Search

Neutron depolarization experiments have shown that the intragranular magnetic domain structure of polycrystalline ferrites exhibits a marked grain size dependence. Below a grain size of around $3~\mu \text{m}$ , the magnetic domain structure changes from the two-domain to the mono-domain state. Ferrites composed of mono-domain grains exhibit low dissipation at megahertz frequencies. This is attributed to the absence of intragranular domain wall movement, i.e., a microscopic origin for dissipation in ferrites has been identified. The implications of this clear observation and evidence for a transition from the mono- to two-domain state in ferrites for micromagnetic theory when a single particle becomes monodomain, as well as for the initial permeability mechanisms in polycrystalline ferrites, are discussed.

This paper proposed a simulation method for the charge transport in single-layer oil-paper insulation. The method of transient upstream finite-element method (FEM) is derived in order to calculate the time variation of charge densities in medium. The numerical simulation of charge transport in the single-layer oil-paper insulation is realized by applying the transient upstream FEM to the transport equations of bipolar charges. With reasonable microparameter, the charge transport in an experimental object is simulated. The simulation results are consistent with the experimental data. A bent model of oil-paper insulation is analyzed to study the charge distribution under the actual condition. This paper provides an exploratory research to the simulation of charge phenomenon in oil-paper, and has guiding significance to the design of oil-paper insulation.

In the pursuit of point-of-care systems that present high sensitivity and fast turnaround time, lateral flow is considered a remarkable promising class of in vitro diagnostics, and popularized by the pregnancy tests. A variety of lateral flow tests have emerged able to provide cardiac panels in emergency conditions, infectious disease screening, drug abuse, among others. However, most commercial tests only provide qualitative results, limiting their applicability for quantification thresholds of most biomarkers. In this paper, we propose a novel detection architecture for quantification of biomolecules labeled with magnetic nanoparticles employing two spin valve sensors. The main goal of this paper is to demonstrate that this architecture can detect and monitor MNPs flowing in a LFT strip for detection and quantification of different solutions varying in MNP concentration. In addition, we present preliminary analytical results that support our strategy for achieving biomolecular quantification using the proposed solution.

A procedure for producing magnetic paper by in situ synthesis of substituted (Co, Ni) ferrites is described. Ferrites are formed in the presence of cellulose fibers and then forced to enter into the fiber lumen where they stay protected from mechanical influences. The remaining particles are washed out of the fibers leaving its external surface clean, so that its papermaking properties are not affected. Multilayer papers were prepared in which the colored magnetic layer is hidden behind white printable surfaces. Finally, the magnetic properties of the different kinds of obtained papers are compared with typical commercial standards, like subway tickets and airport boarding passes.

As the easiest experimental approach, GMR (giant magnetoresistance) is usually measured using the current in plane (CIP)-GMR. The spin-valve transistor has previously been presented as a spectroscopic tool to measure current perpendicular to the planes (CPP)-GMR. Hot electrons cross the magnetic multilayer base quasi-ballistically and the number reaching the collector depends exponentially on the perpendicular hot electron mean free path. Collector current changes of 390% at 77 K have already been measured. Apart from the substantial fundamental value, such properties may be useful for sensor applications. The electron energy range fills the gap between the Fermi surface transport in resistance measurements and other hot electron techniques such as spin polarised electron energy loss spectroscopy (SPEELS). The preparation problem of the spin-valve transistor and metal base transistor structures in general, the deposition of a device quality semiconductor on top of a metal, has now been tackled by bonding of two semiconductor substrates during vacuum deposition of a metal: an excellent bond is achieved at room temperature. TEM photos show a continuous buried metal film. Apart from preparation of various metal base transistor like structures, many other fields may benefit form this new technique

The 38 papers in this special issue were originally presented at the European Magnetic Sensors and Actuators Conference, held in Prague, Czech Republic, on July 1-4, 2012.

The 51 papers in this special issue were originally presented at the 9th International Conference on the Scientific and Clinical Applications of Magnetic Carriers, held May 22-26, 2012, in Minneapolis, MN.

Magnetotactic bacteria (MTB) may be manipulated by the application of magnetic fields. This effect enables motile, magnetic field susceptible MTB to be utilised in the removal of contaminants, such as heavy metals, from wastewater. This paper discusses a process designed for continuous cultivation and extraction of metal loaded MTB. The performance of this recovery system is characterized here with respect to bacterial motility, the number of passes through the separator and the processing rate.

This paper presents the results of pilot-scale studies of sulfur and ash removal from coal by high gradient magnetic separation (HGMS). Work was done on both the liquefied coal and the raw pulverized coal in water slurries. The effects of residence time, field intensity, packing material and density, slurry concentration and recycle on the grade and recovery of the wet separation of sulfur and ash from water slurries of Illinois No. 6 coal were quantitatively examined. The HGMS was effective in reducing the weight percent of total sulfur, ash, and inorganic sulfur by as high as 40, 35, and 80%, respectively; while achieving a maximum recovery of about 95%. The results have also provided the first experimental verification of the applicability of Bean's magnetic filtration model in quantitatively correlating the data obtained from the pilot-scale beneficiation of coal slurries by the HGMS. The successful verification of the model allows one to quantitatively identify the trade-off of operating parameters so as to optimize the magnetic removal of sulfur and ash. A pilot-scale HGMS system for the magnetic sedation of mineral residue from the liquefied coal has been designed and constructed. Typical results from preliminary experiments with the liquefied solvent refined coal (SRC) have been quite encouraging, indicating that the HGMS was effective in reducing the total sulfur and ash contents by as high as 70 and 76%, respectively. Finally, the liquefaction of the magnetically treated Kentucky No. 9/14 coal was studied and compared with that of the untreated coal. It was found that although the mineral matters which had been removed magnetically had a significant catalytic effect on the liquefaction behavior, the organic hydrodesulfurization remained practically the same for both the untreated and treated coals. This suggests that the magnetic removal of mineral matters prior to liquefaction may be advantageous for the SRC and other related liquefaction processes, in which the minimum hydrogenation is especially desired and the hydrodesulfurization is often limiting.

Magnetic circuit components have long been the largest and most difficult components to miniaturize. Printed circuit board (PCB) fabrication methods cannot achieve small diameter, high aspect-ratio vias for high winding turn numbers to achieve high inductance, and microelectronics methods cannot achieve the high-quality and thick ferrite core materials. In this paper, we present an alternative breakthrough method of printed circuit fabrication to significantly reduce the effective via diameter for embedded magnetic devices, boosting the inductance per unit area. To reduce the effective via diameter, high-density via plugs are ex-situ fabricated and shaped, and then embedded into PCB substrate in the same process as standard magnetic core embedding. The structure of the plug is such that precise placement within the substrate, or alignment to the plug with the winding pattern, is not necessary. Devices presented in this paper use via plugs with an effective diameter of 40 μm and a theoretically unlimited aspect ratio, though refinements in the plug fabrication process are expected to reduce the via diameter down to 10μm. The process is experimentally demonstrated with a 14-turn racetrack shaped transformer; novel diagnostic methods using magneto-optic garnet films to image current paths are also demonstrated.

Ferric Hydroxide is a good scavenger for trace concentrations of both heavy metals and many radio nuclides, its precipitation from waste streams could be used as an effective method of clean up if a satisfactory process for the recovery of the ferric floc was available. This paper examines the use of HGMS for this operation and concludes that a practical plant design is feasible for ferric floc separation but would require a large installation. The work is continuing and more recent developments have shown how significant improvements can be made by precipitating the iron as magnetite instead of ferric hydroxide.

Our preliminary experience with using commercially available High Gradient Magnetic Separation (HGMS) instrumentation in water treatment problems is described. Water effluents from both a refinery and a chemical sewer have been used with flocculants to reduce total suspended solids and oil content.

Demagnetization factor and corresponding apparent permeability for multi-wire arrays using the 3D finite element method are calculated in this paper. The effect of distance between magnetic wires on the demagnetization factor and apparent magnetic permeability is studied for various values of relative magnetic permeability. The simulations are compared with experimental results on arrays up to 91 wires. A novel simplified equivalent 2D model for wire arrays is presented in this paper, as a fast method for calculations. The simplified axisymmetrical model consists of a set of hollow cylinders with equivalent volume. The results of the proposed simplified 2D model fit very well the full 3D FEM simulations and experimental results. Two different hexagonal and square arrangements for wires are considered both for the simulations and the measurements.

This paper proposes a rotor design method suitable for double-layer interior permanent magnet synchronous motor (DIPMSM), which can reduce electromagnetic torque ripple and at the same time reduce the electromagnetic noise of the motor. In previous studies, the inverse cosine function (ICF) was used to modify the rotor shape for making the air gap flux density distribution sinusoidal under no-load conditions, which can reduce the torque ripple. However, conventional ICF can only be used in a single-layer interior rotor structure. Consequently, this paper proposes a piecewise inverse cosine function (PICF) based on ICF, which can be applied to DIPMSM. To verify the improvement of the proposed method in the electromagnetic and noise aspects of the motor, the electromagnetic model and a noise prediction model of the 36-slot/8-pole motor are established by the finite element method. The PICF model is compared with the prototype in the aspects of electromagnetic performance and noise. The torque ripple is reduced by 54.16%, from ± 2.4 Nm to ± 1.1 Nm, and the electromagnetic noise is reduced by about 4.9 dB. Finally, the accuracy of the noise prediction model is verified by the noise test of the prototype.

It is well known that the slotted motor has higher power and torque ripple than the slotless motor. But how much the power and torque ripple can increase is rarely reported. In this paper, the analytical method is used to compare the torque of the slotless and slotted motor. First, the armature reaction field and open circuit PM field are solved by the subdomain model. Then, the torque is calculated by the Maxwell stress tensor method. Moreover, we also obtain the back electromotive force (back EMF) and cogging torque. At last, the average torque and the torque ripple of the slotless and slotted motor are compared and discussed. The above analytical model is verified by the 3D FEM and experiment. Results show that the average torque and torque ripple of the slotted motor have increased 52.6% and 22.5 times compared with that of the slotless motor. This paper will provide a useful reference for the design of both the slotted and slotless ultra-high speed AFPM motors.

This paper proposes a modeless prediction scheme to estimate the coupling effect for wireless power transfer (WPT) systems. To address the impact of the variable coupling effect for WPT systems, the acquirement of the coupling effect has been gradually one of the most important research topics in recent years. However, the mutual inductance cannot be directly measured, since it is not only determined by the distance but also by various external factors. Although there are several efforts for the prediction of the mutual inductance which have been made in previous studies, the practicability of existed schemes mostly suffers from limitations caused by the communication link, the complex calculation and the measurement accuracy. Accordingly, this paper proposes a modeless prediction scheme using neural network (NN) to dynamically estimate the varying coupling effect caused by practical working conditions like the variation of relative position between the transmitting and the pickup coils. In this paper, the simulated and experimental results are both given to verify the feasibility of the proposed modeless prediction scheme as well as its salient advantages of communication-free, calculation-simple, and measurement-convenient.

In this paper, a novel winding switching control strategy is proposed to extend the speed range of a consequent-pole ferrite-PM hybrid-excited machine (CPFPM-HEM) for electric vehicle application. The key is that in low-speed range, the AC armature winding and DC field winding are connected in series to achieve large starting torque, while in high-speed range, DC field winding are injected with adjustable DC currents to realize variable speed constant voltage of AC armature winding. Furthermore, consequent-pole rotor is used to reduce the usage of the permanent magnet (PM). In the meantime, ferrite PMs are used to replace rare-earth PMs to reduce the cost with the shortage of rare earth resources. In this paper, the machine configuration, operation principle with dual excitation sources, flux modulation principle and winding switching strategy are illustrated in detail. Then, the electromagnetic performance of the CPFPM-HEM in different speed ranges is investigated. Finally, the speed range extension with winding switching strategy is verified by the Maxwell/Simplorer co-simulation.

With the rapid development of vehicle information systems, liquid crystal displays (LCDs) have been widely used to enhance information experience. A linear vibration motor is usually placed behind the LCD to provide sufficient haptic feedback. A linear vibration motor with a large permanent magnet causes massive flux leakage around the display. As a result, it may cause unpredictable harm to people with implanted medical devices. Therefore, in this paper, a novel magnetic circuit design of a slim-width type linear vibration motor is introduced to reduce the static magnetic flux leakage. The haptic performance of the slim-width type linear vibration motor was analyzed using the electromagnetic-mechanical coupling method. Three types of experimental results were obtained to verify the analysis results. In conclusion, compared to the prototype motor, the slim-width type linear vibration motor proposed in this paper exhibits significant flux leakage reduction of 94.01% and 96.34% at the measuring positions. Furthermore, the slim-width type linear vibration motor exhibits an acceleration similar to that of the prototype motor.

This paper proposes and implements a compact wireless motor drive using orthogonal bipolar coils for the coordinated operation of robotic arms. The key is to orthogonally integrate two bipolar coils to form a compact magnetic coupler (CMC), while each CMC serves as the transmitting coil and receiving coil, respectively. Instead of adopting the one-to-many coil structure and operating at multiple frequencies, in this paper, two bipolar coils in the CMC are mutually decoupled and separately energized to drive two permanent magnet DC (PMDC) motors. As such, the wireless and selective motor drives can be achieved via the shared power-transfer channel at a single resonant frequency. All controls and switches are concentrated at the transmitter so that the receiver is entirely sealable. Accordingly, the coordinated operation of robotic arms can be realized with the high integration and no electrocution. Theoretical calculations and experimental results are given to validate the flexibility and feasibility of the proposed system.

This paper reviews the power density and torque density of permanent magnet motor technology that is currently commercially developed for use in electric aircraft. The review shows that in order to meet the ambitious electrical motor power density goals recently set forth the power density of a motor needs to more than double. The requirements imposed by the maximum propeller rotor tip-speed as well as the diameter constraints set by the aerodynamic requirements will further limit the practical electric motor design sizing options. This paper advocates for considering using magnetic gearing and using an integrated contra-rotating motor propeller co-design approach as a way of both increasing propulsive thrust performance and thereby increasing the aircrafts overall power density.

In this paper, two-dimensional (2D) Airy beam with self-bending and non-diffraction characteristics is generated and verified at microwave frequencies by using a metasurface composed of single-layer of strip resonator. By modifying the rotation angle and structural parameters of the unit cells, the phase and amplitude of the transmission coefficient can be controlled respectively. In addition, the deflection of the main lobe of the generated 2D Airy beam can be manipulated by modifying the attenuation coefficients in 2D Airy function. The novel excitation and deflection control methods designed in this paper propose great application potential in efficient wireless energy transmission at microwave frequencies, particle handling and integrated beam control systems.

This paper proposes a new probe for suppressing the vibration component from the detection signal in eddy current testing. The work is motivated by the desire to develop a new inspection method that can suppress the effects of vibration generated in the manufacturing process of metal parts such as tubes, rods and wires in order to make the current manufacturing process faster. The novelty of the probe lies in its simultaneous use of self and mutual inductions. The proposed probe uses the different effects of the self and mutual inductions to suppress the vibration component. This paper simplifies the discussion by limiting the dynamic vibration of the test specimen to static displacement. The coil distance between the excitation and detection coils should be adjusted for each test specimen for the most effective suppression of the displacement signal. The simulation and measurement results show that the coil distance in the mutual induction probe can control the phase of the displacement signal. It was confirmed that the amplitude of displacement signals measured by the proposed probe was under 6 % of the amplitude measured by the self-induction probe when the optimal coil distance was used. The results obtained suggest that the proposed probe can suppress the vibration component.

This paper presents a method to reduce cogging torque in permanent magnet (PM) machines from dynamic control based on harmonic torque counteract (HTC). We find the possibility of dynamic cancellation of cogging torque and harmonic torque by studying their generation mechanism and period characteristics, and further study the current harmonic injection scheme for cogging torque reduction. Further, two case studies of a integer slot PM machine and a fractional slot PM machine based on finite element analysis well validate the proposed method. Among them, the cogging torque of a 6-slot/2-pole PM synchronous machine is weakened from 932.0mN.m to 56.2mN.m, with a weakening ratio of 94.0%, and the cogging torque of the other with 6-slot/4-pole is weakened from 1.23N.m to 44.21mN.m, with a weakening ratio of 96.4%. The theory of this paper can be extended to PM machines with other different pole/slot combinations and topologies.

A permanent magnet synchronous reluctance machine (PMSynRM) is studied in this paper. It has a stack of surface-mounted permanent magnet (SPM) rotor and a stack of synchronous reluctance (SynR) rotor, which are axially combined on the shaft. Unlike the traditional PM-assisted SynR machine (PMASynRM), the magnets are not located in the flux barriers of the SynR rotor, therefore, the magnets and flux barriers have no more geometric confliction between them. The two rotor stacks can be circumferentially shifted to any relative angle. Clearly, the shifting angle and the axial length ratio between the two rotor stacks, together with the phase angle of the armature current vector, influence the motor performance, and their optimal design is detailed in this paper. Analysis of the prototypes shows that the studied PMSynRM evidently exhibits higher torque density than the conventional PMASynRM.

The field calculus for electrical machines (EMs) is realized solving subdomain problems. Most often, the latter are solved using either finite element analysis (FEA) or the semi-analytical solution of a Laplace or Poisson equation obtained by separation of variables. The first option can capture complex geometries but becomes slow for high accuracy, whereas the second is fast but limited to simple periodic geometries and linear or infinite permeable materials. This paper presents the 2-D implementation of the spectral element method (SEM) for the modeling of EMs. The polynomial basis functions used to approximate the solution in each domain are reaching exponential convergence similar to the semi-analytical solution. Moreover, each element can be represented by a non-square shape resulting in the possibility to model complex geometries. Following the results in this paper, significantly fewer degrees of freedom are needed for the SEM to achieve the approximation similar to the FEA, and consequently less memory and computational time are required.

A magnetic manipulation system for medical applications is designed with its coils widely distributed over a sufficiently large space such that a patient can lie down, an operator can enjoy accessibility and the workspace is sufficiently large. However, this design makes the current references asymmetrical. Moreover, at the corners, some references might exceed the coil current rating, and the magnetic field cannot be synthesized as desired. To address this overcurrent reference problem, this paper proposes a magnetic manipulation system controlled with the minimum infinity-norm current reference. In many magnetic manipulation systems, the current reference for a given motion command of the magnetic field is infinite. And the minimum infinity-norm current reference is the most feasible. The proposed control strategy presents an increased maximum synthesizable magnetic field in an arbitrary direction, including the worst-case direction, compared with the conventional field of Moore–Penrose inverse control. To verify the effectiveness, the worst-case direction of the magnetic field of each method is analytically derived. And, the controllable areas of the 8-coil magnetic manipulation system are compared. This paper also proposes a soft mode transition between the two methods for efficiency enhancement. The experimental results show the effectiveness of the proposed control strategy.

An entirely new level of magnetic filtration technology was put into full commercial production by the kaolin industry of Georgia, U.S.A. during 1973 - 1975. At present, five kaolin producers in Georgia are operating large magnetic filters each capable of producing over 4000 liters of kaolin slurry per minute or over 60 tons of kaolin per hour on a dry basis. When operated at the 4000 liters per minute rate, these five large magnetic filters have a combined capacity approximating the entire waterwashed coating and filler kaolin produced in the U.S.

In this paper, the dc biasing magnetomotive force (mmf) in presaturated core fault current limiter (PCFCL) is replaced with permanent magnet (PM) to overcome the well-known drawbacks of the dc biased PCFCLs. These drawbacks are excessively induced voltage across the terminals of the dc coil during fault condition and high total power losses during the steady-state condition. The novel contributions of this paper are the introduction of the selection criteria of PM material and its representation by actual nonlinear $B$ – $H$ hysteresis loop of Jiles-Atherton method, and the use of PM alone as an equivalent to the dc biasing coils for three-phase fault current limiter (FCL), contrary to work reported in earlier papers. Single- and three-phase PCFCLs are modified by replacement of dc saturation coil by the equivalent PM through time-domain finite element (FE) simulation of COMSOL Multiphysics package. Experimental verification shows that the implementation of accurate nonlinear representation of PM demagnetization curve with FE simulation gives a realistic performance of the PM biased PCFCL, especially in the fault condition. The performance of PCFCL can be evaluated through the voltage drop and total power losses during the steady-state condition and the fault current clipping ratio during fault condition of the grid. Furthermore, a comparative investigation of dynamic behavior is considered between dc and PM biased PCFCLs. It is found that the PM biased PCFCL has enriched capability of limiting any type of fault current with leading advantages of reduced voltage drop and power losses significantly together with risk elimination of the high induced voltage across dc coil terminals. Moreover, the governing parameters of PM biased PCFCLs are subjected to performance analysis to study their inherent effects.

Smart living is a trending and connected lifestyle that envisions efficient and sustainable energy utilization, stable and reliable power supply, intelligent and coordinated transportation and mobility, and personalized and cost-effective healthcare. Its realization needs the Internet of Things (IoT). IoT is a compelling platform connecting trillions of sensors and collecting data for connectivity and analytics. It is more advanced than traditional monitoring systems where limited sensors and wired communication can merely collect fragmented data in the application domains. Spintronic sensors with the superb measuring ability and multiple unique advantages can be one of the critical sensing devices supporting the IoT and enabling smart living. In this paper, we review successful applications of individual spintronic sensors in electrical current sensing, transmission and distribution lines monitoring, vehicle detection, and biodetection that can help to fulfill the promises of smart living in energy management, power delivery, transport, and healthcare. The wireless spintronic sensor networks (WSSNs) working at the massive interconnected network level are proposed and illustrated to provide pervasive monitoring systems, which facilitate the intelligent surveillance and management over building, power grid, transport, and healthcare. The database of collected information will be of great use to policy making in public services and city planning. This paper provides insights for realizing smart living through the integration of IoT with spintronic sensor technology.

Gyrotrons are high-frequency, high-power microwave sources with potential applications in plasma generation, energy generation, spectroscopy, and security. The Department of Science and Technology initiated the development of a 42 GHz, 200 kW, continuous wave (CW) gyrotron for the Indian Tokamak system through a multi-institutional project. The activity is targeted toward indigenous development of India’s first high-power gyrotron. In gyro-devices, frequency of operation is determined by the cyclotron frequency, and thereby the magnetic field. The development of a high-field intensity normal conducting cavity magnet was an imperative step during the testing and integration of the gyrotron tube assembly to achieve the desired beam transmission with a moderate operating cost. A high and spatially homogeneous magnetic field (1.61 T) is required to be established in the beam–wave interaction region by the cavity magnet. The desired magnetic field, as a function of axial distance from the gun to the collector, is governed by the requirements of gun optics, focusing field in the interaction region, and the adiabatic expansion of the beam into the collector. A water cooled electromagnet has been designed to produce the requisite magnetic field in the cavity region over an axial length of 40 mm with field homogeneity better than ±0.35%. Magnet design was optimized to meet the field requirements in the cavity and cathode gun. Magnetic field simulations were carried out in conjunction with the electrostatic field and space charge analysis. This paper presents finite element computations, design optimization, development and testing of a continuous duty iron core electromagnet for a first harmonic interaction mode (TE03) gyrotron cavity. Magnetic, electrical, thermal, and hydraulic design of the electromagnet is discussed in this paper.

The isolation bandwidth of zero stiffness permanent magnet bearing (ZSPMB) is limited by the stiffness variation near the zero stiffness point. This paper proposes an accurate and effective modeling technique to analyze and optimize the stiffness of ZSPMB in working range. Since the stiffness of ZSPMB is very sensitive to modeling errors, the variable current model of the permanent magnet is first derived considering magnetic permeability, the influences of which on the magnetic field and force are attributed to the reluctance effect in this paper. Then, the force exerted between permanent magnets (PMs) is equivalently decomposed into Lorentz force and reluctance force. Based on the Biot–Savart law and elliptic integral, the magnetic field of rings with axial, radial magnetizations and the equivalent Lorentz force (ELF) of typical ZSPMB topologies are calculated analytically. The equivalent reluctance force (ERF) is subsequently obtained by combining the finite element method. Compared with the ELF, the ERF is about one order of magnitude smaller and in the opposite direction and it causes the stiffness-displacement curve to drift and deflect. Finally, a Halbach ZSPMB is optimized with the ELF model, and then the ERF is suppressed by fine-tuning the structural size. The finite element analysis results show that the stiffness variation in the working range is effectively reduced, and the validity of the proposed hybrid analytical-finite element model modeling technique is verified.

Ionized field strength is one of the significant parameters of ultrahigh-voltage direct current (UHVDC) power lines, which determines the geometric design of the lines and human exposure in the electromagnetic environment. It is complex to calculate the ionized field distribution accurately due to the ions generated in the processes of corona discharges on the HV lines’ surfaces. Moreover, the existence of atmospheric fine particles with the diameter order of micrometers ( $\mu \text{m}$ ) makes the ionized field calculation problem more difficult because the fine particles surrounding the HV lines will be charged and distributed in the areas between the lines and the ground. In this paper, the impacts of charged atmospheric fine particles on the ±800 kV UHVDC transmission lines’ ionized field distribution at ground level are investigated by the upstream boundary element method. The algorithm is verified by both calculations and measurements. The contribution of charged particles to the charge density in air is also considered and obtained in the algorithm. This paper may provide some valuable reference for the design of UHVDC transmission lines.

An increasing need for fast and reliable models has led to a continuous development of Fourier-based (FB) analytical modeling. This paper presents an overview of the techniques that are currently available in FB modeling for electric machines. By coupling that overview to the most relevant literature related to the subject, an interesting starting point is provided for anyone who wants to use or improve FB models. The following seven aspects of FB models are discussed in detail: 1) the magnetic potential (scalar or vector potential); 2) the coordinate system and the solution of the partial-differential equations for each magnetic potential and for each coordinate system; 3) the way in which time dependence is accounted for; 4) the implementation of the source terms; 5) the possibilities to account for slotted structures; 6) the modeling of eccentricity; and 7) the post-processing computation of physical quantities, such as flux density, electromotive force, torque, losses, and eddy currents in conductive objects. Furthermore, this paper gives the closed form solution of the Laplace, Poisson, and Helmholtz equations in each coordinate system. In addition, this paper tackles other important features of FB models such as computational time reduction and coupling the machine model to an electric circuit.

In order to ease the manufacture process of very large permanent magnet (PM) machines, such as direct drive wind power generators, modularity technique is usually adopted. Although conventional fractional slot PM machines with all teeth wound windings show good performance, the coils located at the end part of each segment could be easily damaged because of being exposed to the air. In addition, the local winding faults could easily proliferate to the whole machine due to the physical touch of adjacent coils. Thus, a novel modular fractional slot PM machine with redundant teeth is proposed in this paper, while three phases within each set of winding are still balanced. The construction of the proposed modular PM machine having 42-slots/32-poles (42S/32P) combination is described in detail as an example, which can be treated as the integration of six 6S/5P segments and a redundant 6S/2P machine. The reason for using 6S/2P machine is to get rid of the undesirable unbalanced magnetic force (UMF), which usually exists in rotating asymmetric machines, such as 3S/2P PM machine. Since the end part of each segment in the proposed modular PM machine can be covered by half redundant tooth during the production, more protection can be provided for coils located in these regions. Furthermore, the separation of six segments can improve the fault-tolerant capability of the machine. The electromagnetic performance predicted by finite-element analysis (FEA) also demonstrates that the proposed modular machine will perform better if dual three-phase winding is adopted. Finally, the experiments on the prototyped machine validate the analysis in the paper.

This paper deals with modeling and simulation of devices where current-carrying conductors are located close to magnetic bodies. These configurations typically occur in electromechanical energy converters such as in slots of electrical machines. Additional losses due to the inhomogeneous current density distribution (“current” or “field” diffusion) at high excitation frequency are a well-known phenomenon. However, classical approaches reach their limits as soon as field diffusion is influenced by ferromagnetic material with non-linear properties. An accurate but time-consuming computation can be achieved by using time-transient quasi-stationary finite-element analysis (FEA). Current diffusion can be described more efficiently by separating the conductor into parallel filaments, following the partial element equivalent circuit (PEEC) approach. As long as linear material characteristics are prevailing, the problem can, thus, be solved efficiently in the frequency domain. In this paper, a hybrid FEA-PEEC modeling approach is presented, where the magnetization of the ferromagnetic material is represented by equivalent currents obtained by 2-D FEA. It is suitable for complex multi-conductor configurations even including non-linear ferromagnetic material. For the proposed method, the resulting linear system is efficiently solvable in the frequency domain by direct solvers. A numerical example from the field of electric traction motors is presented to emphasize the accuracy and benefit of the proposed method for practical electromagnetic computations.

Electromagnetic tracking has widely been used in many fields, such as virtual reality, motion tracking, and biomedicine. Especially in surgical navigation systems, electromagnetic tracking offers a cost-effective alternative to traditional X-ray fluoroscopy. In this paper, we present a new magnetic tracking method based on phase difference detection. Two 3-axis magnetic sources and one 3-axis sensor are needed in the tracking system. The position and orientation of the sensor can be obtained simply by measuring the phase difference between the square of the synthetic magnetic induction intensity at the position of the sensor and the square of the excitation current of the magnetic source. The experimental results indicate that this method has a good tracking accuracy and speed. The mean position error is less than 0.1 cm, and the theoretical tracking time can be less than 3.5 ms when the frequency of the excitation current is no less than 1 kHz. Furthermore, antinoise simulations show that the tracking performance of this method is more robust against environmental noise than that of existing methods. Therefore, the electromagnetic tracking method proposed in this paper has good application prospects in many respects. It enables real-time tracking with high accuracy and a strong antinoise ability.

This paper presents the comparative analysis of the characteristic features of two 4/2 switched reluctance motors (SRMs) designed for a very high-speed drive. The use of two-phase construction of SRM with irregular air-step gap makes it possible to achieve the required parameters of the drive. The analysis presents the comparison of two distinct structures designed for the same very high-speed drive. In this paper, a novel mathematical model that takes into account the nonlinearity of the magnetic circuit is presented. The results of numerical calculations and laboratory tests of the influence of the possible use of an anisotropic magnetic material in the rotor magnetic circuit are presented. The influence of control parameters on the motor properties is specified. Both the structures were compared with the respect to employed electric parameters. It is important for high-speed structures that a maximal speed of the motor should not affect permissible parameters of the rotor in a negative way. The high-speed structures should be properly designed to ensure a safety margin. The selected laboratory test results that show electric parameters are presented following the specification of the first critical speed based on the Campbell diagram, the maximum speed limited by allowable stresses. It was shown that both the structures analyzed fulfill the condition of a safety margin. A number of thermal problems of the structures analyzed are discussed. The design assumptions related to the possibility of using a higher current density in the motor windings were verified under laboratory conditions.

Ferrite isolators are attractive due to their excellent isolation, low loss, good linearity, and high-power performance. However, these devices usually operate over a single-frequency band. Multiband applications are possible if the isolation bandwidth of an isolator can be tuned. This paper presents a tunable waveguide-based full-mode ferrite isolator as well as a more compact half-mode tunable isolator, both fabricated on yttrium-iron-garnet substrates. For the first time, theory and design guidelines for the center frequency, bandwidth, and tuning of the ferrite isolators’ unidirectional magnetostatic surface wave (MSW) mode are presented. The proposed theoretical model reveals that the isolation bandwidth can exceed 100% if the magnetization-to-bias field ratio is higher than 8. Although the full-mode design is fabricated using a conventional subtractive technique, the half-mode design is implemented using inkjet printing technology. The full-mode isolator provides a maximum bandwidth of 45% and a peak isolator figure of merit (IFM) of over 65 dB at 7 GHz, whereas the half-mode design has a maximum bandwidth of 59% and a peak IFM of 76.7 dB at 7.5 GHz. The tuning of the center frequency is from 7 to 10.7 GHz for the full-mode and from 4.4 to 9.9 GHz for the half-mode design using magnetic field strengths up to 2500 and 2400 Oe, respectively. This paper demonstrates the versatility of ferrite isolators as tunable microwave devices for reconfigurable RF applications.

In this paper, the magnetorheological (MR) absorber with multi-stage parallel coil structure is designed, which can realize various magnetic field variations through the working coil combination to meet different impact applications. To analyze the influence of different magnetic field distributions on the mechanical characteristics of the MR absorber and provide a theoretical basis for the subsequent open-loop control strategy, the coupling simulation analysis and impact test are carried out in this paper. Based on the COMSOL Multiphysics software, the conjugate heat transfer model and magneto-flow coupling simulation model are established. Considering the shear thinning effect of the MR fluid in the impact process, the modified Herschel–Bulkley constitutive model of MR fluid is embedded into the coupling model. The influence of four parameters on the mechanical performance of the MR absorber is considered, which includes the piston movement speed, the current amplitude, the number of working coils, and the distribution state of the magnetic field. In addition, the orthogonal evaluation method is used to quantitatively investigate the influence degree of these factors. Finally, the impact tests are conducted and verified the simulation results, that is, the magnetic field distribution near the fluid channel inlet has a more pronounced throttling effect and can get a greater output force under the symmetrical distribution of magnetic field.

This paper proposes a novel modular relieving-dc-saturation Vernier reluctance machine for electric vehicle application, which integrates the merits of a robust structure, controllable excitation field, strong fault-tolerant capacity, and enhanced torque density, benefiting from its special relieving-dc-saturation design. In the proposed machine, zero-sequence current establishes a modular magnetic path and functions as the dominant excitation source for the torque generation. Especially, slot permanent magnets are introduced into each module, which mitigates the saturation effect in stator core caused by dc-biased flux with the zero-sequence current source. Therefore, the proposed machine can achieve enhanced torque density with relatively high current density. In this paper, the machine structure and operation principle are illustrated in detail, with its electromagnetic performance evaluated by time-stepping finite-element analysis. It is revealed that, due to its relieving-dc-saturation ability, torque density of the proposed machine is enhanced by about 20% with high current density.

This paper investigates the leakage flux of the trans-rotary magnetic gear (TROMAG). TROMAG is a magnetic gear that converts a high-force low-speed linear motion to a low-torque high-speed rotation and vice versa. TROMAG is tailored to force-intensive linear motion applications such as backpack energy harvesting and artificial heart in which the gear is positioned close to the human body and/or electronic devices. In such applications, it is critical to ensure the TROMAG’s magnetic field penetrating the surrounding environment (referred to as the leakage flux hereafter) is below the limits permitted by standards. This paper employs 3-D finite-element analysis (FEA) to study spatial distribution and magnitude of the leakage flux. The FEA calculations of magnetic field are verified by experimental measurements. Both radial and quasi-Halbach configurations are investigated, and it is revealed that the quasi-Halbach configuration exhibits less leakage flux. Moreover, it is shown that the use of a thin iron shield surrounding the TROMAG can effectively reduce the leakage down to permissible values.

Noncontact monitoring technique of mechanical and electrical states is increasingly attractive for the overhead transmission system. This paper proposes a new technique to detect the tower inclination and transmission line sag, and measure transmission current simultaneously. The key of this technique is to use the ground magnetoresistive (MR) sensor to measure the magnetic flux density along the center line from the three-phase transmission lines. Moreover, the magnetic field (MF) calculation formulas for a tilted tower are given in this paper. Finally, with MF calculation formulas, an algorithm based on artificial immune system (AIS) is applied to estimate the transmission line sag and tower tilt angles, and reconstruct currents. Model simulations of an overhead transmission system are carried out to verify the idea. The simulation results validate the feasibility of this noncontact approach to estimate mechanical parameters and reconstruct electrical parameters for overhead transmission system.

This paper proposes a new cableless transportation system that associates a magnetic actuator with the piping system in which it travels. To achieve high-speed transport within the pipe, the proposed actuator must show excellent movement characteristics. An aluminum pipe was cut in half longitudinally, and an alternating current was passed through the cut piping. The proposed cableless actuator powered by an electric current supplied by an electric brush was demonstrated to be capable of high-speed movement in a curved pipe. A scheme of attaching a cargo container to a nodal point of the actuator using a flexible rod was also proposed. The experimental results show that the actuator can be driven through the pipe even when the curved pipe is nearly U-shaped. Furthermore, the cableless actuator transporting a cargo mass of 30 g can be driven at a speed of 87.9 cm/s in a curved aluminum pipe with a curvature angle of 22.5°. The method established in this paper is considered to be applicable to the high-speed transport of lightweight reagents, bacteria, and microfluidic chips.

A novel dual-flux-modulation consequent-pole linear permanent-magnet (DFM-CP-LPM) machine is proposed in this paper, which can be regarded as the combination of a linear flux-switching PM machine and a linear vernier PM machine. Via two sets of interoperable PMs mounted on both the primary and the secondary, the proposed machine can work in a dual-flux-modulation mode, achieving higher thrust density. Meanwhile, the consequent-pole structure is introduced, reducing approximately half of the PM usage compared to a conventional surface-mounted linear PM vernier machine (LPMVM), which will greatly reduce the cost. In this paper, the configuration and the operation principle of the novel DFM-CP-LPM are presented. Then the optimization and several thrust ripple reduction methods are introduced to improve the performance of the machine. Thermal analysis is also carried out to check the demagnetization risk of primary PMs, due to the heat from coils. Finally, the proposed machine is compared to a conventional LPMVM and a consequent-pole linear vernier permanent magnet machine with only PMs set on the secondary. The results verify the superiority of the proposed DFM-CP-LPM.