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In this paper, we carry out a detailed investigation of a recently discovered effect of the increase in the ferromagnetic resonance (FMR) amplitude for cobalt–palladium layered films in the presence of hydrogen gas (H2). We find that this effect is not correlated with the FMR peak shift in the presence of H2 found previously. This follows from observation of a vanishing shift but a change in the amplitude of 69.5% for a sample having a 70 nm thick cobalt layer studied in this paper. The change in amplitude is found to be mainly due to the narrowing of the FMR linewidth, which has its origin in a change in the damping parameter $\alpha $. The increase in the amplitude allows us to measure H2 concentration in nitrogen as a carrier gas in a very broad range—from 0.05% to 70% with sensitivity higher than in our previous papers. [ABSTRACT FROM AUTHOR]

The split ratio, i.e., the ratio of rotor outer diameter to stator outer diameter, is one of the most vital design parameters for permanent-magnet (PM) machines due to its significant impact on the machine torque or power density. However, it has been optimized analytically in the existing papers with due account only for the stator copper loss, which is reasonable for low-to-medium speed PM machines. For high-speed PM machines (HSPMMs), the negligence of stator iron loss and the mechanical stress on the rotor will lead to a deviation of optimal split ratio and actual torque capability. In this paper, the optimal split ratio of HSPMM is investigated analytically with the consideration of stator iron loss as well as the mechanical stress on the rotor. The influence of air-gap length and rotor pole pairs on the optimal split ratio is elaborated. Both the analytical and finite-element analysis reveal that the optimal split ratio for HSPMM will be significantly reduced, when stator iron loss and mechanical constraints are taken into account. [ABSTRACT FROM AUTHOR]

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

The development of a thin and broadband microwave absorber using the microwave absorbing material (MAM) alone is a very challenging task for the researchers and industries. Therefore, a technique for developing a novel hybrid microwave absorbing coating (MAC) using particle-size-controlled hard–soft ferrites with optimized compositions is described and experimentally validated. The novelty of this paper is the possibility of enhancing and tuning the reflection loss (RL) properties of traditional MAMs by simply adjusting their particle size. The main target of this paper is to obtain wideband absorption corresponding to RL ≤ −10 dB and a lower coating thickness (≤ 2 mm). First, ferrite nanoparticles are synthesized and subsequently grown into distinct shapes and sizes by giving judicious heat treatment using a “bottom up” nanofabrication approach. Furthermore, these distinctly shaped and sized particles, i.e., spherical and flaky (20–30 nm), hexagonal (80–100 nm), and pyramidal (200–250 nm), are blended with one another in different proportions (1:1:1, 2:1:1, 1:2:1, and 1:1:2). An extensive morphological and electromagnetic (EM) characterization is carried out. An efficient theoretical and empirical model is used to investigate the EM properties of the heterogeneous MAC with respect to frequency and particle size. A fabricated MAC possesses an RL of −33.5 dB at 10.8 GHz with −10 dB absorption bandwidth of 4.2 GHz (covering the entire X-band region). Moreover, the ferrite layer coating thickness is only 2 mm. A good correlation between theoretical and measured results demonstrates the potential of the adopted approach for various practical EM applications. [ABSTRACT FROM AUTHOR]

A novel hybrid-flux permanent-magnet (PM) generator, which has both axial flux and radial flux, is proposed. An axial-flux PM generator is designed by a reluctance network method and the 3-D finite element method. Using these results, this paper proposes a radial-flux and hybrid-flux machine, whose main dimensions are chosen to the same values as a commercialized one. The proposed hybrid-flux machine has the largest output power per volume. The power density of the proposed generator is 9.4 times larger than that of the commercialized one. The efficiencies of the proposed hybrid generator and a radial generator are same as each other, and are larger than those of an axial and the commercialized generators. [ABSTRACT FROM AUTHOR]

Topology optimization techniques are very promising methods, because they allow one to obtain an initial conceptual structure starting with minimal information on the design object. This paper proposes a novel topology optimization method that takes into account an asymmetrical rotor structure. The phase angle of stator current is not considered in the topology optimization process, thanks to an asymmetrical rotor. This paper designs the rotor topology of a permanent magnet synchronous generator. The obtained rotors have several topologies by considering permanent magnets with different magnetized directions, and have a better performance than that of Prius generator. [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]

Coreless axial flux permanent magnet (AFPM) machines are attracting increasing attention due to their compact structure and high torque density. The torque to weight ratio can be further enhanced by the use of alternate conductor materials, such as carbon nanotube (CNT), or aluminum windings in place of the copper material coils. This paper proposes a coreless AFPM synchronous motor with CNT windings. Analytical equations are developed to allow a systematic comparison of machine designs with different conductor materials. The performance of machine designs with different coil materials, namely, copper, aluminum, and CNT, is evaluated and compared. The calculations are also backed by 3-D finite-element analysis. [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 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]

Through numerical simulations and calibrated experiments, the aim of the work presented in this paper is placed on the development of a polarity changeable magnetizing platform for a rotary magnetic encoder using a permanent magnet and thin silicon steel plate. Parameter studies are conducted via finite-element analyses to obtain optimized geometric design parameters for the magnetizer, leading to desirable magnetic flux density and effective magnetized patterns on the magnetic media. [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]

This paper proposes a meshless method based on the weighted least square method for electrohydrodynamic problems. In this paper, the behavior of a water droplet in a uniform electric field is calculated by this method. The effectiveness of this analysis method is verified through comparison between the analyzed result and theoretical result of the electric potential around the droplet. [ABSTRACT FROM PUBLISHER]

This paper addresses the measurement and calculation of unbalanced magnetic pull (UMP) in a wound rotor induction machine. A new rig for measuring UMP is presented. To our knowledge, this type of rig has not been tested before. This paper details the force calculation method and a method for splitting the UMP and torque. Wound rotor induction machines are now popular as generators in wind turbines. It is important to maintain good operation and low bearing wear, and the UMP in these machines is higher than that of the cage-rotor equivalent because the cage damps the UMP. There is little literature on the UMP in a wound rotor machine. [ABSTRACT FROM AUTHOR]

Magnetic flux leakage (MFL) response predicting is important for defect estimation. This paper first proposes a concept of basic signal by discovering the combination property of the MFL response. The basic signal can be used to predict the MFL response conveniently by a basic signal combination method (BSCM), which is also innovatively put forward in this paper. In this method, the basic signal is calculated in advance, and the MFL response can be calculated by several transformation and combination operations. Both the simulation and experimental results demonstrate the feasibility of BSCM. Compared with other traditional methods (magnetic dipole method and finite-element method), BSCM shows a good performance on both the computational speed and accuracy. [ABSTRACT FROM AUTHOR]

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

In this paper, rotor inter-turn faults in salient-pole synchronous machines are investigated using finite-element analysis. The machine under study is a 22 MVA eight-pole hydropower generator with fractional-slot windings. Simulated faulty cases include 1, 2, 5, 10, and 20 short-circuited turns (out of 58 turns) in one rotor pole. In the electromagnetic analysis, the effect of faults on airgap flux density and radial forces is studied. Furthermore, this paper investigates online detection of inter-turn faults using spectral analysis of stator voltage or current is studied. The amplitude of fault-related harmonics is investigated at various fault severities, as well as at no-load and full-load operations. This paper also discusses the effects of damper bars, an influence of parallel circuits in the stator windings, and influence of the pole pair number. In addition, a comparison between fault-related harmonics in the case of dynamic eccentricity and rotor inter-turn faults is presented. [ABSTRACT FROM AUTHOR]

This paper proposes the multi-material topology optimization for the simultaneous design of segmented permanent magnet (PM) arrays, coil, and iron materials in magnetic actuators. Specifically, the proposed approach can find the optimal layout and shape of PM, coil, and iron materials, as well as the optimal border and magnetization direction of segmented PM arrays. For designing the layout and shape of actuator components, the discrete material optimization-type material interpolation scheme is employed in this paper. To attain the design of segmented PM arrays, an orientation design variable in Cartesian coordinate is utilized with the penalization scheme for the discrete PM magnetization directions. To validate the effectiveness of the proposed actuator design approach, two numerical examples are presented. In the examples, the actuator components (i.e., segmented PM arrays, coil winding, and back iron) are designed aiming for maximizing the magnetic force magnitude acting on the actuator plunger. [ABSTRACT FROM AUTHOR]

Although cogging torque in magnetic gears (MGs) has been studied, the additional degree of freedom inherent to MGs makes it unclear exactly what is defined as the cogging torque of a MG. Although MGs generally have relatively smooth torque transfer characteristics, this paper reveals that when the gear is used in an up-speed configuration, cogging effects may be amplified under startup conditions. This paper distinguishes between two kinds of cogging torque in MGs, termed the synchronous cogging torque and the true cogging torque. Calculation of the true cogging torque is more difficult than the synchronous cogging torque, but an approximation to the true cogging torque can be obtained using the synchronous cogging torque. The theory is verified experimentally and supported further by results from dynamic simulations. The impact on magnetically geared machines is also considered. [ABSTRACT FROM AUTHOR]

This paper presents an approach to obtain high torque density in induction motor (IM) design by optimizing the search algorithms and processes. Optimal design of electrical machines has many sub-optimal peaks and requires significant computation time. To solve this problem, this paper proposes a new cost pattern value method (CPVM) for local search algorithms employed in optimal design. The CPVM concept is an intelligent strategy that digitizes the gradient over the searching region by sharing information between neighboring points. When the algorithm converges quickly to local optimum by a normalized weight method, it provides a mechanism to escape from that region. The validity of the proposed approach was evaluated using a benchmark function, and it was applied to optimal design of a 260 kW IM to maximize torque production based on a finite-element analysis. For better accuracy, we employ slip-frequency analysis compatible with vector control for an IM numerical analysis. [ABSTRACT FROM AUTHOR]

The aim of this paper is to introduce and to study the performance of some multiscale finite-element formulations for the eddy current problem in laminated iron in two dimensions. The case of the main magnetic flux that is parallel to the laminates and assumed to be perpendicular to the plane of projection is considered. Exact solutions of relevant boundary value problems for eddy currents are presented. Multiscale formulations based on the magnetic vector potential (MVP) and the single component current vector potential and on a mixed formulation of the MVP and the current density are discussed. An approach for a multiscale formulation with the MVP is constructed at the best based on an exact solution. The associated weak form of the multiscale finite-element method (MSFEM) is presented. Similar to the MVP, multiscale formulations for the single component current vector potential and for a mixed formulation with the MVP and the current density are studied. This paper does not present a mathematical analysis of the MSFEM for eddy currents in laminates. The performance of the MSFEM is studied by numerous numerical experiments of different examples. This paper covers the topics exact integration versus averaging of coefficients, stability of the MSFEM in a particular case, p-refinement of micro-shape functions and standard finite-element polynomials and edge effect. Simulations show the capability of MSFEM to approximate eddy currents in iron laminates efficiently and accurately. The simulations shall also provide a collection of numerical examples to evaluate other multiscale or homogenization methods. [ABSTRACT FROM AUTHOR]

Space charge distribution is a valuable indicator of ion flow field and is widely utilized to assess electromagnetic environment for transmission line. The finite-element method (FEM) is widely used to solve this problem. However, Kaptzov assumption in FEM assumes that onset voltage is unchangeable after corona occurs, which does not tally with the actual situation. This paper adopted the finite-element iteration method (FEIM), which uses empirical formula instead of assumptions to calculate the charge density. The surface field intensity is not constant in the empirical formula because the empirical formula takes the effects of space charge on surface field into consideration. So this is more consistent with actual situation. In order to verify the accuracy of the algorithm, sound pulse method is applied to measure the charge density around the conductor in the laboratory. Simulation results show that the charge density obtained in this paper agrees with the data in the experiment, which verifies the validity of the empirical formula for calculation of space charge density. Compared with a method considering Kaptzov assumption, FEIM is closer to the experiment in area around conductor line and near the ground. This indicates that empirical formula in FEIM is more effective than Kaptzov assumption in these two domains. [ABSTRACT FROM AUTHOR]

The high stability of the dual-excited synchronous generator (DESG) can enhance the reliability of power supply for critical users. Based on the traditional synchronous generator (TSG), a DESG with two sets of symmetrical field windings on the rotor is presented in this paper. The rotor slots are spaced equally over the whole rotor surface of DESG, which is different from the structure of TSG. Such structures of DESG are expected to enhance the reliability and give the electromagnetic performances, such as air-gap flux density and electromotive force (emf) that are close to those of TSG. For this purpose the relationship between the excitation magnetomotive forces (mmf) of the single- and dual-axis excited DESG is investigated. The mmf with a different rotor pitch is calculated by the finite-element simulation, and the simulation results agree with those by the theoretical derivation. The excitation air-gap flux density, emf, and the magnetic saturation in stator and rotor cores are calculated under different excitation modes, and the results are compared with those of TSG. In order to validate the simulation results, the emf of 10 kW DESG model machine is measured under different excitation modes. This paper provides the theoretical basis for the design and manufacture of large DESGs. [ABSTRACT FROM AUTHOR]

In this paper, the characteristics analysis of the surface-mounted permanent-magnet synchronous motor is carried out using the method of reflecting the axial leakage magnetic flux into the 2-D finite-element analysis (2-D FEA), and the result is discussed. For the method of projecting the axial leakage flux on the 2-D plane, the permeance coefficient was introduced. By using the proposed method, the parameters such as d- and q-axes inductance and linkage flux for d- and q-axes equivalent circuit analysis were calculated, and the characteristics analysis was performed. In order to verify the effectiveness of the proposed 2-D FEA, a speed versus torque experiment was performed and compared with the analysis results. [ABSTRACT FROM AUTHOR]

Accurate and simple magnetic material behavior law is necessary to correctly model complete electromagnetic systems. In this paper, a new formulation based on the scalar quasi-static hysteresis Preisach model extended to dynamic behavior using fractional derivation dynamic contribution is proposed. The fractional contribution is solved using convolution which highly reduces the numerical issues. The order of the fractional derivation provides a new degree of freedom and allows to correctly obtain simulation results on a very large frequency bandwidth. By using such formulation, space discretization techniques (finite differences, finite elements) are avoided which are highly space and time consuming while keeping the global simulation results precise. The numerical implementation of the problem and some experimental validations are shown in this paper. [ABSTRACT FROM AUTHOR]

In this paper, the air-gap flux density components in the eccentric surface-mounted phase modulation (SPM) machines are predicted analytically. In the provided model, the slotting effects of the armature are taken into account. In the modeling process, conformal transformations (CTs) are employed to obtain an equivalent concentric slotless machine for the eccentric slotted PM machine. To satisfy the condition of using CTs, i.e., having a Laplace equation, the PMs are replaced with an equivalent current sheet at the surface of the rotor. The approach of finding this current sheet is approved by the basis of the electromagnetic theory. One of the contributions of this paper is that the provided model is capable of modeling the eccentric SPM machines with any PM magnetization pattern by means of CTs. Substituting the predicted air-gap flux density components in the Maxwell stress tensor, the machine unbalanced magnetic force and its cogging torque are computed. Finally, the accuracy of the obtained results is evaluated by means of finite-element analysis. [ABSTRACT FROM PUBLISHER]

A variable inductor consists of a magnetic core, primary dc windings, and secondary ac windings. The effective inductance of the secondary ac winding can be controlled by the primary dc current because of its nonlinear magnetic characteristic. Hence, variable inductors can be applied as a reactive power compensator for voltage stabilization in electric power systems, and have desirable features such as a simple and robust structure, low cost, and high reliability. In a previous paper, a concentric-winding-type three-phase variable inductor with a 2-D structure has been proposed. It was demonstrated that the 2-D variable inductor has good controllability and a low distortion current. To further increase productivity and reduce costs, this paper presents a novel concentric-winding-type three-phase variable inductor with a 3-D structure. It is demonstrated that the leakage flux of the proposed 3-D variable inductor is reduced by more than 30%. Furthermore, a 6.6 kV–100 kVA 3-D variable inductor is designed and compared to its 2-D counterpart. It is proved that eddy current loss, which is induced within an oil-immersed self-cooled tank because of leakage flux from the variable inductor, can be reduced to one-third of that of the 2-D variable inductor. [ABSTRACT FROM AUTHOR]

We propose a new high performance magnetometer using a single magneto-impedance (MI) sensor with a peak-to-peak voltage detector by synchronized switching (shortened: Pk-pk VD-type MI magnetometer), which is aimed to measure an extremely weak magnetic field ranging from nT ( 10^-9 T) to pT ( 10^-12 T), based upon the conventional MI magnetometer, which is used in the electronic compass. In order to enhance sensitivity and reduce noise, the Pk-pk VD-type MI magnetometer detects both the positive peak and the negative peak in induced voltage waveform of pickup coil. In this paper, for demonstrating the performances of the Pk-pk VD-type MI magnetometer, we investigate the magnetic field sensitivity and the magnetic noise spectral density. We demonstrated that the noise level of the Pk-pk VD-type MI magnetometer is lower than 2 pT/Hz ^1/2 for the frequency range from 1 to 100 Hz, which is much better than the conventional MI magnetometer. We discuss the noise performance of the Pk-pk VD-type MI magnetometer. According to the results obtained in this paper, we expect that this proposed MI magnetometer can be widely used for extremely weak magnetic field detection. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the direct- and quadrature-axis inductances for linear tubular actuators with permanent magnet arrays, highlighting and featuring how they are affected by the end effects. A semi-analytical and an experimental analysis are performed to prove the influence of end effects on self- and mutual inductances. The synchronous parameters, i.e., d - and q -axis inductances of the actuator, are determined using a semi-analytical method and an experimental method. Once the synchronous parameters are all identified, high performance control methods (such as direct force control and vector control) may be implemented. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording (HAMR) is the leading candidate for the next generation of magnetic recording. In HAMR, the thermal profile (with circular contours produced by the near-field transducer) combined with the current writer structures results in recording transitions with noticeable curvature, which causes edge erasure at high linear density and increased transition noise. This transition curvature affects the bit error rate (BER) and is thus important to the model. As the micromagnetic simulations are computationally demanding, in this paper we investigate a fast and simplified write model to capture the transition curvature of HAMR. As the transition curvature causes signal degradation in normally oriented read head array (NHA) having straight gaps, we propose a V-shaped read head array (VHA) by rotating the side readers at appropriate angles to follow the curvature shapes and improve the readback signal. Simulations indicate that, with 2-D signal processing, VHA can provide improved BER performance compared to the NHA in the presence of readback transition curvature on HAMR media. Also this paper indicates that the Curie temperature variance affects BER performance more severely than the anisotropy field variance. [ABSTRACT FROM AUTHOR]

This paper presents the newly proposed heating method named “secondary current heating method” to reduce the iron loss on laminated electrical steel sheet cores for high-efficiency electrical motors. It is well known that the magnetic properties of electrical steel sheets, which are used for electrical motor cores, are deteriorated by the residual stress during manufacturing of the electrical motors, and then the iron loss of the laminated electrical steel sheet cores of the electrical motors increases inevitably. The newly proposed secondary current heating method can improve the magnetic properties on laminated electrical steel sheet cores and reduce the iron loss of them in the very short time in comparison with conventional methods. In this paper, the electromagnetic and heating characteristics of the specimens by the proposed method were confirmed, and then it was applied into the laminated cores to reduce iron loss. [ABSTRACT FROM AUTHOR]

This paper deals with equivalent 2-D finite-element (FE) models of permanent magnet lead screw (PMLS), to accurately predict the thrust force. Due to the helical-shape permanent magnets (PMs), the magnetic fields of PMLS are typically 3-D and non-symmetric. However, the PMLS is approximately symmetric in some cases and an equivalent 2-D axis-symmetric FE model is developed instead of 3-D models. The problem lies in that no evaluation about the accuracy and applicability of the 2-D axis-symmetric FE model was offered in previous literature. In this paper, the 2-D axis-symmetric FE model is derived based on the concept of equivalent current sheets of PMs. The limitations of the existing 2-D axis-symmetric FE model are clarified, and a novel equivalent 2-D torque FE model is then proposed to predict thrust force with the gear ratio when the 2-D axis-symmetric FE model is not appropriate. It is shown that the choice of equivalent 2-D FE model depends on the lead angle of PMLS, 2-D axis-symmetric FE model is applicable in the range of (0°, 15°), and 2-D torque FE model is preferred in the range of (65°, 90°). [ABSTRACT FROM AUTHOR]

On the wheel-rail supported hybrid railway system, the linear synchronous motor (LSM) for very high-speed transit must be a system that can maintain a large air gap, and the maximum vertical displacement must be taken into consideration in designing the LSM. As such, this paper designs two small-scale LSM models that produce equal output power—one with the normal-conducting magnet and the other with the superconducting magnet. In addition, this paper conducts a comparative analysis of the various characteristics by applying the electromagnetic numerical analysis method. Furthermore, this paper manufactures two small-scale LSM prototypes which have the normal-conducting magnet and the superconducting magnet, while also conducting a no-load and load test. Through such comparisons, this paper attempts to verify the characteristic values of the two models. [ABSTRACT FROM AUTHOR]

This paper proposes an improved figure-of-eight coil for transcranial magnetic stimulation (TMS) by using the magnetic resonant coupling (MRC) effect, aiming to improve the treatment effect for psychiatric disorders. The proposed MRC-based figure-of-eight coil consists of two reverse-winding resonance coils, which embraces two series-connected source coils, respectively. Different from conventional figure-of-eight coils, the proposed topology can produce the resonant electromagnetic field to accumulate the stimulation energy. In such ways, the improved TMS system can effectively enhance the stimulation focality and depth while significantly reducing the requirement of the power supply, thus improving the safety as well as facilitating the miniaturization and portability. Last, this paper gives the simulated and experimental results to verify the theoretical analysis, which can further illustrate the feasibility of the proposed MRC-based figure-of-eight coil for TMS systems. [ABSTRACT FROM AUTHOR]

For the purpose of saving energy resources, it is extremely expected to develop highly efficient electric motors. Different types of permanent magnet (PM) arrangement can significantly affect the performance of the motors. Conventionally, the arrangement of the PMs is determined by designer’s experience. This paper focuses on the optimal design of PM arrangement in PM synchronous motors (PMSMs). We present a general pattern of the PM arrangement in PMSM. By varying the parameters of the general pattern, it can produce different types of PM arrangement in the rotor. The employed approach combines the global optimization method with the finite-element method for solving the optimization of the PM structures. Based on the proposed general pattern and optimization methods, the best PM arrangement in the motor can be automatically determined. In order to reduce computing loading, this paper employs the response surface models for reducing the computing time of objective functions. In the end, numerical tests are designed to showcase the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The field calculus for electrical machines (EMs) is realized solving subdomain problems. Most often, the latter are solved using either finite element analysis (FEA) or the semi-analytical solution of a Laplace or Poisson equation obtained by separation of variables. The first option can capture complex geometries but becomes slow for high accuracy, whereas the second is fast but limited to simple periodic geometries and linear or infinite permeable materials. This paper presents the 2-D implementation of the spectral element method (SEM) for the modeling of EMs. The polynomial basis functions used to approximate the solution in each domain are reaching exponential convergence similar to the semi-analytical solution. Moreover, each element can be represented by a non-square shape resulting in the possibility to model complex geometries. Following the results in this paper, significantly fewer degrees of freedom are needed for the SEM to achieve the approximation similar to the FEA, and consequently less memory and computational time are required. [ABSTRACT FROM AUTHOR]

This paper puts forward the design and analysis of an ironless permanent magnet machine for a micro wind power application. The proposed methodology includes comprehensive geometric, magnetic, and electrical dimensioning followed by detailed 2-D finite-element modeling of a synchronous generator. The configuration investigated in this paper shows the generators rotor fixed in the tip of the blades and illustrates the advantages of a large diameter for a microgeneration application. [ABSTRACT FROM AUTHOR]

This paper presents an engineering modeling methodology for magnetostrictive materials based on a simplified piezo-electric governing equation. For verifying the modeling performance, a proof-of-concept non-contact strain sensor utilizing a prototype magnetostrictive (Fe–Ga alloy, Galfenol) strip on a steel plate is used to evaluate sensor performance prediction. Typically, the performance of Galfenol is measured in a compressional load region because it has a higher response. However, in this paper, we are aiming to develop a sensor for tensile stress measurement. To achieve a compression effect from a tension load in the sensing element, a Galfenol strip is aligned perpendicular to a tension bar so that tension in the bar creates compression in the strip via the Poisson effect. The experimental setup in this paper consists of a polycrystalline Galfenol strip bonded in the horizontal direction of a steel dog-bone shaped tension specimen. Permanent magnets are attached at each end of the Galfenol strip to provide an even magnetic bias field through the strip. The magnetic flux through the Galfenol strip is measured with non-contact Hall sensors during the tensile load test. The simulation results agree well with the experiments for the value of $H$ studied. [ABSTRACT FROM AUTHOR]

This paper focuses on the design, performance modeling, and evaluation of probabilistic logic using superparamagnetic nanomagnets for which there exists a strong interplay between deterministic dynamics and intrinsic thermal noise. The switching element in the spin domain is chosen as the giant spin-Hall effect (GSHE) device that operates based on the dipolar coupling phenomenon in a two-magnet system to achieve low-energy ( $\approx ~1.3$ fJ/b) and low-power ( $\approx ~0.5~\mu $ W) switching characteristics. The use of spin currents on the order of a few tens of mA/ $\mu $ m2 in the subcritical regime to operate the GSHE device yields nondeterministic switching behavior with probability of correctness less than 100%. Therefore, the proposed technique allows us to trade off circuit accuracy for tremendous reduction in energy and power dissipation. In this paper, we identify the required dimensions and material parameters of the read–write units to ensure robust magnetic dipolar coupling for reliable operation of the GSHE switch. Then, through Monte Carlo simulations, we evaluate the probabilistic switching behavior of the GSHE switch as a function of the input spin current amplitude and pulsewidth for various orientations of the magnetization vectors. The delay of the GSHE switch is quantified using a probability distribution function owing to the randomness imparted to the dynamics by intrinsic thermal noise of the nanomagnets. The relationship between the probability of correctness and the energy dissipation of the GSHE switch is quantified. The results are extended to evaluate the performance and circuit error rate of complex logic gates, such as NAND and NOR, constructed using the GSHE switch. It is shown that unlike the probabilistic CMOS (PCMOS) logic, the circuit error rate in the GSHE logic becomes a function of the input vector combination and the prior state of the switch. These nuances are captured in the compact model of the circuit error rate of multiple-input GSHE logic developed in this paper. The performance of the probabilistic GSHE logic is compared with that of PCMOS logic at the 14 nm technology node. Since the noise generation process in PCMOS logic has a limited bandwidth of tens of megahertz and consumes tens of microwatt power, the peripheral circuitry becomes prohibitive. By utilizing the inherent thermal stochasticity, nanomagnets provide a clear advantage to implement probabilistic computing platform targeted toward error-tolerant applications such as those from the image processing and machine learning domains. [ABSTRACT FROM AUTHOR]

Vernier permanent magnet (VPM) machines for direct-drive applications are receiving more and more attention due to its small pulsating torque, high torque density at low rotation speed. This paper proposes a novel VPM machine, which has two stators and a sandwiched rotor. The outer stator is a conventional stator with three-phase windings and semi-closed slots, and the inner stator has an iron core and PMs mounted on the surface of it. The rotor has a consequent-pole structure with Halbach-array PMs. In this paper, the operation principles and the feasible slot-pole combinations of the proposed machine are analyzed. Moreover, to verify the superior performances of the proposed VPM machine, it is compared with a regular VPM machine in terms of back electromotive force, average torque, pulsating torque, power factor, efficiency, and overload capabilities. It shows that the proposed machine has higher torque density, larger efficiency, and lower cogging torque. [ABSTRACT FROM AUTHOR]

This paper presents a non-destructive evaluation study on a radiator with cooling fins as a kind of complex shaped specimen. An eddy current testing method, namely multi-frequency excitation and spectrogram method, was employed to detect a removal of radiator cooling fin. Experimental results brought remarkable signal when a fin was removed. Furthermore, the authors discuss the relation between the fin signal and specimen thickness, and concludes the availability for the estimation of thickness of radiator structures. [ABSTRACT FROM AUTHOR]

In this paper, a changeable winding brushless DC (BLDC) motor for the expansion of the speed region is described. The changeable winding BLDC motor is driven by a large number of phase turns at low speeds and by a reduced number of turns at high speeds. For this reason, the section where the winding changes is very important. Ideally, the time at which the windings are to be converted should be same as the time at which the voltage changes. However, if this timing is not exactly synchronized, a large current is generated in the motor, and the demagnetization of the permanent magnet occurs. In addition, a large torque ripple is produced. In this paper, we describe the demagnetization of the permanent magnet in a fault situation when the windings change, and we suggest a design process to solve this problem. [ABSTRACT FROM AUTHOR]

In practical motors, static eccentricity and dynamic eccentricity (DE) (mixed eccentricity) appear rarely with the developed manufacturing techniques nowadays. Curved eccentricity takes up most of the eccentricity. However, the motor is dynamic eccentric in axial cross section when in curved eccentricity. Eccentricity is bound to cause unbalanced magnetic pull (UMP), whereas the study of dynamic UMP under DE in this paper has rarely been mentioned before. According to relevant past papers, UMP is deemed to be invariable numerically. Dynamic UMP is put forward formally for the first time. In addition, UMP during the starting period is a function with time, relatively larger than the steady-state UMP according to the calculation in this paper, namely, UMP during starting period is of greater significance in motor deflection calculation than that during the steady state. The finite-element software is used to analyze the dynamic UMP accurately. [ABSTRACT FROM PUBLISHER]

Recently, dual-rotor motor (DRM) has emerged as an alternative for an induction motor (IM) or a permanent-magnet (PM) motor for electric vehicle application, due to its better drive performance and better torque density. This paper presents an analytical model for the hybrid IM-PM configuration of DRM. The analytical model can be used to predict induced bar currents, electromagnetic torque generated, and magnetic fields in various regions of the motor. The mentioned calculations are performed under steady-state conditions. The analytical method is developed using the subdomain model approach in 2-D polar coordinates. Appropriate governing equations along with boundary conditions across all the sub-domain regions of the DRM are employed to calculate the magnetic vector potential in all the regions. The developed analytical model has been validated with finite-element analysis for various operating conditions, and high accuracy has been achieved for all the results. [ABSTRACT FROM AUTHOR]

This paper introduces an analytical approach for an effective evaluation of the variation of the magnetic field generated by complex coils due to deformations with respect to the nominal configuration. The coils are described with a set of synthetic design parameters, and the deformations can be described as variations of such parameters. This paper proposes a method to evaluate the derivatives of the magnetic field with respect to the design parameters by splitting them into a magnetic factor and a geometrical factor. A comparison with the classical finite-differences approach is carried out. This paper focuses on the context of sensitivity analysis, but the methodology is quite general and can easily be extended in other fields. [ABSTRACT FROM AUTHOR]

This paper presents a numerical method for calculating the resistance, inductance, and capacitance matrices of transformer windings. Importance of their precise calculation is shown in the simulation of voltage distribution over the windings for a lightning-impulse test. The results obtained in frequency domain analysis are in good agreement with the measurement data. All the parameters are calculated using the self-developed solvers, the theory and the novelty of which are described in this paper. The presented approach allows fast and accurate high-frequency modeling of transformer windings. [ABSTRACT FROM AUTHOR]

Three-phase nonoverlapping stator wound-field synchronous (NSWFS) machines employing salient pole rotors are proposed in this paper. Based on the optimized design, the influence of rotor pole number on the proposed machine is investigated. According to 2-D finite-element analysis (FEA), it is found that the proposed machine shows higher torque density and lower torque ripple compared with the existing NSWFS machines. The operation principles of the proposed machine under different pole numbers are presented and compared in this paper. The FEA-predicted back electromotive force, cogging torque, and static torque of NSWFS machines are validated by experiments made on the prototypes. [ABSTRACT FROM AUTHOR]

In shingled magnetic recording, the multihead multitrack (MHMT) detector can better combat the effect of intertrack interference than the single-head single-track detector. Such a detector, however, has prohibitive implementation complexity. In this paper, we propose to use the reduced-state sequence estimation algorithm to significantly reduce the complexity, and render MHMT practical. A commonly used symmetric two-head two-track channel model is considered in this paper. Well-structured reduced-state trellises are constructed by evaluating the effective symbol pair distances and designing proper set partitioning principles. Different trellis configurations are obtained based on the desired performance/complexity tradeoff. Simulation results show that the MHMT detector can achieve near maximum-likelihood performance with a small fraction of the original number of trellis states. [ABSTRACT FROM AUTHOR]

In this paper, a new thermally stable ionic-liquid (IL)-type lubricant has been developed. Since heat is applied intensively on the surface of magnetic disks in heat-assisted magnetic recording (HAMR) systems, a thermally stable lubricant is expected to prolong the life of HAMR drives. To verify this concept experimentally, the depletion of ultrathin film lubricants was evaluated for IL- and perfluoropolyether (PFPE)-type lubricants by far-field laser irradiation. For PFPE, lubricant depletion decreased with increasing bond ratio, whereas lubricant depletion for IL did not depend on its bond ratio. The lubricant depletion quantities of ILs were small and comparable to that of PFPEs with the highest bond ratio. [ABSTRACT FROM AUTHOR]

This paper deals with modeling and simulation of devices where current-carrying conductors are located close to magnetic bodies. These configurations typically occur in electromechanical energy converters such as in slots of electrical machines. Additional losses due to the inhomogeneous current density distribution (“current” or “field” diffusion) at high excitation frequency are a well-known phenomenon. However, classical approaches reach their limits as soon as field diffusion is influenced by ferromagnetic material with non-linear properties. An accurate but time-consuming computation can be achieved by using time-transient quasi-stationary finite-element analysis (FEA). Current diffusion can be described more efficiently by separating the conductor into parallel filaments, following the partial element equivalent circuit (PEEC) approach. As long as linear material characteristics are prevailing, the problem can, thus, be solved efficiently in the frequency domain. In this paper, a hybrid FEA-PEEC modeling approach is presented, where the magnetization of the ferromagnetic material is represented by equivalent currents obtained by 2-D FEA. It is suitable for complex multi-conductor configurations even including non-linear ferromagnetic material. For the proposed method, the resulting linear system is efficiently solvable in the frequency domain by direct solvers. A numerical example from the field of electric traction motors is presented to emphasize the accuracy and benefit of the proposed method for practical electromagnetic computations. [ABSTRACT FROM AUTHOR]