Hasil untuk "Electricity and magnetism"

Zhen Li, Heng Zhang, He Gao et al.

ABSTRACT Modern high‐voltage electrical equipment operates in complex environments where surface conditions are subjected to multifaceted influences from electric fields, thermal gradients, contaminants, irradiation and other extreme environmental factors. Under high‐voltage conditions, surface flashovers frequently initiate at the gas–solid interface of insulators, jeopardising the operational reliability of industrial systems. To address flashover challenges in practical electrical equipment, this review systematically analyses the impact of environmental variables—including gaseous media, voltage waveforms, contaminants and high‐energy irradiation—on surface flashover characteristics. Subsequently, we comprehensively synthesise the mechanisms, contributing factors, suppression techniques and enhancement strategies for surface flashover in four critical equipment categories prone to this phenomenon: high pulsed power systems, spacecraft operating in vacuum environments, gas‐insulated switchgear/transmission lines (GIS/GIL) and outdoor insulators. The environmental dependencies of flashover behaviour in these systems are rigorously examined. Furthermore, to advance flashover prevention in next‐generation industrial applications, this study identifies 25 fundamental scientific questions and 25 technical questions to guide future research directions. By establishing an integrated theoretical framework and methodological foundation for engineering‐oriented flashover studies, this work provides actionable insights and mitigation approaches to enhance the surface insulation of modern industrial infrastructure.

Xiaolong CHEN, Wang YUAN, Xiaolin DU et al.

This study addresses the issue of fine-grained feature extraction and classification for Low-Slow-Small (LSS) targets, such as birds and drones, by proposing a multi-band multi-angle feature fusion classification method. First, data from five types of rotorcraft drones and bird models were collected at multiple angles using K-band and L-band frequency-modulated continuous-wave radars, forming a dataset for LSS target detection. Second, to capture the periodic vibration characteristics of the L-band target signals, empirical mode decomposition was applied to extract high-frequency features and reduce noise interference. For the K-band echo signals, short-time Fourier transform was applied to obtain high-resolution micro-Doppler features from various angles. Based on these features, a Multi-band Multi-angle Feature Fusion Network (MMFFNet) was designed, incorporating an improved convolutional long short-term memory network for temporal feature extraction, along with an attention fusion module and a multiscale feature fusion module. The proposed architecture improves target classification accuracy by integrating features from both bands and angles. Validation using a real-world dataset showed that compared with methods relying on single radar features, the proposed approach improved the classification accuracy for seven types of LSS targets by 3.1% under a high Signal-to-Noise Ratio (SNR) of 5 dB and by 12.3% under a low SNR of −3 dB.

Xiao-Hui Li, Yuan-Ming Lu, Yuan Wan

We show that an electric field can induce nonreciprocal spin wave dispersion in magnetic insulators with negligible spin-orbit coupling. The electric field controls the direction and magnitude of nonreciprocity through a nonlinear magnetoelectric effect without switching the magnetic ground state. By deriving spin space group symmetry constraints, we find only a subset of noncoplanar magnets exhibits this property, and identify a few candidates. For the example of hexagonal lattice tetrahedral antiferromagnet, our effective field theory analysis and microscopic model calculation yield results that are fully consistent with the symmetry analysis.

Christopher Heins, Zeling Xiong, Attila Kákay et al.

Present information and communication technologies are largely based on electronic devices, which suffer from heat generation and high power consumption. Alternatives like spintronics and magnonics, which harness the spin degree of freedom, offer compelling pathways to overcome these fundamental limitations of charge-based electronics. Magnonics relies on spin waves, the collective excitations of magnetic moments in magnetically ordered materials, to achieve processing and transport of information at microwave frequencies without relying on charge currents. However, efficient means for all-electrical, high-resolution, semiconductor-compatible readout of information encoded in spin waves are still missing. Here, we demonstrate the electrical detection of spin waves using a nanoscale magnetic tunnel junction (MTJ) cell fabricated in a state-of-the-art complementary metal-oxide-semiconductor (CMOS) production line. By engineering the dynamic coupling between spin waves and the magnetization state of the MTJ, we demonstrate transduction of spin-wave excitations into measurable electrical signals with high fidelity. Moreover, through these measurements, we find spectral line widths, associated with nonlinear processes, down to a few hundreds of kHz, which opens up new perspectives for spin waves as quantum transducers.

Tobias Verheugen Hvidsten, Maximilian Roithner, Fred Espen Benth et al.

Electric vehicle batteries have a proven flexibility potential which could serve as an alternative to conventional electricity storage solutions. EV batteries could support the balancing of supply and demand and the integration of variable renewable energy into the electricity system. The flexibility potential from electric vehicles, in distinction to conventional battery storage, depends on the vehicle user's willingness and opportunity to make their vehicle available for flexibility. This rate of participation is often not considered in studies, despite the impact electric vehicle flexibility could have on the electricity system. This work presents a modelling study of the Norwegian electricity system, demonstrating how a future net-zero electricity system can benefit from electric vehicles in terms of integrating renewables and balancing supply and demand, while considering the rate of participation. Our findings show electric vehicles' potential to eliminate the need for stationary battery storage with just 50% participation in vehicle-to-grid. We find that the flexibility of electric vehicles contributes to relative reductions in the total cost of the electricity system by almost 4% and 15% assuming 100% participation in flexible charging and vehicle-to-grid, respectively.

Hyun-Soo Oh, Sooyeon Jeong, Young Yun et al.

In this study, we fabricated a coplanar waveguide using a novel graphene-silver nanowire composite structure (GNCS) on a polyethylene terephthalate (PET) substrate and then investigated its radio frequency (RF) characteristics. According to the measured results, the coplanar waveguide employing GNCS exhibited a substantially lower loss of transmission line than conventional waveguides. Furthermore, compared to the conventional graphene-based coplanar waveguide, the proposed structure allowed for lower skin depth and higher conductivity, resulting from the high electric conductivity of the silver nanowire. In addition, repetitive bending tests, which were performed to investigate the electric stability of the graphene-silver nanowire, showed that the coplanar waveguide employing GNCS offered substantially better electrical stability than the conventional graphene-based coplanar waveguide. These results indicate that the graphene-silver nanowire structure is a promising candidate for application in flexible wireless communication systems. Notably, this is also the first study to investigate the RF performance and electrical stability of a graphene-silver nanowire/PET structure.

Zimin ZHU, Jinfang ZHANG, Qing CHANG et al.

Renewable energy collection and output through voltage source converter based high voltage direct current (VSC-HVDC) technology is an effective way to promote renewable energy consumption. However, the continuous increase in the penetration rate of renewable energy has led to a continuous decline in the strength of the power grid, and the traditional grid-following (GFL) converter technology can no longer meet the needs of stable system operation. In order to improve the adaptability of the weak grid of the system and meet the application scenarios of large-scale renewable energy connected to weakly-synchronized support VSC-HVDC system, this paper proposes to adopt VSG control strategy in the converter station of the sending end of the VSC-HVDC system. Firstly, a small signal mathematical model of rectifier-side control is established, and the influence of virtual impedance on system stability is studied by the root locus method. Secondly, an improved virtual synchronous generator (VSG) control algorithm for constructing virtual reactance adaptive adjustment items using electrical quantities such as alternating voltage (AC) change rate and voltage difference is proposed, which can improve the equivalent short-circuit ratio of the AC system at the sending end while ensuring that the equivalent impedance of the system is inductive, so as to improve the overall performance of the system. Finally, the effectiveness of the proposed control strategy is verified by PSCAD/EMTDC electromagnetic transient simulation.

Girdhari Chaudhary, Yongchae Jeong

This paper presents a design for a compact arbitrarily terminated port impedance tunable bandpass filter (BPF) with transmission zeros (TZs) that employs a dual-mode resonator. The proposed dual-mode resonator comprises two varactors along with series transmission lines and a shunt short-circuited stub. The resonant frequency separation of the dual-mode resonator can be adjusted by changing the length or characteristic impedance of the short-circuited stub. To achieve arbitrarily terminated port impedances, the coupling between the source/load and the dual-resonator is modified from the originally designed 50-to-50 Ω termination filter. Frequency selective characteristics are achieved by generating two TZs at the lower and upper frequencies of the passband. The location of the TZs can be changed by controlling the source-load coupling. To experimentally validate the proposed tunable BPF, three prototypes (50-to-50 Ω BPF, 25-to-50 Ω BPF, and 20 + j10-to-50 Ω BPFs) are designed and fabricated. The measurement results revealed that the center frequency can be tuned from 2.10 GHz to 3.02 GHz (920 MHz tunability), where the insertion loss varies from 1.50 to 2.5 dB.

محمد بهنام آبرحیمی, عباس عبدلی آرانی

در این مقاله، با در نظر گرفتن تأثیر میدان مغناطیسی محوری یکنواخت قوی در تانسور گذردهی الکتریکی پلاسما، میدان‌های الکترومغناطیسی و نتایج دیگری در یک موج‌بر با دیواره‌ی فلزی و با سطح مقطعی به شکل منحنی پیت هاین که حاوی پلاسمای سرد و به‌شدت مغناطیده است، با استفاده از یک تقریب مناسب تحقیق و بررسی می‌شوند. در ابتدا با معرفی موج‌بر پیت هاین، معادله‌ی موج الکترومغناطیسی در این نوع موج‌بر، با استفاده از یک تقریب مناسب و به روش جداسازی متغیرها، به‌صورت دو معادله‌ی دیفرانسیلی مجزا، ارائه می‌شود. سپس میدان‌های الکتریکی و مغناطیسی و همچنین معادله‌ی پاشندگی برای مدهای TM و TE در یک موج‌بر پیت هاین با دیواره‌ی فلزی که حاوی پلاسمای سرد به‌شدت مغناطیده است محاسبه و معادلات پاشندگی و میدان‌های به‌دست‌آمده ترسم می‌شوند. در ادامه حرکت یک الکترون تزریق‌شده به داخل این موج‌بر و تأثیر میدان مغناطیسی محوری یکنواخت قوی بر انرژی الکترون بررسی می‌شود. معادلات حرکت و انرژی الکترون در موج‌بر پلاسمایی پیت هاین و در حضور میدان مغناطیسی محوری یکنواخت قوی نوشته می‌شوند و با استفاده از روش رانگ کوتای مرتبه‌ی چهار برای مدهای TM و TE حل می‌گردد. مسیر حرکت و انرژی جنبشی الکترون تزریق‌شده به موج‌بر برای هر دو مد به‌صورت گرافیکی موردتحقیق قرارگرفته‌اند.

B. A. Rodin, B. A. Rodin, B. A. Rodin et al.

<p>Spin relaxation has been at the core of many studies since the early days of nuclear magnetic resonance (NMR) and the underlying theory worked out by its founding fathers. This Bloch–Redfield–Abraham relaxation theory has been recently reinvestigated (<span class="cit" id="xref_altparen.1"><a href="#bib1.bibx5">Bengs and Levitt</a>, <a href="#bib1.bibx5">2020</a></span>) in the perspective of Lindblad theory of quantum Markovian master equations in order to account for situations where the widely used semi-classical relaxation theory breaks down. In this article, we review the conventional approach of quantum mechanical theory of NMR relaxation and show that, under the usual assumptions, it is equivalent to the Lindblad formulation. We also comment on the debate on semi-classical versus quantum versions of spectral density functions involved in relaxation.</p>

S. Fantauzzi, L. Valletti, D. Passi et al.

This paper outlines a novel approach to design a waveguide to microstrip Finline transition, that allows a division by three of the RF power traveling inside a rectangular waveguide. The possibility of obtaining and odd power division of microwave and millimeter wave signals with such Finline transition is completely unexplored yet harbinger of great opportunities. Starting from a 3D CAD model of the structure and continuing with Electromagnetic simulations, the obtained results completely describe a transition able to achieve an almost perfect power splitting by three. Multyphisics simulations, show an intrinsic resistance to vibrations of such transition, allowing it to be installed on aircraft or satellites modules. Thanks to this achievement a total new kind of power devices will come next, exploiting this odd power division in fact, it will be possible to realize different types of microwave amplifiers, increasing the efficiency and decreasing the occupied size. At the Author’s best knowledge it is the first time a divider by three Finline transition is reported in literature.

Zhen DU, Cheng ZHANG, Yue ZHU

In order to systematically analyze the energy and material consumption characteristics of double tower double cycle desulfurization system, testing the power consumption, water consumption and limestone consumption at the exit of double tower double cycle desulfurization systems in 53 ultra-low emission units. And study the effects of inlet SO2 concentration, liquid gas ratio, pH value and Ca/S ratio on the energy and material consumption characteristics of unit mass SO2 removal. The measurement results indicate that the the energy consumption of SO2 removal accounts for 55%~80% of the total removal cost, while the power consumption of circulating slurry pump accounts for 50%~70% of the total energy consumption. The energy consumption per unit of SO2 removal in primary and secondary absorption tower decreases with the increase of inlet SO2 concentration, and the energy consumption per unit of SO2 removal in secondary absorption tower is much higher than that in primary absorption tower, The energy consumption per unit of SO2 removal in the first and second stage absorption towers decreased first and then increased with the increase of pH value. Which shows that in order to reduce the energy and material consumption per unit mass of SO2 in the double tower double cycle desulfurization system, the SO2 concentration at the inlet of the primary absorption tower should be controlled at 4 000~6 000 mg/m3, and the slurry pH value should be controlled at about 5.2; The concentration of SO2 at the inlet of secondary absorption tower should be controlled at 1200 mg/m3, and the pH value of slurry should be controlled at about 6.0.

R. Chacon, A. Leray, J. Kim et al.

We use europium doped single crystalline NaYF$_4$ nanorods for probing the electric and magnetic contributions to the local density of optical states (LDOS). Reciprocically, we determine intrinsic properties of the emitters (oscillator strength, quantum yield) by comparing their measured and simulated optical responses in front of a mirror. We first experimentally determine the specifications of the nanoprobe (orientation and oscillator strength of the electric and magnetic dipoles moments) and show significant orientation sensitivity of the branching ratios associated with electric and magnetic transitions. In a second part, we measure the modification of the LDOS in front of a gold mirror in a Drexhage's experiment. We discuss the role of the electric and magnetic LDOS on the basis of numerical simulations, taking into account the orientation of the dipolar emitters. We demonstrate that they behave like degenerated dipoles sensitive to polarized partial LDOS.

Pulak Gupta, Purbarun Dhar, Devranjan Samanta

A theoretical exploration and an analytical model for the electro-magneto-hydrodynamics (EMHD) of leaky dielectric liquid droplets, suspended in an immiscible confined fluid domain has been presented. The analytical solution for the system, under small deformation approximation, in creeping flow regime, has been put forward. Study of the droplet deformation suggests that its temporal evolution is exponential, and dependents on the electric and magnetic field interaction. Further, the direction of the applied magnetic field with respect to the electric field decides whether the contribution of magnetic forces opposes or aids the interfacial net electrical force due to the electric field. Validation of the proposed model at the asymptotic limits of vanishing magnetic field show that the model accurately reduces to the case of transient electrohydrodynamic model. We also propose a magnetic discriminating function to quantify the steady-state droplet deformation in the presence of interacting electric and magnetic fields. The change of droplets from spherical shape to prolate, and oblate spheroids, correspond to magnetic discriminating function >0 and <0 regimes, respectively. It is shown that with the aid of low magnitude magnetic field, a substantial augmentation in the deformation parameter, and the associated EMHD circulation within and around the droplet is achieved. The analysis also reveals the deformation lag and specific critical parameters that aid or suppressed this lag behaviour; discussed in terms of relevant non-dimensional parameters.

Baichen XIE, Long LU, Na DUAN

Power systems play an important role in China’s energy security strategy. It is of great significance for high-quality social and economic development to comprehensively evaluate the production efficiency of power systems and their divisions in power generation, transmission, and distribution. This article adopts the data envelopment analysis (DEA) method to analyze the production efficiency of China’s power systems from 2014 to 2017. Compared with traditional DEA models, the network DEA model employs the link variables such as the on-grid electricity and distributed electricity to model the internal connections of a power system and explore the internal factors of system inefficiency. The results show that obvious regional differences in the production efficiency exist among China’s power systems, and the new round of power system reform has promoted the power system development. The heterogeneous characteristics of the external environment lead to different development paths for power systems in various regions. The effects of the policies aiming to improve the production performance are heavily dependent on the actual situations and environment where the power system locates.

Qiang WU, Jun HAN, Ting JIN et al.

The wind turbine, photovoltaic, and cooling, heating and power load forecasts have strong random uncertainties, which increase the difficulty of dispatching and operating island microgrids. This paper studies the environmentally and economic dispatch problem of the islanded microgrid with combined cooling, heating and power. The interruptible load is incorporated into the islanded microgrid as a virtual power generation resource to participate in the system operation, while considering the economy and environmental of scheduling. Fuzzy chance constrained programming is used to deal with the uncertainties, and then the model is transformed into deterministic equivalence. A multi-objective processing method based on satisfaction indicators is used to take into account the economic goals and environmental goals. Numerical example verifies the effectiveness of the proposed model.

Tohid Shahsavarian, Xin Wu, Charles Lents et al.

Abstract The safe and reliable operation of insulation material used in key high voltage components under extreme environmental conditions represents the major concerns for manufacturers and operators of More Electric Aircrafts (MEA). Surface discharge occurring in high current carrying components in DC power system diminishes the insulation material’s performance and life, especially at high‐temperature conditions. Here, the surface discharge behaviour of two commonly used high‐temperature insulation materials, ethylene‐tetrafluoroethylene (ETFE) and polyetheretherketone (PEEK) is studied at different temperatures under ramp and DC voltages. Extracted partial discharge (PD) features are presented and the impact of voltage polarity on surface discharge propagation is discussed. Our studies reveal that, while both materials exhibit non‐linear PD behaviour with respect to their electrical conductivity, ETFE generally shows PDs with higher intensity at high temperature above 100°C with a higher possibility of surface discharge due to its lower permittivity. Overall, the PD mechanism in high‐temperature, DC voltage applications is explored, and a basis for the selection of high‐temperature PD suppressing materials is developed.

Wen-jie YANG, Jun HUANG

Solid acid is one of the most widely applied heterogeneous catalysts for industrial hydrocarbon conversion and biomass refining. It is crucial to understand the nature of solid acid such as its local structure and acidic properties. Such knowledge renders effective design of solid acid with better activity and stability for the desired reaction. Recently, solid-state nuclear magnetic resonance (SSNMR) spectroscopy has been applied as a powerful standard method for characterizing the local structure and acidic nature of solid acid in both qualitative and quantitative manners. Additionally, the applications of advanced two-dimensional SSNMR methodologies further reveal the symmetry of surface sites, spatial relationship of different sites, and thereby unmasking the structure-activity relationship. In this review, we summarize the general methods and SSNMR techniques for the routine characterization, focusing on the progresses in the understanding of local structure and acidic properties of solid acids via the application of SSNMR with or without probe molecules.

Yisheng Chai, Dashan Shang, SaeHwan Chun et al.

Transtor and memtranstor are the fourth basic linear and memory elements, which allows direct coupling of charge (q) to magnetic flux (φ) via linear and non-linear ME effects, respectively. It is found here that large variation of magnetization by electric field is realized in both linear and nonlinear hysteretic styles in a magnetoelectric Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22 single-crystal. Moreover, based on the spin current model, the underlying microscopic mechanisms for generating the two types of linear and nonlinear M vs E curves are understood as E induced changes of cone angle and sign of P respectively, establishing the charge-driven transtor and memtranstor in the Y-type hexaferrite system. This work points to a promising pathway to develop unique circuit functionalities using the magnetoelectric materials.