Computational Electromagnetics Research Articles

The Unsung Hero of the Electric Vehicle Revolution: The role of computational electromagnetics in electric machine design and analysis

The Unsung Hero of the Electric Vehicle Revolution: The role of computational electromagnetics in electric machine design and analysis

Analysis of leakage flux, losses, and temperature in large synchronous generator end zone under the multi‐layer screen thickness based on novel iterative method

AbstractThe multi‐layer screen is the key component in the large synchronous generator end zone. The leakage flux, losses, and temperature of end components are significantly affected by the thickness of multi‐layer screen in the synchronous generator. To investigate the influence of multi‐layer screen thickness on the end leakage flux, losses, and temperature in the synchronous generator end zone, 1407MVA nuclear power synchronous generator is studied. Three‐dimensional transient electromagnetic field model of synchronous generator end zone is established. Three‐dimensional transient electromagnetic field in the end zone of 1407MVA synchronous generator with the multi‐layer screen is calculated based on the novel iterative method. The flux density of end components is compared and studied in the end zone under the variation of multi‐layer screen thickness. Influence of the different thicknesses of multi‐layer screen on the losses of the shield plate, screen, finger plate, and stator end core is researched. The losses of end components obtained from 3D end electromagnetic field calculation are applied to the end zone as the heat source in the three‐dimensional fluid and thermal coupled field. The temperature distribution of the end components is determined. The accuracy of the calculated results is validated by the experimental values.

Guest editorial: Recent advances in computational electromagnetics

Guest editorial: Recent advances in computational electromagnetics

Analysis and Design of Embedded High-Temperature Doubly Salient Electro-Magnetic Starter/Generator for Aviation

In view of the high temperature operation characteristics of the embedded starter/generator for the more electric engine (MEE), the influence of material property change on motor performance at high temperature is studied. Furthermore, considering the influence of high temperature, the electromagnetic calculation of doubly salient electro-magnetic machine (DSEM) is carried out, and the excitation design principle of DSEM under high temperature is pointed out. The performance of DSEMs using DW310 silicon steel and 1J22 iron-cobalt alloy material was compared. Based on the silicon steel material, the structural parameters of DSEM are analyzed. According to the key parameters obtained from structural parameter analysis, Box-Behnken method and genetic algorithm were used to carry out the multi-parameter and multi-objective optimization design. The optimization objectives include excitation current, voltage ripple and cogging torque, to meet the torque and power quality requirements of MEE. Then the performance of DSEM at room temperature and high temperature is analyzed by the finite element method, which verifies the effectiveness of the design. Finally, a high-temperature and high-speed DSEM prototype was processed. At the same time, in order to cooperate with the test, a DSEM ground simulation test system platform for MEE was built to test the prototype. Its design experience lays a foundation for the embedded DSEM design of more electric aircraft.

Study on Two-Dimensional Exit Pupil Expansion for Diffractive Waveguide Based on Holographic Volume Grating

Diffraction gratings are becoming a preferred option for waveguide head-mounted in–out coupling devices due to their flexible optical properties and small size and light weight. At present, diffraction waveguide coupling devices for AR head-mounted displays (HMD) have difficulties such as a long development cycle and complicated processing. In this paper, we first establish a set of two-dimensional (2D) grating ray tracing models, based on which we determine the initial architecture of the dual-region two-dimensional exit pupil expansion (2D-EPE) AR-HMD holographic waveguide diffraction system. Second, we propose a honeycomb coupled grating array and optimize the optical energy utilization and brightness uniformity of the holographic waveguide and use a custom dynamic linked library (DLL) function to implement the ray tracing of the 2D grating and add a probabilistic splitting function to the DLL, which reduces the single simulation time from 11.853 min to 1.77 min. We also propose a holographic lithography device composed of holographic optical elements (HOEs) and a method for preparing HOEs. Finally, in order to obtain the diffraction efficiency preoptimized by the above DLL for the uniformity of the exit pupil brightness and light energy utilization, we inverse design with the preparation process parameters as the optimization variables and develop the adaptable electromagnetic calculation program Holo-RCWA. Using Holo-RCWA with nondominated sorting genetic algorithm II (NSGA-II), we inverse design to obtain the process parameters satisfying the diffraction efficiency distribution, and the optimization time of the whole system is reduced from 2–3 days to 10 h. This work is of great significance for AR/VR applications.

A peak time shifting phenomenon in transformer axial short‐circuit electromagnetic force due to the coupling of electromagnetic‐axial vibration

AbstractAccurately calculating axial electromagnetic force is essential to analyse transformer winding axial stability. Prior research has mainly focused on the effect of winding structure on static axial electromagnetic force and studying vibration by substituting the static force in a time‐varying function. However, the coupling effect between axial electromagnetic force and winding vibration has not been addressed, and no calculation method for the axial electromagnetic force that considers both winding meso‐structures and vibration coupling effects has been proposed. Previously the authors presented an electromagnetic force calculation model that considers winding structure characteristics, and an iterative algorithm for magnetic‐structure coupling calculation. Currently, the winding vibration model was first proposed and the dynamic calculation method was formulated. By applying the method to a typical 110kV transformer, the spatial‐temporal distribution of winding axial short‐circuit electromagnetic force was obtained. It was found that the peak value of the axial short‐circuit electromagnetic force of some windings appears at the second or third peak moment of the short‐circuit current, which is called as peak time shift phenomenon. Further stress analysis indicates that existing evaluation methods may overestimate the short‐circuit resistance of windings by only considering short‐circuit electromagnetic force under maximum peak of short‐circuit current.

Fast and accurate electromagnetic field calculation for substrate-supported metasurfaces using the discrete dipole approximation

Abstract Metasurface design tends to be tedious and time-consuming based on sweeping geometric parameters. Common numerical simulation techniques are slow for large areas, ultra-fine grids, and/or three-dimensional simulations. Simulation time can be reduced by combining the principle of the discrete dipole approximation (DDA) with analytical solutions for light scattered by a dipole near a flat surface. The DDA has rarely been used in metasurface design, and comprehensive benchmarking comparisons are lacking. Here, we compare the accuracy and speed of three DDA methods—substrate discretization, two-dimensional Cartesian Green’s functions, and one-dimensional (1D) cylindrical Green’s functions—against the finite difference time domain (FDTD) method. We find that the 1D cylindrical approach performs best. For example, the s-polarized field scattered from a silica-substrate-supported 600 × 180 × 60 nm gold elliptic nanocylinder discretized into 642 dipoles is computed with 0.78 % pattern error and 6.54 % net power error within 294 s, which is 6 times faster than FDTD. Our 1D cylindrical approach takes advantage of parallel processing and also gives transmitted field solutions, which, to the best of our knowledge, is not found in existing tools. We also examine the differences among four polarizability models: Clausius–Mossotti, radiation reaction, lattice dispersion relation, and digitized Green’s function, finding that the radiation reaction dipole model performs best in terms of pattern error, while the digitized Green’s function has the lowest power error.

ArthroNavi framework: stereo endoscope-guided instrument localization for arthroscopic minimally invasive surgeries.

As an example of a minimally invasive arthroscopic surgical procedure, arthroscopic osteochondral autograft transplantation (OAT) is a common option for repairing focal cartilage defects in the knee joints. Arthroscopic OAT offers considerable benefits to patients, such as less post-operative pain and shorter hospital stays. However, performing OAT arthroscopically is an extremely demanding task because the osteochondral graft harvester must remain perpendicular to the cartilage surface to avoid differences in angulation. We present a practical ArthroNavi framework for instrument pose localization by combining a self-developed stereo endoscopy with electromagnetic computation, which equips surgeons with surgical navigation assistance that eases the operational constraints of arthroscopic OAT surgery. A prototype of a stereo endoscope specifically fit for a texture-less scene is introduced extensively. Then, the proposed framework employs the semi-global matching algorithm integrating the matching cubes method for real-time processing of the 3D point cloud. To address issues regarding initialization and occlusion, a displaying method based on patient tracking coordinates is proposed for intra-operative robust navigation. A geometrical constraint method that utilizes the 3D point cloud is used to compute a pose for the instrument. Finally, a hemisphere tabulation method is presented for pose accuracy evaluation. Experimental results show that our endoscope achieves 3D shape measurement with an accuracy of . The mean error of pose localization is 15.4deg (range of 10.3deg to 21.3deg; standard deviation of 3.08deg) in our ArthroNavi method, which is within the same order of magnitude as that achieved by experienced surgeons using a freehand technique. The effectiveness of the proposed ArthroNavi has been validated on a phantom femur. The potential contribution of this framework may provide a new computer-aided option for arthroscopic OAT surgery.

The Complex Impedance of the Hemispherical Ground Electrode: An Open Analytical Problem

The hemispherical ground electrode is a basic electrode whose analysis appears in many textbooks on electromagnetics in chapters dedicated to steady currents. Considering a soil with a given resistivity and an electrode with a given perimeter, the electrode DC resistance is simply calculated from the ratio resistivity/perimeter. Strangely, the generalization of this result to AC regimes is missing. The issue of the frequency-domain impedance of the hemispherical ground electrode has been avoided in the literature despite its trivial geometry. But the problem is indeed not easy; electromagnetic field calculation involves Legendre and Bessel functions; the application of boundary conditions involves an infinite set of points, and some integrals involved need to be calculated recursively. We analyzed the math and physics of the problem but failed to find a closed-form solution. This article with “negative results” can, however, be useful; on one hand it may prevent researchers from wasting their time following the same steps, and, on the other hand, it may attract the interest of new researchers to the subject, ultimately, accelerating its analytical solution (if the solution exists).

Judgment method of the dynamic threshold value of motor protection at a dynamic load rate

To address the shortcomings of traditional motor thermal protection, which uses the motor’s temperature or temperature rise threshold operating at full load as the basis for the judgment method, a dynamic threshold judgment method based on a study of the motor’s temperature rise characteristics under a dynamic load rate is proposed. Taking a forced air-cooled, three-phase asynchronous motor with 11 kW power as the research object, a 2D/3D motor model under steady-state conditions is established. The loss distribution of asynchronous motors at different load rates is obtained through electromagnetic field simulation calculations. The finite element method is used to simulate and calculate the motor’s temperature field. Taking ambient temperature and load factors into account, the study takes place from the perspective of motor temperature rise in order to acquire the law governing the change in motor temperature increase under various working circumstances. A method of converting the temperature and warming between the motor’s stator, winding, and rotor is proposed. A dynamic threshold judgment system for accurate warning of overheating problems in motors under any load rate is set up so that the thermal protection of motors can accurately be judged under variable load conditions, which offers a crucial theoretical foundation for the design of intelligent motor temperature rise prediction systems. It contributes to a methodological underpinning for the diagnosis and early warning of thermal health in smart motor systems.

Investigations on electromagnetic scattering characteristics of aircraft rudder considering electromagnetic discontinuities

This work investigates the scattering characteristics of the rudder structure of aircraft considering electromagnetic discontinuities through multi level fast multipole algorithm (MLFMA) of the computational electromagnetics. Firstly, the scattering characteristics of the rudder seam and its influence on the omnidirectional radar cross section (RCS) are performed. Based on the traditional high-frequency analysis theory, the source and spatial contribution distribution of seam scattering are further studied. Numerical results demonstrate that the sidewall of the rudder seam is an important scattering source, and the radar absorbing material (RAM) coated on the sidewall of the seam has a good RCS reduction effect. In addition, this work presents the influence of the rudder deflection on the stealth performance, analyzes the effect of the rudder movement of the ordinary aileron and the split drag rudder on the scattering characteristics of the whole aircraft. The common aileron has little effect on the stealth performance of the aircraft, and it only causes scattering peak in the direction opposite to the control surface. However, the split drag rudder has great damage to the opposite direction stealth performance of the aircraft. When its deflection angle is 45°, the mean value of the opposite direction RCS increases by about two orders of magnitude compared with the deflection angle 0° state. The results indicate that the structure of aircraft rudder has a significant impact on the RCS characteristics of the whole aircraft.

Accurate inverse design for high-efficiency and broadband terahertz devices by co-simulation with genetic algorithms

In this study, we combined MATLAB with the rigorous electromagnetic field simulation software Computer Simulation Technology to perform a co-simulation method for inverse design of high-efficiency and broadband THz metasurface devices. In the proposed design method, genetic algorithm (GA) is embedded to realize automatic and inverse design. Aiming toward the different requirements of high-efficiency and broadband THz metasurface devices, different objective functions are set to optimize the design of different types of THz metasurface devices. Based on the rigorous electromagnetic simulation and genetic algorithm, the proposed design method can realize automatic and inverse design with high reliability, compared to the theoretical model based on catenary e-field theory. This study provides an important guiding role and an efficient method for designing and optimizing required metasurface devices with practical applied value.

Analysis of rotor fatigue characteristics of permanent magnet synchronous motor spindle in eccentric state

In this paper, the distribution of the air gap magnetic field in the motorized spindle is obtained through theoretical derivation, which is verified by comparing with the finite element simulation results. Based on the original calculation of air gap magnetic field, the rotor eccentricity theory is added, and the distribution of air gap magnetic field after rotor eccentricity is obtained. The correctness of the calculation theory of eccentric air gap magnetic field is verified by the finite element simulation results. Through the electromagnetic force calculation and finite element simulation of asymmetric magnetic field in eccentric state, the influence law of unbalanced electromagnetic force on the fatigue life of motorized spindle rotor is summarized.

Photonic Crystal Waveguides Composed of Hyperbolic Metamaterials for High-FOM Nano-Sensing

This study introduces an innovative integration of hyperbolic metamaterials (HMMs) and photonic crystals (PtCs), each possessing unique dispersion properties that effectively manipulate the propagation of light. We present a PtC waveguide consisting of arrays of HMM nanorods, denoted as HMM PtCs. This waveguide configuration enables the realization of a high figure of merit (FOM) nano-sensor. HMMs and PtCs share the same underlying physics. HMMs can generate surface plasmonics, while PtCs offer a bandgap for the waveguide. This configuration presents a novel sensing solution that directly couples surface plasmonics and waveguide modes. By modifying the refractive indices of the surrounding materials, the PtC waveguide exhibits alterations in absorption and transmission, allowing for the detection of temperature, pressure, and material variations. The refractive indices of the surrounding materials can be adjusted based on the sensor’s intended application. For instance, when the sensor is utilized for temperature sensing, thermal infrared materials can serve as the surrounding medium. As the temperature rises, the refractive index of the surrounding material changes accordingly, impacting the waveguide modes and thereby altering absorption and transmission. We utilized the finite element method to conduct numerical simulations in order to assess the absorption and transmission characteristics of the proposed system. Given that this approach involves a full electromagnetic calculation based on Maxwell’s equations, it closely approximates real-world scenarios. The employed numerical method demonstrates the remarkable performance of this proposed system, achieving a sensitivity of 324.16 nm/RIU (refractive index unit) and an impressive FOM of 469.58 RIU−1. These results signify a substantial improvement over surface plasmonic sensors, which typically exhibit limited FOMs. The direct coupling between surface plasmonics and waveguide modes provides a distinct advantage, allowing the proposed sensor to deliver a superior performance. As a consequence, the HMM PtC waveguide sensor emerges as an exceptionally appealing option for photonic sensing applications. The complexity of the proposed system presents a fabrication challenge. Nevertheless, as fabrication technology continues to advance, we anticipate that this issue can be effectively resolved. The proposed HMM PtC waveguide holds vast potential across diverse fields, including biology, medicine, and clinics, representing an exciting advancement for both industry and scientific research.

Accurate Electromagnetic Force Analysis of Offshore Wind Power Transformer Windings Based on Fractional Order Lumped Parameter Model

Accurate calculation of the electromagnetic force distribution of transformer windings under different loads and fault conditions is of great significance for transformer maintenance, condition evaluation and life prediction. Due to the influence of offshore wind power systems, offshore wind power transformers have high harmonic content and large changes in load rates, which can easily cause the coil destabilization, winding deformation or even damage because of the uneven distribution of the electromagnetic force. To improve the accuracy of electromagnetic force calculation, this paper proposes a fractional order numerical method. First, a three-dimensional axisymmetric transformer model and a symmetrical lumped parameter equivalent circuit model are established, respectively, based on field-circuit coupling. Second, the fractional order approximation of circuit components is realized by using the improved Oustaloup filter. In the fractional order model, the transformer is replaced by the lumped parameter equivalent circuit model. Third, as in the calculation process for integer order electromagnetic force, the integer order current has a large error, and the current waveform does not match the actual power frequency. The fractional order current and electromagnetic force at the 0.9 order are closer to the rated value. Finally, the effects of different load rates, three-phase short circuits and harmonic conditions are studied with the fractional order model. Compared with the traditional integer order finite element electromagnetic model, the fractional order equivalent circuit model established in this paper is more accurate and suitable for electromagnetic force calculation. The proposed method is significant for the structural design and state detection of transformers and also could be applied in the analysis of other dry-type transformers.

Enhancement of Electromagnetic Scattering Computation Acceleration Using LSTM Neural Networks

This paper presents the electromagnetic long short-term memory neural network (EM-LSTMNN) approach to accelerate radar cross-section (RCS) calculations in optimizing low RCS for electrically large targets. The proposed method converts the conventional electromagnetic numerical calculation into an efficient numerical calculation using the LSTM neural network, resulting in a significant improvement in RCS computation speed. To assess the effectiveness of this approach, a downscaled model of a large-sized ship is employed as the target for low RCS optimization. Each modification made to the target’s mesh data during the optimization process is stored in the dataset as a new element. As the ship scaling model undergoes modifications during the optimization process, the new mesh data are recorded, thus adding a new element to the dataset at each time step. This forms a time series representation of the mesh model. By utilizing the dataset collected throughout the optimization process, the proposed EM-LSTMNN model is trained using data-driven approaches, with a training time of approximately 106 s. It is worth noting that this training time is significantly smaller compared to existing methods that employ fully connected neural networks. The performance of the proposed approach is demonstrated by comparing the RCS calculation results obtained through this method with those obtained through traditional electromagnetic simulations.

High Precision Motion Compensation THz-ISAR Imaging Algorithm Based on KT and ME-MN

In recent years, terahertz (THz) radar has been widely researched for its high-resolution imaging. However, the traditional inverse synthetic aperture radar (ISAR) imaging algorithms in the microwave band perform unsatisfactorily in the THz band. Firstly, due to THz radar’s large bandwidth and short wavelength, the rotation of the target will result in serious space-varying(SV) range migration and space-varying phase error. Furthermore, it is challenging to accurately estimate the rotational velocity and compensate for phase errors in the presence of severe range migration effects. Therefore, in this paper, a high-precision THz-ISAR imaging algorithm is proposed. The algorithm includes the following step: First, the SV first-order range migration(FRM) is corrected using keystone transform (KT); then, the minimum entropy based on modified newton (ME-MN) is used to estimate the rotational velocity roughly, and the remaining SV second-order range migration(SRM) is corrected to obtain the range profile with the envelope alignment. Finally, the echo after the envelope alignment is processed for the second time based on ME-MN. The target rotation velocity is accurately estimated, and the phase error is compensated to obtain a well-focused imaging result. The validity of the proposed method is verified by numerical simulation and electromagnetic calculation data.

Internet Data Bandwidth Optimization and Prediction in Higher Learning Institutions Using Lagrange’s Interpolation: A Case of Lagos State University of Science and Technology

Episodic edifices have a diversity of significant solicitations in contemporary machineries and engineering owing to their exclusive electromagnetic properties. Frequently used episodic edifices comprise; occurrence selective surfaces, visual grilles, phased collection projections, photonic bandgap supplies, and numerous metamaterials. The scrutiny of episodic edifices has all the time been a significant area in computational electromagnetics. This episode, describes a precise and effectual arithmetical study, grounded on a higher-order finite element method (FEM), for depicting the electromagnetic properties of an episodic edifices. Grounded on the Floquet theory, episodic frontier conditions and radioactivity conditions are foremost resultant for the unit cell of an episodic edifice. The FEM is formerly applied to unravel Maxwell’s reckonings in the unit cell. To augment the precision and effectiveness of the FEM, rounded elements are employed to discretize the unit cell and higherorder course basis functions are used to enlarge the electrical arena. The asymptotic waveform evaluation (AWE) is applied to implement wild frequency and rawboned curves. To prove the proficiency of the projected FEM, we apply it to the scrutiny of episodic absorbers, incidence selective edifices, and phased collection aerial. For the aerial analysis, a severe waveguide port condition is industrialized to precisely model the aerial feed edifices. In all the occurrences premeditated, acceptable outcomes are obtained. Key words : Episodic, edifice, absorbers, waveguide, electromagnetic. DOI : 10.7176/CEIS/10-1-04

Influence of line current limiting reactor on temporary overvoltage of 500 kV transmission line

In order to limit the temporary overvoltage, the method of the series current limiting reactor in the line is often used in the power grid to limit the overvoltage. The parameters of current limiting reactance directly affect the level of 50Hz overvoltage. The installation of a current limiting reactor changes the positive and zero sequence impedance parameters of the line, which has an impact on the temporary overvoltage of the line. Installing a current limiting reactor on the 500 kV Line’s overvoltage is studied by using electromagnetic transient calculation software EMTP. The simulation results show that the temporary overvoltage of the 500 kV Line can be reduced by adding a current limiting reactor.

Motor Current Model for Detecting Localized Defects in Planet Rolling Bearings

A motor current model for the diagnosis of localized defects in planet rolling bearings (PRBs) is proposed in this study. A dynamic analysis of the motor-driven planetary gearbox system is conducted, and a translational-torsional vibration model of the system is developed. Both the additional time-varying impact caused by localized defects and the influence of the Hertzian contact and radial clearance on the translational support forces of PRBs are considered in the model. Based on the magnetic equivalent circuit network model, vibrational-electromagnetic coupling analysis is performed with the aid of the air-gap permeance and electromagnetic torque. By iteratively solving the nonlinear algebraic differential equations describing the dynamic characteristics of the coupling system, the motor current variation curve with localized defects in the PRB is obtained. Taking a typical motor-driven planetary gearbox system as the object, electromagnetic finite element calculations and dynamic response tests are performed to verify the proposed motor current model. The results show that the characteristic motor current frequencies are a combination of the fault passing frequency and power supply frequency when the inner race of the PRB has a localized spall fault. When the outer race (or roller) has a localized spall fault, the combination of current characteristic frequencies, which generally consists of the fault passing frequency, power supply frequency, and PRB outer-race rotational frequency (outer-race spall) or cage revolution frequency (roller spall), become complex. By discussing the effect of the spall width on the motor current spectra in detail, the characteristic frequencies sensitive to defects are extracted, providing a theoretical basis for the quantitative diagnosis of PRB-localized defects.