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For a segmented dynamic wireless power transfer (DWPT) system, when electric vehicles (EVs) move over two adjacent transmitting coils, the received power fluctuates greatly and has some loss. Arming at this problem, this paper proposes a dual receiver segmented DWPT topology to reduce the received power fluctuation of the receiving coil passing through the rail junction during the moving process of the EV. Through magnetic field analysis in this paper, tuning the current phase difference between two adjacent transmitting coils to 180° can enhance the magnetic field. In this paper, a dual receiver series topology (DRST) is designed to pick up power, which consists of four fully controlled components and four diodes. According to EVs' real-time position, the segment DWPT system has three working modes and six working states under the control of DRST. Finally, experiments are carried out. Compared to the single-receiving-coil system, DRST is effective in improving the average output power from 2.007 to 5.657 W and significantly reducing the power fluctuation. [ABSTRACT FROM AUTHOR]

TEAM Problem 35, a benchmark problem in the optimization of electrical equipment, is a multi-objective, multi-variable optimization problem involving uniform field optimization. This paper proposes a novel guided optimization algorithm to address this problem and achieve optimal magnetic field regulation. First, the deep learning method is used to predict the magnetic field of the solenoid; second, the generated magnetic field cloud map is screened to extract the magnetic field information of the more optimal solution with uniform magnetic field distribution by calculating the variance of the generated magnetic field map; finally, the magnetic field features are combined with the particle swarm optimization algorithm; specifically, the variance of the calculated magnetic field map is added to the objective function of the optimization algorithm to strengthen the optimization process. This integration improves the convergence speed of the optimization process and ensures the continuity and stability of the obtained Pareto solutions. To optimize the solenoid, this paper considers the uniformity of magnetic field distribution and power loss as the primary optimization objectives. The radius of the coil is chosen as the design variable. The optimization results are compared with those obtained by conventional optimization algorithms, demonstrating superior optimization performance. [ABSTRACT FROM AUTHOR]

The performance requirements of motors are gradually increasing, and anisotropic soft magnetic materials have been applied in motors to improve performance, The magnetostriction of anisotropic soft magnetic materials is one of the main contributors in extensive research on anisotropic soft magnetic material transformers. Compared to transformers, the magnetic field in motors has more complex harmonic and multi-directional characteristics. In this paper, the magnetic field of motors stator teeth under both no-load and load conditions is calculated and analyzed to research magnetostriction of anisotropic soft magnetic materials in motor magnetic field and predict the NVH performance of anisotropic soft magnetic material motors accurately. Furthermore, the magnetostriction in different magnetization angles is investigated for the multi-directional characteristics, and the result is explained from microscopic principles. This paper focuses on a splicing oriented silicon steel (OSS) motor, the magnetization angle of OSS in motor varying from 0° to 90°. Firstly, the equivalent formulas of magnetic field are obtained under the analytical and finite element calculations. After that, the frequency and direction of experiment magnetic field are confirmed and the magnetostriction of OSS in different magnetization angle and frequency is measured. In the end, the variation character of magnetostriction of OSS is summarized. [ABSTRACT FROM AUTHOR]

The high temperature superconductors enhanced magnetoplasmadynamic thruster is a promising device for various space mission scenarios. However, a critical issue hindering the enhancement of the thruster's performance is the problem of anode power deposition. Previous studies have identified the anode fall voltage as a major contributor to this power deposition. This paper introduces an approximate analytical formula for calculating anode power deposition resulting from anode fall voltage. The paper further analyzes and calculates the variation of anode fall voltage with an applied magnetic field and discharge current. The findings reveal a direct correlation between applied magnetic field and both anode fall voltage and power, indicating an increase with higher magnetic field values. In contrast, while the anode fall voltage experiences a slight decline with increased discharge current, the anode power deposition remains elevated due to the transition from field ionization to thermal ionization. To gain a comprehensive understanding of anode power deposition, an experiment was conducted to obtain measurements under different operating conditions, involving varying levels of applied magnetic field and discharge current. The experimental results align with the theoretical predictions. These insights have the potential to serve as a valuable reference for enhancing the efficiency of magnetoplasmadynamic thrusters, bringing us closer to unlocking the full potential of these remarkable propulsion systems in the realm of space exploration. [ABSTRACT FROM AUTHOR]

In magnetically coupled wireless charging systems for electric vehicles, it is common for metal objects to enter the charging system. In this case, the strong magnetic field of wireless charging causes an eddy current effect in the metal object, which generates a large amount of heat. This heat accumulation poses a risk of fire. In this paper, a novel metal object detection system designed for wireless charging of electric vehicles is proposed. The system utilizes the principle that the coil impedance and coupling coefficient change with the presence of metal objects, and a set of composite coils is designed to improve the sensitivity of detection. The detection coil and feedback coil in the composite coil are decoupled by reverse series connection. An LC oscillating circuit based on transformer feedback is used to detect metal objects, and the circuit can make good use of the parameter changes of the composite coil. Finally, an experimental platform for wireless charging metal detection in electric vehicles has been built to validate the proposed system. Through testing, it has been demonstrated that the system can detect the presence of metal objects in a timely and accurate manner. [ABSTRACT FROM AUTHOR]

In this paper, a pole-changing (PC) flux reversal permanent magnet (FRPM) motor is proposed for obtaining a wide speed range. According to the general air-gap field modulation theory, the permanent magnet (PM) magnetic field is modulated into a series of harmonics with different pole numbers by rotor teeth. By introducing an especial PM arrangement, two groups of working harmonics with different pole-pair numbers are generated in the proposed 12-7 PC-FRPM motor due to the modulation of rotor teeth. Based on the calculated slot pitch angles of these harmonics, two winding connections can be obtained for PC operation to achieve two operating modes. The electromagnetic performance of PC-FRPM motor before and after PC are analyzed using finite element analysis and verified by the experimental test results. [ABSTRACT FROM AUTHOR]

The drop tower is an important experimental facility to provide a microgravity environment on the ground. The National Precise Gravity Measurement Facility has built a vacuum drop tower at Wuhan in China. The vacuum drop tower has a falling-height of 20 m, a free falling-time of 2.0 s, and a pressure of ∼6.15 Pa after 1 h pumping. The microgravity level of the vacuum drop tower is analyzed in this paper. The error sources include the aerodynamic drag, the difference of gas pressure around the gaps, the misalignment, the rotation, the magnetic field, etc. The evaluated microgravity level of the vacuum drop tower is better than (4.80 ± 3.31) × 10−7g, which is mainly limited by the aerodynamic drag and the rotation of the capsule. In addition, the microgravity level is measured to be better than 3.22 × 10−5g by using the quartz-flexure accelerometer. The vacuum drop tower provides a ground-based public service platform with a microgravity environment on the order of magnitude of 10−7g for further experiments. [ABSTRACT FROM AUTHOR]

To solve the problem of slow simulation calculation of magnetic field in oil-immersed transformers, this paper proposes a fast calculation method based on the proper orthogonal decomposition (POD) and Kriging response surface method. First, based on the POD reduction method, the discrete equation of the magnetic field is reduced to obtain the modal coefficient matrix. Then, taking the transformer load rate as an important parameter, the sample space is determined, and the corresponding snapshot matrix of the sample space is obtained through COMSOL software. Based on the Kriging function, a response function for the load rate and modal coefficients is constructed, and combined with the reduced mode, the winding magnetic field is quickly reconstructed. Finally, to verify the effectiveness of the method, four additional load conditions were selected to analyze the deviation between the reduced-order model and the full-order model from the perspective of computational accuracy and efficiency. The results show that, in terms of computational accuracy, the maximum relative error between the reduced-order model and the simulation model in the verification points is only 1.045%, while the rest of the points are below 1%. In terms of computational efficiency, the method proposed in this article improves the computational efficiency to 4743 times that of the full-order model. It only takes 0.9 s to calculate the results corresponding to a certain operating condition, which can achieve fast calculation. [ABSTRACT FROM AUTHOR]

In this paper, the magnetic immunity model of STT-MRAM is established. The influence of the external magnetic field on the effective energy barrier of STT-MRAM is investigated, which is the crucial issue to influence the reliability of STT-MRAM cells in the standby, active read and active write modes. The influence factors on the magnetic immunity of STT-MRAM array are also discussed in the paper, such as the electrode, package material, insert layer and array spacing, etc. Moreover, the magnetic shield models in the BGA and QFP packages are designed and analyzed for the enhancement of the magnetic immunity of STT-MRAM, whose shielding efficiency is up to 98.2%. [ABSTRACT FROM AUTHOR]

Free-burning arc discharges play important roles in physical processes such as cutting, welding, arc furnaces, and switchgear. Therefore, in this paper, a combination of node-based and edge-based finite-element methods with the finite-volume scheme is developed to investigate the dynamics of these arc discharges. Considering the significant effect of self-induced magnetic fields on the dynamics of the thermal plasma arcs, accurate analysis of these magnetic fields is essential, especially for 3D geometries describing realistic conditions. Accordingly, the edge-based finite-element module is utilized to study the Ampere law in its vector form for estimating the vector potential and the corresponding magnetic field. Furthermore, the current conservation equation is solved using the node-based finite-element technique. The fluid dynamics are also investigated with the well-known finite-volume method. This hybrid model gives more accurate magnetic fields and Lorentz forces. Electromagnetic forces create high-speed streams of thermal plasma and increase the pressure in the near regions of the electrodes. As a result, the pressure and velocity profiles are closer to the predicted results. In addition, the fluid flow changes the temperature distribution in a way that agrees with experimental measurements. [ABSTRACT FROM AUTHOR]

This paper thoroughly investigates the analysis of a modified generalized mean-field Ising model. The thermodynamic limit of free energy is investigated, and both the upper and lower bounds are derived. The lower bound is derived using a standard entropic variational principle, whereas a decoupling method is employed to derive the upper bound. Although the two bounds differ in form, they exhibit the same local maxima. Finally, the impact of a slight external field on the magnetic order is analyzed. [ABSTRACT FROM AUTHOR]

Cryogenic refrigeration technology based on magnetocaloric effects plays a critical role in a variety of technological applications. In this paper, we report the cryogenic magnetocaloric effects of a series of sodium-rare earth fluoride samples (Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb) synthesized by the solid-state reaction method. These compounds all crystallize in a hexagonal crystal structure. Down to 2 K, no magnetic ordering was detected, while all compounds show negative Curie–Weiss temperatures indicative of strong antiferromagnetic coupling. Magnetic fields effectively suppress the magnetic fluctuations, leading to a maximum magnetic entropy change of −56 J kg−1 K−1 in NaGdF4 at the magnetic field change from 0 to 50 kOe. These series of compounds are potentially excellent magnetic refrigerants at low temperatures. [ABSTRACT FROM AUTHOR]

In this article, we present a multi-fluid numerical model developed for application on electron cyclotron resonance ion sources (ECRIS). The 1D-model is matured to compute the density of the ion species in the plasma sheath in the presence of an inhomogeneous magnetic field of a 2.45 GHz ECRIS. The multi-fluid model in cylindrical coordinates is focused on solving the continuity and momentum equations of hydrogen plasma particles to characterize their sheath properties. In addition, 28 important processes, including volume and surface collisions, have been included in the COMSOL Multiphysics package to simulate the ECR plasma. We study the elementary processes containing electron–atom, electron–molecule, atom–molecule, molecule–molecule, and particle–wall interactions. Then, the results of the model and the simulation of a 2D-hydrogen plasma are reported, and future perspectives are discussed throughout the paper. [ABSTRACT FROM AUTHOR]

High-temperature superconducting levitation systems have nonlinear behaviors, such as the period-doubling bifurcation and chaotic vibration under external excitation, in connection with the nonlinear hysteresis interaction between the high-temperature superconductors (HTSC) and permanent magnet. The HTSC is a non-ideal type II superconductor in which the fracture is generated internally during manufacturing, and the material properties are brittle. The HTSC tends to crack under a strong magnetic field and electromagnetic force, and its internal defects are likely to cause structural damage with the variable Lorentz force. The fracture performance of the superconducting magnetic levitation system will affect the temperature variation of HTSC, in which the temperature is coupled with the internal electromagnetic force. In this paper, we analyze the fracture characteristics of the HTSC in nonlinear vibration with thermal effect. A superconducting magnetic levitation system model with boundary cracks is applied to study the coupling of multiple physical fields in dynamic processes. The Maxwell equation and superconducting electromagnetic constitutive equation are used to obtain the superconductor's current density, and the temperature is calculated through the heat conduction equation. The superconducting magnetic flux flow and creep model is applied to analyze the magnetic flux motion inside the superconductors. We compare the superconducting levitation system's electromagnetic force, temperature, and current density with four critical current densities. The numerical results show that the critical current density of superconductors significantly impacts bifurcation motion, and the temperature of the crack tip of the superconductors varies greatly during vibration, causing the superconductor to lose its superconductivity. [ABSTRACT FROM AUTHOR]

In recent years, two-dimensional van der Waals (2D vdWs) heterostructures have attracted great research interest due to their great potential in fundamental physics research and spintronic devices (such as MTJs). Due to its excellent scalability, controllable magnetism and out-of-plane anisotropy, the compact nonvolatile memory controller (NV-MC) based on spintronics is expected to solve the memory bottle-neck problem. At present, a series of in-depth studies have been conducted on advanced 2D vdWs materials, such as MoS2, WSe2, and Fe3GeTe2 (FGT). The results show that the 2D vdWs materials have great TMR value and high SOT switching efficiency, both theoretically reported and experimentally verified. In the paper, a novel MTJ device based on the FGT/WTe2 heterostructure is proposed. In the absence of an external magnetic field, the magnetization direction of the MTJ free layer can still be reversed with certainty when the unipolar write current reaches about 5 mA. Moreover, the DMI effect generated between 2-D material/FM interfaces is also considered, which can promote the performance of SOT-MTJ without the external field. The reading reliability of SOT-MRAM is improved in comparison with the traditional CoFeB-based MTJ device. [ABSTRACT FROM AUTHOR]

CoV2O6, a Brannerite-type material, exists in both monoclinic (α) and triclinic (γ) forms. α- CoV2O6 exhibits quasi-1D ferromagnetic chains of octahedrally-coordinated Co2+ions in the higher spin state. Fe2+ doped α-CoV2O6 (3 mol%) single crystals were synthesized using high temperature melt method. The motivation is to investigate whether disruption of 1D Co2+ ferromagnetic chains by small Fe3+ substitution alters the antiferromagnetic ground state and lead to stronger spin-frustration. In this paper, we report the magnetic and magnetodielectric properties of Fe doped α-CoV2O6 in detail. The strongly anisotropic nature of magnetic and magnetodielectric characteristics were captured well in the data through orientation dependent measurements with H being parallel to a and c axes of the crystal. Relative dielectric permittivity (εr) exhibited sharp peaks coinciding with the plateau edges Hc1 ∼2.2 T and Hc2 ∼4.4 T in the magnetization curves (M-H) for applied H parallel to a-axis. For dielectric measurements under applied H parallel to c-axis, relative dielectric permittivity exhibited sharp peak around Hc2 ∼3.1 T, again coinciding with the M-H behavior. Such closely related magnetic field induced dielectric transitions reflected in both M(H) and εr(H) measurements is a rare phenomenon and representative of strong spin-lattice coupling in this phase. [ABSTRACT FROM AUTHOR]

Recent developments in the standardization of magnetic field generators have been considered for optoelectronic industrial-scale applications. In this work, a strategy to incorporate all optical components that can be used to implement a broad range of functions for communications applications is presented. We propose a circuit design for a magneto-optic interferometric system based on building blocks and subcircuits consisting of an interferometer with magneto-optic phase shifters and a magnetic field generator. The paper shows the building blocks based on elementary 2 × 2 photonics coupling components. We demonstrate that such a design can be configured as a tunable system based on the phase shift experienced by the incoming signals from two input waveguides and their transitions. [ABSTRACT FROM AUTHOR]

A series of inverse split-ring resonators (ISRR) loaded with an yttrium iron garnet (YIG) film were numerically and experimentally studied to provide strong photon–magnon coupling strength and cooperativity enhancement. An increase in the photon–magnon coupling strength and cooperativity has been achieved due to the simultaneous increase in the spatial overlapping between the ISRR microwave electromagnetic field magnetic component and the uniform magnon mode in the YIG, and the appearance of spatial areas with higher ISRR electromagnetic field magnetic component strength. Practically, this was reached for the ISRR by increasing the conducting gap length and changing the conducting gap shape by protrusions forming. Higher values of spin-number-normalized photon–magnon coupling strength gN and cooperativity C were reached in all cases for the ISRR with protrusion (compared with ISSR with identical conducting gap length but without protrusion). All resonators presented in this paper seem to be more prospective for the realization in quantum hybrid systems than conventional split-ring resonators and ISRR. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the impact of an external magnetic field on the Weibel instability driven by temperature anisotropy in a magnetized plasma. The study provides the influence of electron temperature anisotropy, considering both cold as well as warm ions. We derive expressions for the growth rate Γ (s−1) in each case to quantify the effect of some specific parameters on the instability. For example, the growth rate is plotted against the magnetic field for three distinct cases: considering only electrons, including cold ions, and incorporating warm ions. It is observed that the growth rate decreases as the applied magnetic field increases. Furthermore, the addition of both cold and warm ions to the plasma significantly influences the observed effects. It can be explained as follows: in the presence of cold ions, the growth rate is decreased with an increase in the wave number kz (cm−1). In addition, a decrease in the growth rate is observed with an increasing wave number in the case of warm ions. Therefore, it can be seen that the Weibel instability, propelled by thermal anisotropy, holds significant implications owing to its prevalence in both astrophysical and laboratory plasmas. The findings presented here are expected to contribute to the advancements in magnetic field generation and particle acceleration in various astrophysical phenomena, including gamma-ray bursts, relativistic collisionless shock fronts, radio supernovae, and pulsar winds. [ABSTRACT FROM AUTHOR]

This paper investigated a multi-modular magnetic microrobot/millirobot (MMM) with a serial chain structure consisting of multiple identical modules. Depending on the magnet pattern used for the MMM's modules, an MMM can have different equilibrium postures under an external magnetic field, such as assembled ring and disassembled straight-line postures. In this study, we investigated the equilibrium and locomotion characteristics of the MMM by applying two different representative magnet patterns, considered to be effective for magnetic actuation, to the robots. We established various equations to determine and control the assembly, disassembly, and locomotion of the MMM with each magnet pattern. We also conducted various experiments demonstrating the assembly, disassembly, and cargo delivery capabilities of the MMM under different external magnetic fields. Results confirmed that each MMM and their magnet pattern have distinctive and useful characteristics, demonstrating that the two magnet patterns can be selectively and effectively used as MMM in different applications. [ABSTRACT FROM AUTHOR]

In this paper, in order to further reduce torque ripple and improve power factor, a new vernier permanent magnet motor is proposed, in which the design concept of dual-winding hybrid-tooth configuration is incorporated. In order to clarify motor torque ripple and power factor, the winding-magnetomotive-force-based design and analysis method is proposed, in which harmonic characteristics are considered as key factors during the magnetic field modulation process. The relationship between harmonics generated by winding MMF, torque ripple, and power factor are investigated. In addition, the split-tooth vernier permanent magnet motor is also investigated as a referenced motor. Detailed comparisons between the DWHT-VPM motor and ST-VPM motor are carried out, including air gap magnetic field, torque, and power factor. Both theoretical and simulation results verify the reasonability of the proposed DWHT-VPM motor, and the effectiveness of the proposed winding-MMF-based analysis method, which provide a new potential research path for the design and analysis of flux modulation motors. [ABSTRACT FROM AUTHOR]

In this paper, the load effect on the magnetization performance of a stator consequent pole memory machine (SCPMM) is revealed and investigated comprehensively. The topology of the SCPMM is described, and influences of the load effect on the magnetization state (MS) manipulation process are characterized by the magnetic field distributions excited by different types of currents. Subsequently, the demagnetization type induced by the load effect and the cross-coupling phenomenon is identified and analyzed by a virtual linear hysteresis model. The characteristic curves of the magnetizing and demagnetizing processes vs different q-axis armature currents are tested experimentally in a SCPMM prototype. In order to improve the MS manipulation accuracy, a compensation control strategy that takes the load effect into consideration is proposed. Finally, the effectiveness of the proposed compensation control strategy is verified by experiments. [ABSTRACT FROM AUTHOR]

In this paper, a comparative investigation of a C-band long-pulse high-efficiency klystron-like relativistic cavity oscillator is carried out by using numerical simulation and practical experiments. It is indicated that owing to the improper configuration of the solenoid, some returning electrons originating from the cathode supporting rod would hit the entrance of the diode and shunt the input electric power. As a result, the startup process of the device is delayed and the saturated output power is decreased as well. In the initial experiment, the output power and the pulse duration are only about 3.2 GW and 78 ns, respectively. To eliminate the influence of the returning electrons, by increasing the turn number of the winding at both ends of the solenoid, the magnetic field at the diode region is enhanced so that the returning electrons could be guided to the shielding bowl in front of the insulator. As the shielding bowl is under the same potential as the cathode, the returning electrons would not shunt the input power. In contrast, after solenoid compensation, the output power of the device is increased to 4.4 GW at a diode voltage of 700 kV and a current of 14 kA, whereas the pulse duration is extended to 96 ns. Also, the corresponding conversion efficiency achieves about 45%. [ABSTRACT FROM AUTHOR]

With the development of electric motors, high speed and high efficiency have become the new development trend. Therefore, reducing the iron loss of motors has become the focus of academia and industry. Amorphous alloys are gradually being used in high speed motors by virtue of their low loss characteristics at high frequencies. Amorphous alloys generate large internal stresses during the manufacturing process, and annealing is usually required to eliminate the effect of internal stresses on magnetism. Amorphous transformer cores are usually annealed by applying a magnetic field in the direction of the magnetic circuit to improve the magnetic domain state, increase the saturation density in that direction, and reduce iron loss. Since the magnetic field of the motor stator teeth is pulsating, and amorphous annealed under longitudinal magnetic field (AALM) has the most performance along the direction of the annealed magnetic field. Therefore, in this paper, the magnetic properties of AALM, annealed amorphous (AA), and unannealed amorphous (UA) are tested to prove the advantages of the material, and then AALM is spliced as the tooth of the motor. The advantages of this material in the motor species are further demonstrated by designing a comparative simulation scheme in the longitudinal direction (same material with different structure) and in the transverse direction (same structure with different material). [ABSTRACT FROM AUTHOR]

By applying the halbach arrangement, an integrated magnetic bearing structure can be designed that secures the space inside the rotor core as a space for inserting the magnetic bearing. In this case, since the bearing is present inside the rotor, the bearing magnetic flux for controlling the rotor position is affected by the magnetic field of the permanent magnet and the rotating magnetic field of the phase winding of the stator. At this time, in a specific combination of the number of pole slots, the arrangement of the windings of the stator facing the bearing teeth appears asymmetrically for each bearing phase. In this paper, for more linear control, the formula for the number of stator pole slots and the number of bearing teeth to eliminate structurally generated force asymmetry was presented, and the formula was verified by comparative analysis of the force waveform for each axis. The validity of the proposed model was verified using the finite element method. [ABSTRACT FROM AUTHOR]

Magnetoresistive (MR) sensors have great application prospects in the field of weak magnetic field detection due to their high sensitivity, small size, and low power consumption. However, 1/f noise greatly limits the low-frequency detectivity of MR sensors. In order to suppress 1/f noise, this paper proposes a two-dimensional synchronous motion modulation (TDSMM) structure based on microelectromechanical systems (MEMS). This structure can effectively reduce 1/f noise by modulating the frequency of the measured magnetic field in the high-frequency band. Theoretical analysis and finite element simulation were conducted on three different modulation models: TSDMM, magnetic flux concentrators motion modulation, and MR components longitudinal motion modulation. The results showed that the modulation efficiency of the TDSMM reached as high as 127%, which is currently the highest value in MR-MEMS sensors. The TDSMM MEMS structure has been successfully manufactured, and the resonant frequency of the transverse resonator is twice that of the longitudinal resonator, enabling extremely high modulation efficiency. The noise spectral density of giant-magnetoresistive components on a silicon-on-insulator substrate was tested, and the noise level in the high-frequency band was three orders of magnitude lower than that in the low-frequency band. These results position MR-MEMS sensors with TDSMM structures as highly competitive candidates in the field of ultra-weak magnetic field detection. [ABSTRACT FROM AUTHOR]

In this paper, the influence of rectangular holes with different aspect ratios in a cylinder on shielding properties is investigated using the finite element method. The two indicators used to assess the shielding properties of the cylinder are its internal residual magnetic field and its outer-surface magnetic field map. The internal residual magnetic field (B) of a cylinder as a function of the aspect ratio of a rectangular hole and its area is simulated, and the conclusions are as follows: with increasing length of the hole, the value of B increases first and then decreases. A cylindrical shield with square holes (the hole aspect ratio is equal to 1) delivers the worst shielding performance. A cylinder with a smaller hole area has better shielding properties, resulting from a less flux leakage from the environmental magnetic field. The anisotropy of the shielding properties is evaluated, and the magnetic shielding in the radial direction is better than that in the axial direction. This research provides a theoretical guide for the application and optimization of magnetic shields. [ABSTRACT FROM AUTHOR]

An improved method based on the second order improved central difference method is proposed to improve the third-order magnetic gradient tensor, which is affected by noise and characterized by poor stability. The third-order magnetic gradient tensor at the center point is calculated by using the three-component magnetic field at four points along a single route; this approach effectively improves the stability of the third-order magnetic gradient tensor data. In this paper, the errors of the traditional method and the new method in calculating the third-order magnetic gradient tensor are given by the Taylor series. Based on the traditional third-order magnetic gradient tensor system, a new third-order magnetic gradient tensor system and the corresponding measurement method are presented. Through simulations, in the case of noise, it is verified that the proposed method exhibits better stability by comparing the components of the third-order magnetic gradient tensor with the positioning results. In experiments, the root-mean-square error is used to compare the positioning results before and after noise addition. The traditional method changes the root-mean-square error of the positioning results from (1.3626, 3.6573, 0.5766 m) to (3.3661, 9.5966, 1.9465 m), and the root-mean-square error obtained with the new method displays no obvious change. [ABSTRACT FROM AUTHOR]

A superconductor/magnetoresistance (SC/MR) mixed sensor often has very high-precision detection capability, but it is only sensitive to the out-of-plane magnetic field that is perpendicular to the superconducting flux-to-field transformation amplifier (SFTA). This inherent characteristic makes it impossible for a primary SC/MR mixed sensor to measure the in-plane magnetic field, which limits its application in many fields. This paper presents a new architecture of SC/MR mixed sensors with two magnetic flux guides (MFGs) to realize in-plane magnetic field measurement, which is attributed to the combined effects of MFGs and SFTA. The finite element method simulations are used to study the magnetic flux converting effect of MFGs and magnetic field amplification effect of SFTA, which theoretically proves the feasibility of in-plane magnetic field measurement and reveals the influences of the sizes and spacing of MFGs on magnetic field magnification. Experimental results show that the SC/MR mixed sensor with MFGs can simultaneously sense the in-plane and out-of-plane magnetic fields, and the performance of the mixed sensor with MFGs is comparable to the primary one. The magnification and resolution of the mixed sensors with MFGs to the in-plane magnetic fields are, respectively, improved by 2.91 times and 2.23 times compared to those without MFGs to the out-of-plane magnetic fields. The work described in this paper is of great significance for the development of three-component weak magnetic field detection. [ABSTRACT FROM AUTHOR]

Ta/MgO/NiFe/MgO/Ta anisotropic magnetoresistive thin film sensors, which can be used for magnetic scales, were prepared. To improve the magnetoresistance ratio of the sensors, these sensors were vacuum-annealed with the magnetic field applied, and then, both the static and dynamic magnetoresistive responses of the sensors were obtained. The experimental results have shown that the instability of magnetic anisotropy occurs in the sensors after vacuum-annealing, leading to the significant hysteresis and abnormal output voltage peaks. To investigate the underlying physics, the distribution of the non-uniform demagnetizing field along the width of an anisotropic magnetoresistive (AMR) strip is considered, and both the static and dynamic responses of the AMR elements have been calculated on the basis of the Stoner–Wohlfarth model. The results have shown that the calculated results are in good agreement with the experimental data. The calculated results have revealed that the angles between the anisotropic field and the external magnetic field are different during the field cyclings of Hmax (maximum magnetic field) to −Hmax and −Hmax to Hmax. The angle difference is up to 6°, leading to different magnetoresistive responses. This paper is helpful for the understanding about the magnetization rotations in magnetic sensors and the manufacturing of sensors. [ABSTRACT FROM AUTHOR]

Collisionless shocks with low Alfvénic Mach numbers are expected to accelerate electrons, but the underlying physics are still unsolved. Two-dimensional particle-in-cell simulation of low-Mach-number quasi-perpendicular shock in low-β is performed to study the physics of formation of beam-like components with respect to background magnetic fields. The incoming electrons can be trapped and scattered to have velocities along the shock surface by the electrostatic wave in the foot region owing to the free energy in the relative drift between shock reflected ions and upstream electrons. Then fractional electrons can be reflected by the mirror force at the shock overshoot when escaping from the loss cone. The reflection by the mirror force makes the electrons gain quasi-parallel velocities, and the electrons are accelerated in the quasi-parallel direction during trapping in the immediate downstream, forming a beam-like component with respect to magnetic fields. Our results shown in this paper explain the physics of beam formation and could be helpful for accounting for type II radio bursts. [ABSTRACT FROM AUTHOR]

In this paper, it is shown that the static magnetic signature of a propulsor belonging to a ghost ship, whose hull is made of fiberglass, can be calculated by regarding it as a composite ferromagnetic medium. The calculation of the magnetic signature in the static regime is carried out using finite-element method simulations and according to a simple analytical model based on the concepts of volume averaged magnetization arising from a source magnetic field, volume averaged permeability, surface magnetic charges, and the demagnetization tensor applied to a composite magnetic medium. Using targeted simulations, it is demonstrated that the magnetostatic field of demagnetizing nature forming inside the propulsor almost cancels the contribution of the volume averaged magnetization. From the interplay between the numerical simulations and the analytical model, the elements of the demagnetization tensor in the region filled by the propulsor are locally calculated, and their role in determining the localization effects of the magnetic signature is discussed. By replacing the original ferromagnetic materials with weakly ferromagnetic ones, it is shown that, in the underwater region outside the propulsor, the magnetic signature drop is 64%. This analysis suggests an experimental way to use a simple passive method to minimize the magnetic signature of a propulsor as an alternative to more complex and time-consuming methods, such as the deperming and degaussing methods, widely employed to reduce the magnetic signature of ships and underwater objects in military applications. [ABSTRACT FROM AUTHOR]

This paper identifies different methodologies used to design suitable magnetic field generators (MFG) with adjustable characteristics. Variations in parameters, such as pulse frequency and amplitude elicit distinct responses. Assessing the differences between design parameters and experimental observations of magnetic field generators is essential for various applications. The use of magnetic field generator-based techniques is first studied in applications related to optical transmission, transcranial magnetic stimulation devices and magnetic resonance. Decades of research and technological advancement are associated with these methods. The associated nomenclature for describing and characterizing these methods are introduced and discussed. Finally, the paper presents possible future framework and design considerations in functionality where new MFGs are expected to play a key role in the future. [ABSTRACT FROM AUTHOR]

High efficiency and short saturation time have great significance on the practical work of high power microwave devices. A dual-band Cerenkov microwave generator with high-efficiency based on electrical tuning is presented in this paper. Two-segment slow wave structures for the C-band and X-band separately are adopted, which are isolated by a drift cavity. The collimating hole is replaced by a resonant reflector, which can effectively shorten the saturation time. Moreover, in order to realize dual-band microwave output, the electrical tuning method is used in this paper. In particle-in-cell simulation, when the guiding magnetic field is 0.7 T, the output microwaves at the X-band can be obtained with an efficiency of 38% and saturation time for nearly 20 ns; when the guiding magnetic field is 1.5 T, the output microwaves at the C-band can be obtained with an efficiency of 32% and saturation time for nearly 20 ns. Thus, microwaves at the X-band and C-band can be generated separately by modulating the guiding magnetic field, which can be realized just by altering the current in the magnetic coil. It should be mentioned that such a modulating method is much more convenient than mechanical modulation. [ABSTRACT FROM AUTHOR]

This paper introduces the novel self-positioning ability of a sphericon-shaped magnetic millirobot (SSMM) on an inclined surface. The SSMM is comprised of four identical half cones with a cylindrical magnet inserted into the geometric center, and it can roll along a straight line on a surface with repeated rolling cone motions actuated by an external wobbling magnetic field (EWMF). Due to the restoring moment induced by a conservative gravitational force, the SSMM can maintain (self-position) its equilibrium position on the surface, even when the EWMF is removed. This paper derived several equations to quantify the condition in which the SSMM can steadily generate self-positioning motions. It also examined the self-positioning ability of the SSMM by constructing a prototype SSMM and demonstrating its rolling and self-positioning motions by using a magnetic navigation system. [ABSTRACT FROM AUTHOR]

To accurately predict the eddy current loss of silicon steel laminations over broadband frequency range, an improved parametric magneto dynamic model (IPMD) is proposed in this paper. According to the nonuniform distribution of magnetic field in the cross-section of the silicon steel lamination under high-frequency magnetization, the analysis area of the lamination is divided into several slices by nonlinear segmentation, wherein each slice the magnetic field distribution is regarded as uniform. Meanwhile, to accelerate the calculation speed of the IPMD model, the relationship between skin depth and slice number is deduced and verified. Furthermore, the Tellinen (TLN) hysteresis model is used when implementing the IPMD model to further increase the accuracy of eddy current loss calculation. [ABSTRACT FROM AUTHOR]

A Ku band coaxial high power microwave generator with a low magnetic field was investigated without mode competition in this paper. Mode competition is avoided physically by adopting a two-cavity extractor instead of a three-cavity extractor to eliminate the resonance between the modulation slow wave structure and the extractor slow wave structure at any unexpected frequency except the working frequency. Moreover, the efficiency of the device increases due to the separation process of energy extraction and electron collection by adopting the inner conductor collecting structure. Particle simulation results showed that when the magnetic flux density is 0.6 T, the diode voltage is 560 kV, and the diode current is 8 kA, we get 1.55 GW microwaves with an efficiency of 35% and a frequency of 14.7 GHz. Experimental investigation is carried out based on the physical design and simulation results. 1.0 GW microwaves are obtained, and the frequency is 14.8 GHz in the experiment when the magnetic flux density is 0.64 T, the diode voltage is 590 kV, and the diode current is 8.5 kA. No obvious hint of electron emission or bombardment is observed at the surface of the generator after 10 thousand pulses, and the advantage of this kind of generator working in a low magnetic field is proved. [ABSTRACT FROM AUTHOR]

In this paper, we clarify the duplicated electromagnetic characteristics between the proposed two-beam overmoded multi-gap structure published in the paper titled "Tractable resonant structure with two nonuniform beams for a high-power 0.22-THz extended interaction oscillator" [Bi et al., IEEE Electron Device Lett. 42(6), 931–934 (2021)] and conventional multi-gap structures from the physical concept point of view. The replacement of the TE10 mode by the TE30 mode used in the interaction gaps provides the basis for the duplicated electromagnetic field distributions and frequencies between the two structures. The concept of magnetic coupling is proposed to support the resonant condition that supports duplication of the TE30 field and the frequency of the single-gap structure into the periodic standing-wave field of the multi-gap structure. With this concept, the perturbation of different axial phase shifts across one period to the standing-wave field of the TE30-0 mode is analyzed to clarify the profiles of the dispersion curves of the TE30 mode in the overmoded structure and the TE10 mode in the conventional structure. To demonstrate the profiles, a 220-GHz overmoded and conventional structure with nine gaps is designed, and their dispersion curves are obtained by using eigenmode simulations. In addition, the effect of the difference in the boundary conditions of the geometries of these two structures on the magnetic field distribution is analyzed to demonstrate the duplication of the ohmic losses between the two structures. The physical analysis in the duplicated electromagnetic characteristics lays a foundation for the promising design of the overmoded structure with two beams for high frequency extended interaction oscillators. [ABSTRACT FROM AUTHOR]

A low guiding magnetic field facilitates the compactness of high power microwave sources, thus making it more practical. In order to reduce the guiding magnetic field, a focusing cathode is introduced in a Ka-band coaxial transit time oscillator in this paper. Based on the focusing cathode with a large impedance (>100 Ω) coaxial structure, a particle-in-cell simulation is conducted. When the diode voltage is 480 kV and the beam current is 3.62 kA, a microwave with an average power of 800 MW at 31.667 GHz is obtained under a guiding magnetic field of 0.5 T, the corresponding conversion efficiency is 46%, and the saturation time is 25 ns. Meanwhile, the maximum EZ field in the diode region is 350 kV/cm; thus, electron emission beyond the cathode region is avoided. When the guiding magnetic field is 0.5 T and the voltage varies in the range of 430–510 kV, the conversion efficiency is greater than 40%. In addition, when the voltage stays at 480 kV and the guiding magnetic field is in the range of 0.45–1.0 T, the conversion efficiency is also greater than 40%. [ABSTRACT FROM AUTHOR]

REBCO tapes, the so-called second-generation high temperature superconductor, have wide application prospects in electrical engineering and high field magnets because of their high critical current density and superior mechanical and electromagnetic properties. However, a screening current field (SCF) can be induced by the perpendicular component of the magnetic field if the tapes are in a variable magnetic field since the width of the commercial tape is generally more than 2 mm. As a result, the SCF results in an uneven spatial distribution of the magnetic field. In this paper, the SCFs of the quasi-isotropic strand and the directly stacked strand, made of the REBCO tapes, are calculated at 77 K under different orientations of a 300 mT external magnetic field. Then, the experiments are conducted under the same conditions as the simulation. The experimental results are in good agreement with the calculated results. The conclusions of this paper are helpful to understand the SCFs of two kinds of strands and useful in the design of high field magnets in the future. [ABSTRACT FROM AUTHOR]

A novel dual-band nested transit time oscillator (TTO) is proposed in this paper, which consists of an outer X-band coaxial TTO and an inner Ka-band coaxial TTO. It is capable of generating dual-band microwaves simultaneously with three distinctive features. First, the emission processes of inner and outer annular electron beams are independent. Second, the inner and outer high frequency structures are spatially isolated. Third, the inner and outer annular electron beams share the guiding magnetic field. Particle-in-cell simulation is performed where a voltage of 450 kV and a guiding magnetic field of 0.6 T are used. Simulation results demonstrate that microwave output with a frequency of 8.4 GHz and a power of 1.72 GW is obtained for the X-band, corresponding to a conversion efficiency of 42% and a microwave saturation time of 30 ns. Meanwhile, microwave output with a frequency of 31.3 GHz and a power of 1.18 GW is achieved for the Ka-band, corresponding to a conversion efficiency of 40% and a microwave saturation time of 15 ns. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a novel calculation method of magnetic entropy change in an arbitrary ferromagnetic system based on the Landau model for Gibbs free energy and the Arrott–Noakes equation, − Δ S M = 1 1 γ + 1 d A (T) d T M 1 γ + 1 − M S 1 γ + 1 + 1 1 β + 1 γ + 1 d B (T) d T M 1 β + 1 γ + 1 − M S 1 β + 1 γ + 1 − M − M S H 1 γ H 1 − 1 γ . This theoretical study was applied to TbFeSi (TFS) and DyFeSi (DFS) intermetallic compounds. First, the critical exponents (β; γ) are found as (0.46; 1.08) and (0.26; 1) for TFS and DFS, respectively. Second, the limitations of the Arrott–Noakes equation in simulating the hole −ΔSM(H, T) curves were discussed. Third, the usefulness of the new method reported earlier predicted large RCP values of around 810 and 779 J kg−1 under a 10 T magnetic field for TFS and DFS samples, respectively. [ABSTRACT FROM AUTHOR]

A Maxwell coil is a gradient magnetic field source with high uniformity, and it is widely used in the experiment of magnetic effect in space gravitational wave detection, magnetic resonance molecular imaging, and other precision magnetic measurement experiments. In this paper, taking the square Maxwell coil as a research object, the influences of four kinds of assembly errors on the uniformity of magnetic field gradient (UOMFG) are systematically analyzed and the results are verified by simulation using the finite element method. We obtained variation rules of UOMFG changing with the four assembly errors and summarized three useful conclusions. These rules and conclusions are instructive in the design, processing, and assembly of the square Maxwell coil and are beneficial for the optimal utilization of the working area in the precision magnetic measurement experiments. [ABSTRACT FROM AUTHOR]

This paper shows how to model the force density in electrical machines based on the field lines of the magnetic flux density. The force density is written as two vector components: the magnetic tension force and the magnetic pressure gradient force. This approach has been applied in physics but never to forces in engineering problems. The magnetic tension force acts to straighten bent field lines, based on the curvature of the flux density. The magnetic pressure gradient force acts from regions of high flux density to regions of low flux density. Both force densities are derived from the Lorentz force using the tnb-frame of Frenet–Serret formulas and shown to be equivalent to the divergence of the Maxwell stress tensor. It is shown how the force density could describe the forces in a synchronous machine, including both the angular torque of the load and the radial forces between the rotor and the stator. It could also be linked to the power flow and thereby to the energy flux of Poynting's vector. The force densities could be used to improve the understanding of the Maxwell stress tensor, since they are easier to illustrate as vectors compared to the matrix form of the Maxwell stress tensor. It also shows the location of the force density, which could improve the use of enclosing volumes when calculating the force based on the divergence theorem with the Maxwell stress tensor. [ABSTRACT FROM AUTHOR]

In the field of aviation anti-submarine warfare, magnetic detection systems often result in a large number of false alarms due to the inability to effectively distinguish between a local geomagnetic anomaly in the background field and a target magnetic anomaly. To address this problem, this paper proposes a matching detection method for the magnetic anomaly of underwater targets. This method is based on the measured data of the magnetic anomaly in the sea area, and the geomagnetic reference map of the area is generated by interpolation of the Kriging method; then, the background field signal extracted from the geomagnetic reference map and the real-time signal acquired by detection are matched by the similarity metric algorithm; finally, the target detection is realized by using the feature fusion-isolation forest algorithm. Compared with the conventional detection methods, such as time–frequency analysis, the detection rate is improved by nearly 15% and the false alarm rate is reduced by about 40%, indicating that matching detection can effectively filter out the magnetic anomaly in the background field, reduce the false alarm, and improve the detection rate in the real geomagnetic environment, which has certain application value. [ABSTRACT FROM AUTHOR]

This paper proposed an improved magnetostriction model for correlation of anisotropy in non-oriented (NO) silicon steel based on the free energy, which considers stress-induced and magnetocrystalline anisotropy. Firstly, the free energy model, which includes stress-induced anisotropy energy, the energy of magnetic field, and the anisotropic energy of magnetic crystals, is incorporated into the anhysteretic magnetization parameter Man. Then, to obtain the magnetic field and proposed model parameters related to stress-induced and magnetocrystalline anisotropy, the magnetostrictive strain loops at different magnetization directions of NO silicon steel are measured. Finally, based on the parameters obtained from experimental data of the proposed model, magnetostrictive strain loops under varying magnetization directions are simulated. This improved magnetostriction model can be applied to the calculation of the vector magnetostriction of the motor core. [ABSTRACT FROM AUTHOR]

An X-band Cerenkov-type high power microwave (HPM) oscillator driven by a sheet electron beam is proposed and designed in this paper. In order to improve the efficiency of simulation optimization, a research method is proposed in which the large caliber coaxial Cerenkov-type HPM oscillator is taken as an initial model, which is equivalent to that of the planar slow-wave structure (SWS) by using the similarity between the planar SWS and the large caliber coaxial SWS. In addition, the effectiveness of the equivalent method is verified from the geometric structure, the field distribution of the operating mode, dispersion characteristics, and the preliminary particle simulation results of two devices. Based on the results of an X-band large caliber coaxial Cerenkov-type HPM oscillator, an X-band Cerenkov-type HPM oscillator driven by a sheet electron beam is investigated by the 3D particle-in-cell code. The simulation results show that the power conversion efficiency can reach 26.1% at the frequency of 11.9 GHz with the output power of 0.3 GW, while the sheet electron beam has the energy of 486 kV and it carries the current of 2.4 kA conducted by the magnetic field of 2.5 T. [ABSTRACT FROM AUTHOR]

In recent years, two-dimensional van der Waals (2D vdWs) heterostructures have attracted great research interest due to their great potential in fundamental physics research and spintronic devices (such as MTJs). Due to its excellent scalability, controllable magnetism and out-of-plane anisotropy, the compact nonvolatile memory controller (NV-MC) based on spintronics is expected to solve the memory bottle-neck problem. At present, a series of in-depth studies have been conducted on advanced 2D vdWs materials, such as MoS2, WSe2, and Fe3GeTe2 (FGT). The results show that the 2D vdWs materials have great TMR value and high SOT switching efficiency, both theoretically reported and experimentally verified. In the paper, a novel MTJ device based on the FGT/WTe2 heterostructure is proposed. In the absence of an external magnetic field, the magnetization direction of the MTJ free layer can still be reversed with certainty when the unipolar write current reaches about 5 mA. Moreover, the DMI effect generated between 2-D material/FM interfaces is also considered, which can promote the performance of SOT-MTJ without the external field. The reading reliability of SOT-MRAM is improved in comparison with the traditional CoFeB-based MTJ device. [ABSTRACT FROM AUTHOR]

With the rapid development of origami technologies, worm-inspired robots have attracted a great deal of attention due to their flexible locomotion characteristics. In the present work, we have prepared a soft robot inspired by the worms, which can achieve various locomotion patterns under the actuation of magnetic field. First, the origami technique is used to form the backbone of the robot, and two NdFeB discs are adhered on its two ends. Next, the experiments for controlling the Omega motion and rolling of the robot are performed, and the mechanical analyses are given. In the experiments, the Omega locomotion speed and rolling speed can reach ∼5 mm/s and 2π rad/s, respectively. Then, two typical examples on the composite motion, including the Omega motion and rolling, are demonstrated, where the robot can realize the tasks of sweeping objects and obstacle crossing in unstructured environments. We further design a system to mimic the situation when the worm-like robot detects and responds to the dangerous signal, and the power of the electromagnet can be accurately controlled. These findings cast a new light on engineering intelligent robots and devices originating from the inspirations of living creatures. [ABSTRACT FROM AUTHOR]

In many conventional plasma generation methods, a strong electric field is applied to a gas or liquid to generate plasma. In addition, metal oxides such as rare earth minerals and metals require enormous amounts of energy for their reduction reactions. In this paper, we propose a method of directly exciting the plasma from Mg and Ca metal solids, without gas or liquid, using a strong magnetic field and stabilizing it. Electrons and atoms are emitted by the induced current in a resonator operated in the TM110 mode; these electrons and atoms are generated as plasma in a magnetic field. The resonance frequency is then changed slightly from the TM110 mode to the TM111 mode while being limited to ∼40 MHz, ensuring that the microwave energy is supplied stably to the plasma and that light is emitted until the raw material is exhausted. The radicals and ions of the Mg and Ca metals possess sufficient Gibbs free energy for the reduction reactions and can therefore reduce scandium oxide and vanadium oxide at low temperatures. In the future, radicals with sufficient energy can be implemented in energy-saving processes in the field of materials processing. [ABSTRACT FROM AUTHOR]