constant field. The displacement in the $x$ -direction exhibit periodic reliance on the pulsewidth of the $y$ -axis Gaussian field pulse. The threshold value of pulse strength for dual-vortex motion increases with the magnitude of the $x$ -axis constant field. The mechanism of polarity and chirality switching in dual-vortex cores are studied through analyzing the trajectories of vortex cores in the annihilation and nucleation processes. The switching of polarity exhibits an oscillatory dependence on the pulsewidth and strength. The minimum pulse strength required for chirality switching is 120 mT, while the corresponding pulsewidth is influenced by the $x$ -axis constant field. This paper provides insights on the magnetization dynamics of nanostructures containing dual vortices subject to external excitations. [ABSTRACT FROM AUTHOR]

This paper focuses on the computation time and precision of a linear 2-D magnetic gear analytical model. Two main models of magnetic gears are studied: 1) the first with an infinite relative permeability of yokes and 2) the second with a finite relative permeability of yokes. These models are based on the subdomain resolution of Laplace and Poisson equations. To accurately compute the magnetic field distribution, it is necessary to take into account certain harmonics of the various rings and other system harmonics due to modulation. Global system harmonics, which increase the value of computation time, must also be taken into account. If the magnetic gear has a high pole number, then computation time increases even more and no longer allows for system optimization. This paper proposes to compute magnetic field distribution using different harmonic selection methods in order to significantly reduce the computation time for the magnetic torque without any loss of accuracy. [ABSTRACT FROM AUTHOR]

This paper presents the validation of a small-signal finite-element simulation strategy comparing different simulation approaches. At first, a full 3-D non-linear model in the time domain is presented. Then, the small-signal strategy has been applied to the 3-D model achieving a considerable reduction of computational time. In both 3-D models, the eddy currents in the laminations are fully modeled. Then, in order to avoid 3-D model, a 2-D model has been considered. In this case, eddy currents are included adopting a homogenization technique. In the 2-D case, both non-linear time domain simulations and small-signal strategy have been implemented. The results of the four considered simulation strategies are in very good agreement, proving that the small-signal simulation strategy can be profitably used in order to reduce significantly the computational cost. As an example, this paper considers a two-port mutual inductor as a test model. [ABSTRACT FROM AUTHOR]

This paper presents a novel noninvasive electromagnetic brain stimulation system, namely the transcranial magnetic stimulation (TMS), via strongly coupled magnetic resonances, which is used to improve treatment effects, enrich treatment means, and increase energy utilizations. To achieve expected stimulation effects, the conventional TMS system normally needs strict requirements for the power supply and the circuit. Inevitably, it not only deteriorates the implementability and flexibility of the noninvasive electromagnetic brain stimulation, but also increases the manufacture cost and energy consumption, thus significantly impeding the popularization of TMS technologies. Hence, a novel TMS system is proposed by utilizing the magnetic resonant coupling (MRC) mechanism, aiming to offer a brand new way to fulfill expected stimulation effects. By comparing with conventional TMS systems, the proposed system can effectively increase the strength so as to improve the stimulation depth, enhance the focality so as to prevent from impacting on nonfocal zones, and reduce the requirement on the power and frequency so as to promote the popularization of noninvasive electromagnetic treatments. In this paper, both simulation and experimental results are provided to verify the feasibility and superiority of the proposed MRC-based TMS system. [ABSTRACT FROM AUTHOR]

Modern hard disk drive (HDD) systems are subjected to various external disturbances. One particular category, defined as wide-band disturbances, can generate vibrations with their energy highly concentrated at several frequency bands. Such vibrations are commonly time-varying and strongly environment/product-dependent, and the wide spectral peaks can occur at frequencies above the servo bandwidth. This paper considers the attenuation of such challenging vibrations in the track-following problem of HDDs. Due to the fundamental limitation imposed by the Bode’s integral theorem, the attenuation of such wide-band disturbances may cause unacceptable amplifications at other frequencies. To achieve a good performance and an optimal tradeoff, an add-on adaptive vibration-compensation scheme is proposed in this paper. Through parameter adaptation algorithms that online identify both the center frequencies and the widths of the spectral peaks, the proposed control scheme automatically allocates the control efforts with respect to the real-time disturbance characteristics. The effect is that the position error signal in HDDs can be minimized with effective vibration cancelation. Evaluation of the proposed algorithm is performed by experiments on a voice-coil-driven flexible positioner system. [ABSTRACT FROM AUTHOR]

In magnetic flux leakage type nondestructive testing (NDT), there exists velocity effect, which may cause the distortion of the defect signals and reduce the estimated accuracy of defect profile. In this paper, the distortions are analyzed by using finite-element method (FEM), and the influence of velocity effect on reconstruction of defect profiles is discussed under the condition of the simulation and experiment. This paper proposes an effective method for reconstructing arbitrary defect profiles in different velocity conditions. In the proposed method, the FEM considering velocity effect is employed as the forward model. A weighting conjugate gradient algorithm is applied to update the defect profile iteratively in two gradient directions. The algorithms effectiveness is tested on a series of artificial defects under various velocity conditions. The results demonstrate that the proposed model can achieve the better reconstruction accuracy than the ignoring velocity effect models. The properties of the presented method are so stable and robust that they make our approach a promising technique for the practical application of profile reconstruction for NDT. [ABSTRACT FROM AUTHOR]

This paper presents a detailed magnet defect fault detection analysis through fluxgate sensors by monitoring the leakage flux around permanent magnet synchronous motors. The flux spectra of electric machines contain direct and most critical information to monitor and characterize magnet defect faults and their progressions. In the mainstream diagnosis techniques based on phase current and back-EMF analysis, the fault corresponding signature characteristics may vary and cause misleading results depending on motor topology, winding configuration, number and location of defective magnets, and controller parameters. In this paper, it is shown that leakage flux analysis provides some superior results for magnet defect diagnosis. For this purpose, the fault patterns in the leakage flux spectrum are exhaustively analyzed at different torque/speed profiles. Simulation and experimental results show that the deployment of a direction sensitive fluxgate sensor in magnet defect fault detection yields very promising results both in time and frequency domain analyses. [ABSTRACT FROM AUTHOR]

This paper presents models developed through analytical or numerical computation and finite-element analysis to improve the resolution of a new kind of vibrating magnetometers. This peculiar magnetometer uses the piezoelectric transduction to actuate a quartz resonator at its resonance frequency taking advantage of the high $Q$ factor of a quartz resonator to achieve high resolution. The magnetic sensitive element is a thin ferromagnetic film of nickel–cobalt, which is sputtered on the moving beams of the resonator. This magnetic thin film applies a periodic torque on the resonator, shifting its resonance frequency. This torque depends on the magnetic field applied; therefore, the value of the magnetic field can be deduced from the frequency shift measurement. The aim of this paper is to develop and improve sensitivity models, which will be useful tools in the future work to establish the optimal geometry for a resonator and the best position of the magnetic thin film on it in order to improve the sensitivity and resolution of the global sensor. [ABSTRACT FROM PUBLISHER]

This paper presents a detailed theoretical background of the saturation wave model (SWM), which offers a simplified homogenized solution of the nonlinear diffusion phenomena inside soft magnetic steel sheets (SMSSs). The SWM is capable of predicting the complicated dynamic magnetization of SMSS without discretization of the cross section of the SMSSs. Despite its simplicity, the SWM predicts exact solutions of the discussed problems when step-like magnetization curves are assumed and reasonably accurate solutions for real magnetization curves. In this paper, the SWM is analyzed in comparison to the numerical solution of the diffusion phenomena using the parametric magnetodynamic model, where interesting properties of the SWM are discussed and pointed out. [ABSTRACT FROM PUBLISHER]

The use of power electronics has led to a growing importance of higher time-harmonic content in electrical machines. To gain insight in phenomena related to these higher harmonics, such as noise and losses, a good understanding of the magnetic field’s harmonic content is mandatory. Moreover, the development of fast and accurate, harmonic-based, analytical models requires a qualitative knowledge of the machine’s time- and spatial-harmonic content. Although the harmonic content of electric machines is an extensively studied topic, previous publications tended to focus on one type of synchronous machines and often did not consider higher time-harmonic orders. This paper complements the existing theory by providing a more general approach, thereby covering machines and operating points that were not covered until now. It considers both three-phase and multi-phase machines with an odd number of phases. The winding distribution can either have an integer or a fractional number of slots per pole and per phase, and higher time-harmonic content is regarded as well. Note that the saturation is neglected. Despite its general validity, this paper succeeds at providing one simple equation to determine the machine’s time-and spatial-harmonic content. Moreover, this paper also extensively discusses the physical causes of the harmonic content. The combination of this general validity, the simple result, and the insight in the physics makes that this paper is a strong tool to both study harmonic-related phenomena in electric machines and to develop harmonic-based analytical models. [ABSTRACT FROM AUTHOR]

This paper presents the design and optimization of an eddy-current testing system for the imaging of surface-breaking defects in conductive materials. The reconstruction of the defects is obtained by an efficient noniterative method, based on the monotonicity property that makes the approach suitable for real-time imaging. The design of the system is extremely difficult, because its performances and feasibility can be viewed only by many perspectives, leading to a multiobjective optimization problem. The main contributions of this paper are: 1) introducing appropriate indexes for measuring the performances of the system and 2) a related design strategy. Numerical examples prove the effectiveness of the design strategy. [ABSTRACT FROM AUTHOR]

Currently, heat-assisted magnetic recording (HAMR) technology has been proposed as a method for enabling higher storage density. In this paper, the molecular dynamic simulation method was used to investigate the consumption and recovery of the lubricant perfluoropolyether (PFPE) layer under rapid heating and cooling through HAMR. A full-atom model for the 3-D slider-lubricants-disk substrate system was built for this paper. The lubricant adheres to the diamond-like carbon substrate, and the space between the slider and the lubricant is filled with helium atoms. It is found that HAMR laser heating results in the gradual consumption of the PFPE lubricant, and that the target operational temperature T0 significantly affects the consumption of the PFPE lubricant on the disk substrate. The extent of lubricant consumption increases sharply when T0 is above 600 K. The lubricant’s weight percentage on the disk substrate rises up again when cooling occurs. But it cannot be completely recovered. On the other hand, the bearing pressure reduces the degree of consumption of the PFPE lubricant by laser heating. However, the effect of bearing pressure on the amount of remaining PFPE lubricant becomes weak when T0 is above 800 K. [ABSTRACT FROM AUTHOR]

The analytical calculation of magnetic forces is currently an interesting alternative to the time-consuming 3-D finite-element method due to their high accuracy and low computational cost. In this paper, a new semi-analytical solution for determining the levitation force of the repulsive magnetic guidance that has a significant role for controlling and developing high precision magnetic levitation positioning system is presented. An important result is that this new expression, compared with other known equations in the literature, considers the position dependence of the magnetic levitation force over the whole travel range. In order to derive this force, the magnetic field of the permanent magnet is first calculated by introducing and solving the magnetic scalar potential. Taking Lorentz force law into consideration, the proposed equation is finally derived. This semi-analytical equation is suitable for designing and optimizing the magnetic guidance. Furthermore, it can also be used for developing other ironless actuators. The calculated levitation force from the derived equation and the verification by measurements are likewise presented in this paper. [ABSTRACT FROM AUTHOR]

Stick-slip motion is the most well-known phenomenon in nanotribology. Maier et al. previously studied the dependence of slip time on contact geometry. In their paper, they were able to identify the intermediate state during slip motion. However, detailed study of this intermediate state is difficult due to the fast dynamics. The advantage of molecular dynamics (MD) simulation is that it can provide detailed information and direct visualization of the tribological phenomena on a time scale of a few nanoseconds. In this paper, we investigate the detailed mechanism of stick-slip motion in nanoscale. MD simulation precisely mimics friction force microscopy experiments. In MD simulations, a crystalline Si tip slides on a graphene surface, and the tip size is varied. The simulation results provide evidence of the intermediate state during slip motion and reveal the hierarchical structure of the stick-slip motion in nanoscale. Detailed relations among stick-slip motion, contact geometry, and energy state are also analyzed. [ABSTRACT FROM AUTHOR]

Near-field radiation effects in heat-assisted magnetic recording (HAMR) are important to contribute the heat transfer and hence the flying ability at the head disk interface. Investigation of the near-field heat transfer is essential to optimize the head disk interface. An equivalent simulation model of the head disk interface for studying the radiative heat transfer is provided in this paper. Both the head shape and the magnetic properties of material are considered in this paper. The dyadic Green’s functions along with fluctuational electrodynamics as well as scatter matrix are employed to calculate the heat transfer at the head disk interface. The head is simplified as a nanosphere, while the disk is simplified as a semi-infinite multilayered structures, in which the thickness of all layers is in nanoscale. The results show that the near-field radiative heat transfer between the head and disk in HAMR can exceed the values predicted by the Planck blackbody calculation by a few orders of magnitude. The total power is found to exponentially increase when the distance between the head and disk decreases. [ABSTRACT FROM AUTHOR]

The use of a horizontal arrangement of wall shunts is proposed in this paper as a cost-effective way to reduce the stray losses in power transformers. This paper compares the performance of horizontal wall shunts with the available alternative (vertical shunts). A 3-D finite-element analysis (FEA) is used for the calculation of stray losses in tank walls, and other structural parts. A novel hybrid numerical/analytical method is proposed for the calculation of stray losses inside the magnetic shunts. The proposed method is based on the double Fourier series expansions of the magnetic field distribution at the surface of the shunts, which is determined using 3-D FEA. A 200 MVA power transformer is investigated as a case study where the stray losses are calculated with and without the vertical and horizontal shunts. A parametric FEA is carried out to find the optimal placement of the horizontal shunts on the tank walls. Results show that the proposed horizontal magnetic shunts arrangement are as effective as the conventional vertical shunts in reducing the stray losses while reducing the weight of the shields, therefore providing a cost-effective method for magnetic shielding of the transformer tank walls. [ABSTRACT FROM AUTHOR]

This paper presents work completed in order to investigate the importance of magnetic shunts in transverse flux machines. Two types of transverse flux machines with different configurations were designed and tested in the laboratory. The first type of machine is a transverse flux generator with inner rotor. This machine was designed according to one of the patents. The second type of the machine is a transfer flux generator with double coil. Both types of the generators were designed in such a way so that it was possible to implement magnetic shunts inside the machines. Finite-element method analysis and experimental results showed that transverse flux machines without magnetic shunts had a number of disadvantages compared to those with magnetic shunts. These disadvantages are: higher flux leakage in the stator cores, partial cancelation of flux linkage in the coils, higher cogging torque, and increased torque ripple. This paper showed that magnetic shunts played a significant role in the performance of transverse flux machines. As study showed, magnetic shunts complicate a manufacturing process and increase the weight of the machine. However, power to weight ratio of the machines with magnetic shunts is higher than that of the machines without magnetic shunts. [ABSTRACT FROM AUTHOR]

This paper investigates the temperature-dependent behaviors of critical device parameters in 1 Gb perpendicular magnetic tunnel junction (pMTJ) arrays from 25 °C to 125 °C. Despite the fact that pMTJ (45–50 nm in diameter) attributes are generally degraded at elevated temperatures, this paper suggests that an adequate combination of critical device parameters can be obtained through systematic materials and process engineering, including Hc (1760 Oe at 25 °C versus 750 Oe at 125 °C), $H_{{\mathrm{\scriptscriptstyle OFF}}} (<100 Oe), tunneling magnetoresistance ratio (150% versus 115%), \Delta (71 versus 52), I_{c} (120 versus 97~\mu \text{A}$ ), and $V_{{\mathbf {BD}}}$ (1.55 versus 1.43 V). In addition, pMTJs with two different free layers were comparatively assessed to link pMTJ film properties to the temperature sensitivity of device parameters. [ABSTRACT FROM AUTHOR]

Two-dimensional magnetic recording (TDMR) offers the opportunity to provide areal density (AD) gain, but questions were unanswered as to how the gain is achieved and what can be done to maximize the gain from this new technology. In this paper, we offer some reasons why different investigators might report different AD gain opportunities. We present data collected on a spin stand with two reader heads and processed with a commercially available field programmable gate array TDMR channel. The implications of this paper should provide guidelines on reader geometries, placement, and performance. [ABSTRACT FROM AUTHOR]

Both the electrical conductivity and the magnetic permeability of a measured sample have significant impact on the detected signal in eddy current nondestructive testing. Therefore, the problem of obtaining accurate measurement for the electrical conductivity or magnetic permeability has been of great interest to design and manufacturing engineers. In this paper, the conductivity invariance phenomenon (CIP) is investigated and utilized to detect the magnetic permeability of metals. First, the CIP is introduced and its sensitivity factors are investigated using a finite-element method. An experimental platform is set up based on which the CIP is verified. Finally, a magnetic permeability measurement device is proposed, which separates the coupling impact of the sample’s electrical conductivity and magnetic permeability. The work reported in this paper provides an effective approach to accurately estimate the magnetic permeability of metals without the influence of its conductivity. [ABSTRACT FROM AUTHOR]

This paper presents performance improvements of a double excitation synchronous motor by using a reluctance network (RN). The distinguishing feature of the double excitation principle is to use permanent magnets with high energy, while air-gap flux is flexibly controlled by field windings. Therefore, the first contribution of this paper focuses on maximizing air-gap flux range control. Second, an approach for torque ripple reduction is proposed by directly modifying air-gap flux according to the instantaneous torque profile. The achieved resultant torque stays almost constant for a case study. The validity of the RN method is examined by comparisons with 3-D finite element and experimental results for several machines. [ABSTRACT FROM AUTHOR]

A dynamic nonlinear equivalent magnetic network (NEMN) method for a fault-tolerant permanent magnet Vernier machine is proposed in this paper. The key of this paper is to develop two models for no-load and on-load conditions, respectively, because the flux distribution under the no-load condition is different from that under the on-load condition owing to the modulation effect. The no-load model is built based on the precise air-gap modeling method, while the on-load model is developed based on the simplified air-gap modeling method. Meanwhile, a new circuit transformation method is provided for the on-load model to solve the difficulty of low convergence speed in the iteration process. Moreover, iron saturation and fringing effect are considered in the proposed NEMN models. Then, it is used to predict the air-gap flux density, cogging torque, back-electromotive force, and inductance. Finally, both the finite-element method and experimental tests are used to confirm the accuracy and effectiveness of the proposed models. [ABSTRACT FROM PUBLISHER]

How animals navigate in their cross-continental migration has puzzled scientists for centuries. To date, the mechanism behind this mysterious navigation remains unclear. In this paper, a hypothesis is developed and computer simulations have been performed to investigate long-distance animal navigation. Simulation results show that animals may be able to complete their long-distance navigation by observing a spatial angle included by the geomagnetic field line and a geographic direction, without necessarily knowing any prior landmark information. Our results not only match existing observation reports in detail on the long-distance migration routes of animals, but also are able to explain the conflicting evidence on the role of geomagnetic field in animal navigation. We think our results could help reveal the actual mechanism of animal navigation. This paper also provides a potential solution for global and local area navigation of mankind and machines assisted by artificial sensors. [ABSTRACT FROM AUTHOR]

This paper introduces a possible mechanism to explain the changes in neurons following extremely low frequency magnetic fields (ELF-MFs). The model in this paper contains two parts: the physical part and the bio-trigger part. The first part is an electric current equation, which is a generalization of the Nernst–Plank equation with the exposure of ELF-MF, and the second bio-part is a phenomenological model, which is a simple two-state channel with two steady state open (O) state and closed state (C). The two parts are complementary. The first part is utilized to explain changes about synaptic plasticity following ELF-MF exposure at embryonic and postnatal age. The second part is used to simulate the process of three different types of neurons reported by previous papers. According to the results, the present model is feasible for the simulation process. The concept of ion mobility or permeability is emphasized in this paper in part I, and channel state transition probabilities are paid much attention to in part II. In this paper, the ion mobility or permeability is supposed to have close relationships with ion channel transition probabilities, which connects the two parts of the model together. [ABSTRACT FROM PUBLISHER]

In this paper, we present an improved analytical 3-D magnetic flux leakage (MFL) model of the field due to the occurrence of a surface-breaking defect in a ferromagnetic specimen. This model is based on our recent magnetic dipole model (MDM) of the MFL field, which was derived from the first principles of Maxwell’s equations. The MDM assumes a ferromagnetic specimen with a small defect exposed to a uniform external magnetic field, which is strong enough to saturate the specimen locally and causes uniform magnetization around the defect. Under this assumption, the MFL field can be mathematically described as if it is caused by magnetic charges on the surface of the defect. The magnitude and the sign of these magnetic charges are given by the magnetization vector and the local unit vector normal to the surface of the defect. Our original MDM uses only one parameter to describe the normal vector, and can only be used to analyze simple defect shapes, such as cylinders and cuboids. Our improved model in this paper uses two parameters to describe the normal vector, and can be used to analyze a wider range of defects, such as cones, ellipsoids, and real defect shapes. We illustrate our improved model by comparing its solution to that of the original MDM and validating it with the finite-element method simulations for different defect shapes. Our analysis shows that the improved model gives a good approximation of the MFL fields for a much wider range of defect shapes than the original MDM does. [ABSTRACT FROM PUBLISHER]

Analytic modeling techniques of a double-sided interior permanent-magnet flat linear brushless motor (IPM-FLBM) with slot-phase shift and alternate teeth windings are proposed in this paper. Since the buried-type IPM-FLBM with the slot-phase shift and alternate teeth windings is fairly new compared with conventional linear motors, little research has been previously done in modeling and analysis. The analytic models presented in this paper provide the effective and reliable methods for this new type of linear motor. For this purpose, a simplified magnetic equivalent circuit and superposed winding function are investigated. A variable winding function is newly developed in order to evaluate the inductances of the salient motor with the alternate teeth windings. All analytic models are verified with 3-D finite-element analyses (FEAs) step by step. The steady-state thrust force is modeled using a classical closed-form solution for linear brushless ac motors. The static end-effect and cogging forces for the ripple force evaluation are investigated using FEA. The validities for performance parameters are demonstrated experimentally. [ABSTRACT FROM PUBLISHER]

Arrays of nanosized hollow spheres of Ni were studied using micromagnetic simulation by the Object Oriented Micromagnetic Framework. Before all the results, we will present an analysis of the properties for an individual hollow sphere in order to separate the real effects due to the array. The results in this paper are divided into three parts in order to analyze the magnetic behaviors in the static and dynamic regimes. The first part presents calculations for the magnetic field applied parallel to the plane of the array; specifically, we present the magnetization for equilibrium configurations. The obtained magnetization curves show that decreasing the thickness of the shell decreases the coercive field and it is difficult to obtain magnetic saturation. The values of the coercive field obtained in our work are of the same order as reported in experimental studies in the literature. The magnetic response in our study is dominated by the shape effects and we obtained high values for the reduced remanence, Mr/MS = 0.8 . In the second part of this paper, we have changed the orientation of the magnetic field and calculated hysteresis curves to study the angular dependence of the coercive field and remanence. In thin shells, we have observed how the moments are oriented tangentially to the spherical surface. For the inversion of the magnetic moments we have observed the formation of vortex and onion modes. In the third part of this paper, we present an analysis for the process of magnetization reversal in the dynamic regime. The analysis showed that inversion occurs in the nonhomogeneous configuration. We could see that self-demagnetizing effects are predominant in the magnetic properties of the array. We could also observe that there are two contributions: one due to the shell as an independent object and the other due to the effects of the array. [ABSTRACT FROM PUBLISHER]

The 3-D modeling technique presented in this paper, predicts, with high accuracy, electromagnetic fields and corresponding dynamic effects in conducting regions for rotating machines with slotless windings, e.g., self-supporting windings. The presented modeling approach can be applied to a wide variety of slotless winding configurations, including skewing and/or different winding shapes. It is capable to account for induced eddy currents in the conductive rotor parts, e.g., permanent-magnet (PM) eddy-current losses, albeit not iron, and winding ac losses. The specific focus of this paper is to provide the reader with the complete implementation and assumptions details of such a 3-D semianalytical approach, which allows model validations with relatively short calculation times. This model can be used to improve future design optimizations for machines with 3-D slotless windings. It has been applied, in this paper, to calculate fixed parameter Faulhaber, rhombic, and diamond slotless PM machines to illustrate accuracy and applicability. [ABSTRACT FROM PUBLISHER]

In this paper, a new behavioral modeling approach for magneto-static hysteresis is presented. Many accurate models are currently available, but none of them seems to be able to correctly reproduce all the possible $B$ – $H$ paths with low computational cost. By contrast, the approach proposed in this paper is based on simple functions, which do not require calculus to be involved, thus assuring a very good efficiency in the algorithm. In addition, the proposed method enables initial magnetization curves, symmetric loops, minor loops, normal curves, and reversal curves of any order to be reproduced, as demonstrated through the pertinent results provided in this paper. A model example based on the proposed modeling technique is also introduced and used as inductor core, in order to simulate an $LR$ series circuit. Finally, the model ability to emulate hysteretic inductors is proved by the satisfactory agreement achieved when comparing the measured and simulated results. [ABSTRACT FROM AUTHOR]

This paper describes the numerical and experimental validation of a novel non-contact dc electromagnetic propulsion concept. In the proposed approach, a propulsion coil carrying a dc current is surrounded by a dc transversal multipole field created inside of a launch tube. The interaction between the transversal dc magnetic field and a dc propulsion coil results in the generation of axial (thrust) force with no need of sliding contacts. This paper describes a numerical assessment of the field-current-force interactions based on both analytical calculations and finite elements, and the corresponding validation experiments. The experiments demonstrate the generation of contactless axial (thrust) force in a dc launch coil using a dc transversal multipole field, and provide a benchmark for the model-based prediction of the field-current-force interactions. Partial magnetic shielding of the propulsion coil is used to selectively attenuate the magnetic field experienced by the thrust coil in a way that a net thrust force is achieved. Experimental measurements confirmed that it is indeed possible to generate contact-free thrust force on a dc propulsion coil using a dc multipole magnetic field, and the measured values of thrust force are in good agreement with the corresponding predictions. [ABSTRACT FROM PUBLISHER]

The purpose of this paper is to investigate a novel flux-switching permanent magnet (FSPM) machine that is amenable for high-speed operation. The low-pole topology of high-speed machine is favorable to minimize fundamental frequency requirement. The lowest possible three-phase topology of the FSPM machine, with six stator slots and four rotor poles (6/4), has unacceptably large second-order harmonic distortion in the flux linkage and severe cogging torque in its conventional single-stator–single-rotor form. To resolve these challenges, a novel dual-stator structure is proposed that eliminates the even-order harmonics in the flux linkage. Harmonic distortion and cogging torque are notably reduced in the proposed machine. The principles of operation and design methods are described in this paper. The properties of the proposed dual-stator 6/4 FSPM machine are compared with a conventional 6/4 FSPM machine and a conventional 12/10 FSPM machine for a 5 kW, 15 000 r/min design. Comparison results gathered from 3-D finite-element analysis demonstrate that the proposed dual-stator 6/4 FSPM machine achieves significantly better flux linkage, back EMF, and cogging torque than the conventional 6/4 design and better efficiency than the conventional 12/10 FSPM machine. [ABSTRACT FROM PUBLISHER]

Computer simulations of the magnetizing process have been carried out by applying a numerical model to the theory of magnetization and demagnetization for magnetic materials. The numerical model (written using the Python programming language) is able to calculate the magnetization/demagnetization of the permanent magnet material according to its $B$ – H$ curves. This numerical model is combined with an existing finite-element method (FEM) model in which the result of computations is the approximated potential value in the FEM mesh. The aim of this paper was to develop a tool able to simulate the behavior of an anisotropic sintered permanent magnet during the demagnetization process. The permanent magnet material that has been studied in this paper is sintered Nd–Fe–B and it was modeled taking into account an average misalignment angle related to the magnet easy axis. This model also takes into account different demagnetizing field directions, such as a demagnetizing field perpendicular to the orientation direction, which is often ignored. It is shown that even a demagnetizing field perpendicular to the magnetization direction can produce visible demagnetization effects. A Gaussian distribution of the average misalignment angle in the permanent magnet material is also taken into account as well as its variation. Demag curves have been calculated varying the misalignment angle and the intensity and direction of the external magnetic field. The simulation results are in perfect agreement with the {1}/{\cos \theta} law. The model can be applied in many magnetization and magnetic tuning applications. [ABSTRACT FROM PUBLISHER]

Space charge accumulating in oil-paper insulation structure can distort electric field. Transformer-oil, carrying space charge, might change charge transport behavior due to flow properties. In this article, the effect of oil convection on space charge is analyzed by the upstream finite element method based on vector sum. First, the velocity of transformer-oil is obtained by solving Navier–Stokes equations. It is associated with the migration to determine every upstream finite element. And then, the interpolation equation of space charge in flowing fluid is deduced to investigate the movement. Compared to traditional approaches, the velocity of flow is considered to judge the charge transport direction and to update charge density. To consider the temperature effect, a three-electrode experimental system is constructed to measure ion mobility. Finally, a flat rectangular model and a bent oil-path model are built as examples to study the movement characteristics. It is proven that convection makes a significant contribution to charge transport. [ABSTRACT FROM AUTHOR]

A large circular transmitter (power pad) is often utilized for inductively wireless charging so that the power receiver can position itself freely within the power pad. However, the uneven magnetic field distribution leads to the impedance mismatch and the variable transferred power due to the misalignment between a receiving coil and a relatively large transmitter coil. In this paper, the effects of the turn numbers, trace spacing, and coil size on the uniformity of magnetic field distribution over a planar spiral coil (PSC) are investigated based on an analytical model. Then, the genetic algorithm is used to optimize the trace width and spacing of a ten-turn PSC with the fixed outer and inner diameters, whereas the magnetic field is numerically calculated by HFSS software. The geometrically optimal PSC is obtained with the trace width approximately equal to trace spacing for each turn by minimizing the coefficient of variation (COV) of magnetic field within an effective charging area over the coil. The results showed that the simulated and measured COVs of magnetic field were 0.130 and 0.121, respectively, which are obviously less than that of the uniformly spaced regular coil and show a little less than that of the optimally spaced coil with fixed trace width. Therefore, the trace spacing is a major consideration to achieve the uniform magnetic field, whereas the trace width variation is applied to refine the evenness of field. It is also expected that the proposed GA-based optimization is well applied to design other Txs with conformable shape in inductively WPT systems for stable power delivery regardless of the receiver positions. [ABSTRACT FROM AUTHOR]

Over recent years, there has been a growing interest in the field of energy harvesters and their applications across a wide range of areas. In the context of harvesting ambient stray magnetic energy, a magnetoelectric (ME) transducer based on piezoelectric transduction has attracted most scientific attention. Though the ME transducers based on the electromagnetic (EM) induction mechanism promises are highly efficient and much more easier to be integrated, research on this specific type of ME transducer has been scarcely reported. This paper presents the design, fabrication, and experimental results of a novel EM energy harvester. Unlike other EM harvesters that linearly vibrate, the proposed one operates in a rotatory mode, making use of a specially designed magnet array to convert the horizontal ac magnetic field into a vertical spinning magnetic field, as well as the printing coils to scavenge energy from the rotatory magnetic field. In this paper, the influence of the load, the applied magnetic field, and the magnet’s spatial arrangement are studied analytically, and the experimental results obtained by our fabricated prototype are consistent with the simulation results. The fabricated harvester prototype is able to generate 23.1 \mu \textW under a 2 Oe magnetic field at a resonant frequency of 10 Hz, corresponding to a power density of 14.2~\mu \textW /cm3. Simulation and experimental results show that miniaturizing the harvester (i.e., reducing both the volume of magnet array and the area of printing coils) as well as increasing the coil turns can bring about a higher resonant frequency and a higher power density, which makes the micro-machined EM harvester a better fit for the ubiquitous 60 Hz ambient magnetic energy. [ABSTRACT FROM PUBLISHER]

This paper presents the analysis of a brushless doubly fed reluctance machine (BDFRM) for renewable energy applications with an emphasis on the rotor design. The BDFRM stator includes two sets of windings, i.e., the control winding (CW) and power winding (PW). The PW is connected to the grid, while the CW links the grid by a power converter of fractional rating to regulate the operating speed. This reduces the converter cost, and the brushless configuration enhances the reliability. In this paper, the reluctance rotor of the BDFRM, which is similar to that of a synchronous reluctance machine, is designed and analyzed in order to improve the performance. The influence of the total MMF and its allocation to the two stator windings are also discussed in relation to the machine performance. Finite-element analysis is used for performance simulation. The experimental study validates the proposed design for a small BDFRM. [ABSTRACT FROM PUBLISHER]

The rare-earth permanent magnet (PM) is commonly used to improve the performance of high-speed electrical machines to compensate for their high production costs, while it is very likely that the demand for high-speed machines will increase in the near future as markets for new technologies continue to grow. However, a high-speed machine is required to have high performance and low manufacturing cost, because mass production is needed for these applications. Therefore, in this paper, a high-speed machine using a ferrite PM was designed to significantly decrease the manufacturing costs. To examine the performance of the high-speed machine suggested in this paper, the performance of a high-speed model using a ferrite PM is compared with that of a SmCo PM model. A high-speed machine with a specification of 3 kW and 30 000 r/min is designed and manufactured. The designed model is analyzed using the finite-element method. Finally, the no-load back electromotive force in each model is examined through a back-to-back experiment. [ABSTRACT FROM PUBLISHER]

The ongoing miniaturization trend of electric machines increases the demand for higher rotational speeds to provide a required power level at decreased size. In this paper, new concepts for bearingless machines with ultra-high rotational speeds exceeding 25 million rotations per minute are researched. While the mechanical properties of the employed sub-millimeter-sized spherical steel rotors are documented, insufficient information is available on the electromagnetic characteristics that are crucial for magnetic levitation and acceleration. This paper outlines the relations between the relative permeability and conductivity of the rotor material and the achievable active magnetic bearing force and angular acceleration. Measured results for complete hysteresis curves of different rotor steels are presented. [ABSTRACT FROM PUBLISHER]

This paper investigates a double stator linear rotary permanent magnet motor (DSLRPMM) with orthogonally arrayed PMs. The DSLRPMM, which involves linear and/or rotary movements, is constituted of two stators and a hollow mover. The aim of this paper is to study the electromagnetic features and optimize the design parameters of the motor using a 3-D finite-element method (FEM). The topology and the operating principle are described, and the original design is given. The influences of the main designed parameters on the electromagnetic torque, force, and total losses are also analyzed. The optimal parameters are given and a prototype is built and tested. The experimental results are in agreement with that of the 3-D FEM analysis. [ABSTRACT FROM PUBLISHER]