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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.

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.

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.

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.

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.

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.

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 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.

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.

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.

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 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.

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.

Extensive research and experiments have shown that rotational core loss, which usually exists in the corner joints of multi-phase transformers and behind the teeth of rotational motors, may amount to more than 50% of the total core loss. The frequency of rotational magnetic field can reach even kilohertz level in high-speed motors. In this paper, a new magnetizer of double-yoke vertical structure made of ultrathin steel sheet (0.05 mm) and the corresponding $B$ – $H$ sensing structure are proposed and constructed. Both the alternating and 2-D rotational magnetic properties for non-oriented steel B35A210 and grain-oriented steel B27R090 are measured and characterized up to kilohertz. The magnetic anisotropy of silicon steel is observed and analyzed from its origin mechanism. Moreover, the alternating, 2-D circular and elliptical rotational core losses are compared and discussed. This paper can provide a reference for core loss modeling and the calculation of electrical machines or transformers under different magnetization conditions.

In this paper, a new hybrid stator fabrication with 2-D steel sheets lamination and 3-D end cap structure for high-speed motor application is provided. With the additional overhead end cap design, the new motor not only features lower iron losses in high frequency and reduces copper losses like traditional soft magnetic composite (SMC) motor but also achieves higher permeability and lower production cost at the same time. In this paper, the motor characteristics, i.e., back electromotive force and efficiency between the traditional lamination, SMC, and the new hybrid design are investigated by 3-D FEA simulation. Moreover, a prototype is fabricated by 3-D printing for the verification of the analytical and simulation results.

Energy harvesting, particularly through ambient sources, is gaining significant interest in the recent past because of the energy crisis and the pollution associated with fossil fuels. With the emergence of Internet-of-Things (IoT), where billions of IoT devices are expected to communicate with each other, energy harvesting has become even more relevant. In this vision, we have been working on energy harvesting based on magnetic materials, particularly stress-induced domain wall motion. In this paper, we present a detailed overview of our research on stress-induced domain wall motion and the demonstration of energy harvesting. We have carried out micromagnetic simulations, which indicated that an applied stress can change the magnetization direction from transverse direction to the longitudinal direction in a microwire. The experimental results on CoNi/FeCo/CoNi microwires confirmed that such change in domain structure is possible with applied stress. We have shown the details on how a transverse anisotropy is achieved in CoNi/FeCo/CoNi stack. We have also demonstrated that energy can be harvested using the methods described in this paper. The results offer a new magnetic stack, which can be used to achieve energy harvesting through ambient sources.

This paper describes an investigation into the combined effects of magnetoconvection and an externally applied magnetic field on the thermal performance of vegetable oil-based magnetic nanofluids with different volume fractions of magnetic nanoparticles. The mineral-based oil has conventionally been used in power transformers because it has high dielectric strength and good cooling performance under normal operating conditions. Because of the environmental impact, eco-friendly vegetable-based transformer oils have been substituted for mineral-based insulating oils. To date, related studies have only reported on the characteristics of dielectric breakdown in vegetable oil-based magnetic nanofluids without any real electromagnetic systems. Furthermore, the thermal characteristics of vegetable oil-based magnetic nanofluids have not yet been fully investigated. Thus, the aim of this paper was to examine the cooling performance by adding magnetic nanoparticles to the vegetable-based transformer oil. To quantitatively analyze this effect, a multi-physics technique that incorporates magnetic-thermal-fluidic fields was developed as based on quasi-static magnetic field approximation and conjugate heat transfer. To validate the numerical results, corresponding experiments were successfully carried out via application in a simple electromagnetic system with varying insulating liquids.

The wirelessly transferred power as well as charging efficiency will significantly drop due to the large misalignment between the transmitting coil and receiving coil for roadway electric vehicles (EVs). A low-cost and reliable misalignment-tolerant wireless charging technique is indispensable for the rapid commercialization of wireless EV charging. This paper presents a technique to achieve the misalignment-tolerant wireless charging for the dynamic wireless charging (DWC) system by means of a tunneling magnetoresistive (TMR) sensor array as well as the easy-to-fabricate receiving coils. The TMR sensor array provides the coil-misalignment position by measuring the magnetic field component generated from the transmitting coil. The corresponding receiving coils are selected to be in resonance according to the measured coil-misalignment positions. In this paper, a sensor array composed of 29 uniaxial TMR sensors was utilized to measure the magnetic field component. This effectiveness of the proposed technique has been validated by both the finite-element method (FEM) simulations and laboratory experiments. The experimental results demonstrated that the proposed misalignment-tolerant wireless charging system can operate in a relatively wide misalignment range of ±120 mm with charging efficiency higher than 76.2%.

The high-voltage direct current cable insulations consist of polymeric or mass-impregnated paper materials. Their electric conductivities depend on the electric field and the temperature. Losses inside the conductor and in the insulation increase the temperature, resulting in increased losses and in a possible thermal runaway process. In this paper, coupled electro-thermal field simulations including nonlinear field-dependent conductivities are carried out. With a varying applied voltage and a current in the conductor, the condition for a thermal breakdown is computed. To compute the losses inside a 1-D insulation model, the finite-difference method is used. The simulation results conform well to experimental measurements. An approximation of the condition for a thermal breakdown is developed and show equal results in comparison to the coupled electro-thermal field simulations.

This paper discusses the design of a synchronous reluctance motor designed to replace a 5.5 kW industrial induction motor. End plates are axially placed at both ends of an industrial motor to fix the lamination of the rotor. It is manufactured from magnetic materials to ensure manufacturing convenience and price advantage. With its construction from magnetic materials, a lower output of the motor due to axial flux leakage is observed. This paper analyzed the drop in output caused by the axial flux leakage in the end plate constructed of magnetic material and methods to compensate for the said output drop. The first method to improve the output degradation problem was to fabricate the end plate as a non-magnetic material. This, however, was found to be inefficient due to the need for different mass production apparatus for the new material. A new method proposed in this paper involved using the end plate constructed of magnetic material but incorporating a new shape to the end plate with the saliency ratio to resolve the decreased output problem. This method converts the magnetic flux leaked in the axial direction into reluctance torque. The 3-D FEA was performed for the validity of the method, and reliability was verified through the production and testing of the actual models.

This paper presents a magnetic safety evaluation of the static magnetic field produced by magnetic floors with permanent magnet properties utilized in the construction industry. The magnetic floors analyzed in this paper are composed by a concentration of 85% of isotropic strontium (Sr) ferrite powder mixed with chlorinated polyethylene. The magnetic floors are magnetized and tested in the laboratory to measure the magnetic field levels in different regions of the magnetic floors and magnetic subfloors. Finite-element (FE) simulations are carried out to compute the magnetic field produced by magnetic floors. The numerical results and laboratory tests are compared and analyzed. Values of the magnetic field between 2 and 50 mT are computed and measured in different regions of magnetic floors. Finally, the static magnetic field levels obtained in the magnetic floors are compared with the permitted magnetic field values for different electronic devices, pacemakers, and other common objects utilized by persons in buildings. The results obtained in this paper show that magnetic floors are safe, and they can be employed in buildings without putting in risk electronic devices or persons with pacemakers.

Research on tuning the magnetic anisotropy of magnetic heterostructures has been receiving intensive attentions due to their intriguing tuning phenomena. In particular, tuning the magnetic anisotropy by in situ magnetic field during the fabrication process allows a remarkable control of magnetism with energy efficiency and shows significant potential applications for compact, fast, and low-power microwave and electronic devices. In this paper, in situ external out-of-plane and in-plane magnetic fields were applied during the deposition of Fe3O4 thin films on Pt substrates by atomic layer deposition at different temperatures (350 °C, 400 °C, and 450 °C). The effects of in situ magnetic field with different directions on the surface morphologies and magnetic properties of F3O4/Pt heterostructures were characterized. It was found that both the out-of-plane and in-plane external magnetic fields tuned the magnetic anisotropy of ferromagnetic Fe3O4 when deposited at 400 °C with the maximum resonance field changes of 620 and 1930 Oe along in-plane and out-of-plane directions, respectively. This paper achieves tuning the magnetic properties through in situ magnetic field and provides a possibility for spintronic devices.

An electromagnetic energy harvester (EMEH) is proposed in this paper which is designed considering the power requirement of an ice removing device used to remove the ice and snow from power transmission lines. This paper addresses the influence of the material characteristic of the magnetic core to achieve the required power. Three different core materials, namely, silicon (Si) steel, nickel (Ni) steel, and nano crystalline HTX-012 core are used to design single and dual core models with three different airgaps using 3-D finite-element analysis and are compared in terms of the induced voltage, saturation flux density, relative permeability, and core losses. Comparison shows that the EMEH with Si-HTX-012 core and stepped airgap can produce the highest induced voltage.

The nonlinear ac-dc composite electric field in the winding area of the converter transformer was studied by considering the frequency and temperature dependence of the insulation materials in this paper. First, the relative permittivity and conductivity of vegetable oils, mineral oils, and insulation papers were measured at different frequencies and temperatures. Then, the oil-paper insulation structure model of one 500 kV converter transformer valve-side winding was established. The nonlinear composite electric field of the converter transformer insulation with vegetable oils and mineral oils was analyzed. The maximum voltage of the converter transformer with mineral oils is 524.9 kV, at -20 °C and that with vegetable oils is 497.1 kV. The results show that the calculation method proposed in this paper is more accurate than the traditional superposition method.

A coaxial magnetic gear (CMG) consisting of an inner ring, outer ring, and flux modulator exhibits relatively large torque density at low operating cost and low noise level. To guide the selection of soft magnetic materials for the flux modulator, this paper first incorporates the Jiles–Atherton model within a finite-element (FE) framework. The influence of nonlinear magnetic properties on end-effect losses (magnetic flux leakage and fringing) is then investigated with the objective of maximizing the pullout torque. For flux modulators whose initial magnetic permeability and saturation flux density exceed certain threshold value, the pullout torque of a CMG becomes insensitive to magnetic properties and end-effect losses can be efficiently calculated from a 2-D FE model together with a constant torque reduction ratio. This paper presents a systematic torque surface method that can decouple the analysis of average torque and torque ripples. This method has been implemented to evaluate load dependence and rotation speed fluctuation of a CMG.

In this paper, we investigate the magnetoimpedance (MI) response of a double-exchange ferromagnet La0.80Sr0.20MnO3 using a non-contact method with the help of a copper strip coil and an impedance analyzer over a wide frequency range (1 MHz–2.0 GHz). In recent years, MI of metallic soft ferromagnetic alloys was measured by passing radio frequency (RF) currents through a sample and varying an applied magnetic field to obtain the magnetoresistance ( $\Delta \text{R}$ /R0) and magnetoreactance ( $\Delta \text{X}$ /X0). The strip coil method has never been used before to measure MI for bulk metallic systems. In this method, RF current flows through the circumference of the strip coil, instead of the sample, creating an RF magnetic field along the axial direction. Thus, this RF field excites the magnetization in the sample. The MI features observed in this paper have been explained in terms of both the magnetization rotation and ferromagnetic resonance. We also analyze the role of the skin effect in our MI response.

The utilization of a bismuth-substituted iron garnet as a magnetooptic Faraday rotator (MOFR) has been reported for all-optical networking purposes as well as for other applications. Our measurements and observations demonstrate that the MOFR saturates once a significantly large magnetic field (>225 G) is applied. After the applied magnetic field enters the saturation region, the material’s magnetic domains can become pinned at intermediate levels of magnetization. Pinning in this form has not been reported nor well studied for this application. In this paper, a method to detect and describe anomalous pinning in terms of Faraday rotation is presented. Measurements on the changes in the state of polarization that a pinned material produces are examined. This paper will also present practical methods for unpinning the MOFR material, which are traditionally considered to be challenging.

Nd–Fe–B magnets for electric vehicles are required to have high coercivity, and heavy rare earth elements are added. However, it is necessary to reduce the heavy rare earth element that is a scarce resource. Decreasing the grain size is an effective method of increasing $H_{\mathrm {cj}}$ , and hot-deformed magnets which are consisted of rapidly quenched powders are known to have fine grains. This paper focused on coarse grains observed in the microstructure of hot-deformed magnets. Measuring the local magnetic properties by XMCD, it was shown that the coarse grain areas had lower magnetic properties than those of the fine grain areas. The coarsening was located at the powder interface. Therefore, the crystal growth behavior in the powder was investigated in detail. Due to the Fe concentrated in the powder along the wheel side of the melt-spun, Nd2O3 and $\alpha $ -Fe were grown as the primary crystals. It is considered that the coarsening of hot-deformed magnets originates in those heterogeneous crystallizations. In order to prevent the coarsening, this paper focused on the heating rate of heat treatment of powders. The coarsening was prevented under the conditions, over 400 °C/min of heating rate and over 600 °C of heating temperature. The rapid heating of powders using the free-fall-type furnace prevented the coarsening in hot-deformed magnets. As a result of decreasing the coarse grains, $H_{\mathrm {cj}}$ was increased from 1584 to 1614 kA/m and $M_{r}$ was increased from 1.33 to 1.40 T.

This paper proposes a new application of skin effect suppression technology [1]–[4] for long wiring on high-speed & low-delay I/O board (typical wiring length; 200 to 1000 mm). This proposal will overcome the difficulty to further reduce the transmission losses on the I/O board with >50 Gbps data rate, which is currently performed by lowering dielectric substrate losses and surface smoothing of Cu conductor. A major challenge in this paper is to demonstrate the skin effect suppression by electroplated magnetic/conductor multilayer, instead of sputter-deposited thin film in literature [2]–[4], in order to meet coming cost-effective, thick (>5 μm), large area, and high throughput mass productivity requirements. High frequency (>10 GHz) estimation of complex permeability and measurements of low resistance devices are also investigated.

In order to improve magnetic properties of non-oriented electrical steel sheets, effects of heat treatment in a magnetic field to control crystallographic orientation were studied. In this paper, we report on the effects of the amplitude and direction of the magnetic field applied during the heat treatment in comparison to magnetic properties of samples, which the longitudinal direction is parallel to the rolling direction (RD) or rolling transverse direction (TD). To clarify the effects of heat treatment in a magnetic field on the magnetic properties of the electrical steel sheets, heat treatment without magnetic field was firstly carried out and a change rate, defined as a value obtained by dividing the iron loss value after the heat treatment by the iron loss value before the heat treatment, was used in the evaluation. Fig. 1 shows a schematic view of the heat treatment apparatus. The heat treatment apparatus consisted of an electric furnace at inner diameter of a superconducting magnet (10 T - CSM) and a quartz glass tube inserted into the furnace. The quartz tube was depressurized to less than $10 ^{-3}$ Pa with a turbo molecular pump. The heat treatment temperature was controlled at 1023 K, 1123 K, and 1273 K. 10 mm $\times 50$ mm sized samples were prepared by cutting a non-oriented electrical steel sheet, 50A470 (JIS C 2552), with electrical discharge machining. Samples were cut so that their longitudinal direction was parallel to the rolling direction or rolling transverse direction. The samples were placed at the center of the magnetic field in the quartz tube using a holding jig made of quartz in a way that the direction of the magnetic field would be parallel to the longitudinal direction of the samples. The strength of the applied magnetic field was set to a maximum of 10 T. Fig. 2 shows iron loss change rate of the samples heat treated at 1273 K with respect to iron loss before heat treatment. In Fig. 2, for example, “RD-10T” means the sample with longitudinal direction parallel to the rolling direction and applied magnetic field during the heat treatment of 10 T. The vertical axis represents the change rate and the horizontal axis represents the amplitude of the excitation magnetic flux density controlled by the sinusoidal wave of 50 Hz with a small-sized single sheet tester. As shown in Fig. 2, both the RD- and TD-samples heat-treated without magnetic field (0 T) under the temperature condition of 1273 K showed a remarkable change in the magnetic properties. The grain growth was accelerated by the heat treatment, the iron loss was reduced, and the permeability under low excitation conditions was improved. Contrarily, the permeability at 1.6 T or higher decreased. It was also found that the effect of the heat treatment on the reduction of the iron loss was greater in the TD-samples. As for the results of heat-treatment in magnetic field, the iron loss of the RD-sample was reduced after heat treatment in 10 T. On the other hand, the iron loss of the TD-sample increased after heat treatment in 10 T. It was also found that application of the strong magnetic field of 10 T throughout the heat treatment, i.e., during the heating and cooling, caused increase of the iron loss and decrease of the magnetic permeability regardless of the direction of the material. The cause of this phenomenon is possibly the contraction of the polycrystalline specimen in the strong magnetic field. The details will be discussed at the presentation and in the full version of this paper.

Manganese-zinc (MnZn) ferrites have important application in convertors and switching mode power supplies. The core losses ( $\text{P}_{L}$ ) of MnZn ferrites have serious influence on the performance of power conversion devices. It is worth emphasizing that reducing the core losses at high frequency is of great significance for the miniaturization and integration of power conversion devices. Here in this paper, MnZn ferrites have been fabricated by the method of solid-state reaction, and the effect of CaCO3 and V2O5 co-additives on the microstructure and magnetic property has been investigated. This paper illustrated the competition mechanism of grain growth, which originated from the hindrance effect of CaCO3 and acceleration effect of V2O5, as well as the effect of CaCO3 and V2O5 on core losses by means of loss separation method. In addition, as for the MnZn ferrite sample with 0.1 wt% CaCO3 and 0.01 wt% V2O5 co-additives, core losses were suppressed to 46 and 664 kW/m3 corresponding to 3 MHz 10 mT and 3 MHz 30 mT at 25 °C, respectively. The state-of-the-art MnZn ferrites with ultralow core losses own potential application for high-frequency power conversion devices.

In this paper, we carry out a detailed investigation of a recently discovered effect of the increase in the ferromagnetic resonance (FMR) amplitude for cobalt–palladium layered films in the presence of hydrogen gas (H2). We find that this effect is not correlated with the FMR peak shift in the presence of H2 found previously. This follows from observation of a vanishing shift but a change in the amplitude of 69.5% for a sample having a 70 nm thick cobalt layer studied in this paper. The change in amplitude is found to be mainly due to the narrowing of the FMR linewidth, which has its origin in a change in the damping parameter $\alpha $ . The increase in the amplitude allows us to measure H2 concentration in nitrogen as a carrier gas in a very broad range—from 0.05% to 70% with sensitivity higher than in our previous papers.

Iron loss prediction is very important for the evaluation of efficiency, temperature and demagnetization of electrical machines. The models developed in [1]–[4] are most commonly used iron loss models for electrical machine analyses. However, none of these iron loss models considers the influence of temperature, which has been experimentally confirmed in [5]. In [6], an improved iron loss model which can consider temperature dependencies of hysteresis and eddy current losses separately is developed. By applying the improved iron loss model, the temperature influence on the iron loss can be fully considered. It is then possible to couple the thermal and loss analyses with each other by utilizing the improved iron loss model, which will be the subject of this paper. The iron loss model developed in [4] is one of the most accurate iron loss models when the temperature is constant with the help of variable coefficients. The iron loss p Fe can be expressed as: Equation (1) where f is the frequency. B m is the peak value of alternating flux density. k h (f,B m ) and k e (f,B m ) are the hysteresis loss and the eddy current loss coefficients, respectively. It should be noted that the iron loss model (1) cannot consider the influence of temperature on iron loss while the temperature influences iron loss significantly. According to the iron loss model developed in [5], both the hysteresis loss k h (f,B m ) coefficient and the eddy current loss k e (f,B m ) coefficient vary not only with frequency and flux density but also with temperature. Therefore, the improved iron loss model is then developed and can be expressed as: Equation (2) where p Fe,T is the iron loss density at the actual temperature T. k h (T,f,B m ) and k e (T,f, B m ) are the hysteresis loss and eddy current loss coefficients, respectively. In order to evaluate the iron loss models in electrical machines, thermal tests and analyses are carried out in a 12-slot/10-pole IPM machine. The schematic diagram of the test system is shown in Fig. 1(a). The 12-slot/10-pole IPM machine is connected a three phase AC power source. The magnets are removed and the rotor is locked in order to eliminate magnet eddy current and mechanical losses. As shown in Fig. 1(b), four thermal couples are equipped in the electrical machine to measure the temperature at different positions, i.e. the stator tooth, the stator yoke, the rotor magnet slot and the rotor yoke. The temperatures are measured when the electrical machine is powered by the AC power source. For the temperature prediction, the iron losses are calculated by the existing model and the improved model, respectively. The thermal model of the IPM machine is also built in Motor-CAD. The thermal model is then analysed with calculated copper loss and iron losses. The predicted temperatures of the electrical machines can be obtained. Fig. 2 compares the measured and predicted results by the existing iron loss model and the improved model. It can be seen that the predicted temperatures by the existing iron loss model become inaccurate when the temperature is high. This is due to the fact that the existing iron loss model cannot consider the temperature dependency of the iron loss. The input iron loss for the thermal analysis keeps constant while the actual iron loss decreases significantly with the temperature rise. On the other hand, the predicted temperatures keep good accuracy when the temperature reaches 100 degrees Celsius or even higher. This is due to the fact that the improved iron loss model considers the temperature dependency of the iron loss. Input iron losses for the thermal analysis vary with the temperature rise. In other words, the thermal and loss analysis can be coupled with each other by utilising the improved iron loss model, which is more close to the actual condition in electrical machines. The details will be investigated and described in the full paper.

For testing a conductive pipeline, remote field eddy current testing (RFECT) is used, which is composed of solenoidal exciter coil and receiving sensor coils. In RFECT, there is remote field zone where the eddy current distributions are concentrated on the external surface of the pipe wall. Therefore, it is possible to detect a defect that occurs on the external surface of the pipe wall even if the receiving coils are located inside the pipe. From the measured coil signals, it is necessary to decompose background offset and predict the pattern of defect signal in order to estimate the defect size for the maintenance of underground pipelines eventually. In the process, the amplitude variations of the induced magnetic field at sensor coils are closely related to defect depth. Therefore, it is important to analyze and eliminate distortions of measured RFECT signals. This paper analyzes the effects of the induced magnetic field on the sensing signals with respect to different depth sizes in the RFECT system. The amplitude and the distribution pattern of defect signals are computed by a 3-D finite-element method and the method to eliminate the signal distortions caused by induced magnetic fields are presented. Simulated results in this paper agreed well with measuring ones.

In this paper, in order to make a clear principal cause in increasing iron loss of amorphous wound cores in processing, effects of bending stress on magnetic characteristics of a Fe-based amorphous wound core are clarified. The amorphous magnetic materials have been widely used as a core material of power transformers to reduce iron loss due to their excellent soft magnetic characteristics. However, the amorphous magnetic material has an issue that the building factor (B.F.) is very large in comparison with that of grain-oriented electrical steel sheets. The amorphous transformers usually use a wound core formed by stacking plural amorphous sheets in different lengths. Bending stress is, therefore, generated at each corner of the wound core in processing. Due to this bending stress, the magnetic characteristics of the wound core deteriorate. The deterioration of magnetic characteristics of the wound amorphous core is so large because of the large magnetostriction constant. As a result, the B.F. of this material becomes larger. In order to remove the residual stress, which is generated in the wound core including the bending stress, the amorphous wound core is usually annealed in a magnetic field, which is called “a magnetic annealing.” In this paper, the effect of the magnetic annealing on the magnetic properties is studied experimentally by evaluating some wound amorphous model cores. As a result, a suitable magnetic annealing condition is clarified and the iron loss of the wound amorphous model core is reduced by 65.7%.

By introducing the SiC/GaN power devices, the high-frequency switching dc–dc converters are expected to have higher efficiency and lightweight. This paper focuses on the Fe-based amorphous alloy powder (Fe–Si–B–Cr–C based) used in the metal composite bulk magnetic core for high-frequency power inductor and transformer. In terms of eddy-current loss at MHz band or beyond, iron-based metal composites are required to have fine magnetic particles with surface insulation layer. In this paper, the finest amorphous powder with a median diameter of 2.57 $\mu \text{m}$ made by water atomization process was used. In order to fabricate the amorphous powder with surface insulation layer, a surface-modification scheme through the two-step acid solution processing using phosphoric acid and hydrochloric acid was introduced. As a result, the surface-modification scheme enabled to make a single-phase silica thin layer on the surface of the amorphous powder, and the silica thin layer was considered to be derivable from the silicon element in the amorphous (Fe–Si–B–Cr–C based) powder.

The development of a thin and broadband microwave absorber using the microwave absorbing material (MAM) alone is a very challenging task for the researchers and industries. Therefore, a technique for developing a novel hybrid microwave absorbing coating (MAC) using particle-size-controlled hard–soft ferrites with optimized compositions is described and experimentally validated. The novelty of this paper is the possibility of enhancing and tuning the reflection loss (RL) properties of traditional MAMs by simply adjusting their particle size. The main target of this paper is to obtain wideband absorption corresponding to RL ≤ −10 dB and a lower coating thickness (≤ 2 mm). First, ferrite nanoparticles are synthesized and subsequently grown into distinct shapes and sizes by giving judicious heat treatment using a “bottom up” nanofabrication approach. Furthermore, these distinctly shaped and sized particles, i.e., spherical and flaky (20–30 nm), hexagonal (80–100 nm), and pyramidal (200–250 nm), are blended with one another in different proportions (1:1:1, 2:1:1, 1:2:1, and 1:1:2). An extensive morphological and electromagnetic (EM) characterization is carried out. An efficient theoretical and empirical model is used to investigate the EM properties of the heterogeneous MAC with respect to frequency and particle size. A fabricated MAC possesses an RL of −33.5 dB at 10.8 GHz with −10 dB absorption bandwidth of 4.2 GHz (covering the entire X-band region). Moreover, the ferrite layer coating thickness is only 2 mm. A good correlation between theoretical and measured results demonstrates the potential of the adopted approach for various practical EM applications.

The non-destructive testing technique known as magnetic flux leakage (MFL) is used for the inspection of storage tank floors (mild steel plate). This paper focuses on the finite-element analysis of the velocity effects on the induced flux and its distribution in the plate thicknesses of 6 through to 20 mm thick 1020 grade steel. When there is a velocity difference between the plate and the excitation system, eddy currents are induced opposing the applied magnetic field distorting its profile. This has an adverse effect on MFL inspection by altering signal responses thus limiting achievable inspection velocities. An investigation of velocities ranging from 0.5 to 3 m/s is undertaken on both defect-free plates and plates containing spherical 40% through wall thickness defects simulated for both near/top and far/bottom surfaces. From the results, it is indicated that the flux density distribution through the plate decreases as a function of depth. Once a plate depth of 16 mm is reached, it is shown that the flux density is significantly reduced toward the underside of the plate. These combined effects influence defect detectability on larger plate thicknesses for the specific yoke design used in this paper.

In this paper, adsorbents composed of reduced graphene oxide–CoFe2O4 ferrite–polyaniline (RGO/CF/PANI) nanocomposites have been synthesized by different techniques, namely, hydrothermal, graphite exfoliation, reduction, and polymerization. The adsorbents were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and vibrating sample magnetometer. The adsorption of uranium (VI) could be well described by the Langmuir and the pseudosecond-order models. The highest adsorption capacity of the composites for uranium (VI) was evaluated to be 2430 mg/g at pH = 5 and 25 °C. The uranium loaded RGO/CF/PANI could be readily separated from aqueous solutions by an external magnetic field. This paper demonstrates an efficient and convenient approach for the adsorption of uranium (VI) from aqueous solutions.

One of the main engineering applications of ferrofluids is in magnetic fluid seals, working in rotary motion. An area, which has so far been insufficiently examined, is the mechanism of leaks between seal stages in this type of seal. This is an important issue in order to understand the principle of the seal operation and to properly design this type of seal. This paper presents the results of research into the mechanism of leaks between stages in multi-stage magnetic fluid seals. The tests were conducted when the pressure of the sealing air increased and reached its maximum value. The influence of the magnetic fluid properties, such as saturation magnetization or dynamic viscosity, was taken into account. Studies were performed for different seal temperatures. Experiments allowed models for determining the maximum pressure of the multi-stage seal to be proposed, based on the information about this pressure for a one-stage seal. This paper presents the comparative results of the critical pressure value obtained from experimental studies and calculations based on numerical simulations.

In motor manufacturing, blanking process of non-oriented electrical steel inevitably induces plastic deformation and residual stress near the blanked edge and thus leads to the deterioration of magnetic properties. However, as for the newly developed non-oriented electrical steel, the scale of grain size is close to both blanking clearance and thickness. Grain size integrated with blanking clearance thus significantly affects the blanked edge quality. In order to reveal the effects of grain size and blanking clearance on magnetic properties deterioration, systematic blanking tests have been conducted using various non-oriented electrical steel sheets (same chemical composition, three thicknesses, and three grain sizes) in a considered clearance range. The blanked edges are characterized by means of optical microscopy, scanning electron microscopy, and micro-hardness tests. Magnetic domain structures are also observed by magnetic force microscopy. The iron losses are measured by single sheet tester method. The burnished ratio decided by clearance and grain size can be taken as the indicator to assess the deterioration of magnetic properties. The blanked edge with larger burnished ratio leads to lower increase of micro-hardness, less degradation of domain structure, and less deterioration of iron loss. In this paper, about 5.8% iron loss can be reduced by optimization of blanking clearance, which is quite pronounced for energy saving. In further study, an approximate linear function of the ratio of optimum clearance to gain size with $D^{-1/2}$ is empirically proposed to demonstrate the grain size dependence on optimum clearance determination. This paper thus provides an in-depth understanding and guidance for reducing the deterioration of magnetic properties caused by the blanking process.

This paper presents new results on a novel coupled-physics modality called magneto-acousto-electrical tomography (MAET). With static magnetic field, a beam of ultrasound is applied to the sample to be imaged; the ultrasonic vibration can lead to the separation of the charges due to the Lorentz force and produces the current distributed in the object. In this paper, simulations were conducted on biological tissue model, and the electrical properties were reconstructed, which could reflect the state of physiological or pathological. We also conducted experiments to detect the voltage signal of microvolt level by the electrodes placed around the sample. The series of experiments were conducted on low-conductivity (0.2 S/m) animal gelatin phantom and real biological tissue, successively placed in a 260 mT magnetic field and sonicated with a plane ultrasonic transducer of central frequency 2.25 MHz. In this paper, we obtained axis resolution of 1 mm, much more significant improvement than the previous reports. More importantly, the experimental result does also demonstrate the feasibility of MAET to image the electrical properties of biological tissue.

Magnetically mediated thermoacoustic imaging (MM-TAI) is an emerging medical electrical parameter imaging technology; it has the advantages of high contrast of electrical impedance imaging and high resolution of ultrasound imaging; it can realize the early diagnosis of disease in the tissues comparing with structure imaging technology. The magnetically mediated thermoacoustic (TA) effect is analyzed in this paper through the theoretical inference, numerical calculation, and experiment. Pulsed excitation is considered in the analysis, which is different from previously reported research. The pulsed magnetic field is applied to the low conductivity sample such as gel phantoms (0.2, 4, and 2.5 S/m); then the Joule heat is generated inside the objects and an acoustic signal is excited due to heat expansion. The acoustic signal is detected and the image is reconstructed from TA source to conductivity. This paper has laid the foundation for the MM-TAI in biological tissues.

This paper presents the design of cryogenic induction motor submerged in liquefied natural gas (LNG) for operating LNG spray pump. In cryogenic environment of −163 °C, the torque characteristics of induction motor differ greatly from the operating conditions at room temperature. So, in order to obtain the operating characteristics corresponded with design specifications of the induction motor in cryogenic environment, it is necessary to redesign motor dimensions from the result of conventional design by reflecting the changes of material properties under the very low temperature (VLT). This paper focused on the design of cryogenic induction motor considering the variation of resistivity for the stator windings and rotor bars. Also, the distribution of magnetic flux density and magnetic saturation effect on the steel core are analyzed by using 2-D finite-element method for ac sinusoidal time varying excitations under the VLT. The result of proposed method considered the magnetic and electric characteristics of matters in VLT successfully, so that the motor performances at the cryogenic temperature fit well with expected. The designed motor was fabricated and torque performance measured in VLT agreed well with design goals.

In this paper, we propose a design process for a plasmonic grating structure to induce the resonance at a target wavelength. In a specific condition, surface gratings may induce the surface plasmon propagation due to the diffraction and the resonance wavelength of the surface plasmon propagation is dependent on the grating shape. The grating configuration was designed by the topology optimization scheme based on the reaction-diffusion equation. To shift the resonance wavelength to the target wavelength, this paper maps the frequency response function to a probability distribution function (PDF). The mean value from the PDF becomes a part of the objective function and the design objective is set to minimize the distance between the present resonance wavelength and the target wavelength while keeping the energy intensity. The process of simulation and optimization was performed using the commercial package COMSOL combined with MATLAB programming.

This paper presents a research work on the electromagnetic loss modeling and demagnetizations analysis for a high-speed permanent magnet machine (HSPMM). The iron loss is estimated by improved modeling considering harmonics and rotational magnetic field effects to achieve high precision; rotor eddy current loss is researched and comprehensively investigated using finite-element method (FEM). The auxiliary slot and PM beveling are also proposed to reduce the rotor eddy current loss for machine at high-speed operation. Temperature-dependent PM demagnetization modeling is utilized in HSPMM FEM analysis to investigate machine performance due to temperature variation, while optimized rotor structures are proposed and comparatively researched by FEM to improve the machine anti-demagnetization capability in harsh conditions. The HSPMM temperature is estimated based on the calculated loss results and machine computational fluid dynamic modeling. Experimental measurements on the prototype machine verify the effectiveness of the machine electromagnetic and thermal modeling in the paper.