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This paper presents a line-integral formulation for the computation of the magnetic field in the vicinity of a network of magnetic and conductive wires. The formulation is valid in the time-harmonic case and considers eddy currents. A comparison with the results obtained with the finite-element method confirms the accuracy of the proposed formulation. [ABSTRACT FROM AUTHOR]

The exploration for estimation of eddy-current losses is of great significance to optimize the design of the transformer. This paper provides a more accurate formula to calculate the eddy-current losses in rectangle section of electrical steel by solving Maxwell’s equations rigorously, where the 3-D electromagnetic fields problem can be simplified to the 2-D problem because of the grain-oriented nature of steel sheet. Then an analytical model based on the single-layer trapezium steel sheet is established to validate the formula effectiveness through comparing with 3-D finite-element simulation, and the result shows a good approximation when the slope of trapezium steel is small enough. As for practical transformer core made up of multi-layers trapezium steel sheet, the various parameters of dimension in different layers are determined by geometrical analysis and the formula for power dissipation in wound core is proposed. Finally, the formula describing the eddy-current losses of wound core with the feature of semicircle section is obtained and compared with the experimental values after relevant parameter optimization about a nonlinear ferromagnetic material in the calculation, where the proposed methods are demonstrated to be applicable for engineering. [ABSTRACT FROM AUTHOR]

Recently, the demagnetization has been actively researched to reduce the magnetic field of a warship according to the development of the magnetic detection technology of the magnetic mines. In these studies, it was assumed that the warship was composed of one magnetic material in order to establish an effective deperming protocol. However, since the actual warship was composed of various materials, the magnetic interaction between the materials inevitably occurs during the demagnetization process. Due to the interaction, demagnetization may not be performed well. Therefore, in this paper, the effects of interactions in demagnetization of multiple materials were studied by using the Preisach model, and the optimal protocol was proposed. [ABSTRACT FROM AUTHOR]

The bridge of the interior permanent magnet (IPM) machine can reduce the leakage of the machine, which makes the utilization rate of the permanent magnet (PM) improved. However, the asymmetric saturation in the bridges will cause the asymmetry distribution of the magnetic potential on the rotor surface, which will bring challenges to the accurate calculation of inductances. Excited by the armature current at different initial phase angles, the flux distributions in the bridges are analyzed. Meanwhile, the reason why the asymmetric saturation exists in the bridges is revealed theoretically. Based on the above analysis, the rotor magnetic potential (RMP) model for an IPM machine with the bridges is established and used to calculate the armature reaction magnetic field and inductances of the IPM machine. In this paper, the RMP distribution in the bridges is obtained by considering asymmetric saturation, so the RMP model can reflect the rotor surface magnetic potential distribution more accurately, which is evident from the adjacent degree between the calculation results and the finite-element analysis (FEA) ones. [ABSTRACT FROM AUTHOR]

Magnetostrictive (Co70 Fe30)99.8 (NbC)0.2 sheets in 0.3 mm thickness were prepared successfully by forging, hot rolling, and cold rolling. In this paper, the effect of heat treatment on texture evolution and magnetostriction of the (Co70 Fe30)99.8 (NbC)0.2 sheets was investigated. The strong <110> fiber texture along the rolling direction, which originated from the cold-rolling process was retained in the annealed (Co70 Fe30)99.8 (NbC)0.2 sheets with the annealing temperature ranging from 500 °C to 700 °C. When the annealing temperature increased to 800 °C, the proportion of <100>fiber texture markedly increased, and the magnetostriction increased from 93 to 135 ppm. As the annealing temperature reached higher than 900 °C, a proportion of <100> fiber texture gradually reduced due to the secondary recrystallization. As a result, the magnetostriction of (Co70 Fe30)99.8 (NbC)0.2 sheets decreased. [ABSTRACT FROM AUTHOR]

In this paper, analytical formulas for the electric field generated by currents, charges, and magnetization in conductive, dielectric, and magnetic media are presented in the framework of the partial element equivalent circuit (PEEC) method. Under the quasi-static hypothesis, assuming a Manhattan-type tessellation of the geometries and rectangular basis functions, the electric field is exploited in its contributions due to charges, currents, and magnetization. These different contributions require the computation of different type of integrals which are evaluated analytically. The mathematical derivations and the treatment of the singularities are described in detail. Two numerical examples are presented proving the accuracy of the proposed analytical formulas and their speed-up with respect to the numerical computation. [ABSTRACT FROM AUTHOR]

In the interior permanent magnet synchronous motor (IPMSM) design for the traction motor of fuel cell electric vehicles (FCEVs), it is necessary to analyze the nonlinear characteristics including saturation due to the requirement of a high torque density. The finite element method (FEM) is the most widely used technique for electric machine designs because complicated computations can be taken into account. However, a large amount of analysis over the entire design is a computationally large burden. To address this problem, this paper proposes a fast and accurate analysis method, sequential-stage magnetic equivalent circuit (SSMEC). The proposed method consists of no-load, q-axis circuit analysis, d-axis circuit analysis, and motor characteristic calculation. Because the proposed method can quickly and accurately analyze the complex shapes of an IPMSM, it can be used effectively throughout the entire motor design process. The effectiveness of the proposed SSMEC was verified in comparing with experimental results. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to optimize the design of a dual-structure permanent magnet (PM) machine for the low-speed application. Multi-objective optimization using nondominated sorting genetic algorithm II (NSGA-II) is used to maximize the torque and efficiency while reducing the torque ripple of the machine. The torque, torque ripple, and efficiency of the optimized machine have significant improvement by optimizing the machine parameters within a fixed outer axial and radial length. This optimization process can be used to select the best machine design in different aspects’ requirement. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to describe a new algorithmic method to imitate 3-D geometries of soft magnetic composite materials. This method allows constructing various kinds of geometries for experimenting how certain geometric features affect different electromagnetic properties of the materials. Using the geometry imitations, we demonstrate that in order to explain the nonlinear static magnetic behavior of a certain composite, it is not necessary to assume contacts between the neighboring particles in the material. The contacts may instead be replaced by thin gaps. [ABSTRACT FROM AUTHOR]

There is always uncertainty in industrial manufacturing. These uncertainties have an undesirable impact on the products if deterministic optimization approaches are employed. In order to have products as desired, uncertainties must be quantified in the design process. This paper presents a robust design optimization of an outer rotor surface mounted permanent magnet motor with particular application in the hybrid vehicle using the design for six-sigma methodology. Due to very long computational time of robust optimization, a ten high-dimensional surrogate model of the system using the Box–Behnken response surface methodology (RSM) is integrated with the particle swarm optimization (PSO). This causes a significant improvement in the effectiveness and efficiency of optimization. The results acquired from RSM are verified by their simulation using the finite-element method, and the accuracy of RSM is proved. Finally, the deterministic and robust optimized motors are simulated in mass production using Monte Carlo analysis, and six-sigma quality achievements are demonstrated. [ABSTRACT FROM AUTHOR]

Transmission line method (TLM) has been used in 2-D scalar finite-element (FE) analysis due to its parallelism and constant admittance matrix. In this paper, the TLM is extended for the 3-D nonlinear vector FE problem that is more widely used for electromagnetic apparatus in practice. TLM is specially adapted for tetrahedron edge elements to calculate quasi-static electromagnetic field distribution for eddy current problems, and a dummy scalar gauge is applied to make the reduced magnetic vector FE formulation full-ranked and uniquely solvable by TLM. For each element, the nonlinearity is separated by transmission lines and only local small-scale Newton–Rapson iteration is needed, which is suitable for massive parallelization due to the independence between different elements. The TLM is implemented on a many-core GPU for a nonlinear FE power inductor case study, and the comparison of the results with a commercial FE software shows over 50 times speedup with a relative error of less than 2%. [ABSTRACT FROM AUTHOR]

This paper takes a Halbach permanent magnet linear motor (PMLM) without a core as the research subject; based on the traditional structure of a single-layer PM array, an improved PMLM with an optimized double-layer Halbach PM array is proposed to reduce the harmonic components of the air gap magnetic flux density (AGMFD) for direct-drive applications in the feeding system of the machine tool which need high force capability. The 3-D models of PMLMs with single-layer and double-layer Halbach PM arrays are established by using finite element (FE) software; the air gap magnetic field, the back electromotive force (EMF), and the electromagnetic thrust of the two types of motors are analyzed. The simulated results show that the PMLM with an optimized double-layer Halbach PM array can achieve better performances of the motor and reduce the cost of the PMLM. Finally, the experimental results verify that the proposed double-layer Halbach PMLM is effective and practical. [ABSTRACT FROM AUTHOR]

Magnetic particle imaging (MPI) is a novel tomographic imaging method, which allows determining the distribution of superparamagnetic iron-oxide nanoparticles in three dimensions. So far, various MPI systems have been presented with each one emphasizing different scanner features such as large field of view (FOV) or high resolution. For imaging with both high resolution and a large FOV, the optimization and harmonization of hardware parameters as well as tracer material are key prerequisites. The traveling wave MPI (TWMPI) approach uses an array of electromagnets, which can provide a high magnetic field gradient for a high resolution as well as a mouse-sized FOV at the same time. In combination with the tracer LS-008, which is optimized for the MPI technique, a resolution in the sub-millimeter range can be achieved. In this paper, an optimized scanner is presented based on the TWMPI approach featuring a gradient strength up to almost 10 T/m in an FOV with a length of 45 mm providing a high resolution below 500 microns using the optimized LS-008 tracer. [ABSTRACT FROM AUTHOR]

Huygens metasurface, composed of electric and magnetic dipoles, can fully control the transmission and reflection coefficient in theory. In this paper, a multi-phase hologram utilizing Huygens metasurface is presented in microwave regime. Here, we focus on the achievement of holographic rotation around the origin of Cartesian coordinates and the center of images individually. The spatial rotation operations are realized with calculated phase distribution based on time-shifting operations and rotational invariance of Fourier transform. Our designs expand the route to realize more powerful manipulations of electromagnetic (EM) wave propagation for flexible and continuous control of holographic images. [ABSTRACT FROM AUTHOR]

This paper presents a novel magnetic bearing switched reluctance motor (SRM) (MBSRM) with two degrees of freedom suspension, consisting of an SRM and an active magnetic bearing (AMB). In the proposed MBSRM, three-phase armature windings of the SRM and a biased winding of the AMB are fed together by a modified asymmetric half-bridge converter. The rotational torque in SRM and the biased flux used for producing electromagnetic force in AMB are generated simultaneously when the MBSRM works on the traditional switched reluctance excitation mode. First, the structure and working principle of the MBSRM were introduced. Second, its theoretical formulas of suspending forces were given and validated with the finite element analysis. Third, the proposed half-bridge converter is shown, and currents in the biased winding and three-phase armature windings of MBSRM are obtained by the magnetic field–circuit coupling simulation. Moreover, a prototype is manufactured and the experiment results have proved the feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

This paper proposes an electromagnetic analysis using an analytical method for a permanent magnet synchronous generator (PMSG) in a wave energy converter. To prevent the scattering of the rotor magnet of the PMSG with a wide operating range, bolting to the permanent magnet is required, and the analytical solution is calculated by simplifying it to two analytical models. Based on the electromagnetic theory, the analytical solution of each analytical domain is derived. The electromagnetic parameters are derived from the analytical solution and are calculated using the principle of superposition. The validity of the proposed analytical results is verified by comparing nonlinear 2-D and 3-D finite-element analysis with experimental results. [ABSTRACT FROM AUTHOR]

Power losses in soft magnetic materials can be solidly assessed by the statistical theory of losses (STLs), which provides physical foundation to the concept of loss separation. The theory is, however, limited to the conventional case of symmetric hysteresis loops and cannot be straightforwardly applied for a magnetic core operating under a dc bias. We show, in this paper, that such constraint can be released by combining the STL with a simplified approach to the dynamic Preisach model. This approach leads to the more affordable static Preisach model with largely reduced computation time. In this way, the hysteresis and excess loss components, with and without dc bias, are identified and calculated starting from a minimum set of experimental data. We provide a wide-ranging experimental validation of the theory, which is applied to the behavior of the energy loss versus frequency, measured up to $f = 1$ kHz, in non-oriented and grain-oriented iron-silicon sheets and in iron-cobalt alloys, subject to different polarization bias levels. [ABSTRACT FROM AUTHOR]

This paper investigates acoustic noise when an electric motor is fed with three-phase pulsewidth-modulated (PWM) currents with varying modulation indices. The procedure involves using a data-driven process to create a design space for different geometries of an interior permanent magnet synchronous motor. The motor structures are then analyzed using a finite-element analysis package to extract knowledge related to the sound pressure levels from the PWM excitation. It is demonstrated that sampling the air-gap space at a single time instant, which is a routine procedure in acoustic noise calculations, can result in an inaccurate estimation of the sound pressure levels, especially when the noise source is PWM motivated. Multiple-time sampling over the electrical period is proposed as a better approach for analyzing the sound pressure levels, irrespective of the type of supply current quality. [ABSTRACT FROM AUTHOR]

This paper investigates different spatial filtering techniques used with ON/OFF based topology optimization and compares their performances for optimizing a C-core electromagnetic actuator. The filters’ efficacy in dealing with checkerboard patterns, perforations, and floating material pieces and their impact on the armature force and the topology’s smoothness are evaluated and discussed. [ABSTRACT FROM AUTHOR]

In this paper, a new method for generating high-efficiency vortex beam carrying orbital angular momentum (OAM) mode is proposed based on the miniaturized element frequency selective surfaces (MEFSS) in the microwave region. The unit cell is a class of sub-wavelength periodic structure, which is composed of non-resonant elements with a low profile. A flat metalens is designed to control the wavefront of the propagating electromagnetic waves based on different phase responses of eight kinds of MEFSS unit cells. Under linearly-polarized normal incidence, a vortex beam carrying OAM mode with a topological charge of 1 is excited. The measurement results are in good agreement with the theoretical prediction and full-wave simulation. The proposed method shows great potential applications in generating OAM mode with high efficiency at microwave frequencies. [ABSTRACT FROM AUTHOR]

This paper presents the methodology and validation of high-frequency (HF) transformer simulations, which take into account the frequency dependence of the winding resistances and inductances. The parameters’ frequency dependence is approximated by curve fitting of the values computed by the finite element method (FEM) simulations in the frequency domain. After inverse Fourier transformation into the time domain, the convolution integrals are solved efficiently by the trapezoidal integration rule. The simulation results are validated using measurement data. [ABSTRACT FROM AUTHOR]

A magnetic fluid ring, which can be compared to a liquid O-ring, held at a given place by a magnetic field is used for various applications, such as seals, compressors, dampers, or sensors. The work of this type of system is the result of a number of factors, such as the distribution and magnitude of the magnetic field in the gap, rheological and magnetic properties, physical properties of the surrounding environment (interfacial phenomena) and operating conditions (differential pressure and relative velocity). The research area of this publication is related to the recognition and assessment of how the magnetic fluid properties influence the mechanism of the local loss of continuity for a single liquid ring. This applies to the case when the differential pressure on two sides of the magnetic fluid-free surface exceeds a critical value and a leak channel is formed. Previous studies have shown that the process of equalizing the pressure difference in this type of system is related to pressure jumps. This phenomenon has not been linked to such properties as saturation magnetization, dynamic viscosity or surface tension. This paper takes these factors into account. In addition, the shape of the stage (trapezoid and rectangle) on which the fluid is held and the magnetic field value are considered. The loss of continuity is an important issue and the obtained results allow this problem to be better understood and the magnetic fluid to be chosen for appropriate working conditions, e.g., in the case of multistage seals. The studied phenomenon may also contribute to the development of new types of pressure regulators or sensors. [ABSTRACT FROM AUTHOR]

Microwave-assisted magnetic recording (MAMR) is an advanced magnetic recording scheme that is expected to extend the areal density beyond that achieved by conventional perpendicular magnetic recording (PMR). This is done by introducing a high-frequency (HF) oscillating magnetic field during the writing, reducing the write field from the head needed to switch the grains. Grains with larger anisotropy, greater thermal stability, and reduced grain size can thereby be used in the media. 3-D-MAMR uses this same principle not only to assist the writing but also to select a particular layer in a multi-layer medium stack for writing, thereby realizing 3-D magnetic recording. Optimization of a 3-D-MAMR system is complicated by the large number of variables involved and interactions between the recording layers. It is generally difficult to write on a target layer without some degree of unwanted writing on a different layer in a multi-layer stack. In this paper, we perform an optimization of a 3-D-MAMR media stack using the response-surface methodology (RSM), a method used in the design of experiments (DoEs). This results in a media design in which the signal-to-noise ratio (SNR) performance in the target layer and the number of written errors in the other layer are jointly optimized. [ABSTRACT FROM AUTHOR]

This paper proposes a novel symbol-flipping decoding (SFD) algorithm called decision-symbol reliability-based SFD (DRB-SFD) algorithm for nonbinary low-density parity-check (LDPC) codes aiming to improve the error-rate performances of data storage devices with hard-decision channel outputs, e.g., data storage using NAND flash memory. The proposed algorithm generates the reliability information of decision symbols based on a metric for symbol flipping during iterations instead of soft-decision channel outputs. In addition, it quantizes the reliability information into reliability messages that are exchanged between variable and check nodes. The number of quantization levels is carefully chosen to be the same as the field size of coded symbols, which allows the message exchanges to be performed without the additional signal paths. It is also extensively discussed how to decide parameters in the proposed algorithm in an analytic way. We demonstrate that the proposed algorithm featured with the exchanges of reliability messages provides significant performance improvements over existing SFD algorithms on channels with hard-decision outputs. [ABSTRACT FROM AUTHOR]

This paper reports the design, fabrication, and performance of a novel rotational energy harvester, utilizing multiple magnetic actuators and piezoelectric beams for the maximum performance in a wide range of rotational speeds. The harvester can be used in different rotational applications with low or high rotational speed and produce high output. Thin lead–zirconium–titanate (PZT) piezoelectric beams were fixed on the axis of a nonmoving wheel. One end of the beams was fixed to the center axis of the stationary wheel, while the other end hung free. Small magnets were bonded on each of the piezoelectric beams’ free ends and on a concentric wheel, fixed to a working shaft. As the working shaft drove the dynamic wheel, the magnets on the moving surface attracted the magnets on the piezoelectric beams, causing the beams to be plucked into vibration as the magnets passed by one another. The device was tested at six different rotational speeds from 180 to 500 r/min, with two different layouts, single and double plucking magnets. There will be potentials to increase up to six plucking magnets and four piezoelectric beams in this design for an increased performance. Voltage output versus time graphs were analyzed for each speed and setup. It was determined that increasing the number of plucking magnets and rotational speed was the most effective ways to increase the beam vibration and maximize the energy harvester’s performance. This is the most effective approach to increase the performance of the energy harvester in the applications that require lower speeds. The least effective case was the low speed, single magnet design, where the beam vibrated little and approximately half of the energy harvester’s time was idle time, minimizing the power harvested. [ABSTRACT FROM AUTHOR]

Nanocrystalline Ce–Fe–B based rare earth permanent magnets are prepared by spark plasma sintering (SPS) method using grounded ribbons as raw material. The phase compositions, microstructure, magnetic properties, intergranular magnetic interactions, recoil loops, and corrosion resistance of the magnets are investigated systemically. The relationship among sintering processes, microstructures, and magnetic characteristics are discussed in depth by mainly using transmission electron microscope (TEM) and Physical Property Measurement System (PPMS) techniques. It is demonstrated that the sintering temperature has a significant influence on the average grain size and width of coarse grain areas. The optimized magnetic properties of remanent magnetization $J_{r}= 0.37$ T, coercivity $H_{\mathrm {ci}} = 227$ kA/m, and maximum energy product $(BH)_{\mathrm {max}}= 16$ kJ/m3 are obtained at 650 °C under 50 MPa for 2 min. Their exchanging coupling interactions are quite weak compared with those of the counterpart alloys. The exchanged decoupled of soft magnetic materials and inhomogeneous magnetic anisotropy result in open and steep recoil loops. The electrochemical experiment results display that the corrosion resistance of the magnets is improved by sintering at high temperature. This paper plays a role in guiding the future research and development of nanocrystalline Ce–Fe–B based permanent magnetic materials. [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]

Spintronics, being a burgeoning area of research, aims to incorporate magnetic tunnel junction (MTJ), as a basic storage building block, to various electronic applications. In continuation of many device structure using MTJ such as spin-transfer torque (STT)-MTJ, spin Hall effect (SHE)-MTJ, spin–orbit torque (SOT)-MTJ, domain wall-based MTJ, and complementary polarizer MTJ, this paper presents a differential spin Hall effect (DSHE). The working and operational analysis of the DSHE-based memory element is presented. It provides 50% improved write energy and more than 1.5 times faster read as compared to a single-ended SHE-MTJ. The device structure is well suited for various differential circuit applications, for example, nonvolatile static random access memory (NVSRAM), nonvolatile flip flop (NVFF), magnetic full adder, and nonvolatile differential sense latch, with a fast and energy-efficient operation. In addition, DSHE-MTJ application for NVSRAM (named as DSNVM) is proposed. Performance of DSNVM is compared with the STT+SHE-based NVSRAM (named as SHENVM). DSNVM shows improved performance in terms of area overhead, restoration delay, and energy. DSNVM provides 40% faster restoration and 16.7% lesser energy as compared to SHENVM. Furthermore, a computational investigation for cell stability is depicted using butterfly curve and N-curve methods. Usually, write noise margins deteriorate in NVSRAMs due to the constituent NV cell. However, read as well as write noise margin is improved in DSNVM. [ABSTRACT FROM AUTHOR]

In this paper, the coil array commutation algorithm is used to reduce the coil temperature rise of the magnetic levitation planar motor with moving coils. The coil array commutation algorithm is based on the force/torque-current decoupling model of the planar motor. Considering the gradient distribution of cooling power among the three-phase coils, the maximum temperature rise of the coil array is minimized by adjusting the current weighting coefficients of each coil, while ensuring that the coil array provides the force/torque desired for trajectory movement. The simulation and experimental results confirm that without changing the structure of the cooling system, the proposed current proportion commutation algorithm can reduce the temperature rise of the coil array more effectively than the previous direct force/torque-current decoupling method. The research also indicates that the temperature rise of the coil array can be reduced by the commutation algorithm of the coil array when the cooling power distribution is not uniform. [ABSTRACT FROM AUTHOR]

In this paper, a novel genetic algorithm (GA) that employs species differentiation (SD) is proposed. The GA with SD (GA-SD) improves the convergence speed of the GA through the separation and progress of elite species that are classified by a kernel support vector machine. Furthermore, the GA-SD maintains exploration capability through the progress of inferior species and the gradual transition between species. To verify the effectiveness of the GA-SD, GA-SD was compared with the conventional GA on test functions. Finally, we applied the GA-SD for the optimal design of the wind generator. [ABSTRACT FROM AUTHOR]

A scalable, broadband, and physics-based compact model for on-chip spiral inductors with rectangular outline shape is demonstrated for the first time in this paper. A simple dc inductance model is developed based on the current sheet approximation. The reduction in inductance due to the flow of eddy current in a back metal plate is considered using the method of images. A three-ladder network is shown to be sufficient to accurately model skin effect caused due to the magnetic field setup at high frequencies. Geometry-dependent expression suitable for rectangular cross-sectional metal strips is presented to predict the proximity effect. Physics-based expression for the substrate capacitance is derived. The proposed model is also shown to have a good correlation in the presence of a patterned ground shield. The proposed model is verified across CMOS process parameters that affect the inductor performance, such as metal thickness, substrate resistivity, and substrate thickness. Furthermore, model accuracy is also validated across design parameters such as spiral width, spacing between turns, number of turns, and diameter. The model is shown to have a good agreement with both EM simulations and measurements. [ABSTRACT FROM AUTHOR]

A novel flexible three-axial tactile sensor, which is composed of four interdigital capacitors, is presented in this paper. The operation of the sensor is based on the measurement of a load-induced capacitance change. For the configuration of the electrodes, four sensing electrodes and a public electrode are in the same plane, which is based on the fringing effect of the electric field. There are no floating electrodes which are beneficial to flexibility. The dielectric layer consists of air gap and polydimethylsiloxane (PDMS), and the equivalent dielectric constant of the dielectric layer will be changed when the sensor is under external force, which causes the capacitance change. Different from the existing fringing effect tactile sensor, interdigital electrodes are adopted here to enhance the sensitivity and stability of the sensor. Finite element simulation and experimental results show that there is a great enhancement in sensitivity and stability. [ABSTRACT FROM AUTHOR]

This paper proposes a multiphase modular fault-tolerant permanent-magnet (PM) machine with hybrid single/double-layer fractional-slot concentrated winding (FSCW). Comparisons between the proposed machine and conventional FSCW machines are made to indicate the special characteristics in aspects of armature magnetomotive force harmonic distribution, cogging torque, magnetic isolation ability, and torque capability. Then, influences of specific structural parameters, including the angle between single-layer slot (SLS) and double-layer slot (DLS) and the opening widths of SLS and DLS, on machine performances are investigated, and power density of the machine is improved by selecting the parameters appropriately. In addition, two stator modular design schemes are proposed. The influences of gaps between modules on machine performances, such as torque, losses, inductances, and short-circuit current, are investigated. [ABSTRACT FROM AUTHOR]

This paper presents a novel method to measure the magnetic gradient by an Mz atomic magnetometer using a micro-fabricated shaped rubidium vapor cell. The shaped vapor cell is fabricated by a chemical foaming process. Four micro radio frequency (RF) coils are mounted on the shaped rubidium vapor cell. Magnetic fields at the four points corresponding to the RF coils along the laser beam propagation are obtained by measuring Larmor frequency of the rubidium atoms inside the vapor cell. The magnetic gradients are also acquired with the measured magnetic fields. The measurement is performed in a magnetic shield environment. A dc electrical coil is taken to produce an existed magnetic field for the measurement and the theoretical magnetic field distribution is calculated. It is demonstrated that the measured magnetic fields and magnetic gradients correspond well with the calculated ones. Results show that the absolute error of the magnetic field is less than $0.1~\mu \text{T}$ , the relative error of the magnetic field is below 0.8%, and the relative error of the magnetic gradient is below 5.5%. Results also indicate that the atomic magnetometer has a sensitivity of 5 pT/Hz1/2 from 1 to 2 Hz. The Mz atomic magnetometer is potentially useful for applications requiring gradient field information. [ABSTRACT FROM AUTHOR]

The technology for inductive wireless power transfer (IWPT) by using strongly coupled magnetic resonance has been applied successfully to supply energy to several applications such as biomedical implants, radio frequency identification systems, Internet-of-Things sensors, and battery chargers for personal devices. In order to attain high values of efficiency and reach, the technology requires the employment of coils with high values of quality factor. However, this feature can only be found by using large wire coils. A compact IWPT system composed of printed coils, which typically have low values of quality factor, is proposed in this paper. An evolutionary algorithm is used to optimize the printed coil geometry so that it presents the greatest value of quality factor possible, according to the imposed restrictions. With the aim to improve the system efficiency and reach, the effect of metamaterial surfaces inclusion is investigated. In addition, in order to increase the amount of power processed by the system, a low-cost self-oscillating electronic converter is proposed to power it. [ABSTRACT FROM AUTHOR]

This paper presents the magnetic field analysis for the double layer Halbach array voice coil actuator (VCA). This VCA is composed of a stator and a mover supported by the flexure-based bearings. The mover gets three coils winded on the skeleton. The stator comprises the closed yoke and the double layer Halbach array permanent magnets (PMs). The boundary condition of the quadrangularly surrounded yoke and the aperiodic distribution of the Halbach array PMs complicate the magnetic analysis process. An equivalent VCA structure that has almost identical air-gap flux distribution to the original one is, therefore, proposed. For the equivalent structure, the boundary condition is simple and the Halbach array PMs is periodically distributed, thus the analysis process of air-gap flux density distribution via Fourier analysis is simplified. The equivalence between these two structures is validated by finite-element analysis (FEA). The analytical model is built by adopting Fourier analysis. The results of the FEA and experiments confirm the correctness of the developed model and prove the feasibility of the analytic method with the equivalent structure. [ABSTRACT FROM AUTHOR]

In this paper, the mathematical model of an electricity generator with four static magnets and four dynamic magnets is suggested for the electricity generation. The introduced electricity generator is based on the electricity generator with two static magnets and two dynamic magnets, but it has three main advantages: it has more interactions between the static and dynamic magnets, it generates more electricity, and it generates smoother signals. Electricity generators are compared for the electricity generation. [ABSTRACT FROM AUTHOR]

This paper proposes a fast and efficient method for magnetic signature reduction of underwater vessels. The magnetic signature reduction is required to protect the ferromagnetic vessels from magnetic anomaly detectors and mines. We propose a novel machine learning-based approach for degaussing of the vessel. This method adds a degree of bias to the evaluated coefficients in order to handle inherent multicollinearity issues. The proposed algorithm is efficient in terms of computational efforts, speed, and accuracy. More than 90% of signature reduction is achieved, assuming that the signature predicted is accurate. The proposed method is validated for a simulated model of prototype submarine. [ABSTRACT FROM AUTHOR]

This paper addresses uncertainty quantification of electromagnetic devices determined by the eddy current problem. The multilevel Monte Carlo (MLMC) method is used for the treatment of uncertain parameters while the devices are discretized in space by the finite element method. Both methods yield numerical approximations such that the total error is split into stochastic and spatial contributions. We propose a particular implementation where the spatial error is controlled based on a Richardson extrapolation-based error indicator. The stochastic error, in turn, is efficiently reduced in the MLMC approach by distributing the samples on multiple grids. The method is applied to a toy problem with closed-form solution and to a permanent magnet synchronous machine with uncertainties. The uncertainties under consideration are related to the material properties in the stator and the magnets in the rotor. The examples show that the error indicator works reliably, the meshes used for the different levels do not have to be nested, and, most importantly, MLMC reduces the computational cost by at least one order of magnitude compared to standard Monte Carlo. [ABSTRACT FROM AUTHOR]

This paper proposes a fast and accurate electromagnetic optimization method for magnetic levitation planar motors (MLPMs). With the purpose of achieving the maximum force with the minimum power dissipation and cost, a multi-objective optimization is adopted for the MLPM. Furthermore, in order to improve the precision and reduce the computational burden, the levitation force expression in the objective function is analyzed through the numerical model. This model is built by the magnetic charge method and the Gaussian quadrature and implemented in parallel computation. According to the optimal objective, an intelligent optimization algorithm—particle swarm optimization (PSO)—is used to undertake the optimization variables of the planar motor for a global optimal solution. The precision and effectiveness of the proposed method are validated by both the finite-element method (FEM) commercial software COMSOL and a boundary element software program named Radia. The comparative results with other optimization methods are also presented to highlight the performance of the proposed optimization method. [ABSTRACT FROM AUTHOR]

A numerical methodology is proposed to discretize a nonlinear low-frequency approximation to Maxwell’s equations using a local discontinuous Galerkin (DG) finite element method, with an upwind-like numerical flux, for modeling superconductors. In this paper, we focus on high-temperature superconductors (HTS) and the electrical resistivity is modeled using a power law. Nodal elements and the Whitney element are used. Numerical studies have been performed to verify the proposed methodology: a problem with a manufactured solution, the nonlinear magnetic front problem, and the magnetization of HTS wires. Based on the final time that can be reached for a given time-step size, the proposed strategy is compared with the $\mathbf {H}$ formulation discretized using the Galerkin finite element method with the Whitney element for the magnetic front problem. The proposed local DG strategy allows the use of a larger time-step size over a longer time interval, particularly, when we use the Whitney element. The proposed methodology can also capture sharp gradients of the current density with limited spurious oscillations. The numerical results are in agreement with Bean’s model for large values of power-law’s exponent. The proposed local DG strategy could be generalized to more complex electrical resistivity models, including multiphysics models. [ABSTRACT FROM AUTHOR]

This paper shows that there is very little effect of the silicon content on the hysteresis component of the magnetic losses when two steels with 2.45% and 3.3% silicon were compared. Two non-oriented steels with 2.45 wt% and 3.3 wt% Si have been investigated. The Hysteresis component was measured by two techniques, in an Epstein frame: by a quasi-static test at 5 MHz and by extrapolating the total loss from frequencies above 50 Hz. The results showed that the quasi-static hysteresis loss (5 MHz) is not affected by increased Si content. The method of measurement by extrapolating—from frequencies above 50 Hz—($W_{h}^\ast $) proved inaccurate, as it is influenced by the electrical resistivity of the steels. [ABSTRACT FROM AUTHOR]

This paper proposes a subdomain model for open-circuit field prediction in dual-stator consequent-pole permanent magnet machines. The whole field domain is composed of four types of sub-domains, including magnets, air gaps, slot openings, and slots. The proposed model takes the effect of tooth-tips into account, which can accurately calculate the flux density in slots and cogging torque. The finite-element (FE) model is established, which validates that the proposed subdomain model can quickly and accurately predict the magnetic field distribution and cogging torque in dual-stator consequent-pole permanent magnet machines. [ABSTRACT FROM AUTHOR]

Magnetic skyrmion (MS), a vortexlike region with reversed magnetization in nanomagnets, has recently emerged as an exciting development in the field of spintronics. It has a number of beneficial features, including remarkably high stability, ultralow depinning current density, and extremely compact size. Due to these benefits, skyrmions have generated great interest in the design of spintronic memory. In this paper, we evaluate the use of skyrmion-based memory as a last-level cache for general-purpose processors. In the skyrmion-based memory structure, data can be densely packed as multiple bits in a long magnetic nanotrack. Write operations are performed by injecting a spin-polarized current in the nanotrack. Since multiple skyrmions (each representing a bit) are packed into a single nanotrack, they need to be accessed by shifting them along the nanotrack with a charge current passing through a spin-Hall metal (SHM). We identify the following key challenges associated with MS-based cache design: 1) the high-current requirements for skyrmion nucleation limit the density benefits offered by these structures, since the transistor supplying write currents is the limiting factor that determines the bit-cell area; 2) the proposed nanotrack structure results in significant performance overheads due to the latency arising from the shift operations; 3) the skyrmions move toward the edge of the nanotrack during shift operations owing to the Magnus force. Hence, an additional idle operation time is required to relax skyrmions back through the repulsive force from the edge; and 4) to avoid annihilation of skyrmions from the edge, the duration and the current density of the shift operation have to be well controlled. To overcome these challenges, a multi-bit skyrmion cell with appropriate peripheral circuit is proposed, considering the heterogeneity in the read/write characteristics. The density benefits are explored by performing the layout of different multi-bit cells. We perform a systematic device-circuit-architecture co-design to evaluate the feasibility of our proposal. Our experiments demonstrate the potential of, and the challenges involved in, using skyrmion-based memory as last-level caches. [ABSTRACT FROM AUTHOR]

In this paper, we study a typical nonlinear phenomenon of phase locking or synchronization in spin-torque nano oscillators (STNOs). To start with, the oscillators are considered as uncoupled but interlinked through either a common microwave current or a microwave field. We identify the phase locking of an array of STNOs (first for two and then for 100 oscillators) by means of injection locking which represents locking the oscillations to a common alternating spin current or a common microwave magnetic field. We characterize the locking of STNOs through both the first and second harmonic lockings in an array. We find that the second harmonic lockings takes lesser value of microwave current and field than the first-harmonic lockings. Our results also show that oscillating microwave current can induce integer harmonic locking while microwave field can induce both integer and several fractional harmonic lockings. We also extend our analysis to study the locking behavior of two STNOs by introducing time delay feedback and coupling through a current injection and bring out the associated locking characteristics. Finally, we have also analyzed the stability of synchronization of an identical array of STNOs with current coupling by using master stability function formalism. [ABSTRACT FROM AUTHOR]

Electric machine design optimization is a popular topic in electrical engineering. Thanks to major accomplishments in Mathematics and Computer Science, nowadays the investigation of thousands of designs for particular optimization tasks is possible. Huge effort is made for developing evermore complex multi-physics simulation models including, e.g., thermal or mechanical aspects besides electromagnetic performance investigation. The impact of tolerances is often disregarded. This paper gives an overview of recent activities in machine design optimization. Consequently, the implementation of tolerance analyses for machine designs is explained. A categorization based on mathematical tolerance representations, typical tolerance-affected parameters and their respective modeling effort, as well as measures for evaluating the impact of tolerances, i.e., the design’s robustness, are discussed. An exemplary sensitivity analysis featuring an interior permanent magnet synchronous machine with spoke-type rotor structure is introduced. The performance of two different designs in the presence of uncertainties is investigated. Results reveal the importance of incorporating tolerance analyses to electric machine design optimization. [ABSTRACT FROM AUTHOR]

The effect of the thicknesses of the Pt intermediate layer and FePt magnetic layer in CrV/Pt/FePt multilayers on the microstructure and magnetic properties for the perpendicular magnetic anisotropy was investigated. The Pt (0–4 nm) and FePt (7–28 nm) layers were deposited on a 90 nm-thick Cr94V6 underlayer at 350 °C, and the crystal structure and magnetic properties of the fabricated CrV/Pt/FePt multilayers were characterized. X-ray diffraction and vibrating sample magnetometer measurements revealed that the out-of-plane coercivity (Hc-out) and squareness increase when the Pt intermediate layer is deposited between CrV and FePt because it protects against diffusion of Cr and V atoms into the FePt magnetic layer during deposition. In addition, we confirmed that Hc-out and squareness decrease with increasing FePt layer thickness in the range of 7–28 nm. As a result, the maximum Hc-out, S, and squareness were obtained for a multilayer with a CrV thickness of 90 nm, Pt thickness of 2 nm, and FePt thickness of 7 nm. This paper shows that highly ordered FePt L10 (001) can be fabricated by sublayer thickness control. [ABSTRACT FROM AUTHOR]

Proton precession magnetometer (PPM) is a potential device to measure the low-frequency geomagnetic field in the time domain. Nevertheless, the uncontrollable noise such as power frequency noise, random noise, etc., severely affects the detection results. In this paper, aimed to boost the performance of the PPM, a novel real-time processing algorithm for the optimization of PPM output strategy based on the low-rank constraint (LRC) is proposed, and a new efficient framework, dubbed LRC-based geomagnetic data readout optimizer (LRC-GDRO), is implemented. This method aims to extract the dominant principal components of the pure magnetic signal and identify the singular values of noise. Thereby, the relative ideal signal without external noise, which still contains the ambient field information is yielded. Moreover, we develop a prototype device and compare the test results before and after using the proposed method. Consequently, compared with traditional PPM, the performance of the PPM using the proposed method has been significantly improved with a measurement accuracy of ± 0.2 nT. Furthermore, the experimental results reveal that the LRC-optimized PPM is comparable to a very high-accuracy Overhauser magnetometer in terms of 12 h geomagnetic field observation. [ABSTRACT FROM AUTHOR]

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]