Search

The High Luminosity LHC (HL-LHC) Project is planning to install 16 cold-masses made with Nb3Sn quadrupole magnets in the LHC Interaction Regions to significantly increase its luminosity. Half of these cold masses are fabricated at BNL, FNAL, and LBNL under the US Accelerator Research Program (AUP). Each cold mass includes two identical Nb3Sn quadrupole magnets, called MQXFA with a magnetic length of 4.2 m. Currently, the AUP project has completed the fabrication and test of the first 5 pre-series magnets, and is working on the following 16 magnets for the series production. The brittleness and strain sensitivity of the Nb3Sn superconducting material requires a careful definition of the allowable maximum stress in the windings during magnet assembly and pre-load, and a tight control of their variation within the whole coil length. Therefore, a series of assembly and pre-load specifications have been defined with the goals of minimizing the risk of conductor degradation and providing the mechanical support required to reach the nominal current during powering. In this paper we present the specifications defined for the MQXFA magnets and applied during the different assembly phases and during the pre-load process of the first 5 pre-series magnets.

Superconducting electron cyclotron resonance ion sources (ECRISs) using NbTi coils and optimized for 28 GHz resonant heating have been successfully operated for almost two decades. Moving to higher heating frequencies requires increased magnetic fields, but traditional racetrack-and-solenoid ECRIS structures are at their limit using NbTi. Rather than moving to a superconductor untested in this field, the Mixed Axial and Radial field System (MARS) being developed at Lawrence Berkeley National Laboratory employs a novel closed-loop-coil design that more efficiently utilizes conductor fields and will allow the use of NbTi in a next-generation, 45 GHz ECRIS. This article presents the design of the shell-based support structure central to the MARS-D magnet design, as well as structural analysis of its components and optimization of pre-load parameters that will guarantee its successful operation.

A dc–dc converter used for fuel cell vehicles should be characterized by a wide voltage-gain range and low input current ripple. In order to meet the above requirements, a new nonisolated dc–dc converter consisting of an active switched-inductor cell, a zero current ripple cell, and a switched-capacitor (SC) cell was proposed in this article. The proposed converter integrates with the advantages of a wide voltage-gain range, zero input current ripple, low voltage stresses across power semiconductors, and common ground structure. Thanks to the use of a zero current ripple cell, not only the input current ripple is reduced but also the energy transfer path of the SC cell is changed, thereby reducing the instantaneous peak current of the SC structure. The operating principles, the characteristics analysis, and the parameter design of the proposed converter are given. In addition, to show the merits of the proposed converter, a comparison study is demonstrated. Finally, a prototype of 400 V, 1000 W/50 kHz is developed to validate the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

A two-dimensional constitutive model based on micromechanical domain rotation events is presented in this work to demonstrate the nonlinear actuator behavior of magnetostrictive materials, in particular, Galfenol. The model constructed upon thermodynamic principles accounts back fields which resist or aid the domain rotation events inside a grain due to external magnetomechanical loading. The developed model is then incorporated into the polygonal finite element technique that combines Voronoi-based discretization with the hybrid finite element method. In this approach, the stress and magnetic flux density are treated as approximate functions inside the element, but the mechanical displacement and magnetic potential, which act as degrees of freedom, are defined only along the element boundary. This approach allows each randomly generated Voronoi polygon in the plane discretization to act as a single finite element mimicking an individual magnetomechanical grain in a polycrystalline Galfenol, eliminating the need for further subdiscretization of the Voronoi polygon. This coupled framework simulates the nonlinear actuator characteristics of the magnetostrictive material under complex magnetomechanical loading conditions in line with the experimental observations reported in the literature. [ABSTRACT FROM AUTHOR]

The physical origin of the magnetoplastic effect was experimentally identified in Al polycrystalline alloy. Exposure of the nominally pure industrial Al-Mg-Si-Fe alloy to magnetic field 0.7 T induces residual changes that provide a creep rate increase up to 25% and microhardness decrease down to 30%. FeAl inclusions of ∼1 μm size were revealed in the alloy. Magnetostriction of the ferromagnetic inclusions providing local mechanical stresses and generation of fresh dislocations in the vicinity of the inclusions is the main reason for magnetoplasticity. Ferro-, antiferro-, and paramagnetic contributions of the inclusions and/or Fe atoms distributed in the Al matrix have been distinguished. The chemical composition of FeAl inclusions determined by transition electron microscopy and local field probed by the Mossbauer technique are in good agreement with saturation magnetization of the FeAl alloys. [ABSTRACT FROM AUTHOR]

The Vernier machine can utilize magnetic-gear effect, which conspicuously improves the torque production over other type of synchronous machines. However, a dual-rotor/dual-stator structure enabled high torque density Vernier design is often unfavorable for industrial applications, due to manufacturing complexity and thermal management challenges. This article successfully addresses this problem, by building magnetic-gear effect into a consequent pole enabled alternating flux barrier structure with single-rotor single-stator (SRSS). In this way, the proposed machine can achieve a superior torque density as a Vernier machine does, while maintaining an equivalent manufacturing complexity as a conventional SRSS synchronous machine. This article begins with elaborating generic analytical equations, which can transform into a Vernier machine or an SRSS synchronous machine. More specifically, the magnetic-gear effect is manifested in the equations, via stator teeth originating flux modulation concept and resulting multiharmonic field coupling effects. An SRSS Vernier topology with consequent pole and V-shape magnet is then proposed. A considerable 52.6% improvement on the torque production with comparable efficiency is validated by experiments, where the comparison is made over that of a benchmark rare earth PM machine. Power factor would fall behind with increasing current load. Overall, this new design achieves an outstanding torque density, showing solid potential and feasibility for industry adoption. [ABSTRACT FROM AUTHOR]

A conventional asymmetrical half-bridge (AHB) converter is one of the widely used topologies in low to medium power applications. However, when it is designed in a wide input voltage range, it operates with a low duty ratio at nominal input voltage. In addition, it has disadvantages, such as a dc offset of magnetizing current, an unbalanced average current of the diode, and a nonlinear voltage gain due to asymmetrical operation. To solve these disadvantages, an AHB converter with linear voltage gain is proposed. The proposed converter has a structure in which a capacitor is added as a voltage source to obtain a symmetrical operation by extending the commutation period. Therefore, it has a narrow range of operating duty ratio and a zero dc offset of magnetizing current. Due to the zero dc offset of magnetizing current, it has a small size transformer and improved zero-voltage switching conditions of the primary-side switches. In addition, it has a low primary rms current and a balanced average current of the diode. Consequently, the proposed converter has high efficiency under the entire load conditions. A 300–400 V input and 48 V/400 W output prototype is tested to verify the feasibility of the proposed converter. [ABSTRACT FROM AUTHOR]

As technology size scales down, magnetic tunnel junctions (MTJs) as a promising technology are becoming more and more sensitive to process variation, especially in oxide barrier thickness. Process variation particularly affects the cell resistance and the critical switching current for the smaller dimensions. This article proposes an MTJ cell with one free and two pinned layers, which highly improves the process variation robustness. By employing the spin transfer torque (STT)-spin-Hall effect (SHE) switching method, our proposed MTJ cell improves the switching speed and lowers the switching power consumption. Per simulations, an MRAM cell built with the proposed MTJ cell offers up to 36% lower total power consumption, up to 32% higher write performance, and 35% higher read performance over the previous state-of-the-art MRAMs. Also, the error rate resulting from process variation is 1.4%, which is about one-tenth of the best examples reported in the literature. [ABSTRACT FROM AUTHOR]

While various magnetic sensors have been developed over the years, the capability of passive wireless magnetic field detection is still lacking. Magnetic surface acoustic wave (MSAW) devices, combining magnetostrictive with piezoelectric materials, may be one of the candidates for wireless magnetic field sensing. This work proposes a novel microelectromechanical system (MEMS) MSAW resonator based on the AlN/Si/(Fe90Co10)78Si12B10 structure. The frequency responses of the resonator were measured when applying a dc magnetic field along the magnetic easy and hard axes. The results indicate that the resonator has higher magnetic sensitivity along the hard axis, with a maximum magnetic sensitivity of 11 kHz/Oe. When performing a magnetic field loop measurement for the hard axis, the resonator’s quality factor and resonance frequency showed almost the same variation tendency against the magnetic field. Moreover, the quality factor can attain about 3700 at the position of maximum magnetic sensitivity, which could simultaneously meet the needs of wireless interrogation and high sensitivity. Our work reveals that such an MEMS MSAW resonator has clear potential in the realization of wireless magnetic field sensors with miniaturization, low power, and high complementary metal–oxide–semiconductor (CMOS) compatibility for the future development of the Internet of Things (IoT). [ABSTRACT FROM AUTHOR]

A magneto-structural combined dimensional and topology optimization approach for interior permanent magnet synchronous machine (IPMSM) rotor design is proposed using the solid isotropic material with penalization (SIMP) density-based topology optimization method. This method optimizes the location and dimensions of the permanent magnets (PMs) embedded in the rotor, while simultaneously optimizing the lamination flux barriers using topology optimization. To allow for the location and dimensions of the PMs to change a Laplace smoothing mesh deformation technique is used. Three examples of IPMSM rotor optimizations are presented to demonstrate the proposed approach. In addition, a geometric template-based optimization is carried out for a comparison to one of the dimensional and topology optimized examples to better illustrate the difference. [ABSTRACT FROM AUTHOR]

This article presents numerical and experimental investigations of the structural control of multilayer high temperature superconducting (HTS) tapes, using eddy current thermography at room temperature. A rotating magnet wheel is used as inductor to avoid the thermal disturbance of current supplied inductors. A 3-D magnetothermal modeling approach based on an integro-differential formulation in terms of the electric vector potential is developed for eddy current computation in the HTS tapes; associated to a thermal modeling using the finite difference method. The source magnetic field is calculated using the magnetic surface charge model. The simulation results are confirmed by the measurements, both highlighting the potential of such control to detect structural defects, such as delamination. [ABSTRACT FROM AUTHOR]

The magnetomechanical behavior of ferromagnetic shape memory alloys such as Ni-Mn-Ga, and hence the relationship between structure and nanoscale magnetomechanical properties, is of interest for their potential applications in actuators. Furthermore, due to its crystal structure, the behavior of Ni-Mn-Ga is anisotropic. Accordingly, nanoindentation and magnetic force microscopy were used to probe the nanoscale mechanical and magnetic properties of electropolished single crystalline 10M martensitic Ni-Mn-Ga as a function of the crystallographic c-axis (easy magnetization) direction relative to the indentation surface (i.e., c-axis in-plane versus out-of-plane). Load-displacement curves from 5–10 mN indentations on in-plane regions exhibited pop-in during loading, whereas this phenomenon was absent in out-of-plane regions. Additionally, the reduced elastic modulus measured for the c-axis out-of-plane orientation was ∼50% greater than for in-plane. Although heating above the transition temperature to the austenitic phase followed by cooling to the room temperature martensitic phase led to partial recovery of the indentation deformation, the magnitude and direction of recovery depended on the original relative orientation of the crystallographic c-axis: positive recovery for the in-plane orientation versus negative recovery (i.e., increased indent depth) for out-of-plane. Moreover, the c-axis orientation for out-of-plane regions switched to in-plane upon thermal cycling, whereas the number of twins in the in-plane regions increased. We hypothesize that dislocation plasticity contributes to the permanent deformation, while pseudoelastic twinning causes pop-in during loading and large recovery during unloading in the c-axis in-plane case. Minimization of indent strain energy accounts for the observed changes in twin orientation and number following thermal cycling. [ABSTRACT FROM AUTHOR]

Magnetically actuated small-scale robots have great potential for numerous applications in remote, confined, or enclosed environments. Multiple small-scale robots enable cooperation and increase the operating efficiency. However, independent control of multiple magnetic small-scale robots is a great challenge, because the robots receive identical control inputs from the same external magnetic field. In this article, we propose a novel strategy of completely decoupled independent control of magnetically actuated flexible swimming millirobots. A flexible millirobot shows a crawling motion on a flat plane within an oscillating magnetic field. Millirobots with different magnetization directions have the same velocity response curve to the oscillating magnetic field but with a difference of phase. We designed and fabricated a group of up to four heterogeneous millirobots with identical geometries and different magnetization directions. According to their velocity response curves, an optimal direction of oscillating magnetic field is calculated to induce a desired velocity vector for the millirobot group, one of which is nonzero and the others are approximately zero. The strategy is verified by experiments of independent position control of up to four millirobots and independent path following control of up to three millirobots with small errors. We further expect that with this independent control strategy, the millirobots will be able to cooperate to finish complicated tasks. [ABSTRACT FROM AUTHOR]

A review of the latest theoretical advances in the description of magnetomechanical effects and phenomena observed in magnetoactive elastomers (MAEs), i.e., polymer networks filled with magnetic micro- and/or nanoparticles, under the action of external magnetic fields is presented. Theoretical modeling of magnetomechanical coupling is considered on various spatial scales: from the behavior of individual magnetic particles constrained in an elastic medium to the mechanical properties of an MAE sample as a whole. It is demonstrated how theoretical models enable qualitative and quantitative interpretation of experimental results. The limitations and challenges of current approaches are discussed and some information about the most promising lines of research in this area is provided. The review is aimed at specialists involved in the study of not only the magnetomechanical properties of MAEs, but also a wide range of other physical phenomena occurring in magnetic polymer composites in external magnetic fields. [ABSTRACT FROM AUTHOR]

In this article, two configurations of the quadratic quasi-Z-source (Q-qZS) isolated dc–dc converters are presented, namely continuous input current and discontinuous input current configurations. The operating principles and steady state of the continuous input current topology analyzed in this article is characterized with the following features: 1) wider operating range due to buck and boost functions in a single stage; 2) draws continuous input current; 3) low input current ripple compared with other qZS-based isolated dc–dc converters; 4) better reliability and good immunity against EMI noise; 5) common ground between the input source and the inverting bridge; and 6) continuous control over the entire operating range. Compared with other qZS-based isolated dc–dc converters, lower current stresses on active and passive components used are realized. Hence, the total magnetic volume/energy required by the proposed converter is reduced with the potential of achieving high power density. A prototype of 40–140 V input voltage, 300 V output, and 550 W rated power is developed to validate the performance of the proposed converter presented. [ABSTRACT FROM AUTHOR]

Long stroke nanopositioning stages with high natural frequency and compact size are demanded in precision engineering. However, in previous researches, the natural frequency of the long stroke nanopositioning stage is normally below 50 Hz because the actuated force, moving mass, stiffness, motion range, and damping ratio are not considered simultaneously and optimized thereafter. To solve this problem, a long stroke nanopositioning stage driven by the self-damping moving magnet actuator (SMMA) and supported by the flexure guide is integrated and designed in this article. The SMMA consists of two identical tooth-slot structure stators and one moving magnet which is embedded inside the flexure guide. Copper plates that functioned as eddy-current dampers are attached on the tooth surfaces to suppress the resonance peak at the natural frequency. An integrated dynamics model that consists of force, damping coefficient, and stiffness is established. The dimensional parameters of the proposed positioning stage are optimized to improve the system performances based on the developed model. Experimental results show that the natural frequency of the positioning stage reaches up to 71 Hz. The stage can achieve 20 nm positioning resolution within a motion range of $\pm$ 5 mm, and the root mean square tracking errors for 1 Hz sinusoidal and triangular commands are below 0.1% of the trajectory amplitudes. [ABSTRACT FROM AUTHOR]

This letter proposed a coupled resonant inductor structure for CLLC bidirectional converter, which can effectively reduce the number and volume of magnetic components and the oscillation caused by parasitic parameters. An optimized current detection method based on magnetic element voltage detection is also proposed to avoid the use of bulky and costly current sensors. Synchronous rectification is realized with the detection to improve efficiency. The effectiveness is verified by a 3 kW CLLC converter. [ABSTRACT FROM AUTHOR]

The Y-source impedance network is truly referred to as the origin of the magnetically coupled impedance source inverters. The key characteristics, including high boost capability and design flexibility, are associated with the coupled inductor turn ratio. However, the magnetic element brings some practical challenges, such as voltage spikes, high shoot-through (ST) current, and bulky coupled inductors. This article proposes two new Y-source inverters with clamped dc-link voltage. Due to the high boost ability, they are suitable for single-stage high gain inversions. Additionally, the significant reduction in the amplitude of the ST current leads to a reduction of the total power loss and capacity of the reactive component. Another attractive characteristic is that the Y-shaped coupled inductor's stored energy is no longer affected by the power rating of the converter, as a result of the zero dc magnetizing current. All these contribute to the high efficiency and power density of the proposed converters. The design guidelines of the components are presented and a thorough comparison with the state of the art is carried out. The achievements are then confirmed through extensive tests on a 500 W laboratory setup. [ABSTRACT FROM AUTHOR]

Magnetic components have become one of the primary barriers to high power density converters, especially to current-source converters (CSCs). In CSCs, the inductors/transformers have a predominantly dc flux to store energy, which can be offset by standard permanent magnets (PMs). However, eddy currents in standard PMs induce significant losses and thermal stress for medium-frequency applications. This article proposes using laminated PMs to offset the dc flux while reducing eddy currents, leading to significant reductions in the size, cost, and losses of inductors/transformers. Furthermore, the laminated PMs’ optimal location, orientation, and distribution are investigated to generalize this approach for maximum benefits. Three-dimensional finite-element analysis simulation and hardware experiments are presented to validate the effectiveness of the proposed approach in a medium-frequency transformer (MFT) for CSCs. Compared with standard PMs, the proposed use of laminated PMs reduces aggregate core-plus-PM losses by 85% in experiments, and thus, relaxes the MFT thermal design. Finally, the proposed approach is experimentally validated in a $\text{40}\,\text{kVA}$ flyback-type MFT for a soft-switching solid-state transformer. Compared to the traditional design without any PMs, the proposed design increases the saturation current by 46% while inducing only 5% more losses, leading to significant savings in magnetics cost and size. [ABSTRACT FROM AUTHOR]

The wideband high-power microwave systems have the advantages of wide energy spectrum, electron beam independence, compactness, and low cost. The gyromagnetic nonlinear transmission line (GNLTL) has drawn much attention for its potential as a novel solid-state, frequency-agile, and compact wideband source. The working mechanism of GNLTL is different from that of the traditional electric vacuum tubes, and the strong dispersion and nonlinear characteristics make it difficult to be accurately theoretically calculated and simulated. In this article, a 100-MW-level GNLTL system based on a Tesla-type driver was designed and constructed. A series of test experiments were then carried out to investigate the effects of different configurations, including delay line length, ferrite cores’ assembly orientation, transmission line length, bias magnetic field magnitude, and excitation voltage. The changing laws of the key parameters of the output microwaves including the peak power, modulation depth, center frequency, and percentage band are summarized and the underlying physical mechanisms are analyzed. The results may be instructive for the predesign of GNLTLs, especially for the devices operating at high power. In addition, a multiple center frequency points’ phenomenon was discovered in the output signal, which may bring new application possibilities for GNLTL. [ABSTRACT FROM AUTHOR]

This article presents crucial issues regarding the design, manufacture, and testing of a steel rotor for a 0.5-kWh flywheel energy storage system. A prototype was built using standard industrial components. The rotor has a maximum operating speed of 24 000 min−1 and is magnetically suspended. The introduced critical issues regarding the manufacture include the thermal stress during the rotor hardening process, the fixation for the rotor components of the drive machine and the magnetic bearings, etc. The rotor strength was validated by the overspeed testing according to the standard IEC 60034-1. A rotation of up to 28 800 min−1 (120% of the maximum speed) was realized and maintained for 2 min. The proved rotor was suspended by commercial magnetic bearings in the flywheel system. Despite simple decentralized control, the rotor was successfully driven up to the designed maximum speed. The rotor dynamic behavior is analyzed by analytical calculation, simulation, and measurements. Different eigenmodes are identified. The results prove the possibilities to build and operate a flywheel system using standard industrial components, showing potential for cost-effective designs. [ABSTRACT FROM AUTHOR]

A triple-coil pulsed magnet aiming at 100 T (Tesla) was designed and tested at the Wuhan National High Magnetic Field Center. The magnet was powered by a 100 MJ pulse generator, a battery bank, and 25 kV capacitor banks in combination. The magnet failed at 83 T, while the whole structure remained intact. The failure process was analyzed by using the recorded waveforms of the voltage and the current, as well as disassembling and dismantling the failed magnet. It shows that the inner coil broke down first, and then the electrical breakdown occurred between the middle and outer coils. The possible reasons were also discussed. The buckling analysis results show that the inner and middle coils would buckle at 71 T and 83 T, respectively, which were consistent with the experimental results. The cross-ply reinforcement method is proposed to enhance the structural stability of high field magnets. [ABSTRACT FROM AUTHOR]

Flux-Pinning Docking Interfaces (FPDI) in satellite systems were developed using bulk superconductors and permanent magnets in previous works. However, such FPDIs have limited magnetic field strength, consist of heavy-weight material, and can only be used with a single purpose, i.e., as chasing or docking satellite. Replacing the magnetic material in the FPDI by a trapped field (TF)-magnet would enable the interface to operate for both purposes, i.e., generating a (stronger) magnetic field and trapping it. We show the requirements for such a system and discuss the possible gains when using a TF-FPDI in satellites. To reduce the system weight, the use of superconducting foams as superconducting material is discussed in detail. Furthermore, the use of superconducting foams, the size of which can be easily upscaled, may also comprise the function of the damping material, so even more weight could be saved for the payload. [ABSTRACT FROM AUTHOR]

This article presents a detailed analysis and design of a high step-down converter. The proposed converter achieves high step-down voltage gain without the need of extreme duty cycles by using coupled inductor. The converter features low switch stresses, which reduces the conduction loss by using low voltage MOSFETs. Moreover, the magnetizing current of the coupled inductor is zero, which reduces the magnetic size. The leakage energy of the coupled inductor is recycled. Zero voltage switching is achieved to reduce switching loss and improve the EMI performance. In addition, continuous output current is achieved; hence, small filtering capacitor can be used. A hardware prototype is built and experimental results verify the feasibility of the step-down converter. [ABSTRACT FROM AUTHOR]

This article proposes a multiloop control structure for isolated multiport power converters (IMPCs), which includes a multiloop load-disturbance attenuation controller (MLDAC) and also an improved multiloop power-mismatch mitigation controller (MPMMC). The inherent capability of the IMPC to use a common magnetic link (CML) instead of multiple magnetic links offers an attractive solution to design a compact multimodule-based IMPC. With the proposed MLDAC, the IMPC can regulate the system voltage for any load disturbance without requiring any feedforward output current sensor. Moreover, the proposed MPMMC effectively mitigates leakage parameter mismatch and strictly balances the power routing in the multiple ports of the IMPC. The proposed MLDAC and MPMMC are decoupled with an improved decoupling mechanism. Additionally, this article develops a control law to indicate a safe operating area of the MPMMC. The strict voltage regulation of the IMPC under random load disturbance facilitates plug-n-play connectivity and supply of power to pulsed power loads. Moreover, eliminating the power-mismatch issues in the CML ensures equal thermal stresses and duty-life cycles of the solid-state switching devices. The performance of the proposed MLDAC is tested and compared with existing disturbance attenuation techniques. The simulation and the experimental results substantiate the superiority of the proposed MLDAC and MPMMC. [ABSTRACT FROM AUTHOR]

This study focuses on the magnetic conductivity of magnetorheological fluids (MRFs) and magnetorheological elastomer (MRE) in variable inhomogeneous magnetic field. It aims to provide a simple method for measuring the permeability of magnetic material and explore the magnetic properties and application advantages of the MRF and MRE. By analyzing the experimental data measured by a magnetic force test device and simulation results, the relative magnetic permeability of MRF and MRE is obtained. The results indicate that the magnetic permeability of MRE can be assuredly enhanced by arranging the magnetic particles in the nonmagnetic medium along the direction of the external driving magnetic field. Additionally, increasing the particle concentration of MRF or MRE is a conventional but quite effective method to improve the permeability of MRF or MRE. Within the scope of this study, the magnetic conductivity of MRF with the same concentration is significantly stronger than that of MRE, and its relative permeability can be higher than 80%. The high flowability of MRF enables the dispersed particles to form chainlike structures along the magnetic lines of flux, which enhances the magnetic induction intensity of the magnetic particles. Considering, a shaping magnetic field with the same distribution of the driving field applied on MRE in the solidification process can unexpectedly improve the magnetic conductivity of MRE. Moreover, compared with the change amplitude of the permeability of MRF, the relative permeability of MRE changes less in different driving magnetic fields due to the constraint of the suspended particles position. [ABSTRACT FROM AUTHOR]

Soft magnetic composites (SMC) are an alternative to laminated steels for the design of smaller and lighter electromagnetic devices. Such electromagnetic devices might be subjected to significant mechanical stresses that can alter their electromagnetic properties. This article presents a homogenization model that provides estimates for both the nonlinear magnetic response and the eddy current (EC) losses of SMC subjected to a stress state. [ABSTRACT FROM AUTHOR]

The classical laws of physics are usually invariant under time reversal. Here, we reveal a novel class of magnetomechanical effects rigorously breaking time-reversal symmetry. These effects are based on the mechanical rotation of a hard magnet around its magnetization axis in the presence of friction and an external magnetic field, which we call spin revolution. The spin revolution leads to a variety of symmetry breaking phenomena including upward propulsion on vertical surfaces defying gravity as well as magnetic gyroscopic motion that is perpendicular to the applied force. The angular momentum of spin revolution differs from those of the magnetic field, the magnetic torque, the rolling axis, and the net torque about the rolling axis. The spin revolution emerges spontaneously, without external rotations, and offers various applications in areas such as magnetism, robotics and energy harvesting. [ABSTRACT FROM AUTHOR]

Topological spin textures are the next-generation spintronic building blocks for storing and processing information because of their controllable formation and annihilation. Memory, logic, and neuromorphic computing applications are reported using such devices having 2-D and 3-D spin textures, namely, vortex, skyrmions, localized bullet, and so on. A robust device-to-circuit-to-system level design is required for developing a neural network (NN) or a neuromorphic computing system (NCS) using these spin devices. Hence, in this work, we present a Verilog-A-based analytical model of a vortex spin-torque nano oscillator (V-STNO) for enabling circuit-level simulation. The model presented here is functional for both linear and nonlinear dynamics of the magnetic vortex core. The nonlinear dynamics show the formation and annihilation of the magnetic vortex depending on its critical currents. Furthermore, the developed model is analyzed for the nanopillar’s diameter and free layer thickness variations. Moreover, an investigation of the temperature effect on the device performance for a range of −40°C to 140 °C is carried out. [ABSTRACT FROM AUTHOR]

This article studies system-generated electromagnetic pulse (EMP) and coupling in a reentrant cavity—a simplified spacecraft model with the annular slit and internal shaft, numerically by using the three-dimensional conformal particle-in-cell method. The results indicate that when the electromagnetic fields arrive at the annular slit, obvious field-coupling will be induced that EMP may enter or escape from the slit without many restrictions at the low-irradiation fluence. In this case, the total field can be acquired by linearly summing the EMPs derived from the moving electrons released separately by the external and internal emitting surfaces. The reentrant cavity is to form a repetitive-oscillating capacitor model, while the electromagnetic waves of damped oscillation with comparatively large amplitude are found near the annular slit and the internal shaft. The frequency of the damped oscillation is mainly influenced by the cavity geometrical factor and is going to converge to the natural frequency of the reentrant cavity. Furthermore, the reason accounting for the change of both the frequencies is revealed. [ABSTRACT FROM AUTHOR]

This work couples a magnetic multi-stable mechanism to a pendulum vibration energy harvester so as to widen its bandwidth, especially in low-frequency operation. Multiple stable points are formed by a movable permanent magnet installed on the pendulum and two fixed permanent magnets installed symmetrically on the base of the energy harvester. Thus, the pendulum can swing between the stable points at two sides, which causes large motion amplitude and power generation. In designing the prototype of the energy harvester, dynamical modeling and potential energy analysis are carried out to achieve a low threshold for snap through. An experimental setup is developed and a series of comparative experiments are implemented to investigate prototype performance. It is shown that the energy harvester with the fixed magnets can generate a noticeable normalized induced voltage at 0.7 Hz, while the energy harvester without the fixed magnets requires the excitation frequency of 1.0 Hz to reach a similar level. The electrical outputs varying with vibration acceleration and load resistance are also examined. In general, the experimental results verify the effectiveness of the proposed structure on enlarging frequency bandwidth. This work can provide a promising candidate of energy harvesting for low-frequency applications such as ocean wave. [ABSTRACT FROM AUTHOR]

This work investigates a 2-D vector field behavioral model to describe the anisotropic magnetic permeability and losses in Grain-Oriented Electrical Steels (GOES) within quasi-static and magneto-harmonic working conditions. The model includes the an-hysteretic magnetic field driven by the total anisotropy, the coercive force responsible for the quasi-static hysteresis losses, and the dynamic damping eddy field responsible for the extra losses. Each field contribution requires the definition of a tensor property whose diagonal and non-diagonal coupling components are experimentally identified as a function of the flux density magnitude $B$ and its angle $\theta $ with the Rolling Direction (RD). The static behavior is identified at low frequency and the dynamic one takes the frequency-dependent field diffusion into account. Diagonalization tools reveal main characteristic magnetic axis for the separate properties with deflections at the macroscale. [ABSTRACT FROM AUTHOR]

We compare two different approaches to compute the spin Hall torque at the interface between a spin Hall metallic layer and a ferromagnet. In one approach, one attributes a spin mixing conductance $g_{\uparrow \downarrow }$ to the interface, while the other employs the thermodynamic theory for the magnetic moment currents. The main difference between the outcomes of the two approaches is the field-like torque term that, in the first approach, is due to the imaginary part of the spin mixing conductance $\text {Im}[g_{\uparrow \downarrow }]$ and, in the second one, is proportional to the effective damping $\alpha ^{\prime }$ of the ferromagnet. [ABSTRACT FROM AUTHOR]

This article proposes an improved tubular single-phase permanent magnet linear oscillation actuator (SP-PMLOA) considering eliminating detent force for direct drive compressor applications. First, the flux tube method and Maxwell stress tensor are used to derive the end force and cogging force formulations based on the magnetic flux leakage of the magnet rings. Then, a novel model with minimum detent force is presented by finite element parametric sweeping. Finally, the electromagnetic performance of the three SP-PMLOAs is compared using 2-D finite element analysis (FEA), whose merits are evaluated, and the thermal distribution of the optimal PMLOA is analyzed using 3-D FEA. The predicted results show that the proposed structure not only can significantly reduce the detent force and the mover axial length but also can increase the thrust force-moving magnet mass ratio. [ABSTRACT FROM AUTHOR]

A magnetron is one of the most common microwave power generators used in commercial or industrial applications. There are a few methods for optimizing the magnetron to enhance its efficiency, which include the selection of the building materials, increasing the resonant cavity, enlarging operation space size, and modifying the anode structure. This article proposes the modification of magnetron cathode for high-frequency and low-power applications using gallium nitride (GaN)-coated cathode replacing the current barium oxide (BaO) coat. The highlighted optimization is intended to modify the control of magnetron electron drift velocity, heat dissipation, operation frequency, and power generation. Simulation and experimental results have been extracted at 2.45 GHz to generate 5 W microwave power and tested for over 30 ft. of power transmission using a rectenna interface, which results in an efficiency of 88.37%, compared with 51.8% using BaO coat. [ABSTRACT FROM AUTHOR]

Ac low voltage stabilizers with thyristor-based onload tap-changers are effective and cover 300 VA to 300 kVA applications. Among the solutions to reduce the internal short-circuit derived from the make-before-break changes, the multiwinding coil for years has proven to be reliable. This article shows a new operating mode of the coil that allows extra output voltages from every tap-switch using a magnetically coupled Nonius. The number of main taps is greatly reduced allowing, in a typical 10 MVA 34.5 kV line tap-changer, to save 33% of the cost of thyristors compared to the previous best solution without Nonius. In total, 29 voltage states can be obtained with only eight main taps and six auxiliary small Nonius taps per phase. Medium voltage stabilizers up to 36 MVA can be implemented using standard phase control thyristors with no series, nor parallel, association. Simulations and physical tests, controlled by digital signal processor, show that the new Nonius operating mode of the coil does not penalize the current rate of the switches, nor the flux of the coil core. Thus, magnetic-Nonius tap-changers achieve cost-effective stabilization with the fine regulation obtained by mechanical solutions with many taps. [ABSTRACT FROM AUTHOR]

This article presents a three degrees of freedom (3-DOF) permanent maglev platform for a cleanroom conveyor system supported by four magnetic poles that utilize a variable flux path mechanism. Since the magnetic force of poles is generated and controlled entirely by the rotation of disk-type permanent magnets (PMs), the system exhibits a quasi-zero power consumption and anti-adsorption capability. First, the system mechanism is illustrated, and the magnetic force of the variable flux path pole is measured. Then the mathematical model and state-space of the maglev platform are established based on dynamic analysis. Afterward, a double closed-loop controller is designed for stable levitation and motion control, and the coordinate transformation matrix is used to decouple the control system. Finally, the simulations and experiments were implemented, and stable levitation and 3-DOF motion control were realized with a remarkable positioning precision. The results indicate that the controller and decoupling strategy are effective. [ABSTRACT FROM AUTHOR]

In this study, bulk Pr2Fe14B/ $\alpha $ -Fe nanocomposite magnets were fabricated from amorphous Pr9Fe86-x ${\text {Cu}}_{x}\text{B}$ 5 ($x$ = 0–1.5 at.%) precursors by a rapid high-pressure thermal compression (HPTC) technique, and the effects of Cu content on the texture and magnetic properties of the deformed magnets were investigated systematically. Results showed that the magnetic anisotropy $A_{m}$ and remanence $B_{r}$ of the deformed magnets increase evidently with increasing Cu content, whereas the coercivity $H_{\mathrm {ci}}$ decreases dramatically, thereby resulting in the maximum energy product (BH)max initial increase and then decrease. A magnetic anisotropy of $A_{m}$ = 0.44 and the optimal magnetic properties of (BH)max = 21.4 MGOe, $B_{r}$ = 13.1 kG, and $H_{\mathrm {ci}}$ = 3.52 kOe were achieved at x = 1.0 at.%, which can mainly be attributed to the strong ($00l$) crystallographic alignment of Pr2Fe14B nanocrystals and excellent exchange coupling between hard and soft nanocrystals. The present research is important for developing anisotropic bulk nanocomposites with high-energy products. [ABSTRACT FROM AUTHOR]

A typically new semi-analytical finite element approach has been used to calculate the force and moment of permanent magnet bearing (PMB) in this article. PMB stator and rotor consist of ring-type cylindrical magnets having an axial magnetization. This article focuses on the characterization of magnetic moment, stiffness matrix, model validation, and comparisons of the moment with other simulating software. This article also explains how angular stiffness or resisting magnetic moment of PMB improves with the change of rotor magnet length and positional shift of the rotor. [ABSTRACT FROM AUTHOR]

Based on spark plasma sintered (SPS) Nd-Fe-B magnets with PrCu sintering aid, hot deformed (HD) magnets are prepared through hot deformation technique. After that, using PrCu as the diffusion source, grain boundary diffusion (GBD) is implemented on HD magnet. Eventually, GBD magnet is subjected to hot deformation to regulate the distribution of RE-rich phase and increase $c$ -axis orientation, referred to as the secondary deformation (SD). The results show that hot deformation processes have an important influence on magnetic properties and microstructure, among which the deformation condition of 700 °C/0.5 h is the most favorable to obtain optimal magnetic properties. Through GBD, the coercivity, as high as 2117 kA/m, can be obtained, increasing by 7.5% comparing with that of the initial SPS sample. Moreover, it is found that the SD can effectively optimize the distribution of RE-rich phase, and improve $c$ -axis orientation of grains. Eventually, a good balance between coercivity and remanence is achieved. In addition, both GBD and SD can increase the thermal stability of HD magnets. [ABSTRACT FROM AUTHOR]

Surge is one of the main factors affecting the stability of the centrifugal compressor. This article investigates surge disturbance suppression of active magnetic bearing (AMB)-rotor systems in magnetically suspension centrifugal compressors. An active disturbance control method is adopted to make the rotor stably levitate under surge disturbance. First, the dynamic model of the magnetic bearing rotor is established and simplified into a single-channel model. Second, a third-order linear extended state observer (LESO) and a linear active disturbance rejection controller are designed. The performance analysis of the controller shows that the estimation error accumulation of the observer is bounded and the estimation errors decrease with the increase of the observer bandwidth. Furthermore, the variable differential parameter added in the differential link of the controller can flexibly adjust the system damping. A method of tuning parameters for linear active disturbance rejection control (LADRC) is proposed to suppress surge disturbance while satisfying the stability of the system. Finally, the results of the experiment demonstrate that the proposed scheme is effective in suppressing the large-scale vibration effect of the surge disturbance on the rotor, and the magnetically suspended centrifugal compressor (MSCC) can run stably with low amplitude under the modified surge and mild surge. [ABSTRACT FROM AUTHOR]

As part of the European Strategy for Particle Physics there is an ongoing development towards a Future Circular Collider (FCC-ee) where electron-positron collisions could be used to study the entire electro-weak sector in a low background environment. Particle detectors are used to study these collisions and a strong magnetic field is required to measure the particles’ momenta. Currently, two detector concepts are being studied: the Innovative Detector for Electron-positron Accelerators (IDEA) and the CLIC-Like Detector (CLD). Both these detectors include a superconducting solenoid magnet with a central field of $2 \,\mathrm{T}$ of which the designs are presented here. The IDEA magnet has an stored magnetic energy density of 14 kJ/kg and in CLD this is 12 kJ/kg. Taking into account their respective free-bore diameters of $4.2 \,\mathrm{m}$ for IDEA and $7.2 \,\mathrm{m}$ for CLD this results in very challenging designs for which the mechanical and quench studies are presented. Their results are promising, but extensive R&D on these magnets would be needed in the future to reach the goals set out in the Conceptual Design Report (CDR). [ABSTRACT FROM AUTHOR]

The High Luminosity LHC (HL-LHC) Project is planning to install 16 cold-masses made with Nb3Sn quadrupole magnets in the LHC Interaction Regions to significantly increase its luminosity. Half of these cold masses are fabricated at BNL, FNAL, and LBNL under the US Accelerator Research Program (AUP). Each cold mass includes two identical Nb3Sn quadrupole magnets, called MQXFA with a magnetic length of 4.2 m. Currently, the AUP project has completed the fabrication and test of the first 5 pre-series magnets, and is working on the following 16 magnets for the series production. The brittleness and strain sensitivity of the Nb3Sn superconducting material requires a careful definition of the allowable maximum stress in the windings during magnet assembly and pre-load, and a tight control of their variation within the whole coil length. Therefore, a series of assembly and pre-load specifications have been defined with the goals of minimizing the risk of conductor degradation and providing the mechanical support required to reach the nominal current during powering. In this paper we present the specifications defined for the MQXFA magnets and applied during the different assembly phases and during the pre-load process of the first 5 pre-series magnets. [ABSTRACT FROM AUTHOR]

This work reports a frequency domain analysis on alternating current (AC) response of a metal-insulation (MI) high temperature superconducting (HTS) coil. An 85-turn MI test coil was wound and operated in a liquid nitrogen bath at 77 K. Sinusoidal current was applied to the test coil to measure the AC responses. The test coil’s total voltage and the central magnetic field were measured from 0.01 Hz to 5 Hz. The phase difference between the total voltage and the azimuthal current was calculated from the measured data. To explain the phase difference between the total voltage and the azimuthal current, the additional frequency-dependent resistive component was adopted. The results demonstrate that the discrepancy between the measurement and the simulation results from the lumped-circuit model tends to increase with frequency. [ABSTRACT FROM AUTHOR]

The cooperation of coherent and dissipative coupling produces nonreciprocity in cavity magnonic devices, in which the isolation ratio can theoretically be infinite at a matching condition (zero-damping condition). In this article, we report the design of such a prototype, where a yttrium–iron–garnet sphere is strongly coupled to a planar microwave cavity resonator. Three different microwave isolator design schemes have been constructed according to the latest developed theory, resulting in considerable isolation, design flexibility, and device size reduction. Fabricated devices achieved the isolation of 65.8, 40.5, and 31.0 dB and the corresponding insertion loss of 23.6, 0.7, and 0.7 dB, respectively. These devices promise to be useful in microwave range applications that demand miniature, low cost, and narrowband. Furthermore, our magnonic device may open a promising way for signal processing through the manipulation of coherent and dissipative coupling. [ABSTRACT FROM AUTHOR]

This letter proposes a novel step-up/down series-connected partial power converter (S-PPC) for string photovoltaic (PV) applications. The proposed bidirectional two-switch forward (BFwd) dc–dc S-PPC performs partial power processing, reducing component stresses and losses. The PV active power is unidirectional, but the BFwd alone operates with bidirectional active power flow; with bidirectional current at the input and bipolar voltage at the output, characterizing two distinct modes of operation. To validate the analysis, a 950-W system prototype of the novel BFwd S-PPC was implemented experimentally for a realistic PV application example, where the transformer turns ratio was designed to decrease the nonactive power processed, resulting in a high power factor ($ >\text{0.75}$). The prototype reached a rated/peak system efficiency of 98.68%/99.48%. Compared with previously published step-up/down S-PPCs, the BFwd S-PPC employs fewer active switches (and gate drivers), which reduces its complexity and cost; but moreover, increases its performance. In fact, the proposed BFwd S-PPC presents higher efficiencies than most step-up/down S-PPCs in the literature. [ABSTRACT FROM AUTHOR]

In this article, we present the characterization and an experimentally validated electromechanical model of a dual-transduction receiver for electrodynamic wireless power transfer (EWPT) system. This dual-transduction EWPT receiver contains two unimorph-type, series-connected piezoelectric transducers and an electrodynamic transducer within a compact footprint and low-profile design. The receiver makes simultaneous use of both piezoelectric and electrodynamic transducers to generate electrical power while operating at its torsion mode mechanical resonance at ∼744 Hz. The electromechanical system behavior and output performance under low-frequency, magnetic near-fields are analyzed by establishing an equivalent lumped-element equivalent electrical circuit model. A prototype device is fabricated, assembled, characterized, and the experimental results are compared with the model predictions under various excitation and loading conditions. A maximum of 49 μW average power is generated by the prototype under 120 μTrms, which corresponds to 0.54 mW·cm–3 power density and 37 mW·cm–3·mT–2 normalized power density. This chip-sized (0.09 cm3) design offers an innovative and volume-efficient architecture for application in wirelessly charging wearable and implantable medical devices. [ABSTRACT FROM AUTHOR]

To study the clamping device in reluctance force launcher, the Maxwell stress tensor method is extended to contact force calculations. It is generally believed that the Maxwell stress tensor method is only suitable for objects surrounded by air or vacuum. However, in this article, the Maxwell stress tensor applicable to ferromagnetic materials is re-derived, and the classical Maxwell stress tensor is successfully reproduced. Its integral region is determined as the outer surface of the interface between the object and the outside world, which means that the Maxwell stress tensor method can be used for contact force calculations. Subsequently, the Maxwell stress tensor method was used for force studies in the clamping device. The needed clamping force of the clamping device is calculated. The reducing effect of ferromagnetic materials on the clamping force and the effect on the acceleration force of the projectile are analyzed. Finally, based on the determined integral region, the reason why the integral result of Maxwell stress tensor method is related to the integral path is successfully explained, which provides another theoretical basis for the contact force calculation method in this article. [ABSTRACT FROM AUTHOR]

This article proposes a ferrofluid soft capsule robot (FSCR) with magnetic actuation for diagnostic and therapeutic medical applications inside the human stomach. A composite shell consisted of ferrofluid, permanent magnet rings, and soft elastomer is developed for the FSCR, which is actuated remotely by an external permanent magnet. The proposed FSCR presents two novel characteristics. First, the composite shell not only has a soft outer surface that reduces damage to contact tissue but also an improved magnetic circuit with a combination of the ferrofluid and permanent magnet rings makes the locomotion of the device more controllable and secure. Second, the FSCR is equipped with a specific oscillation module that enables advanced functions such as drug-releasing. Detailed structure design and fabrication of the FSCR are presented in this study. The surface rolling locomotion of the FSCR is modeled and evaluated by numerical simulations, as well as the drug-releasing function. In order to verify the simulation result, an FSCR prototype is manufactured to perform experimental validation. The analysis result demonstrates the feasibility and efficiency of the proposed FSCR for drug releasing inside a printed human stomach model. [ABSTRACT FROM AUTHOR]

In the last two decades, the micromanipulation technique has been widely utilized in industrial and biological fields. However, existing micromanipulation methods can hardly meet all the demands in both fields. In this article, we present an all-purpose magnetically driven micromanipulation system with designed contact and noncontact modes for numerous industrial and biological applications, respectively. In the system, a micropipette containing the ferromagnetic beads driven by themagnetic field presentshigh-precision and high-speed motions. With another micropipette, this two-finger microhand can efficiently perform the chopstick-like grasp motion by physical contact. The vibration-based active release relying on the high-speed motion can help release the targets adhering to the end-effector. Besides, local whirling flow surrounding the micropipette induced by high-speed circular motion can trap, transport, and rotate microtargets without contact like a hydrodynamic tweezer to operate micro bio-targets without any damages. In experiments, microbeads are grasped and releasedefficiently in the desired positions using the chopstick-like two-finger microhand mode, and the arrays of a hexagon and “TMECH” have been assembled. The hydrodynamic tweezer mode is adopted to trap, transport, and rotate the microbeads and further applied in the operations of the mouse egg cells. We believe the proposed magnetic micromanipulation system, as an all-purpose tool at the microscale, holds great potential in industrial and biological applications. [ABSTRACT FROM AUTHOR]