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In this article, boundary conditions for Landau–Lifshitz equations at the interface between two ferromagnets with different interfacial Dzyaloshinskii–Moriya interactions (iDMIs) are derived. We calculated and verified the analytical expression for the energy flux density continuity for the spin-wave (SW) propagation through the ferromagnet with stepwise iDMI considering the boundary conditions mentioned. Analytical expressions for reflection, transmission coefficients, and the nonreciprocity factor are calculated in the case of SW propagation through a ferromagnet with the stepwise iDMI. Two different types of nonreciprocity effects for SW propagation through a ferromagnet with the stepwise interface Dzyaloshinskii–Moriya interaction are revealed for opposite orientations of Dzyaloshinskii–Moriya vector. The material parameters of a ferromagnet and the stepwise iDMIs are found for which the extremely high nonreciprocity factor (>10) is expected according to the results of calculations. The results of this article deepen the knowledge about the SW propagation control in magnonic devices. [ABSTRACT FROM AUTHOR]

Based on thermoelectric analogy method, a thermal network model coupled with electromagnetic loss is presented. According to the actual structure of dry-type transformer windings, an accurate thermal network is established. Considering the distribution characteristics of heat source along the cooling ducts inside the dry-type transformer, the thermal parameters such as heat flux and convective heat transfer coefficients are calculated by finite element method (FEM) analysis and computational fluid dynamics (CFD). Based on the temperature rise experiment, the hottest spot located at the top of the outmost high-voltage (HV) winding is 151.8 °C, which verified the correctness of thermal network model. [ABSTRACT FROM AUTHOR]

In this article, a novel fault-tolerant design process of the spoke-type interior permanent magnet (IPM) motor is proposed to prevent the increase of cogging torque and torque ripple due to partial demagnetization fault and to minimize the motor size. First, unlike other research papers on the irreversible partial irreversible demagnetization of permanent magnet (PM), in this article, the effect of partial irreversible demagnetization faults on the cogging torque and torque ripple for the fault cases is investigated. Then, a novel fault-tolerant design process is proposed to solve the problem of partial demagnetization faults that increase the cogging torque and torque ripple. In the novel fault-tolerant design process, first, to solve the problem of increasing cogging torque and torque ripple due to the partial demagnetization fault, a process for implementing a uniform irreversible PM demagnetization is proposed. Second, to compensate for the motor torque constant decreased by degraded PM, which is caused by irreversible demagnetization of PM, a torque compensation coefficient is also proposed. The proposed fault-tolerant design process is applied to the motor design for the integrated electric brake (IEB) system that requires high torque density. In the optimal design process, Latin hypercube sampling (LHS), a kriging method, and a genetic algorithm are utilized. To verify the effectiveness of the proposed fault-tolerant design process, it is compared with the conventional optimized design results in which irreversible demagnetization of PM is not allowed at all to prevent the partial demagnetization faults. As a result of comparing the optimal design results, the proposed optimization model utilizing the fault-tolerant design process can significantly reduce the motor volume by 12.9%, compared to the conventional optimization model. [ABSTRACT FROM AUTHOR]

This article serves as an overview of existing models of permanent magnets (PMs) for electrical machines. The review study starts with the linear recoil model, which is commonly used to describe the reversible part of the demagnetizing curve. It is a simple model, especially useful for representing materials with high anisotropy, such as ferrite, NdFeB, and SmCo. The model is harder to apply for nonlinear materials, such as Alnico, but still possible since their recoil curves are linear. The study shows how the linear recoil model could be extended to include irreversible demagnetization, temperature dependence, and angular dependence. All such models have their advantages and disadvantages, which will be discussed further. Both the magnetization and the risk of demagnetization are temperature-dependent. It could be noted that NdFeB has an increased risk of demagnetization at high temperatures, while ferrite has it at very low temperatures. The temperature dependence is described and compared for several materials, also including simplifying models. There are different methods to include the inclination angle of an applied magnetic field when studying the demagnetization of PMs. Several models describe different phenomena associated with the underlying dynamics of magnetism. Such models could then consider coercivity mechanisms and coherent rotation of magnetization, both with the Stoner–Wohlfarth model and models of domain wall motions. [ABSTRACT FROM AUTHOR]

In this work, a simple method is proposed to simultaneously reduce the size and cross-polarization level (XPL) of quarter-wave microstrip antennas by reconstructing the magnetic currents along the radiation edges. A design example of five shorted elements is given with a comparison of the quarter-wave microstrip antennas at 1.88 GHz. Measured results show an over 64% size reduction and 17-dB cross-polarization suppression enhancement for the proposed scheme as compared with the conventional one. Moreover, the proposed scheme exhibits good broadside radiation patterns with a gain of 5.4 dBi and the half-power beamwidths of about 104° in the E-plane and 84° in the H-plane. [ABSTRACT FROM AUTHOR]

The laser beam melting (LBM) additive manufacturing (AM) technology is used for processing a high silicon steel (Fe 6.5%wtSi). The effects of LBM machine parameters over microstructure and magnetic properties are studied. Particular attention is dedicated to determining the influence of a normalized energy density over the material density, the grain size, and the crystallographic texture and their impact on the magnetic properties: magnetic flux density and coercivity. [ABSTRACT FROM AUTHOR]

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This article presents the electromagnetic and mechanical design and analyses of a 7.67:1 gear ratio magnetic gear (MG) for a wave energy converter demonstrator. A 2-D and 3-D magnetostatic finite-element analysis (FEA) was conducted to maximize the mass torque density. To increase torque without increasing the diameter, a unique dual-stack rotor topology was used along with a 12-segment per pole-pair inner rotor Halbach array and a four-segment per pole-pair outer rotor Halbach topology. The eddy current loss within the MG was mitigated by using laminated magnets and low-loss electrical steel. The experimentally tested MG had a peak torque of 1796.8 $\text{N}\cdot \text{m}$ , which corresponds to an active region volumetric and mass torque density of 221.1 $\text{N}\cdot \text{m}$ /L and 105.74 $\text{N}\cdot \text{m}$ /kg, respectively. The efficiency at rated speed and maximum torque was measured to be 95%. A new in-plane eddy current loss mechanism was identified as being a primary reason for the measured electrical losses being higher than the initially calculated one. [ABSTRACT FROM AUTHOR]

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers. [ABSTRACT FROM AUTHOR]

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With the emergence of electric vehicles and electric aircraft technologies, lightweight motors have become a requirement. Conventional motors are generally made up of coils, permanent magnets, heavy iron stators, and rotor cores. This article presents complete analytical modeling and design of a novel coreless multi-phase magnetic resonant motor (MMRM), conceptualized through the approach of magnetic resonance coupling. The removal of magnetic iron cores drastically reduces the weight of the resulting motor. The stator and rotor cores of the motor are made of reinforced plastic fibers and can be 3-D printed. Unrelated to the general operating principle of the existing conventional electric motors, resonant wireless power transfer (WPT) is the key feature of these motors. All the essential machine characteristics, such as self-inductance, mutual inductance, torque, and frequency domains, are fully developed. The mathematical modeling of the machine’s physical phenomena is linked to its operation by simulation. This article shows the design concept and discusses the simulation procedure used to verify the developed analytical model through a finite-element analysis (FEA) from the established modeling topology equivalent to the proposed configuration motor model. Although the design is straightforward, an accurate analytical modeling and analysis are significant challenges to consider. [ABSTRACT FROM AUTHOR]

Electrically evoked compound action potential (ECAP) represents a synchronous response of a group of nerve fibers activated by electrical stimulation. ECAP has been an important physiological signal for the cochlear implant (CI) used in various clinical studies. A 3-D CI model based on a patient’s medical images was created to simulate ECAP using the finite element method (FEM) and neuron models in this study. ECAPs obtained by alternating polarity approach were recorded by several sensing electrodes with different current levels. The least-square optimization method was used to calibrate the ECAP simulation results and they were compared with a patient’s clinical ECAP measurements. Results showed that calibrated simulations of ECAPs were consistent with the ECAP measurements. This study demonstrated that simulated ECAP based on CI models could be used as a reference for patient-specific CI studies for CI objective programming. [ABSTRACT FROM AUTHOR]

This article presents an accurate analytical model (AM) for synchronous reluctance machine (SynRM) that incorporates the effect of stator slots on the air gap flux density and torque waveforms. From the formulation of magnetic potential in the air gap for both the stator and rotor, the flux density is obtained, considering the first harmonic of the flux density and the electric loading, the average torque is calculated using the Lorentz’s force. The ripple torque is obtained from the energy stored in magnetic circuit. The method is developed for a rotor with one flux barrier per pole and then extended to a larger number of barriers. To validate the results obtained by the AM proposed finite element analysis have been carried out. Several comparisons have been derived considering different rotor positions as well as different harmonic orders, and the pros and cons of the method are highlighted. The model performs fast and can predict results with high accuracy, and can be adopted to speed up the preliminary design and optimizations of this type of motors, with respect to finite element. In addition, from the analytical expressions it is possible to obtain all the correlations between electrical, magnetic, and geometrical characteristics of the machine, with the advantage of enabling a faster machine design. [ABSTRACT FROM AUTHOR]

Since the torque characteristic of a surface permanent magnet synchronous motor (SPMSM) is strongly dependent on its magnetization distribution (MD), the prior estimation of MD is essential for its practical design. An effective method for estimating MD involves minimizing the squared function of the difference between the measured magnetic flux density and the flux density derived from the numerical analysis of the region surrounding the permanent magnet. However, as there are countless MDs for reconstructing the specified magnetic flux density, it is important to estimate the realistic MD. In this article, we proposed an estimation method to derive the realistic MD based on the Biot–Savart law incorporated with mathematical programming (steepest descent method and quasi-Newton method). In this method, MD was formulated in the spherical coordinate system. Since the constraints regarding magnetization intensity and angle were defined by the sigmoid function, both quantities were definitely distributed within the constraints. Consequently, the generation of nonphysical MD was efficiently suppressed. Furthermore, the validity of the proposed method was illustrated in comparison with other estimation methods, such as the least-square method, Tikhonov regularization, and the truncated singular value decomposition (TSVD) method. [ABSTRACT FROM AUTHOR]

A low residual environmental magnetic field is required for the proper operation of most optically pumped magnetometers (OPMs). This is achieved using a combination of passive and active magnetic shielding. Passive magnetic shielding often uses multiple layers of highly permeable materials. A realistic two-layer magnetically shielded room (MSR) for biomagnetic measurements is numerically studied using the finite element method. A measured B-H characteristic of Mumetal is used, which is linearly extrapolated from the Rayleigh region (RR) into the low magnetic field range. This extension of the magnetization curve yields no significant differences compared to using a constant permeability value for the low magnetic field range. Furthermore, we model the MSR with only one shield and apply a simple analytical method of images (MOI). The MOI yields on average a 100-fold reduction in computation time. The relative difference of the magnetic flux density computed with MOI and finite element method (FEM) is smaller than < 1% at the center of a spherical region of interest (ROI) with a radius of 0.3 m desired from the point of magnetoencephalography (MEG) using OPMs. The achieved accuracy of the MOI makes it suitable for the optimization of active shielding coils. [ABSTRACT FROM AUTHOR]

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A measurement system capable of in situ measurements of formation permeability is described. The measurement method relies upon imaging the distribution of magnetic permeability fluid injected into a wellbore system through mutual inductance measurements between pairs of coils and relating the change in distribution of this fluid over time to a direct measurement of formation phase permeability. Analysis of the mutual inductance measurement method shows a unique response to distributions of magnetic permeability for various coil spacings and insensitivity to other confounding electrical parameters. The lower bound of measurement variance for this system is modeled for a continuum of coil spacings and radii of investigation for a perturbation in magnetic permeability. [ABSTRACT FROM AUTHOR]

The aim of this article is to analyze the design of a magnetic spring-based nonlinear oscillator system and investigate its magnetic properties, the effect of gravitational force, the accuracy of the modeled magnetic restoring force, the coefficient of the magnetic restoring force, and the nonlinear response of the proposed system. The proposed magnetic spring-based nonlinear oscillator system consists of a nonmagnetic shaft, floating magnet, and two fixed magnets where all magnets are placed in such a way that each magnet can repel the other. The magnetic properties of the proposed system are studied numerically and analytically to provide insight into its role in the nonlinear oscillatory behavior of the system. The effect of the gravitational force, which changes the equilibrium position and the nonlinear behavior of the magnetic spring, is studied. The numerical analysis of the magnetic flux density and magnetic restoring force is validated using an analytical and experimental analysis. Different orders of polynomial curve fittings, such as cubic and quintic, are used to model the magnetic restoring force between the moving magnet and the two fixed end magnets. Finally, the linear and nonlinear coefficients of the magnetic spring-based system for different positions of the floating magnet are investigated. [ABSTRACT FROM AUTHOR]

We investigated the effects of sputtering conditions for the deposition of an Iridium (Ir) layer in a [Co/Pt]m/Co/Ir/[Co/Pt]n/Co/W/CoFeB synthetic antiferromagnetic reference layer (Ir-SyF) on the magnetic properties and tunnel magnetoresistance ratio (TMR ratio) of magnetic tunnel junctions (MTJs) stacks annealed at 400 °C for 1 h. The exchange coupling field ($H_{\mathrm {ex}}$) of Ir-SyF was improved by reducing the energy of Ir recoil ions and two times larger than that with Ru-SyF. Energy dispersive X-ray (EDX) spectrometry line analysis revealed greater interlayer diffusion in Ir when Ir was sputtered by using a conditions with large recoiled energy. This could cause the deterioration of the $H_{\mathrm {ex}}$ of the Ir-SyF. Despite the larger $H_{\mathrm {ex}}$ , the TMR ratio of the MTJ with Ir-SyF is smaller than that with Ru-SyF. The $m$ – $H$ curve of MTJ with Ru-SyF showed a large plateau region around zero magnetic field, whereas that with Ir-SyF did not. These results indicated the degradation of perpendicular magnetic anisotropy (PMA) in the top part of the Co/Pt multilayer with CoFeB reference layer and a large biquadratic coupling effect in the thin Ir layer. This causes the deterioration of the TMR ratio of the MTJ with Ir-SyF. TEM image of the Co/Pt layer in the MTJ with Ir shows some lattice defects. The EDX line analysis revealed that a large amount of Pt in the top Co/Pt layer diffused toward CoFeB reference layer in the Ir-SyF, resulting in the degradation of PMA. The structural analysis by X-ray diffraction showed the lattice spacing of CoPt (111) in Ir-SyF to be larger than that in Ru-SyF, indicating the occurrence of strain relaxation at the Co/Pt interface. These crystallographic changes in Ir-SyF might be related to a larger Pt diffusion. Suppression of Pt diffusion as well as low damage Ir deposition in the reference layer is crucial to utilize Ir-SyF. [ABSTRACT FROM AUTHOR]

The effects of annealing temperature ($T_{a}$ , 600 °C–950 °C) and Sm content on the phase transformation and magnetic properties of SmxFe11Ti ($x $ = 0.9, 1.0, and 1.1) alloys prepared by the melt-spinning method were investigated. In all specimens with different compositions, the crystal structure was transformed from the TbCu7 to ThMn12 structure as $T_{a}$ increased. The coercivity reached 6.3 kOe in a SmFe11Ti ribbon annealed at 850 °C. However, the grain size of this ribbon was much smaller than the critical single domain size of the SmFe11Ti alloy. The microstructural analysis revealed that the ribbons were highly strained. To overcome the abnormal low coercivity of SmFe11Ti alloy, precise control of the composition and removal of strain without grain growth are the critical factors. [ABSTRACT FROM AUTHOR]

In this work, we develop the hybrid current sensor comprising a microfluxgate and a current transformer (CT) for wide-bandwidth current measurement. The microfluxgate consists of two microcoil chips 3.5 mm $\times1.75$ mm in dimension made by using the standard Complementary Metal-Oxide Semiconductor MicroElectroMechanical Systems (CMOS-MEMS) $0.35 ~\mu \text{m}$ process. The aluminum wire-bonding technique is used to construct the top excitation coil surrounding the amorphous soft magnetic core patterned by photolithography and wet etching techniques. Under the optimal excitation condition, the response of the microfluxgate current sensor becomes linear with a maximized sensitivity. The in-house made CT is combined with the microfluxgate driving system to form the hybrid current sensor by using a summing amplifier. The hybrid current sensor has a spectral current noise of 0.4 mA/ $\surd $ Hz at 1 Hz. The maximum sensing range is ±10 A, and the non-linearity is less than 2% within the ±4.6 A range, corresponding to a linear dynamic range of 60 dB in a 10 Hz bandwidth. The hybrid microfluxgate-and-CT sensor has a flat bandwidth from dc to 100 kHz. It has the potential to become a practical miniature device featuring a high-dynamic range, wide bandwidth, and low-temperature drift. [ABSTRACT FROM AUTHOR]

The change of magnetic properties by varying spin angle is focused in this article. The (Fe)-doped-MoSe2 monolayer (ML) has been studied for both ferromagnetic (FM) and anti-FM (AFM) stability with varying spin angle from 0° to 360° and is found to be AFM stable. Furthermore, the three different AFM configurations are analyzed namely AFM-A, C, and G. The minimum energy has been obtained for AFM-A configuration and the electronic stability is studied in terms of both formation ($E_{\mathrm {form}}$) and binding ($E_{b}$) energy. The total density of states (TDOS) and band structure have been reported as electronic properties with magnetic nature confirmed with asymmetry in TDOS of (Fe)-doped-MoSe2 ML. Secondly, the reduced band gap of 1.04 eV is witnessed with increased electron population in the conduction band (CB). The magnetic anisotropic energy (MAE) is emphasized as a critical magnetic property and is plotted graphically with varying spin angle. An asymmetrical lobe is obtained with maximum amplitude at 270° and minimum at 225° owing to different charge distribution in the d-orbital. The d-orbital contribution in the asymmetrical MAE is discussed in depth. Moreover, the two parameters namely, Neel’s temperature ($T_{N}$) and magnetic exchange coupling ($J$) is explored as an application of MAE. Interestingly, $T_{N}$ is extracted below the room temperature indicating robust AFM attitude and negative value of $J$ shows AFM nature which is in alignment with reported configuration. [ABSTRACT FROM AUTHOR]

Transcranial magnetic stimulation (TMS) is a treatment procedure for some neuropsychiatric disorders, and it has been used for brain mapping, as well as diagnosis and treatment of neuromuscular dysfunctions. There is a disconnect between TMS modeling and clinical data: several groups have reported the simulated induced electric field and measured resting motor threshold (RMT) with inconsistent results in the relationship between RMT and brain scalp distance. This necessitates the use of simulation parameters that further account for individual differences in neuroanatomy. We recruited ten healthy subjects and obtained empirical RMT, magnetic resonance imaging (MRI), and diffusion tensor imaging (DTI). We developed anatomically accurate brain models from MRI and simulated TMS to determine the percent depolarized volume of gray matter (DVG) from TMS-induced electric fields. Corticospinal fiber tracts were extracted from the primary motor cortex from DTI to obtain fiber tract surface areas (FTSAs) for each participant. Linear mixed-effects models were used to evaluate the effect of DVG and FTSA on RMT. We report that DVG correlates with RMT when accounting for corticospinal FTSA. [ABSTRACT FROM AUTHOR]

Microwave-assisted magnetic recording (MAMR) is a promising technique for improving the recording density of hard disk drives (HDDs). We propose a spin-torque oscillator (STO) structure with two field generation layers (FGLs) and two spin-injection layers (SILs) for microwave generation. By using a macrospin model and micromagnetic simulations, we numerically demonstrate the low current operation of the STO. The nearly antiparallel oscillations of the FGLs, which make suitable microwave distribution for MAMR, are stabilized by slight modulation of the in-plane phases of the FGLs and synchronization of the SILs. The enlarged spacing between the FGLs enhances the microwave amplitude at the media plane. These results indicate that, by using the dual-SIL dual-FGL STO, write heads for MAMR can operate using little energy to achieve high recording density. [ABSTRACT FROM AUTHOR]

This article presents a new analytical approach for the calculation of mutual inductance based on magnetic vector potential (MVP). To demonstrate the proposed mutual inductance calculation method, planar spiral coils of polygonal shape with an arbitrary number of sides are discussed. The coils considered in this work are coaxial and assumed to be composed of concentric filaments. The flux produced by the primary and linking the secondary is calculated by the line integral of the MVP. In order to simplify the calculation strategy, the MVP contribution of only one side of each single-turn filament of the primary is considered due to the symmetry of the coils’ shapes. Accordingly, coupling flux across the surface surrounded by each turn of the secondary is calculated by the line integral of the MVP over half path of the filament’s turn. The accuracy of the new analytical approach is confirmed by examining coil systems with a different primary and secondary in terms of the number of sides, the number of turns, and size. Results of the new approach are compared with those obtained from Ansys Maxwell, analytical studies in the literature, and experimental to demonstrate the validity of the proposed method. Results from this work are in good agreement with those obtained from simulation, studies in the literature, and experiment that proves the feasibility of formulas used in this work. [ABSTRACT FROM AUTHOR]

Current-induced domain wall motion (CIDWM) shows promising prospects with low power, high density, high speed, and so on. Recent studies have demonstrated that magnetic tunnel junction (MTJ) based on CIDWM has great potential in mimicking a non-volatile artificial neuron and synapse. By combining the effect of the interfacial Dzyaloshinskii–Moriya interaction (DMI) to stabilize the Néel-type domain wall (DW) and the high-speed low-power advantages of spin orbit torque (SOT), the novel MTJ device is experimentally demonstrated with low threshold current and high propagation speed, which shows potential applications in the field of the artificial neuron and synapse. In this article, a compact model for CIDWM-MTJ based on SOT and DMI is presented. The model integrates the SOT mechanism for magnetization reversal and DW nucleation, CIDWM behaviors, and tunnel resistance theory of MTJ nanopillar. The micromagnetic simulation and the temporal evolution of the DW position are implemented by solving the Landau–Lifshitz–Gilbert (LLG) equation and the 1-D model. Based on the developed model, a hybrid CIDWM-MTJ/CMOS circuit is simulated for verification. The presented model combines the CIDWM dynamics and the MTJ magnetic dynamics, showing potential application for the simulation of all-spin artificial neural network (ANN). [ABSTRACT FROM AUTHOR]

A quick and easy method to detect Fusobacterium species has been developed to utilize magnetic nanoparticles’ magnetic response and is applied by switching magnetic fields. The bacterium can be detected without the washing process. The magnetic nanoparticles and Fusobacterium species are bound by an antigen–antibody reaction and aggregated into a spherical shape using a needle-shaped magnetic yoke. The aggregation of magnetic nanoparticles improves the signal-to-noise ratio to detect the bacterium. We report that a clear tendency for the concentration of Fusobacterium nucleatum can be derived by analyzing the amount of reverse magnetization and the correlation coefficient of a waveform, as well as checking the principal component analysis. This analysis is useful for an accurate evaluation of the antigen. Specific detection of Fusobacterium nucleatum was demonstrated through the cross-reaction using Candida albicans. The optical density (OD) sensitivity value was around 10−4–10−3. [ABSTRACT FROM AUTHOR]

This article presents a new type of surface-mounted three-phase permanent magnet synchronous motor with the same number of poles and slots which has obvious advantages in cogging torque. Since the same-pole and same-slot three-phase permanent magnet motor has three or more slot types and the slots are not evenly distributed on the circumference, this article adopts an accurate subdomain model that considers the position and slot width of each slot separately to perform an analytical calculation of the magnetic field. The motor is divided into three subdomains and modeled by Maxwell’s equations, and the magnetic scalar vector equation satisfied by each subdomain is solved by the method of separation of variables. A 24-pole 24-slot three-phase permanent magnet motor consisting of 13-pole 12-slot and 11-pole 12-slot is used to verify the correctness of the proposed analytical computational model. Compared with the finite element analysis, the proposed analytical model shows high accuracy in the calculations of the magnetic flux density of the three subdomains. [ABSTRACT FROM AUTHOR]