Search

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the estimation of moisture content of the inverted-type oil-immersed current transformer (IOCT) insulation system, the interfacial polarization between oil-immersed insulation paper and semi-conductive paper should be considered. The classical model functions of frequency-domain dielectric spectroscopy (FDS) are no longer applicable. Therefore, the planar layered two-phase system model is applied in this paper. First, the FDS of oil-immersed paper and semi-conductive paper with certain moisture content is measured using Alpha-A broadband dielectric spectrometer. Then, the FDS of oil-immersed insulation paper is explained using the Havriliak–Negami (H–N) model function and the amendatory H–N model function considering that the dc conductance is used to explain the FDS of semi-conductive paper. The two functions are substituted into the planar layered two-phase system model. The model parameters are fit by means of least-squares technique. Finally, the numerical relationship between the chosen characteristic parameter and the moisture content of the IOCT insulation system is obtained by least-squares technique. In engineering, one can use the results considering the influence of interfacial polarization to estimate the moisture content of the IOCT insulation system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This comment concerns some doubtful results included in the above paper. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper introduces an alternative pathway to designing an efficient interior permanent magnet machine (IPMM) for direct–drive (D-D) wind energy applications. It analyzes the design optimization methodology in great detail, employing multiple experimental verifications to acutely pinpoint the most desirable and feasible format. The focal objectives of minimizing cogging torque, torque ripple, and maximizing efficiency were among the priority design goals and obtained through design optimization. It is demonstrated in the process that both the torque ripple and the cogging torque can be reduced to less than 5% by adjusting the slot and pole dimensions, without any other alterations in rotor pole shaping or skewing. This paper leads the way, pioneering experimental substantiation of theory, by varying existing geometrical parameters, winding, and pole design of a basic IPMM to come up with a highly efficient wind turbine generator with negligible cogging torque and torque ripple. The electromagnetic is at the heart of this paper’s design goals, as parameter optimization is essential for a wind turbine application. The winding layout is brought under scrutiny and both the distributed and concentrated wound IPMMs are compared to further adopt the design optimization. The superiority of the concentrated-wound design is demonstrated, and consequently a prototype machine is constructed based on the proposed design for experimental verification. The results from the experiment verify the feasibility of the proposed design for D-D wind turbine applications. [ABSTRACT FROM AUTHOR]

This paper focuses on analytical methods of a finite-element method (FEM)-based edge heating system. The edge heating system plays a role in maintaining the temperature in the hot rolling process of carbon steel. Carbon steel moves along the production line and maintains the temperature by the edge heating system in the process. Power-of-the-edge heating system is transmitted to carbon steel during the process. Eddy currents are generated in carbon steel by Faraday’s law of electromagnetic induction, and eddy current loss serves as a heat source to increase the temperature. Thus, there is a need for accurate electromagnetic-field analysis and thermal analysis because the eddy current path generated in carbon steel greatly affects the heat distribution in carbon steel. This multiphysics analysis requires high reliability. Accordingly, this paper presents a coupling analysis method using an FEM-based coordinate mapping method as a more accurate analytical method. This paper also established an analytical approach to the edge heating system using the ductility analytical method of this coordinate mapping method. [ABSTRACT FROM AUTHOR]

This paper presents study of design characteristics with wide constant power speed range (CPSR) for electric vehicle Propulsion. Through analysis of interior permanent magnet synchronous motor (IPMSM) control logic, design characteristic of extending CPSR is proposed. To achieve wide CPSR, center of voltage limit ellipse should be placed at cross point of current limit circle and d -axis. To analyze characteristic of voltage ellipse, four types of representative IPMSM rotor topologies are selected. Through rotor topology analysis, tendency of \phi _{f} and L_{\mathrm{ ds}} $ parameters which decide center of voltage limit ellipse is analyzed. This paper also considers shifting of voltage limit ellipse center according to change in motor speed. Reflecting the result, this paper focuses on center of voltage limit ellipse position at maximum speed, because central coordinates of high-speed range determine characteristics of CPSR. Through the analysis result, this paper suggests direction of IPMSM design for wide CPSR. [ABSTRACT FROM AUTHOR]

In this paper, a new finite element Gaussian belief propagation (FGaBP) method is presented for time-domain applications. The unconditionally stable Newmark time-stepping scheme is combined with FGaBP for this purpose. As shown empirically, the method converges for increasing time step sizes without losing stability. The combined FGaBP-time stepping is able to retain the parallel scalability from FGaBP as in previous work. In addition, this paper also shows that lossy material properties can be easily supported by the method with minimal changes to its formulation. [ABSTRACT FROM AUTHOR]

This paper employs an overhang structure for axial flux permanent magnet motor to enhance the torque density. However, the overhang structure requires a computationally expensive 3-D finite-element method (FEM) for analysis, because a quasi-3-D FEM cannot be applied to such a geometry. Thus, in order to reduce the computational cost of above-mentioned topology, this paper adopts a field reconstruction method (FRM). The conventional FRM is applicable only in the case, where the slot pitch to teeth length ratio is the same along radial direction. To address this problem, we introduce a virtual air gap concept so that it can take into account parallel slot effect as well as overhang effect. In this paper, the effectiveness of the proposed method is verified by the 3-D FEM and experimental results. [ABSTRACT FROM AUTHOR]

This paper focuses on the light interference in biogenic guanine crystals that have interesting optical properties such as high reflectivity and optical biaxiality. In this paper, we find that a Moiré effect pattern is generated on a single guanine crystal of goldfish combining with the mirror surface substrate. An observation system, in this paper, is consisted with telecentric lens and coaxial vertical illumination using blue LED light source. It is clearly seen that homogeneous light and shade stripe patterns are observed on the broadest surface of the single guanine crystal plate floating in water. By contrast, when the guanine crystals are set on the substrates having the diffused reflection surface, this light and shade stripe pattern is not observed on the single guanine crystal but observed on two cross-stacked crystals as reported before. These results show that the light and shade stripe pattern on the single guanine crystal is produced by the optical interference, so-called Moiré effect, between guanine crystal and the mirror substrate surface. The angle dependence of reflection brightness and the magnetic orientation of guanine crystal are investigated by using Moiré patterns. Furthermore, we demonstrate that small curvatures and steps can be optically detected and estimated by the pattern change of Moiré stripes. It is confirmed that the direction of curvature is detected by controlling the guanine crystal orientation with magnetic fields and the curvature shape is reproduced from the Moiré pattern. [ABSTRACT FROM AUTHOR]

As CMOS technology scales down to the nanoscale, high leakage power consumption becomes one of the major concerns in the design of electronic circuits. To overcome this challenge, nano-emerging technologies and logic-in-memory (LIM) structures are being studied. Magnetic tunnel junction (MTJ) is an emerging spin-based device, which consumes very minimal leakage power in conjunction with CMOS transistors. In this paper, we propose a novel MTJ/CMOS design, which consumes low power and has lower delay than the existing LIM-based MTJ/CMOS designs. The proposed MTJ/CMOS designs have lower power and lower delay by charge sharing the output nodes during the pre-charge phase. The designs are simulated using 45 nm CMOS technology with perpendicular anistropy CoFeB/MgO MTJ model using a Cadence Spectre simulator. From the simulation results, we can see that the proposed MTJ/CMOS OR, AND, XOR, MUX, and full adder designs have 31.35%, 40.15%, 49.17%, 35.86%, and 42.62% lower power-delay-product, respectively, compared with the existing MTJ/CMOS designs. Furthermore, in this paper, we have also studied the usage of integrating nano-electronic devices, such as a carbon nanotube field-effect transistor and a Fin field-effect transistor, in the proposed circuits along with the MTJ devices. [ABSTRACT FROM AUTHOR]

The analytical calculation of magnetic forces is currently an interesting alternative to the time-consuming 3-D finite-element method due to their high accuracy and low computational cost. In this paper, a new semi-analytical solution for determining the levitation force of the repulsive magnetic guidance that has a significant role for controlling and developing high precision magnetic levitation positioning system is presented. An important result is that this new expression, compared with other known equations in the literature, considers the position dependence of the magnetic levitation force over the whole travel range. In order to derive this force, the magnetic field of the permanent magnet is first calculated by introducing and solving the magnetic scalar potential. Taking Lorentz force law into consideration, the proposed equation is finally derived. This semi-analytical equation is suitable for designing and optimizing the magnetic guidance. Furthermore, it can also be used for developing other ironless actuators. The calculated levitation force from the derived equation and the verification by measurements are likewise presented in this paper. [ABSTRACT FROM AUTHOR]