Hasil untuk "Electricity and magnetism"

V. Nadjari, Javad Nourinia, Changiz Ghobadi

A single-substrate-layer Frequency Selective Surface (FSS) is designed with a 1.6 mm thick FR4 substrate for triple band-stop frequency filtering applications, that are for Bluetooth, WLAN, WiMAX, and X-band. The proposed FSS unit cell consists of two polygon loops on the front side and a square loop with four annular rings attached to its corners on the backside. The offered design covers three frequency bands: 2.3-4 GHz, 5-6 GHz, and 8-12 GHz. There are three resonances at 3.3 GHz, 5.6 GHz, and 9.9 GHz. The equivalent circuit model of the proposed structure and the formulas of the LC parameters were presented. A prototype of this structure was manufactured in size of 26 cm × 26 cm and experimentally verified in the antenna and microwave laboratory. The software used for design and simulation is HFSS from Ansys, which uses the finite element method. A comparison with similar structures was performed to demonstrate the performance of the proposed structure. The advantages of the proposed filter include adequate bandwidth, simple structure, as well as small size. In addition, it is unaffected by variant angles of incidence for TE polarization and TM polarization. Furthermore, due to its symmetrical design, it shows a polarization-independent feature. Experimental results for both polarizations verify the merits of the proposed approach, as shown before in the simulation results as well.

Muhammad Rizwan Akram, Abbas Semnani

The natural source of a magnetic dipole in antennas is typically an electrically small loop, which can be utilized in conjunction with an electric dipole to realize an electrically small Huygens' antenna. However, these antennas suffer from low radiation efficiency and their theoretical directivity limit is 4.8 dBi. Magnetic dipoles with an electrical size larger than 0.5lambda are highly desirable for high-gain applications. This paper builds on the development of a magnetic dipole source that utilizes a 0.5lambda slot positioned near a printed dipole with a length twice that of the slot. Such a combination of electric and magnetic dipoles yields a highly directive radiation pattern, resulting in a higher gain than a uniformly illuminated antenna of similar size. The prototype is designed to operate at 4.5 GHz, with a directivity of up to 8.37 dBi. The analytical, numerical, and measured results agree fully. This high-gain superdirective antenna is highly desirable due to its excellent features, including being low-profile, PCB compatible, and having a low-complexity feeding topology, compared to the existing approach of the two-element end-fire array.

Matthew Reece, Tom Rudelius, Christopher Tudball

Towers of electrically and magnetically charged states in quantum gravity often exhibit two important properties. First, the ratio of the mass (or tension) of electrically charged states to magnetically charged states is of order $e^2/(4π)$, which we refer to as "co-scaling." Second, in theories of multiple gauge fields, the towers of states that exhibit co-scaling have charges that point in approximately the same direction in charge space as measured by the gauge kinetic matrix, which we refer to as "alignment." After motivating these ideas with some heuristic arguments, we examine the spectrum of BPS states in the 5d supergravity landscape arising from M-theory on a Calabi-Yau threefold. In this setting, every tower of magnetically charged strings is paired with a corresponding tower of electrically charged particles that exhibits co-scaling and rapid alignment. In particular, this motivates a sharp mathematical characterization of the magnetic infinity cone in Calabi-Yau geometry. We propose a universal conjecture about quantum gravity: towers of charged states which, in some limit in moduli space, have maximally divergent charge-to-mass ratios always have corresponding magnetic partner states exhibiting co-scaling and alignment. Co-scaling is not a general feature of extremal black hole solutions in theories of gauge fields and scalars, suggesting that it is a principle of UV complete quantum gravity. We briefly remark on possible phenomenological applications, including to axion physics.

Pingping LUO, Ao SHENG, Jikeng LIN et al.

The violent fluctuation of power load level under typhoon weather threatens the power balance of power grid. Therefore, load scenario generation under typhoon weather conditions has attracted increasing attention from power supply companies. A load scenario generation algorithm based on conditional generative adversarial network (CGAN) model for typhoon weather is proposed. Firstly, considering the fact that the typhoon samples have the characteristics of scattered landing locations, different duration periods and different grades, a load sample classification and label setting method for typhoon weather is proposed. Then, a sample expansion strategy based on conditional probability is proposed to expand the sample set to solve the problem of scarce load samples under typhoon weather. Finally, in order to further improve the actual effectiveness of the sample set, based on the idea of migration training, the load samples under normal weather are firstly used to train the CGAN, and then the typhoon sample sets are applied to train CGAN. After the model training is completed, the corresponding load scenarios can be quickly generated by inputting random noise and typhoon labels. The effectiveness and advancement of the proposed model and algorithm are verified by data set from a practical power system.

G. A. González-Sprinberg

Precise measurements of magnetic and electric dipole moments are important tests of the Standard Model and beyond Standard Model physics, particularly for the electron and the muon. However, the situation presents distinctive challenges when dealing with the tau lepton due to its very short lifetime and relatively high mass. Here, we review the theoretical predictions and experimental measurements of both the anomalous magnetic and electric dipole moments of the tau lepton. Note: Contribution to the proceedings of the 17th International Workshop on Tau Lepton Physics, Louisville, USA, 4-8 December 2023

Li‐Jie Xu, Lang Xu, Cong‐Tian Zhang et al.

Abstract Based on transmission line theory, a 4‐way wideband coupled‐line Wilkinson power divider is designed by the authors, operating from 6 to 18 GHz. It is established by using a novel manufacturing technology with 3D stacked micro‐coaxial line, realising attractive advantages of low insertion (IL) loss and compact size. The simulated result shows that the proposed power divider of 23.5 × 14.46 × 0.9 mm obtains a maximum IL of 0.42 dB over the entire operating band. Measured results are obtained by connecting this micro‐coaxial power divider with printed circuit board, showing that the proposed structure is suitable for microwave communication systems.

Houda Zhu, Qing Chen, Hongbin Li et al.

Abstract As voltage measuring devices are widely used in the high voltage power system with a primary‐secondary‐fusion structure, electronic voltage transformers are directly connected to the primary conductor and would face much more serious electromagnetic environments than general secondary equipment. As a result, they would still experience failures even when general protection measures are adopted to suppress overvoltages' amplitudes. To address this issue, an innovative method is proposed after analyses are conducted on the resonance between a transformer and an overvoltage. Within this method, an air‐cored coil is installed in a transformer to artificially shift its natural frequency and to dodge the high‐frequency dominant component of a transient overvoltage, avoiding the aforementioned resonance and suppressing the secondary overvoltage. In addition, simulations and laboratory tests are conducted to prove this method's validity.

Yunqi Xing, Bin Wang, Mingyang Wang et al.

Abstract Bisphenol F epoxy resin (EP) is often used in terminal current lead insulation of superconducting equipment because of its good insulation performance, high mechanical strength, good toughness at cryogenic temperatures, and resistance to cold shock and heat shock. However, due to the wide temperature range of 80–300 K and the strong electric field, the EP‐N2 interface is prone to surface flashover, resulting in terminal insulation failure. To improve the reliability of the current lead insulation, non‐linear conductive EP/strontium titanate (SrTiO3) composites were prepared by modification with nano filling. The changes of dielectric, surface discharge, flashover, and trap distribution characteristics of composite materials were studied, and the mechanism of SrTiO3 on the surface flashover of composite materials was analysed. The results show that the conductivity of the composite increases with the rise of SrTiO3 filling content, and the amplitude of improvement is greater under the strong electric field, showing a more significant non‐linearity. The composite has a lower trap energy level and a greater number of shallow traps compared to pure EP, which accelerates surface charge de‐trapping and reduces charge accumulation, effectively enhancing the discharge and surface flashover voltage of the composite.

Yu ZHANG, Xinchi WEI, Kaihui FENG et al.

In the context of carbon peaking and carbon neutrality goals and new power system construction, China’s distributed photovoltaic (PV) development accelerates. Areas with a high proportion of distributed PV access are prone to grid voltage rise over the limit, reverse tide equipment overload, and other problems, affecting the distribution grid carrying capacity with the distributed PV access. This paper fully considers the regulating role of independent energy storage on the distribution grid side and proposes an optimal configuration of independent energy storage and charging/discharging strategy for improving the carrying capacity of the grid with distributed PV access. Specifically, the comprehensive cost effectiveness of the independent energy storage application of the distribution grid side based on the time-series tide and two-step iteration is considered, and the independent energy storage configuration capacity and charging/discharging control strategy are scientifically and reasonably determined based on the principle of the minimum system cost. The low-voltage distribution grid of a village is selected as a case study, and the effectiveness of the independent energy storage charging and discharging control strategy proposed in this paper is simulated and analyzed by the Distribution System Analysis and Optimization Platform (DSAP).

Yi LI, Weijie XIA, Jianjiang ZHOU et al.

Single snapshot forward-looking imaging technology with high performance and resolution is crucial for enabling the development of automotive radars. However, range migration issues can limit the implementation of coherent integration methods, and improving system resolution is generally difficult due to hardware parameter limitations. Based on the Time-Division Multiplexing Multiple-Input-Multiple-Output (TDM-MIMO) forward-looking imaging systems of automotive millimeter wave radar, this paper proposes Doppler domain compensation and point-to-point echo correction measures for achieving multidomain signal decoupling. However, the accuracy of traditional single-dimension range and angle imaging is limited by the number of finite array elements and significant noise interference. Therefore, this paper proposes a multidomain joint estimation algorithm based on the Improved Bayesian Matching Pursuit (IBMP) method. The Bayesian method is based on the Bernoulli-Gaussian (BG) model, and the estimated parameters and support domain are iteratively updated in this method while adhering to the Maximum a Posteriori (MAP) criterion constraint to achieve the high-precision reconstruction of multidimensional joint signals. The final set of simulation and actual measurement results demonstrate that the proposed method can effectively solve the problem of range migration and improve the angle resolution of radar forward-looking imaging while exhibiting excellent noise robustness.

Shuwen DONG, Baozhu LIU, Junjie HU

In order to address the new challenges brought by the large-scale integration of new energy into the power system represented by wind power, a wind power grid expansion planning model considering line optimization, switching, and current limiting is proposed. First of all, from the perspective of conventional thermal power unit startup and shutdown caused by system load change, the short circuit current constraint in typical scenarios is converted into the constraint under the corresponding unit startup and shutdown status. The equivalent expression of wind farm is studied by the structural equivalence of wind farm’s power collection system, and the short circuit current constraint considering the wind power connection is introduced. Secondly, by determining the overall idea of power grid expansion planning and taking the minimum total investment as the objective function, the mixed integer linear programming model of power grid planning is established and solved that comprehensively considers the energy storage, demand-side response and short-circuit current constraints. Finally, taking IEEE-RTS 24-node system as an example, the effectiveness of the proposed method is verified by setting different cases for comparative analysis.

Shunsheng ZHANG, Shuang CHEN, Xiaoying CHEN et al.

Jamming recognition is a prerequisite for radar antijamming and actual radar deception jamming recognition; however, there is a problem of insufficient samples. To address this issue, we propose a multimodal radar active deception jamming recognition method based on small samples in this paper. This method is based on two modal information—feature parameters and time-frequency images extracted from radar signals—and utilizes prototype networks to train multimodal features. Furthermore, the model adopts the image denoising method and weighted Euclidean distance to improve the recognition performance at low signal-to-noise ratios. Thus, radar deception jamming recognition can be achieved under small sample conditions. Simulation results reveal that the proposed method achieves an average recognition accuracy of over 97% across 10 types of radar deception jamming when the jamming-to-signal ratio is 3 dB. Moreover, the test results from the simulator data verify the good generalization performance of the proposed method.

Jeahoon Cho, Jiwoong Park, Hyoungseuk Jin et al.

In this work, we propose an efficient finite-difference time-domain (FDTD) simulation technique for the electromagnetic (EM) wave analysis of the Faraday rotation angle in the ionosphere. For this purpose, we first model the physical ionosphere as a scaled-down FDTD computational domain by a space-compression factor. Next, the Faraday rotation angle calculated from the FDTD simulation is calibrated by multiplying the space-compression factor. Numerical examples demonstrate that this novel space-compression-and-calibration technique can lead to a computationally efficient FDTD simulation for the EM analysis of the Faraday rotation angle without accuracy degradation.

Weizheng CAI, Kunli GUO, Luyu LIU et al.

Aiming at solving the problem of subsynchronous oscillations (SSOs) induced by direct-drive wind turbines connected to the weak AC power grid, this paper proposes a first-order linear active disturbance rejection control (LADRC) strategy to suppress this phenomenon, thereby improving system stability. Firstly, the grid-connected mathematical model of direct-drive wind turbines is built, and the propagation mechanism of frequency disturbance components of SSOs is analyzed. On this basis, we design the first-order LADRC inner-loop current controller and optimize and tune the parameters, and the analysis indicates that the controller has a strong inhibitory effect on the frequency disturbance components of SSOs. Finally, using PSCAD/EMTDC simulation software, we build an electromagnetic transient simulation model of direct-drive wind turbines controlled by traditional PI and first-order LADRC. The results demonstrate that the proposed method can block the frequency disturbance components of SSOs and effectively suppress SSOs.

Kaiwen TAN, Limin ZHANG, Wenjun YAN et al.

This paper proposes an SEI method based on cost-sensitive learning and semisupervised generative adversarial networks to address the problem of incomplete sample labels and imbalanced data category distribution in Specific Emitter Identification (SEI), which leads to a decline in inaccuracy. Through semisupervised training, the method optimizes the network parameters of the generator and discriminator, adds a multiscale topological block to ResNet to fuse the multi-dimensional resolution features of the time-domain signal, and attributes additional labels to the generated samples to directly use the discriminator to complete the classification. Simultaneously, a cost-sensitive loss is designed to alleviate the imbalance of gradient propagation caused by the dominant samples and improve the recognition performance of the classifier on the class-imbalanced dataset. The experimental results on four types of imbalanced datasets show that in the presence of 40% unlabeled samples, the average recognition accuracy for five emitters is improved by 5.34% and 2.69%, respectively, compared with the cross-entropy loss and focus loss. This provides a new idea for solving the problem of SEI under the conditions of insufficient data labels and an unbalanced distribution of data.

Seung Mo Seo, Yeoreum Choi, Ho Lim et al.

The proposed approach achieves the reliable accuracy of synthetic aperture radar-automatic target recognition (SAR-ATR) with a simulation database. The simulation images of targets-of-interest are generated from inverse SAR using high-frequency techniques. A measurement image translation-automatic target recognition (MIT-ATR) uses two deep learning networks. The unique feature of the MIT-ATR is that the measurement images are translated to the simulation-like images by cycle generative adversarial network (CycleGAN). CycleGAN does not need to have a dataset of paired images between the measurement and simulation images. The generated simulation-like images are used as the inputs of the Visual Geometry Group (VGG) network. The VGG network is trained on a simulation database with a softmax layer of multi-classes. Five classes, including a T-72 tank, are considered in the numerical experiments. The images of each class are simulated at all azimuth angles, but the elevation angles range from 6° to 30°. The accuracy of the proposed approach is 63% better than that of the traditional method with only the VGG network. The simulation database could definitely supplement the lack of measurement data. The accuracy of MIT-ATR is properly handled by CycleGAN and the VGG network.

Biaojun LI, Haiyang CHU, Zhifa ZHUANG et al.

Since reliability test of Press-pack IGBT (PPI) still not been researched enough, based on its application in industry, A cycle aging test methods aimed at VSC-HVDC power unit are proposed. The junction temperature formulas for all test methods are obtained by analyzing promising test waveforms and thermal impedance models under the specific test conditions. Experiments results illustrate measured junction temperature waveforms of PPI that under the aging tests, and proposed methods are validated.

Mingzhe Li, Bin Cao, Yuhao Liu et al.

Abstract The lack of hydrophobicity transfer capability has restricted the applications of insulating materials in environments with heavy contamination. In this study, an epoxy resin insulating composite was prepared using a micro‐capsule system to achieve hydrophobicity transfer triggered by creepage discharge. The influence of the micro‐capsules on the electrical properties of insulating materials and the hydrophobicity of the test samples before and after the creepage discharge test was analysed. The results show that the poly(urea‐formaldehyde) micro‐capsules, which contained hydrogen silicone oil, have good morphology and thermal stability characteristics at temperatures below 222°C. Micro‐capsules have minor effects on the electrical properties of epoxy insulating materials. Further, the hydrophobicity transfer capability of the test piece was improved considerably compared with that of the pure epoxy insulating material. This study expands the application of micro‐capsule technology in the field of insulating materials and provides a reference for the development of next‐generation insulating materials.

M. V. Rudenko, N. V. Gaponenko, E. B. Chubenko et al.

Erbium-doped barium titanate (BaTiO3:Er) xerogel film with a thickness of about 500 nm was formed on the porous strontium titanate ([Formula: see text] xerogel film on Si substrate after annealing at 800[Formula: see text]C or 900[Formula: see text]C. The elaborated structures show room temperature upconversion luminescence under 980 nm excitation with the photoluminescence (PL) bands at 523, 546, 658, 800 and 830 nm corresponding to 2[Formula: see text]4[Formula: see text], 4[Formula: see text][Formula: see text], 4[Formula: see text][Formula: see text] and 4[Formula: see text]4[Formula: see text] transitions of trivalent erbium. Raman and X-ray diffraction (XRD) analysis of BaTiO3:Er\porous SrTiO3\Si structure showed the presence of perovskite phases. Its excellent up-conversion optical performance will greatly broaden its applications in perovskite solar cells and high-end anti-counterfeiting technologies.

Lennart Bours, Maria Teresa Mercaldo, Mario Cuoco et al.

We demonstrate that superconducting aluminium nano-bridges can be driven into a state with complete suppression of the critical supercurrent via electrostatic gating. Probing both in- and out-of-plane magnetic field responses in the presence of electrostatic gating can unveil the mechanisms that primarily cause the superconducting electric field effects. Remarkably, we find that a magnetic field, independently of its orientation, has only a weak influence on the critical electric field that identifies the transition from the superconducting state to a phase with vanishing critical supercurrent. This observation points to the absence of a direct coupling between the electric field and the amplitude of the superconducting order parameter or $2π$-phase slips via vortex generation. The magnetic field effect observed in the presence of electrostatic gating is described within a microscopic model where a spatially uniform inter-band $π$-phase is stabilized by the electric field. Such an intrinsic superconducting phase rearrangement can account for the suppression of the supercurrent, as well as for the weak dependence of the critical magnetic fields on the electric field.