Search Results (131)

High-precision sensor co-registration is a critical prerequisite for achieving high-resolution imaging in Optically Pumped Magnetometer–Magnetoencephalography (OPM-MEG) systems. The conventional magnetic dipole fitting method, essentially a multipole expansion approximation of a finite-size coil, exhibits accuracy that strongly depends on spatial geometric factors such as coil–sensor distance, dipole orientation, and the projection angle of the sensor’s sensitive axis. Moreover, the approximation error increases significantly when sensors are placed either too close to the coils or at an unfavorable angular coupling. To address this issue, we propose a sensor localization and orientation method that combines magnetic dipole-equivalent modeling with a rigid coil structure (RCS). The RCS provides stable geometric constraints and eliminates uncertainties introduced by scalp-attached coils. In addition, three objective functions (the standard Frobenius norm, a weighted Frobenius norm and the structural similarity index (SSIM)) are formulated to mitigate the imbalance caused by near-field strong signals and to improve stability under noise and error propagation. Simulation results demonstrate that both under ideal conditions and with assembly perturbations, the weighted Frobenius norm and SSIM methods consistently achieve position errors below 1 mm and orientation errors below 1°, which effectively suppress large outlier deviations and achieve better performance than the standard Frobenius norm. The results confirm the effectiveness of the proposed method in achieving both high accuracy and robustness. Beyond clarifying the primary factors influencing magnetic dipole approximation errors, this study provides a geometry-constrained and optimization-based framework, offering a feasible pathway toward the practical implementation of high-precision, multi-channel OPM-MEG systems. Full article

We study unconventional multipole moments arising from noncollinear magnetic structures within an augmented framework encompassing electric, magnetic, magnetic toroidal, and electric toroidal multipoles. Employing a tight-binding model for an s-p hybridized orbital system, we analyze two spiral magnetic textures and classify the resulting multipoles according to magnetic point group symmetry. Different spiral wave types, such as cycloidal and proper-screw forms, activate distinct multipole components, with odd-parity multipoles emerging from local s-p parity mixing induced by magnetically driven inversion-symmetry breaking. Calculated multipole structure factors reveal finite-q peaks originating from higher-order magnetic-dipole-scattering processes and their characteristic couplings between Fourier components of the magnetic dipole texture. Our results demonstrate that magnetic ordering can generate parity-mixed states without intrinsic structural inversion asymmetry, offering new pathways to realize cross-correlation phenomena in functional magnetic materials. Full article

The ferroaxial moment, a time-reversal-even axial dipole degree of freedom, plays a key role not only in conventional quantum states of matter but also in anomalous off-diagonal cross-correlated responses. Here, we theoretically demonstrate that a skyrmion crystal with a swirling non-coplanar spin texture can exhibit ferroaxiality. In particular, we show that a hybrid skyrmion crystal, formed by the superposition of Néel- and Bloch-type vortices, hosts a finite ferroaxial moment. The degree of ferroaxiality is quantified by calculating the expectation value of the electric toroidal dipole within a multi-orbital tight-binding model based on multipole representation theory. We further reveal characteristic off-diagonal responses associated with magnetic and magnetic toroidal multipoles under external magnetic fields. These results establish the hybrid skyrmion crystal as a promising platform for exploring the fundamental nature of ferroaxial moments. Full article

The increasing penetration of electrified vehicles is accelerating the evolution of on-board and off-board charging systems, which must deliver higher efficiency, power density, safety, and bidirectionality under increasingly demanding constraints. This article presents a system-level review of state-of-the-art charging architectures, with a focus on galvanically isolated power conversion stages, wide-bandgap-based switching devices, battery pack design, and real-world implementation trends. The analysis spans the full energy path—from grid interface to battery terminals—highlighting key aspects such as AC/DC front-end topologies (Boost, Totem-Pole, Vienna, T-Type), high-frequency isolated DC/DC converters (LLC, PSFB, DAB), transformer modeling and optimization, and the functional integration of the Battery Management System (BMS). Attention is also given to electrochemical cell characteristics, pack architecture, and their impact on OBC design constraints, including voltage range, ripple sensitivity, and control bandwidth. Commercial solutions are examined across Tier 1–3 suppliers, illustrating how technical enablers such as SiC/GaN semiconductors, planar magnetics, and high-resolution BMS coordination are shaping production-grade OBCs. A system perspective is maintained throughout, emphasizing co-design approaches across hardware, firmware, and vehicle-level integration. The review concludes with a discussion of emerging trends in multi-functional power stages, V2G-enabled interfaces, predictive control, and platform-level convergence, positioning the on-board charger as a key node in the energy and information architecture of future electric vehicles. Full article

During the detailed design of magnets for the storage ring of Siam Photon Source II (SPS-II), the influence of magnetic crosstalk between adjacent magnets in the compact Double Triple Bend Achromat (DTBA) lattice was investigated. Using Opera-3D magnetostatic simulation, six magnet pairs were analyzed to investigate the changes in magnetic field distribution along the electron trajectory and integrated magnetic field within each magnet aperture. The study employed polynomial and Fourier analyses to calculate multipole field components. Results indicate that magnetic crosstalk affects the field distribution in the region between magnets, particularly for the defocusing quadrupole and dipole magnets (QD2-D01) and the focusing quadrupole and octupole magnets (QF42-OF1) pairs, which have the pole-to-pole distances of 153.37 mm and 116.45 mm, respectively. Although these separations exceed the estimated fringe field regions, deviations of up to 1% in the main field components were observed. Notably, even an unpowered neighboring magnet contributes to magnetic field distortion due to the modified magnetic flux distribution. Crosstalk effects on the higher-order multipole fields are mostly within the acceptable limit, except for the extra quadrupole field from QD2 found in the dipole D01 magnet. This study highlights the effects of magnetic interference in tightly packed lattice and underscores the need to include a complete multipole field data with crosstalk consideration in the SPS-II lattice model in order to ensure an accurate beam dynamics simulation and predict the operating current adjustments for machine commissioning. Full article

The flux-reversal permanent magnet machine (FRPMM) exhibits superior energy conversion efficiency, enhanced fault resilience, and structural simplicity. It demonstrates excellent adaptability across variable speed conditions. Nevertheless, high torque ripple remains a primary constraint on the application prospects of FRPMMs. A novel FRPMM with concave stator poles and auxiliary teeth is proposed to address this issue. Sensitivity analysis is carried out, and the dominant parameters affecting the electromechanical characteristics of the machine are determined to be the rotor tooth radian, the permanent magnet tooth radian, and the auxiliary tooth width. Furthermore, the response surface method (RSM) is utilized in conjunction with a multi-objective genetic algorithm (MOGA) to optimize the parameters. Finally, a comparative analysis of electromagnetic characteristics between the proposed FRPMM and a conventional FRPMM is conducted. The results show that the proposed FRPMM can reduce torque ripple, improve output torque, and reduce the amount of permanent magnet. Full article

Interior permanent magnet (IPM) synchronous motors have gained widespread adoption in electric vehicles (EVs) owing to their durable rotor configurations, expansive operational speed range, and superior efficiency. Nonetheless, typical IPM motor designs frequently exhibit high torque ripple and constrained torque density. To address these issues, a torque enhancement method is introduced by applying both filleting and notching techniques to the stator core. These techniques help reshape the magnetic field directly at the stator, allowing for more precise control of torque production and torque ripple reduction while keeping the rotor structure unchanged. Design variables of the stator in a 12-slot/8-pole fractional-slot V-shaped IPM motor are optimized using a multi-objective genetic algorithm based on a sensitivity constraint for unidirectional operation. The electromagnetic performance of the motor is analyzed through 2D finite element simulations for both no-load and loaded scenarios. The proposed motor increases average torque by 2.45% and significantly reduces torque ripple by 47.73% compared to the conventional motor. These reflect a significant advancement in torque capability. Furthermore, the efficiency of the proposed motor reaches 93.8%. The findings suggest the potential of the proposed filleting and notching techniques for torque capability improvement in EV applications. Full article

In this paper, the multi-objective optimization of the 12-pole radial active magnetic bearing (RAMB) is investigated. In the optimization of the RAMB, the decision-maker is more interested in the Pareto-optimal solutions in a certain region. This paper proposes a decomposition-based and preference-based multi-objective evolutionary algorithm (MOEA/D-Pref). The proposed MOEA/D-Pref not only allows the number of Pareto-optimal solutions to be more concentrated in the region of interest but also preserves solutions in other regions. These preserved solutions enable decision-makers to observe a more complete Pareto front, thus gaining more comprehensive insights. In this paper, a mathematical model of the 12-pole RAMB is established, and, with the help of this model and the proposed algorithm, the optimal design of the 12-pole RAMB is completed. The difference between the current stiffness coefficients of the optimized RAMB, calculated by the proposed algorithm and by the finite element method, is 2.3%. The difference between the displacement stiffness coefficient of the optimized RAMB as calculated by the proposed algorithm and by the finite element method is 3.9%. These differences, being less than 4%, are relatively low and verify the reliability of the mathematical model established. Full article

To enhance the electromagnetic performance of flat-wire permanent magnet synchronous motors, three different groove structures were designed for the rotor, and a multi-objective optimization algorithm combining a genetic algorithm (GA) with the TOPSIS method was proposed. Firstly, an 8-pole 48-slot flat-wire motor model was established, and the cogging torque was analytically calculated to compare the motor’s performance under different groove schemes. Secondly, global multi-objective optimization of the rotor groove dimensions was performed using a combined simulation approach involving Maxwell, Workbench, and Optislang, and the optimal rotor groove size structure was selected using the TOPSIS method. Finally, a comparative analysis of the motor’s performance under both rated-load and no-load conditions was conducted for the pre- and post-optimization designs, followed by verification of the mechanical strength of the optimized rotor structure. The research results demonstrate that the combined optimization approach utilizing the genetic algorithm and the TOPSIS method significantly enhances the torque characteristics of the motor. The computational results indicate that the average torque is increased to 165.32 N·m, with the torque ripple reduced from 28.37% to 13.32% and the cogging torque decreased from 896.88 mN·m to 187.9 mN·m. Moreover, the total distortion rates of the air-gap magnetic flux density and the no-load back EMF are significantly suppressed, confirming the rationality of the proposed motor design. Full article

Noncoplanar spin textures give rise not only to unusual magnetic structures but also to emergent electromagnetic responses stemming from scalar spin chirality, such as the topological Hall effect. In this study, we theoretically investigate nonreciprocal transport phenomena induced by noncoplanar magnetic orderings through microscopic model analyses. By focusing on meron–antimeron spin textures that exhibit local scalar spin chirality while maintaining vanishing global chirality, we demonstrate that the electronic band structure becomes asymmetrically modulated, which leads to the emergence of nonreciprocal transport. The present mechanism arises purely from the noncoplanar magnetic texture itself and requires neither net magnetization nor relativistic spin–orbit coupling. We further discuss the potential relevance of our findings to the compound Gd₂PdSi₃, which has been suggested to host a meron–antimeron crystal phase at low temperatures. Full article

To overcome the limitations of single-objective optimization in permanent magnet synchronous motor (PMSM) performance enhancement, this study proposes an adaptive moving least squares (AMLS) for a 12-pole/36-slot built-in PMSM. Through comprehensive exploration of the design space, a systematic approach is established for holistic motor performance improvement. The Gaussian weight function is modified to improve the model’s fitting accuracy, and the decay rate of the control weight is optimized. The optimal adaptive meta-model for the built-in PMSM is selected based on the coefficient of determination. Subsequently, sensitivity analysis is conducted to identify the parameters that most significantly influence key performance indicators, including torque ripple, stator core loss, electromagnetic force amplitude, and average output torque. These parameters are then chosen as the optimal design variables. A multi-objective optimization framework, built upon the optimal adaptive meta-model, is developed to address the multi-objective optimization problem. The results demonstrate increased output torque, along with reductions in stator core loss, torque ripple, and radial electromagnetic force, thereby significantly improving the overall performance of the motor. Full article

We consider the scattering of electromagnetic radiation by a spherical particle, known as Mie scattering. The electric and magnetic fields are represented by multipole fields, and the amplitudes are the Mie scattering coefficients. Properties of the particle are mainly contained in these coefficients. We have studied the dependence of these coefficients on the various parameters, with an emphasis on the dependence on the particle radius. Central to this discussion is what is known as the ‘Mie circle’. Without absorption in the particle or the embedding medium, the Mie scattering coefficients lie on this universal circle in the complex plane. We have studied the location of the Mie scattering coefficients on this circle as a function of the particle radius. The Mie circle also serves as a reference for the case when there is absorption in the particle or the medium. In the limit of a small particle, a peculiar divergence appears in the expression for the Mie coefficients, known as the Fröhlich resonance. We show that this apparent singularity is a consequence of the fact that the limit of a small particle fails in the neighborhood of this resonance, and we derive an expression for the correct small-particle limit in the neighborhood of this resonance. Full article

We introduce the concept of the magnetic metapole—a theoretical extension of classical multipole theory involving a fractional j pole count (related to the harmonic degree n as j = 2ⁿ). Defined by a scalar potential with colatitudinal dependence and no radial variation, the metapole yields a magnetic field that decays as 1/r and is oriented along spherical surfaces. Unlike classical multipoles, the metapole cannot be described as a point source; rather, it corresponds to an extended or filamentary magnetic distribution as derived from Maxwell’s equations. We demonstrate that pairs of oppositely oriented metapoles (up/down) can, at large distances, produce magnetic fields resembling those of classical monopoles. A regularized formulation of the potential resolves singularities for the potential and the field. When applied in a bounded region, it yields finite field energy, enabling practical modeling applications. We propose that the metapole can serve as a conceptual and computational framework for representing large-scale magnetic field structures particularly where standard dipole-based models fall short. This construct may have utility in both geophysical and astrophysical contexts, and it provides a new tool for equivalent source modeling and magnetic field decomposition. Full article

A magnetic toroidal monopole, which characterizes time-reversal-odd polar-charge quantity, manifests itself not only in antiferromagnetism but also in time-reversal switching physical responses. We theoretically investigate an atomic-scale description of the magnetic toroidal monopole based on multipole representation theory, which consists of four types of multipoles. We show that the magnetic toroidal monopole degree of freedom is activated as the off-diagonal imaginary hybridization between the single-site orbitals with the same orbital angular momentum but different principal quantum numbers. We demonstrate that the expectation value of the magnetic toroidal monopole becomes nonzero when both electric and magnetic fields are applied to the system. Full article

Magnetic toroidal multipoles have recently emerged as key descriptors of unconventional cross-correlation phenomena in antiferromagnetic systems. Among them, the rank-2 magnetic toroidal quadrupole, which is characterized as a time-reversal-odd polar tensor, has been theoretically associated with a variety of cross-correlation phenomena arising from the time-reversal symmetry breaking. In this study, we investigate the interplay between magnetic toroidal quadrupoles and electric toroidal dipoles in antiferromagnets, with a particular focus on magnetic field-induced ferroaxiality. Through symmetry analysis and microscopic model calculations, we demonstrate that ferroaxiality can be induced by an external magnetic field, depending on both the field direction and the type of the magnetic toroidal quadrupole. We classify all magnetic point groups that possess magnetic toroidal quadrupoles and identify various candidate materials based on the MAGNDATA database. Our findings reveal a route to coupling spin and lattice degrees of freedom via toroidal multipoles. Full article