Hasil untuk "Electricity and magnetism"

Hansoo Yoo, Yungseon Eo

In this study, the physical behavior of a surface acoustic wave resonator is formulated with the aid of a distributed four-port transmission line circuit model. Propagation losses of surface acoustic waves are modeled based on frequency-variant circuit model parameters (i.e., resistance, conductance, and attenuation). Furthermore, the loss resulting from metal fingers and leakage toward the bulk substrate are modeled by means of series resistance and frequency-variant parallel conductance, respectively. In addition, the attenuation of high-frequency spurious resonances is modeled using a frequency-variant damping factor. The validity of the proposed model is verified by test filters fabricated on 42°YX-LiTaO3 (piezoelectric substrate). The S-parameters calculated using the proposed model show excellent agreement with the experimental S-parameters measured at the wafer level.

Maoxin CHEN, Kailun WANG, Yu SHEN et al.

For offshore wind power transmission systems based on diode rectifier-based DC transmission, the voltage and frequency support of the offshore AC grid based on the grid-forming control of offshore wind turbines has become a key issue. For the currently most studied Q/f droop-based grid-forming control (GFM) scheme and the newly emerged P/f droop-based GFM control scheme, a detailed analysis of the multi-machine power coupling characteristics and the stability aspects of the two schemes is carried out. The analysis of the control mechanism reveals that the Q/f droop-based GFM control scheme has coupling characteristics between active and reactive power control path, while the P/f droop-based GFM control scheme has a natural power decoupling characteristic. Detailed analysis based on the small signal model shows that the power control coupling characteristics of the Q/f droop-based GFM control scheme may lead to power oscillation problems between multiple machines. And the P/f droop-based GFM control scheme has a natural decoupling characteristic and has better stability robustness under different load conditions, making it more conducive to achieving the synchronous and stable operation of hundreds of wind turbines in offshore high-capacity wind farms.

Kayode Adedotun Oyesina, Alex M. H. Wong

Recent explorations and advancements in communications systems have sparked a renewed fascination with beam-steerable high-gain antennas. While conventional active phased arrays have been long seen as a feasible solution, the associated cost is a major impediment for electrically large millimeter-wave apertures. In this paper, we present an all-metal metamaterial-loaded Huygens box antenna that facilitates independent steering of radiation in azimuth and elevation directions and a dramatic reduction in the number of phased elements. The antenna encloses an artificial dielectric medium with an active Huygens metasurface arranged around the enclosure’s periphery. We present simulation and experiment results for a representative \begin{document}$ 4{\lambda }_{0}\times 4{\lambda }_{0} $\end{document} square aperture, where \begin{document}${\lambda }_{0} $\end{document} is the free-space wavelength. The results show that the antenna radiates similarly to a phased array of similar aperture size, with a quadratic-to-linear reduction ratio in the number of required elements, leading to over 10-fold reduction for large-aperture antennas. The tremendous reduction in the number of excited elements positions the antenna as a cost-saving alternative, especially in large aperture millimeter-wave regime.

MA Yingxue, ZHAO Yanqiang, YANG Xiaodong et al.

Magnetic resonance imaging (MRI), as a non-invasive, high-resolution medical imaging technology, is a powerful tool for clinical disease diagnosis. Current MRI systems are advancing towards higher magnetic field strength. High-field (HF) and ultra-high-field (UHF) MRI have demonstrated substantial advantages in clinical diagnosis and emerging cutting-edge imaging technologies, making them a focus of global competition. HF and UHF MRI equipment serves as a fundamental guarantee for scientific research and clinical applications, and is emphasized and supported as a strategic industry in many countries. This paper comprehensively analyzes the global market landscape and core technology competition in HF and UHF MRI equipment, highlights opportunities and challenges for China’s development in this field, and proposes targeted recommendations.

Le Li, Huajie Shen, Zhongyuan Zhang et al.

Abstract The authors aim to explore the effectiveness of two‐component polyurea materials applied to transmission line towers (on the ground potential side) in improving the insulation performance of the conductor–tower gap. The physicochemical and electrical properties of the polyurea materials were first analysed and a conductor–tower gap testing platform was constructed to investigate the effects of the length and thickness of the polyurea layer on the ground potential side under a 50‐Hz AC voltage on the breakdown characteristics. Experimental studies revealed that the characteristic breakdown voltages of polyurea layers of different lengths (40, 100, 200, and 400 cm) are approximate. Compared with the air‐insulated gap before the application of polyurea, thinner polyurea layers (1 and 2 mm) showed no significant improvement in the breakdown voltage, whereas thicker layers (3, 4, and 5 mm) significantly improved it. In particular, with a polyurea layer thickness of 4 mm and gap distance of 20 cm, the characteristic breakdown voltage increased from 138.43 to 155.71 kV. In addition, the withstand voltage distance decreased from 4 to 3 cm without any breakdown, even when the high‐voltage conductor directly contacted the polyurea layer and the layer was not penetrated. The authors provide theoretical support and experimental data for improving the conductor–tower gap insulation performance by applying a polyurea layer on the ground potential side.

ZHANG Mingyu, XIAO Sa, SHI Shengjie et al.

Hyperpolarized 129Xe magnetic resonance imaging (MRI) is an emerging medical imaging technique that plays an important role in the diagnosis and treatment of numerous lung diseases. However, the noise generated during the acquisition process affects the data quality and limits the reliability of the technique in clinical diagnosis and treatment. In this paper, we propose a multimodal feature-enhanced conditional diffusion model based on deep learning that aims to remove noise and improve image quality. The model inputs acquired 1H MRI as constraints, and a multimodal feature enhancement module is specially designed, which aims to enhance the effectiveness of the model in exploiting multimodal information and the sensitivity to changes in local details of the image. The experimental results show that the method has the best denoising performance and detail preservation compared to other methods, and demonstrate in a ventilation defect segmentation task that the method can enhance the reliability of 129Xe MRI in clinical practice.

Riku Iimori, Yuta Kodani, Shaojie Hu et al.

2D van der Waals (vdW) ferromagnets have emerged as promising materials for spintronic applications due to their unique magnetic properties and tunability. Controlling ferromagnetism via external stimuli is critical for both fundamental research and device integration. In particular, modulation of magnetic anisotropy and exchange interactions through strain offers a viable pathway for functional control. Owing to their weak interlayer coupling, vdW ferromagnets exhibit pronounced sensitivity to strain, enabling effective tuning of their magnetic states. In this study, electric-field-induced magnetoelectric coupling is investigated in the above-room-temperature vdW ferromagnet Fe$_3$GaTe$_2$ integrated on a ferroelectric PMN-PT substrate. It is demonstrated that application of an electric field leads to a substantial reduction in coercive force along with dynamic reconfiguration of the magnetic domain structure. These effects are attributed to electric-field-induced modulation of the vdW interlayer gap and enhancement of the Dzyaloshinskii-Moriya interaction. These findings reveal a strong interplay between electric fields and magnetism in vdW systems, offering a viable route toward the development of low-power, multifunctional magnetic devices. This work establishes a foundation for the electric-field control of magnetic properties in vdW ferromagnets and highlights their potential in next-generation spintronic technologies.

Teruya Nakagawara, Minoru Kanega, Shunsuke C. Furuya et al.

Electric-field controls of Dzyaloshinskii-Moriya interactions (DMIs) have recently been discussed from the microscopic viewpoint. Since the DMI plays a critical role in generating topological spin textures (TSTs) such as the chiral soliton, the magnetic skyrmion, and the magnetic hedgehog, electric-field controls of these TSTs have become an important issue. This paper shows that such electric-field-induced DMI indeed creates and annihilates TSTs by numerically solving the Landau-Lifshitz-Gilbert (LLG) equation for many-body spin systems at finite temperatures. We show that when a strong electric field is applied in a proper way to one- or two-dimensional ferromagnets, the Hamiltonians are changed into the well-known spin models for the chiral soliton or the skyrmion lattice, and the TST states emerge. We utilize a machine-learning method to count the number of generated TSTs. In the three-dimensional (3D) case, we demonstrate the electric-field induction of a magnetic hedgehog structure as follows: Applying a strong enough electric field along a proper direction to a skyrmion-string state (a triple-$\boldsymbol{q}$ state) at low but finite temperatures, we find that the field-induced DMI can drive a quadruple-$\boldsymbol{q}$ state with hedgehog-antihedgehog pairs. This result indicates that we have succeeded in constructing a simple 3D short-range interacting spin model hosting a magnetic hedgehog structure.

Hui WU, Ziwei ZOU, Fengming XIAO et al.

Phasor measurement unit (PMU) plays a crucial role in smart grids, enabling precise synchronized acquisition of electric power data. Due to the use of the global positioning system (GPS) for time synchronization, the PMU is vulnerable to GPS spoofing attack (GSA), which impacts the normal data acquisition. The existing GSA defense methods have low restoration accuracy and require additional hardware costs. To address the aforementioned issues, this paper proposes a GSA defense method based on bidirectional long short-term memory (BiLSTM) network and self-attention mechanism generative adversarial network. Firstly, an improved WGAN-GP model is proposed to redesign the network architecture of the generator and discriminator, and the BiLSTM network and self-attention mechanism are incorporated into the generator and discriminator to enhance the model's generative performance and discriminative ability. Secondly, based on the proposed WGAN-GP model, a GSA defense model is constructed, which includes two crucial modules: an attack detection network and a data restoration network that are employed to detect the smart grid GSA and repair the compromised PMU measurement data, respectively. Finally, We simulated GSA attacks in the IEEE-39 bus system and validated the effectiveness of the proposed method on the corresponding dataset. The results show that compared to existing methods, the proposed approach outperforms in most performance indicators.

S.V. Bulanov, G.M. Grittani, R. Shaisultanov et al.

Radiative cooling of electron beams interacting with counter-propagating electromagnetic waves is analyzed, taking into account the quantum modification of the radiation friction force. Central attention is paid to the evolution of the energy spectrum of electrons accelerated by the laser wake field acceleration mechanism. As an electron beam loses energy to radiation, the mean energy decreases and the form of the energy distribution also changes due to quantum-mechanical spectral broadening.

Marek Rogatko

Uniqueness of static, asymptotically flat, non-extremal {\it photon sphere} in Einstein-Maxwell spacetime with electric and magnetic charges has been proved. Using conformal positive energy theorem, as well as, the positive mass theorem and adequate conformal transformations, we envisage the two alternative ways of proving that the exterior region of a certain radius of the studied static {\it photon sphere}, is characterized by ADM mass, electric and magnetic charges.

Ruiqi WANG, Xinli WANG, Guanghua GUO et al.

This paper aims to investigate the dispatch role played by renewable energy hydrogen production and biogas fermentation in the rural integrated energy system. Firstly, based on the biogas fermentation kinetics model and thermal load characteristics, we constructed an electricity-heat-cold-gas integrated energy system model, which consists of PV hydrogen production, combined heat and power generation, biogas fermentation and energy storage. Then, we established a two stage robust optimization based day-ahead dispatch model with the goal of minimizing daily operation cost, and obtained the day-ahead dispatch plan under the worst scenario by solving the model with column-and-constraint generation (C&CG) algorithm. Moreover, we finished the intra-day dispatch in light of short-term forecasting value of PV power and electric load, realizing the stable and economic operation of the integrated energy system. Finally, a case study was conducted on a rural agricultural park integrated energy system, which indicates that the PV hydrogen production and biogas fermentation have energy storage characteristics and can make contributions to alleviate “source-load” uncertainty, and are proved to have a certain economic value.

Shun ZHANG, Zhenguo WANG, Wendong JIANG et al.

In this paper, the wind load characteristics of the Ultra-High Voltage transmission tower under tornado are studied based on the CFD (computational fluid dynamics) numerical simulation method. The numerical model of a full-scale tornado is established. The measured radar data of Spencer tornado as the velocity inlet are adopted to generate the tornado-like wind field, and the impacts of the surface roughness are considered. The tangential velocity and core radius at different heights are obtained, then contrasted with the measured data to verify the rationality of the tornado-like vortex structure. Next, the overall refined CFD numerical modeling of the transmission tower is established, then the SST k-ω turbulence model based on RANS is used to simulate the flow around the transmission tower under tornado. The effects of the different locations and wind directions on the shape coefficients of each section of the transmission tower are studied. It is found that the wind loads of the top section 1 to section 4 of the transmission tower would take the maximum when the tower is located at the wind field of 1.5D (D is the core radius), and the wind loads of the bottom section 5 to section 9 of the transmission tower are the maximum when the tower is located at the wind field of 1.0D. The wind loads of transmission tower reach the maximum when the tower is located at the wind field of 1.0D. The worst wind attack angle of the transverse directions of the transmission tower increases from 60° to 90°, and the worst wind attack angle of the longitudinal directions of the transmission tower varies in the range of 0° to 30° as the distance from the center of tornado increases. The simulated wind load shape coefficient of the transmission tower at the locations of 1.0D and 1.5D are larger than the code values, and all sections (except for the section 7, 8 and 9 at the location of 1.5D) are also larger than the code values.

Francesco D'Agostino, Flaminio Ferrara, Claudio Gennarelli et al.

Abstract In this article, a bi‐polar near‐field‐to‐far‐field (NFTFF) transformation with probe compensation, which is very convenient from the data reduction standpoint when characterising a flat antenna under test (AUT), is developed. It takes advantage from the non‐redundant sampling representations of the electromagnetic fields to devise a sampling representation on the scanning plane, which requires the knowledge of the bi‐polar NF samples at a reduced number of sampling points. To account for the AUT geometry, it properly adopts as modelling surface a disc having diameter equal to the largest size of such an AUT. This surface allows a more effective AUT modelling from the NF data reduction standpoint than the formerly proposed modelling surfaces for quasi‐planar antennas (the oblate ellipsoid or the two‐bowls), because, unlike these last, it has the capability to best fit the AUT geometry, thus reducing very significantly the involved volumetric redundancy. An ad hoc developed two‐dimensional optimal sampling, interpolation formula is then employed to reconstruct the plane‐rectangular NF data which would be necessary to execute the classical NFTFF transformation developed by Leach and Paris. Some results of numerical simulations and experimental proofs are reported to demonstrate the efficiency of the so developed technique.

مظفر والی, طاهر نیکنام, حامد گرگین پور et al.

ماشین Vernier PM1 به عنوان یک ماشین با گشتاور بالا و سرعت پایین شناخته می‌شود که دارای مزایای مختلفی از جمله چگالی گشتاور بالاتر، حجم ماده PM کمتر، گشتاور دندانه‌ای پایین‌تر، بهبود کارایی و ساختار ساده‌تر و مقاوم‌تر در مقایسه با سایر ساختارهای ارائه شده بر مبنای مغناطیس دائم می‌باشد. این ماشین‏ها گزینه مناسبی برای استفاده در خودروهای الکتریکی هستند. یکی از ساختارهای ارائه شده که برای این منظور مناسب است، ساختار ماشین Dual-Stator Consequent-Pole Vernier PM است که چگالی گشتاور بالا، مشخصات کارکردی مطلوب و حجم آهنربای مصرفی کمتری دارد. اما برای طراحی کامل این ساختار باید مطالعات مکانیکی شامل مطالعات حرارتی و ارتعاشی نیز روی ساختار الکترومغناطیسی طراحی شده صورت گیرد. اهمیت این مسئله به دلیل هندسه متفاوت ماشین‌های شار شعاعی معمولی، نیروهای مغناطیسی نامتعادل و محدودیت‌های مکانیکی و حرارتی می‌باشد. در این مقاله، طراحی سیستم انتقال حرارت و ساختار مکانیکی ماشین DS-CP-VPM صورت گرفته و مطالعات حرارتی و ارتعاشی انجام شده است. متغیرهای طراحی بر اساس آنالیز حساسیت با استفاده از روش اجزای محدود انتخاب شده‌اند. چندین محدودیت طراحی در ابعاد هندسی، چگالی جریان و چگالی شار مغناطیسی در مناطق مختلف و نیروهای مکانیکی درنظر گرفته شده است. نتایج حاصل برای یک ماشین 10 کیلو وات با گشتاور 2 کیلو نیوتن متر برای کاربرد وسیله نقلیه الکتریکی با استفاده از روش اجزای محدود سه بعدی تأیید می‌شود. در این مقاله تجزیه و تحلیل حرارتی – مکانیکی موتور مورد نظر را انجام داده و نتایج شبیه‌سازی در نرم افزار Comsol مورد ارزیابی قرار می‌گیرد.

Alexandru Maries, Mary Jane Brundage, Chandralekha Singh

The Conceptual Survey of Electricity and Magnetism (CSEM) is a multiple-choice survey that contains a variety of electricity and magnetism concepts from Coulomb’s law to Faraday’s law at the level of introductory physics used to help inform instructors of student mastery of those concepts. Prior studies suggest that many concepts on the survey are challenging for introductory physics students and the average student scores after traditional instruction are low. The research presented here investigates the progression in student understanding on the CSEM. We compare the performance of students in introductory and advanced level physics courses to understand the evolution of student understanding of concepts covered in the CSEM after traditional lecture-based instruction. We find that on all CSEM questions on which less than 50% of the introductory physics students answered a question correctly after instruction, less than two-thirds of the upper-level undergraduate students provided the correct response after traditional instruction. We also analyzed the CSEM data from graduate students for benchmarking purposes. We discuss the CSEM questions that remain challenging and the common alternative conceptions among upper-level students. The findings presented here at least partly point to the fact that traditional instruction in upper-level courses which typically focuses primarily on quantitative problem solving and incentivizes use of algorithmic approaches is not effective for helping students develop a solid understanding of these concepts. However, it is important for helping students integrate conceptual and quantitative aspects of learning in order to build a robust knowledge structure of basic concepts in electricity and magnetism.

Hongwei LI, Li PAN, Lu HAN et al.

The linear power flow calculation method can provide better robustness and higher efficiency for active distribution network analysis and operation regulation. In this paper, a new three-phase unbalanced linear power flow calculation method is proposed. The voltage magnitude of the three-phase power flow equation is transformed into logarithmic form under polar coordinates. And then a reasonable linear approximation is formed according to the actual characteristics of the three-phase distribution network. The proposed method avoids iterating and can directly calculate the three-phase unbalanced power flow of the radial and weak-loop distribution networks as well as the distribution networks containing PV nodes.The proposed method is tested and compared through an IEEE33 three-phase unbalanced example, and its effectiveness has been verified.

Xiaofang Zhang, Xiujuan Lin, Rui Guo et al.

To improve the acoustic radiation performance of the spherical transducer, a prestressed layer is formed in the transducer through fiber winding. The influence of the prestressed layer on the transducer is studied from the effects of the radial prestress ([Formula: see text][Formula: see text]) and acoustic impedance, respectively. First, a theoretical estimation of [Formula: see text][Formula: see text] is established with a thin shell approximation of the prestressed layer. Then, the acoustic impedance is measured to evaluate the efficiency of sound energy transmission within the prestressed layer. Further, the ideal effects of [Formula: see text][Formula: see text] on the sound radiation performances of the transducer are analyzed through finite element analysis (FEA). Finally, four spherical transducers are fabricated and tested to investigate their dependence of actual properties on the prestressed layer. The results show that with the growth of [Formula: see text][Formula: see text], the acoustic impedance of the prestressed layer grows, mitigating the enormous impedance mismatch between the piezoelectric ceramic and water, while increasing attenuation of the acoustic energy, resulting in a peak value of the maximum transmitting voltage response ([Formula: see text]) at 1.18 MPa. The maximum drive voltage increases with [Formula: see text][Formula: see text], leading to a steady growth of the maximum transmitting sound level ([Formula: see text]), with a noticeable ascend of 3.9 dB at a 3.44 MPa [Formula: see text][Formula: see text]. This is a strong credibility that the prestressed layer could improve the sound radiation performance of the spherical transducer.

Ye Li, Xuebao Li, Wei Meng et al.

Abstract PEEK (polyetheretherketone) and N2 are used in the packaging of high‐voltage power electronics as the frame material and insulation gas, respectively. The surface discharge behaviours of PEEK in N2 under positive repetitive square voltage are the main concerns for the packaging insulation design. However, the influence of N2 pressure on discharge characteristics and mechanisms has not been investigated. Herein, the optical images of streamer propagation and surface discharge current pulses of PEEK in N2 with different pressures are obtained under positive repetitive square voltage. The effects of different N2 pressures on the surface discharge initial voltage (SDIV), pulse parameters of discharge current, time lag of discharge and streamer propagation length are analysed in detail. The effects of N2 pressure on the memory effects of residual charges during surface discharge, effective ionisation rate and electron desorption rate are revealed. Furthermore, the time lag theory is used to analyse the influence of N2 pressure on the time lag of forward and backward discharge. The effects of N2 pressure on pulse parameters of discharge current, surface discharge initial voltage and streamer propagation length are also explained on the basis of the process of surface charges accumulation under different N2 pressures. The presented results can provide guidance for the packaging of press pack IGBT (insulated gate bipolar transistor) and reveal the surface discharge mechanism with different N2 pressures under positive repetitive square voltage.

Yana Taryana, Yosef Sarwanto, Wisnu Ari Adi

Ba1-xLaxFe12O19 with ion substitution La3+ (x = 0 – 0.7) has been produced via the mechanical milling technique of the solid reaction method. Considering that Ba1-xLaxFe12O19 is expected to be used as a microwave absorbent, it is necessary to characterize its structural and magnetic features. The refinement results of the X-ray diffraction (XRD) data show that a single-phase hexagonal structure (space group P63/mmc) is obtained for x = 0 and x  = 1, while for the composition of x 0.1 is multiphase. The lattice parameters and crystal volume decreased, whereas the lattice strain was found to advance with increasing La substitution in the sample. For x = 0.1, the crystallite size is constant while the lattice strain increases. Employing a scanning electron microscope (SEM), the observation of particle morphology shows that the single-phase (x = 0 and x  = 0.1) has a comparably unvarying particle size circulation, while for x 0.1, different particle shapes and sizes are found. The saturation magnetization raises while the coercivity field reduces due to the substitution of La for x = 0.1. Furthermore, for x 0.1, the saturation magnetization decreases while the coercivity field increases.