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In this paper, we develop and examine permanent magnet synchronous motors (PMSMs) by use of both stator and rotor cores made of nanocrystalline magnetic materials (NMMs). We report core loss properties of the PMSM with the NMM under inverter excitation. In addition, we compare core losses of the PMSM with conventional non-oriented (NO) steel sheets under inverter excitation to discuss the core loss characteristics of the NMM motor. In average, under inverter excitation, the reduction ratio in core loss of the PMSM made of NMM is about 60% as compared with the core loss of the PMSM with NO sheets. In particular, the average decrease obtained by using NMM rotor core instead of NO rotor core is about 30%. [ABSTRACT FROM AUTHOR]

This paper presents the detail analysis of the radial force and bending moment responsible for vibration in the stator permanent magnet synchronous motors (PMSMs). The vibration characteristics, especially vibration mode, of stator PMSM are studied. First, the air-gap flux density distribution and radial force density distribution are derived in detail. Then, two types of vibration modes, called pulsating and bending modes, and their reasons as pulsating force and bending moment are analyzed and elaborated which are not analyzed and verified before. In addition, the relationships between these two vibration shapes and pole width, pole number, and slot number are analyzed. To confirm the analysis and theory, the multi-probe mode-included test method of vibration acceleration is used to obtain the vibration mode information of motors, and the experimental results on a 6-pole/36-slot stator PMSM match well with the simulation results. [ABSTRACT FROM AUTHOR]

In this paper, the response surface method (RSM) is exploited in the cooling system design optimization of oil-immersed transformers. To generate the training data for RSM, a 3-D computational fluid dynamic model for the transformer under study is constructed and solved, followed by verification on the solutions. Based on the simulation data, two types of RSMs, i.e., the second-order polynomial method and the Kriging method, are employed to evaluate their performance for this specific problem. The response surface with the best performance is used in the optimization process. The solution is compared with that found by the direct optimization method to showcase the effectiveness of applying RSM to oil-immersed transformer cooling system design. Details of implementation of the studied transformer are also presented. [ABSTRACT FROM AUTHOR]

By introducing the SiC/GaN power devices, the high-frequency switching dc–dc converters are expected to have higher efficiency and lightweight. This paper focuses on the Fe-based amorphous alloy powder (Fe–Si–B–Cr–C based) used in the metal composite bulk magnetic core for high-frequency power inductor and transformer. In terms of eddy-current loss at MHz band or beyond, iron-based metal composites are required to have fine magnetic particles with surface insulation layer. In this paper, the finest amorphous powder with a median diameter of 2.57 $\mu \text{m}$ made by water atomization process was used. In order to fabricate the amorphous powder with surface insulation layer, a surface-modification scheme through the two-step acid solution processing using phosphoric acid and hydrochloric acid was introduced. As a result, the surface-modification scheme enabled to make a single-phase silica thin layer on the surface of the amorphous powder, and the silica thin layer was considered to be derivable from the silicon element in the amorphous (Fe–Si–B–Cr–C based) powder. [ABSTRACT FROM AUTHOR]

This paper is performed to apply superconducting magnetic bearings (SMBs) to a high-speed turbine rotor. First, we analyze the system by using the finite-element method and design the structure whose vibrations are suppressed well. Then, we have made an experimental setup using the theoretical result. The experimental setup consists of two SMBs, a permanent magnet motor and a rotor with many turbine blades. We perform some experiments using this experimental setup in a vacuum chamber. In this paper, we discuss the dynamic characteristics of the spinning rotor with many turbine blades. [ABSTRACT FROM AUTHOR]

In this paper, interlaced magnetic recording (IMR) is generalized with a flexible inter-track interference cancellation (F-ITIC) scheme to enhance the overall areal density capability (ADC) by balancing and mitigating the mutual ITI between neighboring tracks. The IMR showed ADC gain by interlaced recording of aggressive bit density (BD) top and relaxed BD bottom tracks, where asynchronous ITI mitigation was applied to the bottom ones. On the other hand, IMR configuration can be generalized by the selective write width control, such that narrower relaxed BD top tracks are recorded over wider aggressive BD bottom tracks. In this generalized IMR (G-IMR), balanced ITI between interlaced tracks can provide ADC gain over legacy IMR (L-IMR) and customized F-ITIC for both tracks can further increase the gain. Note that the ITI processing scheme for G-IMR should be flexible in order to manage the ITI signals from high BD affecting low BD tracks, or vice versa. To evaluate the performance of G-IMR with the F-ITIC, numerical evaluations are conducted with the micro-pixelated magnetic channel model. The results show that G-IMR provides a favorable tradeoff between both tracks’ BDs and track density associated mutual ITIs, which offers a tangible ADC gain with the ITI cancellation over the L-IMR. [ABSTRACT FROM AUTHOR]

Ultrahigh-speed magnetization switching mechanism is strongly pursued, as it can improve the write performance of the magnetic random access memory (MRAM) and further extend the application area of spintronics. Currently, a well-studied switching mechanism is the spin transfer torque (STT), whose speed, however, is limited by an intrinsic incubation delay. Recently, spin–orbit torque (SOT) was proposed to solve the speed bottleneck of the STT. In this paper, we evaluate the potential of two types of SOT-MRAMs, whose data can be ultrafast written based on the recently discovered field-free SOT mechanisms, respectively. A cross-layer analysis is presented involving device modeling, circuit-level optimization, and architecture-level evaluation. First, the principle of the magnetization switching is analyzed with the macrospin simulation. Then, the optimization strategies at the circuit level are generalized through the SPICE-type simulation. Finally, we build up the memory architecture with the SOT-MRAMs, STT-MRAM, and static RAM. Their read/write performances are evaluated with NVSim software. It is demonstrated that one of the studied SOT-MRAMs shows the promising prospect in the non-volatile memory, especially suitable for high-capacity cache. [ABSTRACT FROM AUTHOR]

The Curie temperature distribution induced from grain size variation in heat-assisted magnetic recording (HAMR) can be alleviated by including the thermally insulating magnetic grain boundaries. In this paper, we present a systematic micromagnetic study on this new type of HAMR media, focusing on the impact to the recording behaviors from the exchange coupled magnetic boundary (shell). It is found that the soft magnetic shell of higher Curie temperature is capable of assisting the switching of FePt grain in both magnetization and transition process. The important implication of the proposed media for practical HAMR recording is that optimal performance now can be accomplished with relaxed recording conditions in both head field intensity and the heating source, eventually enhancing area density capability and the overall HAMR system stability. [ABSTRACT FROM AUTHOR]

High-speed electric machines with permanent magnets are sometimes equipped with a shielding cylinder; a conductive sleeve that is wrapped around the magnets in order to reduce the rotor losses and/or retain the magnets. Despite the every increasing popularity of such high-speed permanent-magnet synchronous machines (PMSMs), there are still a lot of question regarding the effect of the shielding cylinder. Earlier work in literature evaluates how the shielding cylinder’s design affects the machine’s performance. However, that work assumes a sinusoidal current, hence neglects the stator current’s higher time-harmonic orders. Therefore, this paper aims at evaluating how different stator sources affect the way in which the shielding cylinder influences the torque production in high-speed PMSMs. The study is performed using a 2-D analytical subdomain model that accounts for slotting and the eddy current reaction field. Both current and voltage sources are considered. The torque is divided in two components, the classical torque due to interaction between the magnets and the stator currents and the torque due to interaction with the eddy currents in the shielding cylinder. This approach results in a better insight in the machine’s physics. [ABSTRACT FROM AUTHOR]

Current density distribution in electric arcs inside low-voltage circuit breakers (LVCBs) is a crucial parameter for us to understand the complex physical behavior during the arcing process. In this paper, we investigate the inverse problem of reconstructing the current density distribution in arcs by inverting the magnetic field. This paper is focused on the modeling and computational phase for the magnetic inverse problem when linear ferromagnetic regions are considered in the model. To address the ill-posedness of the inverse problem, the standard method of least-squares approximation by Tikhonov regularization is studied, complemented with the generalized cross-validation criterion for regularization parameter selection. Considering the inclusion of a ferromagnetic region, two regularization approaches have been analyzed for the formulation of the currents in splitters and their corresponding magnetic field contribution. Effects of several features on the performance of the regularized solution have been investigated, including the signal-to-noise ratio, the value of permeability of the splitters, and the measurement distance. The numerical tests show the direct accessibility for the 3-D current density distribution with the proposed scheme, providing the accuracy and robustness for the applicability to study the arc behavior in LVCBs. [ABSTRACT FROM AUTHOR]

This paper presents a methodology that allows taking advantage of the geometrical periodicity of electrical machines together with the modeling of rotor motion. It enables by means of the discrete Fourier transform (DFT) to reduce the large-scale system obtained from the finite-element model to several smaller independent subsystems, allowing a shortening of the computational time. Due to DFT properties, the computational time can be more reduced especially when we consider the inter-dependence of the spectral components under either balanced or unbalanced supply condition. In addition, a further reduction is possible in the case of balanced regimes where the distribution of the eventual numerical solution is governed by a limited number of prevailing harmonics. [ABSTRACT FROM AUTHOR]

Cogging torque is due to the interaction between a magnet’s magnetomotive force and a slotted stator or rotor structure. In this paper, a compact equation for cogging torque is presented for surface-mounted permanent magnet motors. This equation has four terms of field interactions involving tangential and radial components of airgap flux density. These four terms are considered as sources of cogging. Variations of these sources with pole embrace are examined. In earlier publications, closed-form expressions for pole embrace corresponding to the minimum cogging were presented considering only radial fields. In this paper, an attempt is made to recognize the influence of tangential fields in cogging. The compact form given here distinctly reflects the significance of both radial and tangential field components. Furthermore, to study the trends of cogging sources with pole number and airgap radius, simplified expressions for harmonic content of field components are derived using the first-order binomial approximation. The analysis on cogging presented in this paper helps in determining search domains in which optimum embrace for minimum cogging can be found when both the radial and tangential field components are considered. [ABSTRACT FROM AUTHOR]

This paper presents a novel flux-modulated type dual-axis motor that has two mechanical inputs/outputs, since it consists of a stator, a permanent magnet rotor, and a modulating rotor. Furthermore, since the dual-axis motor has a function the same as a planetary type magnetic gear, it can transmit torque with arbitrary gear ratio and divide mechanical input/output into two rotors without any mechanical contact. In this paper, first, conventional and proposed flux-modulated type dual-axis motors are optimized and compared using finite-element analysis. Next, the proposed dual-axis motor is prototyped and demonstrates the validity and availability by experiment. [ABSTRACT FROM AUTHOR]

Incipient stator winding fault in permanent magnet synchronous wind generators (PMSWGs) is very difficult to be detected as the fault generated variations in terminal electrical parameters are very weak and chaotic. This paper simulates the incipient stator winding faults at different degree of insulation degradation of one turn in the winding of a PMSWG. Cosimulation method by combining finite element model and external circuits is used. Hilbert–Huang transformation is applied to detect the very early stage fault in interturn insulation by analyzing the stator current. Detection results show that the minimum detectable severity degree of interturn fault in this paper is 0.1488%, which is much better than the best record in the literature. [ABSTRACT FROM AUTHOR]

This paper presents a disk-spacer damper (DSD), a new damper structure, for reducing disk flutter. Three types of DSD structures, which consist of an aluminum disk spacer having grooves embedded with viscoelastic (VE) films, have been developed in this paper. First, we investigated the material properties of the VE film, such as shear modulus and discrete relaxation spectra, and then carried out numerical analysis of the damping effect using the material properties. Further, we measured the damping effect of each DSD structure and confirmed that the proposed DSD reduces the disk flutter amplitude between the (0,1) mode and the (0,4) mode by 20%–30%. [ABSTRACT FROM AUTHOR]

This paper proposes an approach for a 2-D representation of Shannon wavelets for highly reliable fault diagnosis of multiple induction motor defects. Since the wavelet transform is efficient for analyzing non-stationary and non-deterministic vibration signals, this paper utilizes wavelet coefficients deduced from the Shannon mother wavelet function with varying dilation and translation parameters to create 2-D gray-level images. Using the resulting images and their associated texture characteristics, this paper extracts features by generating global neighborhood structure maps, which are used to extract global image features. The texture features are then used as inputs in one-against-all multi-class support vector machines to identify faults in the induction machine. To evaluate the performance of the proposed approach, it is compared with five conventional state-of-the-art algorithms in terms of classification accuracy. In addition, this paper explores the robustness of the proposed approach in noisy environments by adding white Gaussian noise to the acquired vibration signals. The experimental results indicate that the proposed approach outperforms conventional algorithms in terms of the classification accuracy. Moreover, the proposed approach achieves higher classification accuracy, even in noisy environments. [ABSTRACT FROM PUBLISHER]

Electromagnetic tracking systems are used extensively in biomedical devices, gaming consoles, and animation because they are inexpensive and do not require line of sight. However, the measurement range is limited by the amplitude of the induced voltage in the sensing coil. The induced voltage is a function of the transmitter parameters such as the coil dimensions, signal power, and frequency. The transmitted power is typically restricted by the physical constraints in the application. This paper develops an algorithm to optimize the dimensions of the transmitting coil for maximum induced voltage. The proposed method is suitable for a transmitter consisting of three concentric orthogonal transmitting coils of the type commonly used in six-degree-of-freedom localization. The simulation and experimental results are presented, which demonstrate the efficacy of the proposed method. [ABSTRACT FROM PUBLISHER]

This paper deals with an analytical model of the virtual air gap (VAG) function in order to define design rules when this technique is used inside complex devices. The establishment of those design rules constitutes the main originality of the developments presented in this paper, which are about a single-phase magnetic core. It is based on the definition of a nonlinear reluctance network that takes simultaneously into account the effects of dc and ac magnetic flux components in the disturbed area that contains the VAG. The results are validated using a finite-element analysis and experimentally. [ABSTRACT FROM AUTHOR]

Skin depth is an important parameter that quantifies depth of inspection of eddy current (EC) nondestructive testing. The formula which states that the skin depth is inversely proportional to the square root of the product of frequency, permeability, and conductivity has been widely used for calculating skin depth for many decades. It has been noticed that the true skin depth is less than that obtained by the formula when the EC is excited by the ac current in a pancake coil. In-depth and convincible explanation of this discrepancy has not been published. This paper studies this problem by finite-element analysis and concludes that the difference is due to two reasons. One is that the EC associated with pancake coil diffuses with increasing depth, whereas there is no diffusion effect of EC associated with uniform plane field which is the assumption of the conventional formula. The other reason is that the ECs induced by wire segments symmetric about the coil axis cancel each other and the cancellation becomes more severe with increasing depth due to the diffusion of EC. This paper also investigates the influence of each of coil parameters on skin depth. Then, a new formula for estimating skin depth is proposed. [ABSTRACT FROM AUTHOR]

In this paper, a new breast cancer detection method is presented that combines thermography and high-frequency excitation techniques. The proposed method uses distribution and variation of the temperature on the breast surface to estimate the location and size of a malignant tissue (a cancerous tumor). The idea of this paper stems from the analysis of the radio frequency (RF) radiation effects on the human body. In this paper, a description of RF effects on the human body and simulation results are provided. To validate the proposed method, a multilayer 3-D breast model is simulated. First, breast tissue is excited with different types of RF antennas, which is followed with an electromagnetic analysis. Next, the heat transfer equation is applied for thermal analysis to estimate the distribution of surface temperature. Simulation results show that both the temperature and the specific absorption rate increase as the tumor becomes bigger or closer to the surface. Finally, thermal responses of multiple tumors are employed to estimate breast cancer existence. [ABSTRACT FROM AUTHOR]

Linear antenna arrays consisting of dipole antennas find wide applications in wireless communication systems. Typically, arrangements with uniform spacing between the array elements are applied to gain highly directive radiation patterns while controlling the radiation intensity in the side lobes. To describe such arrangements, the so-called pattern multiplication (PM) technique is frequently applied, which inherently neglects the inter-element coupling. In this paper, an antenna array arrangement with non-uniformly spacing between the array elements is synthesized in the multi-objective sense. Therefore, the PM technique is deficient. Hence, numerical techniques have to be applied to compute the electromagnetic field during the optimization process. Due to its simplicity and the consequently reduced computational costs, the partial element equivalent circuit method is applied within the field computation process. The optimization relies on a stochastic particle swarm optimization strategy, namely the firefly algorithm. In this paper, an extended version of the general algorithm with additional hierarchical clustering is applied. Special attention is drawn to the development of a suitable objective function. [ABSTRACT FROM AUTHOR]

A method of getting the more accurate equivalent core length through 3-D electromagnetic finite element method (FEM) (3-D FEM) is presented in this paper. It is a matter of course that 2-D FEM is mostly used to evaluate the rotating machine performance instead of 3-D FEM. It takes 106 times longer to complete 3-D FEM than to complete 2-D FEM according to the simulation data in this paper. The motor has the radial air-cooling ducts in the stator. The use of radial air-cooling ducts has an effect on the electrical performance of its machine due to the fringing effect between ducts. The way to consider that effect is that the actual core length has to be replaced with the equivalent core length to reflect the magnetic circuit of 2-D perspective. However, there is 12% error of the root mean square no-load voltage between 2-D and 3-D FEM in 16 MVA salient pole synchronous motor. The cause of the error is the miscalculated equivalent core length in 2-D FEM. The purpose of this paper is to study the cause of the error through 3-D FEM to get the more accurate equivalent core length in 2-D FEM. Finally, Generator open circuit characteristic test is also carried out to verify the no-load voltage of 2-D and 3-D FEM. [ABSTRACT FROM AUTHOR]

In this paper, an analytical torque ripple model for interior permanent magnet synchronous machine (IPMSM) is introduced at first, which can be used to estimate the torque ripple. Then, the inductance variation due to magnetic saturation is analyzed through experimental investigations, which demonstrates that magnetic saturation has a great influence on the inductances, and hence the torque ripple minimization performance. Thus, this paper proposes an online parameter identification approach to estimate the inductances and incorporates them into the torque ripple minimization. The proposed parameter identification approach can estimate the dq-axis inductances accurately such that it brings significant torque ripple minimization improvement for IPMSMs. Numerical and experimental investigations have been conducted to validate the proposed approach based on a laboratory IPMSM. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hybrid excitation vernier permanent magnet machine (HE-VPM). The characteristics of the proposed machine are: 1) the PMs are embedded in the stator teeth, which is helpful for the heat dissipation; 2) the rotor is salient structure without PMs and windings, which ensures the reliability of high-speed operation; 3) the nonoverlapping concentrated winding shortens the end-connection, and improves the torque density, 4) only half of the stator teeth possess PMs, and the total amount of PMs are decreased; and 5) the dc current are injected to the armature coils, therefore, the exciting field can be adjusted flexibly. In this paper, the electromagnetic performance, including back electromotive force, torque, etc. are analyzed with finite element analysis. The results show that the proposed machine exhibits flexible field adjustment capability, which may be suitable for applications requiring wide speed range operation. Besides, it is found that, compared with the existing pure sinusoidal phase current, higher torque density can be obtained with dc-biased phase current under constant stator copper loss. [ABSTRACT FROM AUTHOR]

Globally, the efficiency of industrial motors is regulated through minimum energy performance standards (MEPS) to reduce energy consumption and CO2 emission. Induction motor, used as a representative industrial motor, has a limit to efficiency improvement as the result of the additional copper loss of the rotor. To replace the induction motor, design of synchronous reluctance motor (SynRM) and permanent magnet assisted synchronous reluctance motor (PMa-SynRM), and the application of a small amount of permanent magnet, is actively studied in the industry. However, it is necessary to develop an ultrapremium efficiency motor beyond the superpremium efficiency to fulfill MEPS, which will be strengthened in the future. Therefore, this paper presents the optimal design method of SynRM by using the finite element method and response surface method to achieve superpremium efficiency. Furthermore, the redefinition of the loading ratio with shape parameters, and the design method of PMa-SynRM, using the loading ratio, is proposed to meet the ultrapremium efficiency. It is an effective design method that can shorten the time and process when designing ultrapremium efficiency PMa-SynRM from the existing SynRM, which is already mass-produced. [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]

Dynamic operational behavior (DOB) of electrical machines can cause effects that are difficult to describe and understand. The short-circuit behavior (SCB) in particular is a dangerous DOB for machine and human. It could destroy the machine itself and cause heavy damage to the power supply unit and mechanical coupling components. Analytical calculation of the SCB is simplified and thus not highly accurate. Therefore, the finite element method simulation of the SCB is an important tool for understanding these effects without the danger of damaging the machine by experiments. In this paper, a suitable field formulation, modeling details, and simulation methods for dynamic analysis of synchronous machines are presented in detail. In particular, the accuracy of 2-D and 3-D transient electromagnetic simulations is analyzed by comparison against the available measurements performed on a chosen testing salient pole synchronous machine under the conditions of three-phase, two-phase, and single-phase short circuit. [ABSTRACT FROM AUTHOR]

Coreless axial flux machines are of interest because of the absence of stator core losses and cogging torque. These machines generally employ concentrated windings. One of the challenges with such a winding is that the torque producing MMF component that corresponds to the fundamental of the magnet excitation is accompanied by substantial asynchronous components. These harmonics cause losses in the rotor core and magnets, which can become significant at high speeds. This paper proposes a new multilayer winding arrangement to eliminate the non-torque producing MMF components. This winding is applied to a 12-coil 16-pole coreless axial flux machine. The efficacy of the winding is established by 3-D finite-element analysis. [ABSTRACT FROM AUTHOR]

In nuclear fusion devices, numerical algorithms to model the plasma behavior and all of the other field sources are needed for the control system, especially when plasma instabilities are present. The control measures have to be taken in very strict time intervals (real-time problems); therefore, the involved codes have to be very fast. These days, suitable identification procedures are mainly based on information coming from the magnetic measurements, typically in the axisymmetric frame. Unfortunately, the presence of iron materials strongly increases the complexity of the identification, for both the lack of linear behavior and 2-D hypothesis. This paper proposes fast and effective iron modeling useful for practical real-time applications; the iron is modeled by means of an integral approach, whereas an inverse problem that relates the available magnetic measurements with the unknown currents and magnetizations is solved in a fast way by means of modern graphical-processing unit architectures. [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 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]

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]

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]

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]

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]

On behalf of the Publications Committee, I am pleased to present a selection of papers from the 11th edition of the European Magnetic Sensors and Actuators Conference (EMSA 2016), which was held in Torino, Italy, on July 12–15, 2016. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a luminance and color correction scheme for multiview image compression for a 3-DTV system. According to characteristics of luminance and chrominance, we propose a 3-D discrete cosine transform (3-D DCT) for 3-D image compression. Then, a cubic memory-based 3-D DCT is proposed for 3-D image compression in this paper. 3-D display technology has become an important technology lately. TFT-based multiview 3-D display has the advantage of convenient setup, mass production, and a large amount of 3-D content support, making it a popular 3-D display product. However, multiview 3-D signals need huge storage space and wide channel bandwidth, especially when view number is larger than two views. To overcome the obstacles, we propose a 3-D DCT component based on cubic memory to perform 3-D image compression in this paper. The presented architecture reduces a great quantity of memory space and provides efficient 3-D signal storage. [ABSTRACT FROM PUBLISHER]

Magnetic anisotropy is always known to decrease with temperature and so far there has been no work in the literature reporting about any experimental observation of the increment of magnetic anisotropy with temperature in any thin films other than the one reported in our previous papers. In this paper, we demonstrate that gradient-composition sputtering technique is a method to fabricate magnetic thin films having an in-plane magnetic anisotropy increased with temperature. In particular, our composition-graded magnetic thin films of FeCoX (X \(=\) Ta, Zr, Hf, Lu) show an increase of ferromagnetic resonance frequency when the temperature is elevated, which evidently indicates the increase of magnetic anisotropy with temperature. This peculiar behavior is ascribed to the stress-induced origin of the magnetic anisotropy present in the films grown by gradient-composition sputtering in which the stress of the films is increased with temperature. In order to gain a deeper understanding of the mechanism of this unusual thermal behavior, an additional set of composition-graded FeCoTa thin films were fabricated onto different substrates showing that the increase of magnetic anisotropy with temperature is present in all the films regardless of the substrates used. This experimental result unambiguously implies that the increasing of stress with temperature is not only due to the difference between the thermal expansion coefficients between the substrates and the films, but also owing to the intrinsic nature of the composition gradient of the films. [ABSTRACT FROM PUBLISHER]

In this paper, we introduce for the first time the representation of parameterized complex intensity for 3-D magnetic field and apply it to derive migration imaging formulas for rapid interpretation of magnetic vector field data. Two migration transforms are achieved, one is for imaging full-vectorial magnetization intensity, and the other is for the divergence of full-vectorial magnetization intensity, named the equivalent magnetic charge intensity in this paper. They are obtained by the downward continuation of well-behaved analytical functions and are expected to be robust to noise in the observed data. Unlike most of the existing approaches for interpreting magnetic data, the proposed algorithms make no assumption that there is only induced magnetic field. Another contribution of this paper is that we derive the point spread functions and use them to do the resolution analysis of proposed migration imaging formulas. The performance of the proposed approach is tested using generated numerical data. [ABSTRACT FROM AUTHOR]

This paper presents a method for determination of heat transfer coefficients for finite-element method housing model of medium-voltage switchgear cell. Suggested method is based on the particle swarm optimization algorithm. For that purpose, a real test model of partition wall has been created as well as an equivalent numerical FE model. Since the preciseness of thermal model is dependent on the preciseness of thermal coefficients, the goal of the optimization procedure is to assure even better match between the measured and the FE model calculated temperature values. Because of the fact that the temperature field is a consequence of eddy currents that appear in metal parts of switchgear devices, this paper deals with a coupled problem. Nonlinear calculation of magnetic field is also considered. [ABSTRACT FROM AUTHOR]

Cogging torque is a source of vibration and noise in PM machines. Its reduction is always sought by electrical machine designers. While its study, in radial-flux PM machines, can often be done using 2-D finite element analysis (FEA), 3-D FEA is always required when it comes to its study in axial-flux PM machines (AFPM). AFPM machines have an inherent 3-D electromagnetic structure. There is a rich literature concerning the study of cogging torque in AFPM machines. Indeed, most of the authors use 3-D FEA for its study. However, 3-D FEA is time consuming and always requires expertise to be done correctly. The goal of this paper is to show that alternative techniques, to study cogging torque in AFPM machines, do exist. It is shown that the analytical approach, used in this paper, can be as efficient as the 3-D FEA while saving a huge amount of time and necessitating less initial expertise. [ABSTRACT FROM AUTHOR]

This paper proposes a new design of SPOKE-type PM brushless direct current (BLDC) motor without using neodymium PM (Nd-PM). The proposed model has an improved output characteristic as it uses the properties of the magnetic flux effect of the SPOKE-type motor with an additional pushing assistant magnet and subassistant magnet in the shape of spoke. In this paper, ferrite PM (Fe-PM) is used instead of Nd-PM. First, the air-gap flux density and backelectromotive force (BEMF) are obtained based on the field model. Second, the analytical expressions of magnet field strength and magnet flux density are obtained in the air gap produced by Fe-PM. The developed analytical model is obtained by solving the magnetic scalar potential. Finally, the air-gap field distribution and BEMF of SPOKE-type motor are analyzed. The analysis works for internal rotor motor topologies. This paper validates results of the analytical model by finite-element analysis for wing-shaped SPOKE-type BLDC motors. [ABSTRACT FROM AUTHOR]

In the design of high-temperature superconductor (HTS)-based electromagnetic devices, some of the major challenges include ac loss reduction, minimization of heat leakage, and reduction of the amount of HTS material used to decrease costs. This paper considers a computer model of HTS-based leads involving a multiphysics scenario that considers the electromagnetic and thermal behavior of the system. This paper attempts to address the requirements mentioned and provides an optimum solution by applying an approach based on multiobjective optimization. The differential evolution technique, a stochastic method, widely known for the ease of use and its ability to handle adequately non-differentiable, non-linear, and multimodal cost functions was used. The proposed framework provides a technique to optimize effectively HTS leads, which not only deals with the non-linear aspect of HTS materials, but also includes a multiphysics environment. [ABSTRACT FROM AUTHOR]

This paper investigates the stray magnetic and electric fields of a multifunctional power converter operation while connected to a system involving an induction motor. The impacts of the switching techniques on the radiated fields of the converter were studied for the purpose of electromagnetic interference (EMI) evaluation and fault detection. This was achieved through the inspection of the magnetic and electric fields. Two of the most commonly used switching techniques were implemented through a hardware-in-the-loop system studied in terms of the stray. Various fault and failure conditions were applied to the converter to monitor the converter condition through the stray field observations. A coil and a rod antenna were connected to an EMI receiver to capture the fields. The fields were employed in further analyses. The harmonics and interharmonics of the stray fields were studied in detail for system monitoring purposes. The importance of this paper is to enable the evaluation of the optimum switching pattern for lower EMI field levels from the converter and for condition monitoring and fault diagnosis purposes. [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]

Zeroth mode of vibration is investigated in low-speed high-torque surface-mounted permanent magnet (PM) machines with non-overlapping concentrated windings. Magnetic field distribution in the air gap is computed using time-stepping finite-element analysis, and Maxwell stress tensor is then employed to calculate the radial force density. Based on the time variation of the mean value of the radial force density spatial distribution, the zeroth-order radial forces are studied. Simple structural equations are used to compare the stator deformations for the machines under investigation. Contribution of the zeroth mode to produce vibration is analyzed and compared with the lowest non-zero mode. The influence of pole and slot combinations and the effect of rectifier load are discussed. This paper is carried out to investigate whether or not the zeroth-order radial forces can be of importance in the presented surface-mounted PM machines that are not connected to pulsewidth modulation (PWM) converters. [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]