• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-20

Presents the front cover for this issue of the publication.

更新日期：2020-01-21
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-20

更新日期：2020-01-21
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-17
Joseph Um; Mohammad Reza Zamani Kouhpanji; Samuel Liu; Zohreh Nemati Porshokouh; Sang-Yeob Sung; Jürgen Kosel; Bethanie Stadler

Large-scale long-range ordered anodic aluminum oxide and multilayered nanowires (NWs) are attractive to 3-D nanostructured material applications, such as high-density 3-D magnetic memory. This article demonstrates long-range ordered aluminum oxide made by simple and inexpensive double imprinting with line-patterned stamp and uniform iron–gold multilayered NWs fabricated by galvanostatic electrochemical deposition with a single electrolyte bath. These two structural features show potential for future high-density recording systems that require long-range ordered devices separated from each other by insulation to eliminate crosstalk.

更新日期：2020-01-21
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
L. Krähenbühl; R. Scorretti; A. Bréard; C. Vollaire; J.-M. Guichon; O. Chadebec; G. Meunier; A. Urdaneta-Calzadilla; V. C. Silva; C. A. F. Sartori

We studied the harmonic magnetodynamic behavior (without free space wave propagation) of a resonant surface metamaterial, made of many identical and regularly arranged LC cells. The circuit model gives the exact solution, but it is not numerically efficient for simulating very large structures (e.g., $1000 \times 1000$ cells giving 10 6 unknowns with a full $10^{6} \times 10^{6}$ matrix). For the first time, we highlight the modal characteristics of the spatial solutions, which make it possible to explain their frequency- and spatial-related properties. From these results, we show under what assumptions it is possible to significantly lighten the system of equations, which opens up the way to develop more efficient numerical methods.

更新日期：2020-01-21
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-08
L. Bernard; B. J. Mailhé; S. L. Ávila; L. Daniel; N. J. Batistela; N. Sadowski

Based on multiscale modeling of the anhysteretic magnetization considering mechanical stress and crystallographic texture effects, an extension of the Jiles–Atherton (J-A) hysteresis model is proposed. The magnetization and the volume fractions given by the multiscale approach are advantageously used in the J-A model to modify the anhysteretic magnetization and the pinning parameter. The parameters of the proposed model are identified in order to fit with the characterization results under compressive stress using two sets of experimental data. Using the same optimized parameters, the model is tested for the representation of loops under other stress conditions to evaluate its prediction capabilities.

更新日期：2020-01-21
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
N. M’zali; F. Martin; R. Sundaria; T. Henneron; A. Benabou; A. Belahcen

In this article, the anhysteretic Sablik model is identified from measurements and implemented in a finite-element (FE) code. The model takes into account the effect of the plastic deformation through the dislocation density, and thus, enables to account for the degradation of the magnetic properties. A new model for magnetostriction is proposed and implemented in the Sablik model. Experimental data are used to identify the parameters of both Sablik model and proposed magnetostriction. Furthermore, the mechanical punching process of an electrical steel sheet is simulated in view of evaluating the plastic strain distribution near the punched edge. Based on the Sablik model and the simulated plastic strain, FE simulations are carried out on a steel sheet and a cage induction machine. The effect of the punching process on the distribution of magnetic-flux density and the magnetization current is analyzed.

更新日期：2020-01-21
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-14
L. A. J. Friedrich; B. L. J. Gysen; J. W. Jansen; E. A. Lomonova

This article concerns the modeling and design of a slitted stator core for single-sided axial-flux permanent-magnet machine application. The stator core is specially designed to maximize the magnetic-flux density in the air gap and to minimize the eddy-current losses occurring at high rotational speeds. To reduce the effort needed for computing the motional eddy-current distribution in the presence of nonlinear material characteristics, a novel method is proposed. It combines the harmonic balance method, which is advantageous for simulating in the frequency domain the steady-state periodic response of a nonlinear system under harmonic excitation, together with a source description that introduces a complex magnetization that mimics the displacement of the permanent-magnet array. Following this method, time-domain distributions and losses can be reconstructed accurately with a low number of harmonics. A 3-D periodic model of the slotless axial-flux machine is built in the framework of isogeometric analysis (IGA) and a mixed formulation is employed, which relies on high-order Nédélec edge elements. The proposed model is embedded into a gradient-based optimization problem to determine the optimal shape of the slits in the stator core of the motor. This results in a novel cost-effective solution for improving the efficiency of axial-flux permanent-magnet machines.

更新日期：2020-01-21
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
Frederic Maurer; Basile Kawkabani; Jonas Kristiansen Nøland

The computation of 3-D magnetic fields is a demanding task in the analysis of electrical machines and other electromagnetic devices. In this context, integral field calculation provides a smooth solution, high precision and resolution, “on-demand”-calculation, and an origin-based formulation of the magnetic field and the magnetic vector potential. However, conventional elliptic methods lead to huge parallelizable computing efforts and significant errors. In this article, a 3-D generic current-carrying arc segment with rectangular cross section is studied. A new analytic formulation is proposed to speed up the computation of magnetic fields and reduce the error by more than three orders of magnitude. In addition, the proposed magnetic vector potential expression has a similar accuracy as numerical integration. In fact, a significant reduction of the error level has been showcased clearly with respect to the existing approaches. This article is promising for improving the design methodology and optimization of large superconducting dipole magnets or arched end-winding geometries of large electrical machines.

更新日期：2020-01-21
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-20

更新日期：2020-01-21
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-20

更新日期：2020-01-21
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-15

In this article, Bi 1–x Co x Fe 0.8 Mn 0.2 O 3 (BCFMO) nanoparticles with x = 0.0, 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 were synthesized at 650°C and annealed for 1 h by the sol–gel method. Then, the structural, magnetic, dielectric, and optical properties of BCFMO nanoparticles were investigated with the substitution of cobalt and manganese elements for bismuth and iron under various percentages. X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and ultraviolet (UV)–visible spectrophotometer were used to characterize the prepared samples. By using LCR meter, the dielectric constant ( $\varepsilon ^{\prime }$ ), the dielectric loss factor (tan $\delta$ ), the dielectric loss ( $\varepsilon ^{\prime \prime }$ ), and the electrical conductivity amounts of ac ( $\sigma _{\mathrm {ac}}$ ) for BCFMO nanoparticles were measured at the annealing temperature of 650°C for 1 h in the frequency range of 100 Hz–5 MHz.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
L. Evangelista; Matheus A. Carvalho; P. A. P. Wendhausen

This article presents the study of the dependence of the Steinmetz coefficients on the technological processing parameters for commercially available SMC Somaloy 3P 700. The work was carried under a Box–Behnken design of experiments considering pressing pressure, heat treatment temperature, and soaking time as relevant factors over the total power losses. Based on the values of $K_{H}$ , $x$ , and $K_{D}$ extracted from the measured losses, equations for predicting the values of the Steinmetz coefficients with the processing parameters as inputs were generated. The results presented high correlation between the measured and modeled losses and can easily be applied to electrical machine design software.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
Sajjad Ur Rehman; Qingzheng Jiang; Qiulan Tan; Kai Liu; Anwar Ul Haq; Zhenchen Zhong

The magnetic properties of alnico alloys are highly dependent on the spinodally decomposed nanostructure. In this article, we report the fabrication of alnico nanoribbons and the effects of various heat treatments on the magnetic properties, spinodal decomposition, microstructure, and temperature stability. It is found that the spinodal decomposition occurs in a wider range of temperatures from 800 °C to 860 °C. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses of the microstructure confirmed that the nanostructure phases develop in a wide temperature range. Aspect ratio of the order of ~20 is obtained by optimizing the heat treatment conditions. Magnetic properties of $H_{\mathrm {cj}} = 815$ Oe, $B_{r} = 6.70$ kG, and (BH) max = 1.88 MGOe are obtained after simplified heat treatment. The magnetic properties of the alloys are measured at low (10 K) and at high (800 K) temperature, and it is shown by calculating temperature coefficient of remanence ( $\alpha$ ) and temperature coefficient of coercivity ( $\beta$ ) that alnico ribbons possess extraordinary temperature stability at low and high temperatures.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
Shaahin Angizi; Zhezhi He; An Chen; Deliang Fan

In this article, we initially present a hybrid spin-CMOS polymorphic logic gate (HPLG) using a novel 5-terminal magnetic domain wall motion device. The proposed HPLG is able to perform a full set of 1- and 2-input Boolean logic functions (i.e., NOT, AND/NAND, OR/NOR, and XOR/XNOR) by configuring the applied keys. We further show that our proposed HPLG could become a promising hardware security primitive to address IC counterfeiting or reverse engineering by logic locking and polymorphic transformation. The experimental results on a set of ISCAS-89, ITC-99, and École Polytechnique Fédérale de Lausanne (EPFL) benchmarks show that HPLG obtains up to 51.4% and 10% average performance improvements on the power-delay product (PDP) compared with recent non-volatile logic and CMOS-based designs, respectively. We then leverage this gate to realize a novel processing-in-memory architecture (HPLG-PIM) for highly flexible, efficient, and secure logic computation. Instead of integrating complex logic units in cost-sensitive memory, this architecture exploits a hardware-friendly approach to implement the complex logic functions between multiple operands combining a reconfigurable sense amplifier and an HPLG unit to reduce the latency and the power-hungry data movement further. The device-to-architecture co-simulation results for widely used graph processing tasks running on three social network data sets indicate roughly $3.6\times$ higher energy efficiency and $5.3\times$ speedup over recent resistive RAM (ReRAM) accelerators. In addition, an HPLG-PIM achieves $\sim 4\times$ higher energy efficiency and $5.1\times$ speedup over recent processing-in-DRAM acceleration methods.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
X. P. Xu; T. Z. Liu; M. Zhu; J. G. Wang

Large dc current is typically measured by an open-loop sensor without a magnetic core. The widely used configuration uses a differential magnetic sensor inserted into the busbar hole or a differential magnetic sensor placed on the upper and lower surfaces of the busbar. The use of a differential sensor has the advantage of being resistant to external magnetic fields. In this article, a new differential ultra-small magnetic sensor with the size of 23.2 mm $\times16.5$ mm $\times7.2$ mm is designed. The sensor is based on tunneling magnetoresistance (TMR) and is placed on the upper surface edge of the busbar. The supply voltage is 5 V, the rated current measurement range is ±150 A, and the peak current measurement range is ±250 A, corresponding to 2.5 ± 2 V output at ±250 A dc peak current. The relative accuracy is less than ±1% at 25 °C and is less than ±2% over the full temperature range from −40 °C to 105 °C.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Hao Jiang; Jilong Zhang; Zhenfeng Xu; Yufeng Xu; Kai Chen; Guangmin Li; Pan Zeng; Timing Qu

Fluxgate magnetometer is an important device for weak magnetic-field measurements. By adding a large dc bias excitation current, the performances of fluxgate can be highly improved. In this article, based on the assumption of the single-domain state within the probe core wire, the quasi-static Stoner–Wohlfarth model (SW model) was used to construct a mathematic model for the output signal of the orthogonal fluxgate probe operated in fundamental mode (FM-OFG). The dynamic hysteresis loop characteristics were also considered here, and the expected first-harmonic output signal corresponding to the theoretical analysis was obtained from our model. A prototype FM-OFG probe was fabricated by using a 20 mm-long Co–Fe–Nb–Si–B amorphous microwire as core wire and a 1500-turn solenoid as pickup coils. Output performances were analyzed at different external fields, ac excitation currents, and dc bias currents. A good agreement between the modeling results and the experimental ones was found. The noise level was reduced down to 9.01 pT/rt (Hz).@.1 Hz. The simulation method and experiment results provide theoretical guidance for the subsequent design and improvement of the FM-OFG.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Juan P. Rigla; Franz Bodker; Amir Anari; Eduardo Pallás; Daniel Grau; Guillermo Puchalt; José M. González; Miguel Corberán; Elena Díaz; José M. Algarín; Alfonso Ríos; José M. Benlloch; Joseba Alonso

This article presents the design and experimental characterization of an electromagnet rampable up to 1 T and tailored to meet the demands of a magnetic resonance imaging (MRI) system conceived for spatial resolutions at the level of tens of microns. For high image quality, MRI requires a homogeneous magnetic field over the field of view (FoV) where the sample is imaged. We have opted for passive shimming based on optimal pole profiling and measure a relative field inhomogeneity of 71 parts per million over a spherical FoV of 20 mm diameter. Fringe-field lines are strongly confined to avoid interference with other devices. The magnet performance closely follows our expectations from numerical simulations in all of the experimental tests carried out. In addition, we present the solutions adopted for thermal management and the design of a mechanical structure to distribute the weight and integrate the platform to move the sample in and out of the magnet.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-14
Hongyi Qu; Yaohui Wang; Chaoqun Niu; Yang Liu; Qiuliang Wang

With few exceptions, a fresh magnetic resonance imaging (MRI) scanner may fail to achieve the magnetic field specifications, due to the existence of engineering errors or surrounding ferromagnetic materials. Excellent field homogeneity is one of the most important criteria for imaging quality; therefore, the shimming technique must be employed to bring the magnetic field homogeneity within the MRI requirements. The commonly used method is passive shimming (PS), which utilizes the shim pieces (iron pieces) with a different thickness in specific positions to generate a “corrective” magnetic field. In conventional PS, the inhomogeneous field over the measured volume (MV) is shimmed to be the best as much as possible. However, in fact, since the MV and the real imaging volumes (IVs) are different, a problem may exist as the field over the MV is good enough but may not be sufficiently qualified over some IVs. As a result, a multi-volumes PS strategy is proposed in this article, which pays more attention to the magnetic field over some potential IVs other than the MV. Compared with the conventional single-constraint method, the new method increases the shimming targets and constraints tailored to imaging, without increasing any computing burden and additional iron consumption. In addition, the PS test on a 1.5 T MRI scanner is performed using the conventional and proposed algorithms, respectively. The magnetic field obtained by a new strategy is obviously superior to that of the conventional method, evaluated from some specific volumes for parts of human body imaging, demonstrating the effectiveness of the multi-volumes shimming strategy.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Jan-Ove Hall; Henrik Claésson; Jonas Kjäll; Gösta Ljungdahl

In this article, we present a new versatile algorithm for the decomposition of the ferromagnetic signature into permanent and induced magnetization components. It can be directly implemented at existing magnetic ranges for a more robust and less error-prone calibration of degaussing systems on naval vessels. A source model is formulated for describing the signature. The model consists of two collections of magnetic dipoles, representing the permanent and induced magnetization. The induced part of the source model depends on the heading of the ship relative to the geomagnetic field. A general linear relation between the induced moment and the external magnetic field is assumed. The parameters of the model are determined by formulating and solving a regularized inverse problem using magnetic-field data from multiple passages of the ship over the sensors. Data from at least three passages with different headings are co-processed to obtain an estimate of the model parameters. The analysis uses raw data from magnetic ranges without any assumptions on the induced field. We demonstrate how to apply the algorithm with two examples. The first is a finite-element study, with a single sensor line with three-axis magnetometers, where a surface ship is modeled by a generic geometry and magnetization state. The second is a study of a real ship engine, in an indoor magnetic ranging facility with full control of all parameters. For both, field maps of the permanent and induced fields are calculated and compared to data using the resulting source model.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-08
Pedro P. C. Bhagubai; João F. P. Fernandes

The pursue for electrical machines with higher power densities and efficiencies is a constant research topic among the research and industrial communities. This article focuses on the optimization of an electrical machine’s magnetic core using a vanadium–cobalt–iron (VaCoFe) alloy to increase its power density and electrical efficiency. This alloy presents, as its main differentiable characteristics, a higher magnetic saturation point, about 2.4 T, but also higher iron core losses than typical silicon–iron (FeSi) materials. In order to study the impact of using this material in electrical machines magnetic cores, this article focuses on the optimization of magnetic cores with two different materials: VaCoFe alloy and a typical FeSi material. The optimizations are done using a genetic algorithm and using the electromagnetic and thermal lumped parameter models to maximize power density, while reducing magnetic core volumes. Results show that the VaCoFe allows the increase of the power density of the magnetic core in about 25% for low frequencies; however, due to its higher iron core losses, for higher frequencies, the advantages of using this new alloy are not clear. Due to temperature limits, for higher frequencies, it is not possible to work on the VaCoFe best magnetic saturation point. Therefore, results show that for low values electrical frequency ranges, this material can outperform the typical FeSi, while for higher ones, the VaCoFe can be outperformed by the FeSi.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
Yuwei Qin; Jian-Gang Zhu

The application of a deep neural network (DNN) as the detection channel for hard disk drive (HDD) data recovery at high user bit density and the prominent magnetic transition jitter noise are investigated in this article. Directly trained with the un-equalized readback signals without any prior knowledge of the magnetic recording channel, the DNN can automatically learn the signal characteristics, in particular the correlations between the input signals and the impact from the noise. As a result, the DNN read channel not only adapts the inter-symbol interference (ISI) but also demonstrates strong resilience against the colored magnetic noise. Our simulation results also reveal that to fully harness the learning power of the DNN data detection channel, the neural network inputs must cover the ISI spread. In addition, the training data must be sufficiently representative so that the inductive bias learned by the DNN detection channel can be used as good prior knowledge for actual detection.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
Brian Chen; Jen-Yuan Chang

Linear magnetic recording medium is a crucial and necessary component in a linear magnetic position sensing system. During the manufacturing of the magnetic medium, shape defects would often be observed due to various manufacturing processes. As a result, shape defects in the magnetic medium would alter the recording accuracy during position measurement of the magnetic reader. Thus, a flattening process is introduced for flattening of curved magnetic medium. Previous studies have demonstrated its effectiveness in flattening of magnetic medium. In this article, a further step is taken to examine the crack formation in the microstructure of the magnetic medium during flattening process to ensure the quality and recording accuracy of the magnetic medium. The experimental results have demonstrated that crack propagation would continue to grow under the influence of flattening process if crack initiation is found prior to the flattening process. Nonetheless, the measured linear position accuracy showed that the accuracy improved after the flattening process despite crack propagation occurring on the mechanical quality of the medium. In other words, the results have demonstrated that the effect of mechanical shape defects on linear position accuracy is more important than that of crack formation on the magnetic medium. Through understanding the crack formation of the magnetic medium, the accuracy of the recording medium can be improved by modification of the magnetic medium and flattening conditions.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
Weiwei Xu; Felippe J. Pavinatto; G. Z. Cao; J. Devin MacKenzie; I. Y. Shen

A lead–zirconate–titanate (PZT) thin film additively manufactured on a flexible substrate is demonstrated in this article as an actuator. PZT nano-particles (NPs) are first fabricated via a hydrothermal process. The NPs are then suspended in ethanol with a polymer additive to form PZT ink. The PZT ink is later drop-cast on a flexible substrate with two electrode designs for evaluation: sandwich electrodes and interdigitated electrodes (IDEs). The design of sandwich electrodes is difficult to realize because silver electrodes cannot be properly printed onto the PZT film with good conductivity and dimension accuracy. In contrast, a pair of IDEs is successfully inkjet printed on polyethylene terephthalate (PET) tape. Then the PZT ink is drop-cast to form a PZT film. Sinusoidal voltage applied over the electrodes drives the device into resonance serving as a resonator. For hard-disk drives, the 3-D printed PZT films can be used as dual-stage actuators or as absorbers to actively or passively reduce flex cable vibration.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
A. Heya; K. Hirata; T. Matsushita; Y. Kono

Oscillatory actuators are expected for various applications such as entertainment systems, consumer products, and so on. In addition, the oscillatory motion is expanded to multiple-degrees-of-freedom. A three-degree-of-freedom linear oscillatory actuator (3DOF-LOA) has been developed. A conventional 3DOF-LOA needs five sets of coils for a three-degree-of-freedom motion, and the forces on each axis have interfered with each other. This article proposes a novel 3DOF-LOA with three sets of coils, and its forces on each axis do not interfere with each other. The magnetic structure and the operating principle of the proposed 3DOF-LOA are described. The force characteristics are calculated using a 3-D finite-element method. It is investigated that the proposed actuator can be driven three-axis by only three-coils, and has no interference of forces between each axis.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Banda Kane; Antoine Pierquin; Guillaume Wasselynck; Didier Trichet

The analysis of the electrical behavior of a unidirectional (UD) composite material requires a lot of resources and measurement techniques. To overcome this constraint, the real composite material is replaced by a virtual material with same overall behavior. In this article, an approach to determine the setting parameters of the virtual material model is presented to accurately reconstruct the electrical behavior of a real UD material in the three spatial directions.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
Jakub Mojsiejuk; Paweł Kulig; Jakub Chęciński; Marek Frankowski

Micromagnetic simulations can present both time- and cost-savings, as complicated phenomena simulated a priori provide a valuable intuition in adjusting experimental parameters. However, they require insightful post-analysis, which can be tedious because local changes in magnetization occur rapidly. We have developed an application that allows for viewing multiple data objects such as graphs, 2-D layer visualizations, or 3-D graphic structures synchronized with each other. We believe that it could be of help for scientists who wish to investigate and verify the results obtained from simulation software like OOMMF or MuMax3 in a deeper context. In this article, we present a complete software suite built using the Qt framework for graphical user interface and the PyOpenGL framework for 3-D representation of magnetic structures.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-15
P. Kharitonskii; S. Kirillova; K. Gareev; A. Kamzin; A. Gurylev; A. Kosterov; E. Sergienko; A. Valiullin; E. Shevchenko

Fe m O n –TiO 2 particle aggregates have been obtained using the sol–gel method and hydrothermal treatment. It is shown that the synthesis conditions favor forming composites that contain titanomagnetite in very low concentrations. Hysteresis loops and demagnetization curves of anhysteretic remanent magnetization were measured with a vibration sample and a SQUID magnetometer, respectively. Mössbauer spectroscopy, bulk magnetic properties, scanning electron microscopy (SEM) observations, coupled with the theoretical analysis of magnetostatic interaction between finely dispersed particles lead to a conclusion that the studied composites can be viewed as groups of interacting clusters 2– $20~\mu \text{m}$ in size, consisting of chemically heterogeneous, mostly single-domain or close to single-domain particles with an average size of about 100 nm.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
Ting Wang; Lele Cheng; Chengxu Wang; Weiming Cheng; Haiwei Wang; Huajun Sun; Jincai Chen; Xiangshui Miao

Pt/BiFeO 3 /SrRuO 3 /SrTiO 3 heterostructures with significant resistive switching characteristics have been successfully fabricated via magnetron sputtering, and the effect of thicknesses and deposition temperatures on the resistive switching properties has also been investigated. The resistive behaviors and conduction mechanisms can be modulated by the thickness and deposition temperatures of bismuth ferrite perovskite oxide (BFO) films. BFO films with a smaller thickness of 80 nm and higher deposition temperature of 670 °C show larger memory window over 1000 and lower switching voltage below 1.5 V. Moreover, the conduction mechanisms of Pt/BiFeO 3 /SrRuO 3 /SrTiO 3 resistive cell change from the space charge-limited conduction model to the conductive filament type with the decrease of BFO film thickness possibly due to more oxygen vacancies and defects. Furthermore, oxygen partial pressure also influences the memory window and conduction mechanism of BFO resistive cells by increasing or decreasing the oxygen vacancy defects in BFO films.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
Jincheng Yu; Chunhua Liu

This article proposes the dc-biased operation of a new double-stator hybrid flux switching permanent-magnet (DSH-FSPM) machine. Through directly injecting the dc current into the armature windings, the dc-biased strategy contributes both the flux-enhancing (FE) and flux-weakening (FW) capabilities into the proposed machine design. First, the machine optimization is carried out to obtain the optimal dc-biased current, with the criteria of the torque performances. Then, when compared with the pure-armature-current and max-dc-current strategies, the optimal dc-biased operation increases the average steady torque by 41.3% and 65.5%, respectively. Moreover, the high torque–speed capability is analyzed with the cooperation of the FE and FW operating modes. With 2 A FW dc-biased current injection, the rotational speed is extended to two rated speed with the half-rate output torque. Under the max-dc-current FW operation, the speed can maximumly expand to six rated speed. Consequently, the wide speed range is realized with the integration of the FE and FW modes. Also, the loss and efficiency analysis are carried out based on the whole machine speed range. The simulations are performed to verify the feasibility of the proposed dc-biased DSH-FSPM machine.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-08
Yong Kong; Mingyao Lin; Lun Jia

In this article, a novel high power density permanent-magnet synchronous machine (HPDPMSM) is proposed. The flux-weakening ability and efficiency at high speed are improved by the proposed bypass-ribs added in the flux barriers. The working principle of the bypass-rib is analyzed, and the effects of the main parameters of the bypass-rib on the characteristics are investigated. The performances of the proposed HPDPMSM are analyzed and compared with that of the HPDPMSM without bypass-rib on 2-D finite-element analysis (FEA), including the cogging torque, output torque, constant-power speed range, losses, and efficiency. The results show that both HPDPMSMs generate comparable output torque and have the same maximum output power, while the proposed HPDPMSM has lower torque ripple, wider constant-power operation range, and higher efficiency in the flux-weakening operation region.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-08
D. Giraud; B. Ristagno; J. Fontchastagner; D. Netter; N. Labbe; V. Lanfranchi; N. Takorabet

In this article, an easily implementable method to reduce the CPU time for some 3-D finite-element method (FEM) problems is presented. A translational displacement between two parts on both sides of a planar air gap is considered with a change of coordinates in the air-gap region along the $z$ -axis. To achieve this, formulation and postprocessing are slightly adapted. The proposed method is applied to an academic problem and to an axial electric rotating machine. Results are compared with a usual method. Time savings, ease of implementation, and precision on results are really encouraging with a strong reduction in the CPU time, keeping a low relative deviation. The method could be easily applied to any configurations with the planar air gap as an axial motor.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-08
Toshihito Shimotani; Hajime Igarashi; Eiji Hashimoto; Hiroyuki Imanari

This article presents a method to synthesize the equivalent circuit of an induction heating (IH) machine used in the hot strip mill (HSM) process. The equivalent circuit not only allows to evaluate eddy current losses in different forms, such as iron plate and coils, but also compute the transient responses in online environments. The frequency characteristic of the IH machine is effectively computed by proper orthogonal decomposition. The equivalent circuit of the IH is synthesized through curve fitting to the computed characteristics in conjunction with Tikhonov’s regularization. The equivalent circuit is shown to have good accuracy and works much faster than the finite-element method. The proposed equivalent circuit is expected to be used in online control of the HSM process.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-14
Seung Geon Hong; Il Han Park

This article proposes a continuum-sensitivity-based method to obtain the optimal design for an interior permanent magnet synchronous motor (IPMSM). Compared with the finite difference method, the continuum sensitivity analysis shortens the computation time significantly when there are numerous design variables. We combine the continuum sensitivity with the shape constraint so that both the shape and the size can be optimized simultaneously and within a short time. This proposed design optimization method is applied to IPMSM rotor design, and its feasibility is verified. The proposed method is expected to be effective for various design problems that require the shape and the size to be optimized simultaneously.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
Lilli Kuen; Rolf Schuhmann

The perfectly matched layer (PML) technique is a general-purpose absorbing boundary condition for finite methods which is usually applied within explicit time-domain schemes. There are a number of slightly different implementations of the extended update equations, and many of them have been reported in the literature to show some long-term instabilities, typically only weakly depending on the time step size. In this contribution, we present a hybrid implicit–explicit algorithm that introduces two additional parameters to control the stability. The implicit part of the algorithm is used only locally within the PML region, and for a simple setup, stability is reached for a certain range of the additional parameters.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
Xiao Xiao; Fabian Müller; Gregor Bavendiek; Nora Leuning; Pengfei Zhang; Jun Zou; Kay Hameyer

The magnetization behavior and thus the form of the magnetization curve of electrical steel strongly depend on the direction of the magnetic field, frequency of excitation, external mechanical stress, and cut edge effect. These factors influence the performance of electrical machines and need to be considered in advanced machine design processes or numerical modeling. Most of the aforementioned effects occur locally in the machine and, therefore, need to be described locally. It is crucial to characterize the material under realistic conditions for adequate identification and quantification of the influences. In this article, modeling and simulation of soft magnetic material are performed based on a detailed magnetic characterization, considering magnetization amplitude, angle with respect to the rolling direction of magnetization, mechanical stress, and cut edge effect. The dependent soft magnetic material characteristics are derived from the magnetic measurement data and concluded into interpolation surfaces. Subsequently, these surfaces are used to simulate a synchronous machine designed for a traction drive of an electric vehicle by finite-element simulation. One of the main challenges is the correct determination of the local material properties, depending on the operating point, which influences global quantities such as losses and torque. This article provides a methodology to consider different local influences on the magnetization behavior of electrical steel in a finite-element simulation, thus offering the potential for improving electromagnetic circuit design.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Shingo Hiruma; Hajime Igarashi

This article proposes a novel homogenization method based on the unit cell approach which provides the continued fraction and, equivalently, the Cauer circuit representation of the complex permeability of fine structure materials. The proposed method makes it possible to perform the homogenization analysis in time domain. It is shown that the proposed method provides a more accurate resistance factor in comparison to the Dowell method and other classical methods.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-08
Hamed Eskandari; Tetsuji Matsuo

An approximation approach is proposed for the analysis of nonlinear quasi-static eddy currents adopting a Cauer ladder network (CLN). When there are nonlinear magnetic materials in the analysis domain, the electric and magnetic modes and their corresponding values for resistors and inductors in the CLN may vary according to the level of saturation in the core. Considering the effects of the modes and their magnitudes on the saturation imposes a heavy computational burden, which brings the efficiency of the CLN method into question. This article studies a first-order approximation of the nonlinear CLN method to keep the nonlinearization procedure computationally effective, simple, and accurate. Numerical tests are carried out for a 2-D nonlinear inductor excited with rectangular and sinusoidal excitations to show the accuracy of the proposed nonlinear resolution method.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Yilun Li; Lei Liu; Shiyou Yang; Zhuoxiang Ren; Yanhong Ma

In this article, a multi-objective topology optimization (MOTO) methodology based on the hybridization of the Non-dominated Sorting Genetic Algorithm II (NSGAII) and Differential Evolutionary (DE) algorithm is proposed. The framework of the proposed hybrid multiobjective optimization (MOO) algorithm is elaborated, and its performances and advantages over existing standard MOO methods are evaluated and demonstrated by solving typical mathematical test functions. To validate the proposed hybrid MOTO methodology, it is applied to the topology optimization of an electromagnetic actuator. Both linear and nonlinear cases are investigated. The numerical results demonstrate that a set of novel topologies with improved multiple objectives is obtained.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Hiroki Sakamoto; Kazuya Okamoto; Hajime Igarashi

This article proposes a simplified model-order reduction for the fast dynamic simulation of electric motors. The magnetic fields are snapshotted for different input currents at each mechanical angle to construct a data matrix. The basis vectors are then computed by the singular value decomposition applied to the data matrix. The interpolation along the mechanical angle is performed by the dynamic mode decomposition. Fast computation of the magnetic field for arbitrary input current and mechanical angle is performed through interpolation of the basis vectors in the space of input currents for the dynamic analysis of motors.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-08
Liangliang Wei; Taketsune Nakamura

This article proposes a dual-stator switched flux consequent pole permanent-magnet (DS-SFCPM) machine with unequal length teeth and carries out optimal design of the DS-SFCPM machine. Compared with a conventional dual-stator switched flux permanent-magnet (SFPM) machine, it can be regarded as a combination of two different dual-stator machines, so as to significantly enhance the torque density, and has good flux-regulating capability (FRC) with field winding. First, the basic principle of the proposed DS-SFCPM is explained, and the torque-generating mechanism and flux-regulating performance are analyzed based on the superposition of the above two dual-stator machines. Then, the influence of the unequal length teeth on the torque density and FRC is analyzed, the evaluation indexes of optimization are also introduced, and the parameters of unequal length teeth and permanent magnets (PMs) are optimized by sensitivity analysis. Various finite-element analysis (FEA) simulation, optimization, and comparison studies of the proposed machine are performed. The results verified the effectiveness of the proposed structure.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
Zaixin Song; Chunhua Liu; Feng Chai; Hang Zhao

The permanent-magnet Vernier (PMV) machine has been welcomed for direct-drive applications recently. Also, the fault tolerance is critical for special machine design in hostile conditions. This article proposes an efficient PMV machine with the modular winding configuration, which takes the fault-tolerant capability into account, especially the open-circuit fault. With the modular winding design, the better isolation between phases and modules can be obtained instead of dividing the stator core into segments. Meanwhile, the high efficiency needs to be guaranteed under both normal and partial-module operations. Therefore, the machine design, basic characteristics, and the fault-tolerant operation are performed and verified. Finally, the efficiency performances under normal and modular operations are analyzed and compared, which demonstrates the validity of the proposed idea and relevant considerations.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Shogo Fujita; Shingo Hiruma; Hajime Igarashi

A magnetically shielded wire (MSW) is effective for the reduction of the eddy-current loss due to the proximity effect. When using the finite-element method (FEM), it is challenging to analyze the electric apparatus, including MSWs, because its radius is much smaller than the overall machine size. This problem can be circumvented by modeling a multiturn MS coil (MSC) as uniform material with the macroscopic complex permeability defined in the frequency domain. This article presents an extension of this homogenization method to the time domain. The inverse Laplace transform is effectively performed by expanding the complex permeability into partial fractions. It is shown that the proposed method is accurate even when the magnetic saturation of the magnetic core is in effect.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
Zoran Andjelic; Kazuhisa Ishibashi; Christian Lage; Paolo Di Barba

The double-layer approach (DLA) possesses superior features for the analysis of static electromagnetic problems. In this article, dealing with the magnetostatic analysis, we introduce two kinds of double layers: the first one on the surface of the magnetic body and the second one on the cut-surface within the exciting current loop. From the double layers on the cut-surface, we were able to derive a novel, unified exciting potential, which facilitates the treatment of any magnetostatic problem, including multiply connected problems. Furthermore, in this article, we use for the first time DLA for the analysis of magnetic forces acting on the magnetic bodies. The law of action and reaction provides a self-check function within DLA, enabling thus the simple and reliable tool for the confirmation if the computed results are adequate and accurate. This improved, DLA-based approach for the force analysis together with the introduced “action-reaction” principle for the self-checking of the force calculation are, to the authors’ best knowledge, not known in the scientific community so far. Finally, we would like to emphasize that the presented DLA enables accurate, self-checked, generic analysis of the real-world devices, providing advanced treatment of both geometrical singularities (edges, corners) and materials used (high permeability, nonlinearities).

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Maria-Thaleia Passia; Traianos V. Yioultsis

In this article, a rigorous temporal coupled-mode theory (CMT) formalism is developed, to analyze metasurface (MTS)-based structures. Such MTSs are generally rather complex, requiring extensive, full-wave simulations. To facilitate their design and minimize the associated computational demand, the CMT solves a small linear system of equations, fed by the results of certain much simpler and less time- and memory-consuming eigenvalue problems. The proposed method is versatile and offers an initial, valuable estimation of the structure’s frequency response, which may be used as a guideline for the final MTS fine tuning. As proof of concept, split-ring resonator (SRR) MTSs coupled to microstrip lines are analyzed, and their response is compared with the full-wave finite-element method (FEM) results.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
Tetsuji Matsuo; Takayuki Fujiwara; Kenta Kuriyama; Kengo Sugahara; Akihisa Kameari; Tadashi Tokumasu; Yuji Shindo

To achieve efficient multi-port model order reduction, a multi-port Cauer ladder network (CLN) method is formulated that directly yields resistance and inductance matrices that constitute the network elements in the matrix Cauer form. The eddy-current field driven by multiple power sources is accurately reconstructed using a small number of network elements. The matrix Cauer form achieves faster convergence of the transfer function than a single-port CLN method and almost the same convergence as a block Padé via Lanczos (PVL) method.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Shuai Yan; Xiaoyu Xu; Pengfei Lyu; Zhuoxiang Ren

Full-wave solutions of Maxwell’s equations defined on a wide-range parametric space can be necessary for modeling and design of high-frequency electronic systems. Model order reduction (MOR) techniques can be used to develop efficient solvers for accelerating the parameter sweeping process. In this article, we implement two MOR methods for solving parametric full-wave problems. One is the well-known proper orthogonal decomposition (POD) method and the other is a more recent and novel method, which is proper generalized decomposition (PGD). The two methods are applied on a wave propagation problem in both frequency domain and frequency-permittivity domain. Results show that both POD and PGD can model the field changes in the parametric space accurately. The efficiency and behavior of the reduction modes of both methods are compared and discussed.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Zezhi Xing; Wenliang Zhao; Xiuhe Wang; Yining Sun

Electromagnetic vibration is excited by the electromagnetic force waves generated by the air-gap magnetic field acting on the machine core. In this article, a fast and accurate calculation method of radial electromagnetic force density of surface-mounted permanent-magnet synchronous motors (SPMSMs) is proposed, and the radial force density including amplitude, frequency, and order is obtained. Comprehensively considering that the effect of the PM segmentation on electromagnetic force waves, cogging torque, and the no-load back electromotive force (back EMF), the optimal determination of the number of PM segmentation in different slot–pole combinations of SPMSMs is summarized, and six slot–pole combinations of SPMSMs with 6p36s, 4p36s, 6p9s, 8p9s, 8p12s, and 10p12s are calculated and analyzed to verify the universality of the conclusions, which lays a theoretical foundation for the weakening of the radial electromagnetic force.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-16
Paavo Rasilo; Joonas Vesa; Johan Gyselinck

We present a novel approach for stochastic finite-element (FE) modeling of the electromagnetic field in ferrites, combining a thin shell model (TSM) for highly permittive grain boundaries with a Voronoi-tessellation-based geometry generation algorithm. The TSM is validated in the case of a periodic grain structure in a linear 2-D time-harmonic case over a frequency range of 10 kHz–1 GHz, and problems related to standard FE discretization are discussed. The TSM is then applied in a stochastic study for simulating the effect of varying grain structure on the effective resistivity, losses, and reactive power densities of a ferrite core.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Lun Jia; Mingyao Lin; Wei Le; Nian Li; Yong Kong

Reduction of the cogging torque is preferred during the design process of a permanent magnet (PM) synchronous machine (PMSM), especially in the low-speed traction applications. This article presents a dual-skew magnet technique to minimize the cogging torque in the axial-flux permanent-magnet (AFPM) motor with a yokeless and segmented armature (YASA). The theoretical expression of the cogging torque of the AFPM machine is deduced, and the advantages of the dual-skew magnet are verified by comparing with a sector shape magnet and a conventional skew magnet using the 3-D finite-element method (FEM). The simulation results show that, compared with the other two magnet topologies, the machine equipped with the dual-skew magnet shows its advantages in the reduction of cogging torque, torque ripple, and magnet eddy current loss.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Xiaojie Zhu; Xikui Ma; Jinghui Shao; Shuli Yin

A novel numerical method, referred to as the Riccati precise-integration time-domain (Riccati-PITD) method, is proposed to reduce the memory requirement of the conventional PITD method. In the Riccati-PITD method, the electromagnetic field components of the transverse electric/transverse magnetic (TE/TM) wave are arranged in a matrix for constructing the Riccati matrix differential equations (RDEs) about Maxwell’s curl equations. Then the precise integration technique is adopted for the numerical integration of the RDEs. Theoretical analyses about the memory requirements of the conventional and the Riccati-PITD methods are presented. It is found that the memory requirement can be more greatly reduced by solving the electromagnetic-field components in the form of the matrices in the Riccati-PITD method rather than in the form of the vectors in the conventional PITD method. Numerical examples are also given to confirm that the proposed method has significant advantages over the conventional PITD method with respect to the execution time and the memory requirement.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
L. A. M. D’Angelo; Z. Bontinck; S. Schöps; H. De Gersem

This article focuses on the robust optimization of a permanent-magnet (PM) synchronous machine while considering a driving cycle. The robustification is obtained by considering geometrical uncertainties caused by manufacturing inaccuracies, uncertainties linked to different driving styles, and uncertainties related to ambient parameters such as traffic and weather conditions. The optimization goal is to minimize the PM’s volume while maintaining the machine performance, i.e., the energy efficiency over the driving cycle and the maximal torque. The magnetic behavior of the machine is described by a partial differential equation (PDE) and is simulated by the finite-element method, employing an affine decomposition to avoid the reassembling of the system of equations due to the changing geometry. Sequential quadratic programming is used for the optimization, and stochastic collocation is applied to compute the moments of stochastic quantities. The robustness of the optimized configurations is validated by a Monte Carlo sampling. It is found that the uncertainties have a significant influence on the optimal PM configuration.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
David S. Abraham; Dennis D. Giannacopoulos

In this article, a novel use of graphics processing units (GPUs) is presented for the acceleration of finite-element time-domain (FETD) methods containing electrically complex media. By leveraging the massively parallel architecture of the GPU via NVIDIA’s Compute Unified Device Architecture (CUDA) language, the immense computational burden imposed by these materials can be largely alleviated, facilitating their modeling and incorporation into electromagnetic devices and systems. To that end, an analysis of both mixed and vector wave equation-based nonlinear dispersive FETD algorithms is presented in order to both identify computational bottlenecks and determine their amenability to parallelization. Based on this analysis, a parallel elemental matrix-evaluation procedure is proposed, which when coupled to the recently derived Gaussian belief propagation method for matrix assembly and solution, demonstrates a performance increase of up to 200 times as compared with a traditionally serial implementation.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Idoia Cortes Garcia; Iryna Kulchytska-Ruchka; Sebastian Schöps

This article proposes an efficient parallelized computation of field/circuit coupled systems co-simulated with the waveform-relaxation (WR) technique. The main idea of the introduced approach lies in the application of the parallel-in-time method parareal to the WR framework. Acceleration obtained by the time-parallelization is further increased in the context of micro/macro-parareal. Here, the field system is replaced by a lumped model in the circuit environment for the sequential computations of parareal. The introduced algorithm is tested with a model of a single-phase isolation transformer coupled to a rectifier circuit.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Wenliang Zhao; Mengmeng Tian; Xiuhe Wang; Yining Sun

This article presents a novel 6/8-pole changing line-start permanent-magnet synchronous motor (LSPMSM) for improving the starting and synchronization capabilities. A 6/8-pole changing stator winding with simple structure, convenient switching, and speed detection capability is designed and studied. The synchronization process, which follows the 6/8-pole winding switching process, is analyzed. The effects of the switching speed, switching phase difference, and the rotor resistance on the synchronization process, respectively, are studied. Moreover, on the basis of the improvement of the starting capability utilizing the pole changing starting strategy, the rotor resistance is appropriately designed smaller to simultaneously balance the synchronization capability. The larger maximum moment of inertia that the motor can pull into synchronization validates the analysis. Through processing, both starting and synchronization capabilities have been improved for the proposed 6/8-pole changing LSPMSM compared with the conventional 8-pole LSPMSM.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Mauro Passarotto; Ruben Specogna

This contribution addresses the solution of eddy-current problems by means of a volume integral formulation based on the electric vector potential on a computational domain that exhibits a cyclic symmetry. Even if grids discretizing the domain are typically composed of tetrahedral or hexahedral elements, the proposed approach also works for general polyhedral meshes, such as those ones obtained by subgridding . In this article, an algorithm to compute a set of suitable cohomology generators needed when the conductors are not simply connected is introduced first. Besides being purely combinatorial, with linear-time worst case complexity and suitable with polyhedral meshes, it reuses a code that computes generators for triangular surface meshes, with obvious advantages concerning the implementation effort. Second, the formulation and the algorithm for cohomology computation are tweaked to be able to solve eddy-current problems with cyclic symmetry reserving specific attention to the construction of suitable tree–cotree decomposition for the problem gauging.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-15
Takehito Mizuma; Amane Takei

An eddy-current analysis ( $A$ - $\phi$ method) based on a domain decomposition method is proposed. A conjugate orthogonal conjugate gradient with an incomplete Cholesky factorization method is generally applied to solve the subdomain problems because the matrices become a singular system. However, it is difficult to achieve high-accuracy solutions using iterative methods because the solutions contain truncation errors. Therefore, the authors propose a method of improving the convergence by applying a direct method based on a singular value decomposition as the subdomain solver. As a result, it is thus confirmed that the improvement of convergence can be realized with the direct method. This article describes the proposed method and the performance evaluation with some examinations.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-10
K. Hollaus; J. Schöberl; M. Schöbinger

The multiscale finite-element method (MSFEM) reduces the computational costs for the simulation of eddy currents (ECs) in laminated iron cores compared with the standard finite-element method (SFEM) essentially. Nevertheless, the complexity of the resulting problem is still too large to solve it conveniently. The idea is to additionally exploit model order reduction (MOR). Snapshots (SNSs) for a reduced basis are cheaply calculated by the MSFEM. Numerical simulations of a small transformer show exceptional performance. This is well demonstrated by the overall EC losses and by the distribution of the magnetic-flux density, both with respect to those obtained by the MSFEM.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-09
C. Dalle

The radio frequency (RF) operation of a planar waveguide THz oscillator based on the distributed transferred electron device (DTED) is theoretically investigated by means of 2-D time-domain numerical physical modeling based on the self-consistent solution of the Maxwell and free electron energy-momentum macroscopic transport equations.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Károly Marák; Jan Kracek; Sándor Bilicz

In this article, we investigate a novel iterative antenna array synthesis method. The method is based on the iterative addition of antenna array elements. After defining the synthesis algorithm, we prove that the discrepancy between the goal and the synthesized pattern converges to the theoretical lower bound in the sense of a certain norm. The algorithm is also extended to iteratively replace already placed elements and for the synthesis of multiple goal patterns with the same array geometry but with different excitations. Some numerical examples are shown to illustrate the convergence properties of the proposed method. Possible applications include circularly polarized patterns, since the algorithm can handle the rotation as well as translation of the antenna elements.

更新日期：2020-01-17
• IEEE T. Magn. (IF 1.651) Pub Date : 2020-01-13
Raj Sahu; Pierre Pellerey; Konstantinos Laskaris

In this article, a new analytical method is proposed to estimate eddy currents inside linear conductive materials. The novel closed-form formulation takes into account the effects of both conductor reaction field that dominates at high frequencies as well as the spatially non-homogeneous nature of the magnetic field penetrating the material. Although the model is suitable for most kinds of permanent magnet machines, it is particularly useful for Surface-mounted Permanent Magnet (SPM) machines where both of these phenomena are prominent. The numerical implementation of the proposed model, which consists of a combination of the method of images and 4-D Fourier transform, is presented. The model is then validated against 2-D and 3-D finite element models (FEMs) for a simple magnetic circuit, showing good agreement. Finally, the eddy current magnet loss in an SPM synchronous machine is evaluated and results are discussed.

更新日期：2020-01-17
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