Hasil untuk "Electricity and magnetism"

Umair Hafeez Khan, Abdul Basit, Nauman Anwar Baig et al.

ABSTRACT In this paper, we propose a Double Pulse‐based Dual Coprime Frequency Diverse Array Multiple Input Multiple Output (DCFDA‐MIMO) radar for enhanced target parameter estimation, including range, angle, and Doppler. The proposed model employs an unstructured approach for parameter estimation using the recently developed DCFDA‐MIMO radar, which has garnered significant attention due to its superior target resolution compared to traditional Frequency Diverse Array MIMO (FDA‐MIMO) radar. Because most conventional designs rely on a structured approach using a single pulse, conventional FDA‐MIMO radar suffers from increased computational complexity due to multiple signal classification (MUSIC) and strong coupling between range and angle parameters. To address these challenges, we introduce an efficient, low‐complexity method that effectively reduces range‐angle coupling and improves target parameter estimation. Unlike existing techniques, the proposed approach uses the Double Pulse method, transmitting the first pulse without frequency increments to estimate the angle. In contrast, the second pulse incorporates suitable frequency increments to estimate range and Doppler separately by incorporating the estimated angle information. Monte Carlo simulations validate that the proposed DCFDA‐MIMO‐based Double Pulse method significantly improves target parameter estimation in terms of signal‐to‐noise ratio (SNR), signal‐to‐interference‐and‐noise ratio (SINR), and Cramér–Rao lower bound (CRLB) compared to existing array structures.

Xu ZHANG, Chun WANG, Yitao HU et al.

Aiming at the problem of short-term overload and long-term light-load operation of rural distribution transformers, a bi-layer optimization method for optimizing energy storage configuration and scheduling on distribution transformer side based on economic benefit evaluation is proposed in this paper. The upper model aims at the optimal economic benefit of the system, and decides the rated power and capacity of the energy storage system by Levy flying particle swarm optimization. The lower layer model, embedded in a simple calculation model of energy storage life consumption, aims at minimizing active power fluctuation on the low voltage side of distribution transformer, minimizing energy storage life consumption and optimizing dispatching economic benefits, and decides the scheduling strategy of energy storage system by commercial solver Gurobi. When constructing the economic benefit evaluation model of energy storage system on the side of distribution transformer, taking into account the influence of battery life consumption and dynamic load rate of distribution transformer on economic benefit, the investment cost model of lithium iron phosphate energy storage system based on equivalent total cycle number and the fault risk-return model of distribution transformer considering the effect of dynamic load rate on fault probability are established. The results of numerical examples show that the proposed method can improve the economy of the distribution transformer side connected to the energy storage system while ensuring the safe and stable operation of the distribution network.

Bohang ZHANG, Jun QI, Luyao XIE et al.

The new type of power system is facing the problem of increasing risk of frequency instability due to reduced inertia and decreased frequency regulation capacity. As a flexible frequency regulation technology, demand response (DR) has become an important means to solve the frequency instability of power systems. Firstly, a frequency stability analysis and load frequency control (LFC) model for demand-side resources participating in frequency regulation of interconnected power systems are established. Secondly, a distributed model predictive control (DMPC) algorithm for demand-side resources participating in frequency regulation of interconnected power systems is designed. The prediction model of DMPC controlling DR to participate in frequency regulation of interconnected power systems is derived, and then the frequency regulation controller of DMPC for interconnected power systems is designed. Finally, the impact of automatic generation control mode, DR mode, DR capacity and DR communication delay on system frequency stability is analyzed through simulation. Simulation examples show that the designed frequency regulation controller has good frequency regulation performance and DR can enhance the system’s frequency transient stability.

Yingfan Zhang, Haohuan Wang, Zhengyong Huang et al.

Abstract Surface flashover is a crucial issue for the miniaturisation of electronic facilities in military, industrial, and aerospace engineering. The oriented hexagonal boron nitride (hBN) composites, due to excellent thermal and electrical insulating properties, show a potential application in high‐voltage power equipment, while the surface flashover performance of hBN composites dependent on oriented hBN texture is rarely reported. The effects of hBN orientation and contents on the surface flashover performances of oriented hBN composites are investigated. The isothermal surface potential decay of the oriented hBN composites was also studied. It is found that the charge transportation could be adjusted by the hBN orientation, thus regulating surface flashover strength. The DC flashover voltage of the in‐plane oriented hBN composites with a thickness of 15 μm reached the maximum of 27.6 kV at the hBN loading of 20 wt%, 14.5% higher than that of the pure resin. The carrier mobility of out‐of‐plane oriented hBN composites is about three times greater than that of the in‐plane oriented composites, indicating that the charges are easily transported along the hBN basal plane. The larger carrier mobility causes charge dissipation in composites near the electrode at the hBN basal plane parallel to the axis of electrodes and inhibits the distortion of the surface electric field on the composites, thus enhancing the surface flashover. Consequently, developing oriented insulators for high‐voltage applications and enabling an optimum insulation design would be beneficial because of the compactness and high reliability of power apparatus for use in power grids.

Van-Tra Nguyen, Chi-Thanh Vu, Van-Sang Doan

This paper presents a novel method for removing noise from range-Doppler images by using a filter prior to conducting target classification using a deep neural network. Specifically, Kuan, Frost, and Lee filters are employed to eliminate speckle noise components from radar data images. Furthermore, a neural network that combines residual and inception blocks (RINet) is proposed. The RINet model is trained and tested on the RAD-DAR dataset—a collection of range-Doppler feature maps. The analysis results show that the application of a Lee filter with a window size of 7 in the RAD-DAR dataset demonstrates the most improvement in the model’s classification performance. On applying this noise filter to the dataset, the RINet model successfully classified radar targets, exhibiting a 4.51% increase in accuracy and a 14.07% decrease in loss compared to the classification results achieved for the original data. Furthermore, a comparison of the RINet model with the noise filtering solution with five other networks was conducted, the results of which show that the proposed model significantly outperforms the others.

Sagini E. Mochumbe, Youngoo Yang

While an ideal Doherty power amplifier has a linear response, the load modulated balanced amplifier (LMBA) has a compressive response under ideal conditions. This inherent nonlinear characteristic is due to the lower power contribution of the single auxiliary device as the balanced amplifier transistors approach compression. This article presents an LMBA with a two-stage control signal amplifier in place of the single auxiliary device. The idea is to preserve a high and constant gain across the high- and low-power regions by tuning the two-stage gain control signal to match the balanced amplifier gain. An optimal load trajectory can be found for a high-efficiency design by appropriately terminating the second harmonic while ensuring an optimal impedance match in all devices. At the same time, by setting an optimal output power from the auxiliary device, sufficient power is provided to linearize the response of the main power amplifier beyond the output back-off power boundary. As proof of concept, a prototype is designed and implemented. The experimental measurements demonstrate a drain efficiency of 59%–64% at maximum output power and 46%–52% at 7.5 dB output back-off power over the target frequency range of 3.3–3.8 GHz.

Wei Rao, Yuqing Wang, Lu Guo

Abstract A transmitarray adopting dual‐layer polarisation rotating (PR) elements is proposed. The element comprises a pair of perpendicularly placed C‐shaped slots etched on the two sides of a single‐layer substrate and orthogonally rotates transmission wave polarisation with regard to the incidence. By adjusting C‐shaped slot's dimension as well as mirroring the bottom layer of the element, a 360° phase shift with a high transmission magnitude is achieved. Based on the proposed unit‐cell, a dual‐layer transmitarray composed of 529 elements is designed and developed. The experimental 1‐dB gain bandwidth and peak aperture efficiency are 13% and 44% respectively. Furthermore, sidelobe level of 20 dB and cross polarisation level of 26 dB are obtained at 10 GHz. These promising properties demonstrate the superiority of the element for transmitarray designs. In addition, this element can be also a good candidate for folded transmitarray designs.

K. Karaçuha, F. T. Çelik, H. I. Helvaci

This study investigates a multi-mode pattern diverse microstrip patch antenna operating at 2.45 GHz. The study aims to have a flat top gain covering more than 900 in the elevation plane to provide equal service quality to everyone in the region of interest. In order to achieve such a crucial goal, the cavity model approach for the rectangular patches is employed. TM01 and TM02 modes are selected for the design since their corresponding radiation patterns are suitable for scanning a wide range. The superposition of boreside and conical (monopole-like) beams form a wide beam radiation pattern in elevation. Coupling between different modes is reduced by placing two radiators perpendicular to each other. In addition, the design aims to reduce both initial dimensions of the antenna by using fractalization, slotting, and perpendicular positioning techniques. These techniques reduce the original dimension of the design to less than its 60%. The simulation and experimental results reveal many similarities regarding the scattering parameters, radiation patterns, and gain. The scattering parameters, |S11| and |S22| at the operating frequency, are less than -10 dB, and the wide beam radiation pattern (more than 900) is obtained in the elevation plane.

Dong Yun Jung, Kun Sik Park, Jong Il Won et al.

This letter introduces a power limiter that limits the input power to protect the receiver when a large power enters the radio frequency receiver. When the power limiter receives a large power signal, a positive-intrinsic-negative (PIN) diode is turned on to limit the input power by lowering the impedance. We analyzed the characteristics of the power limiter according to the method of connecting the PIN diode in parallel with the input and output transmission lines of the power limiter. By embedding a PIN diode into the cavity and minimizing the length of the wire, a power limiter was designed and implemented to minimize parasitic inductance. In the S-band, the proposed power limiter’s insertion loss was below 0.5 dB, and the reflection loss characteristics were below 15 dB. Furthermore, it achieved an output P1dB of 21.8 dBm at 3.5 GHz.

Xiaolong GUO, Jiangfei ZHANG, Pengpeng KANG et al.

Under traditional control strategy, UHVDC transmission system lacks inertia and damping characteristics, so it can't effectively adjust the frequency of AC system dynamically. In order to solve this problem, a VSG (virtual synchronous generator)-based control strategy for UHVDC converter stations is proposed, in which two key parameters, including synchronous generator rotational inertia and damping coefficient, are retained. Meanwhile, the calculation method for frequency in virtual rotor is improved, and the PI controller-based secondary frequency regulation is added. Aiming at the situation of load mutation, a two-terminal VSG system model is built for simulation with Matlab/Simulink. The results show that the proposed control strategy has the characteristics of inertia and damping, which can reduce the amplitude, speed and overshoot of frequency fluctuation, suppress the voltage fluctuation of DC system, and realize isochronous control of frequency.

Tim Gehring, Santiago Eizaguirre, Qihao Jin et al.

Inductively Coupled Plasma (ICP) discharges are part of intense research. Predicting different plasma parameters, like the distribution and temperature of the present species, is of great interest for many applications. Iodine- or halide-containing plasmas in particular have an important function, for example, in the development of mercury-free UV radiation sources. Therefore, a 2D simulation model of a xenon- and iodine-containing ICP was created by using the Finite Element Method (FEM) software COMSOL Multiphysics^®. The included species and the used reactions are presented in this paper. To verify the simulation in relation to the plasma distribution, the results were compared with measurements from literature. The temperature of the lamp vessel was measured in relation to the temperature distribution and also compared with the results of the simulation. It could be shown that the simulation reproduces the plasma distribution with a maximal deviation of ≈6.5% to the measured values and that the temperature distribution in the examined area can be predicted with deviations of up to ≈24% for long vessel dimensions and ≈3% for shorter dimensions. However, despite the deviating absolute values, the general plasma behaviour is reproduced by the simulation. The simulation thus offers a fast and cost-effective method to estimate an effective geometrical range of iodine-containing ICPs.

Sangbong Jeon, Wook Jang, Ae-Kyoung Lee et al.

We investigate the whole-body average specific absorption rate (WBA-SAR) of rats under various plane wave exposure characteristics, including different polarizations, incidence angles, distances between rats, and total number of rats. Unlike many other studies, we start our SAR analysis from one rat and expand it to 27 rats facing random directions in a three-dimensional area. In a one-rat analysis, we examine how the incidence direction and polarization affect the SAR of a single rat. Moreover, we look into how various incidence polarizations behave differently after they are transmited through a rat, the information of which is then used to analyze the effect of spacing among 27 randomly arranged rats. Next, we analyze the effect on spacing of the 27 rats deployed under a 52-plane-wave exposure, which is introduced to mimic a realistic reverberation chamber (RC) environment. We show the deviation in WBA-SAR according to the distance between rats, which provides guidelines for selecting the appropriate rat distance based on the number of animals and the exposure deviation within a limited working volume in an RC for large-scale experiments.

Zhengzheng MENG, Xu LI, Yang YU et al.

Based on the analysis of the characteristics of the buffer material, this paper discusses the research status of buffer layer failure at home and abroad, and provides suggestions for future research. Summary studies show that discharge is the direct cause of ablation failure of the buffer layer, and the moisture of the cable is a necessary condition for such failures. Long-term exposure to moisture will induce the increase of the resistivity of the buffer layer and accelerate the production of high-resistance white powder. When there is an air gap between the aluminum sheath and the insulating shielding layer, the increase in resistivity of the buffer layer, the production of white powder and the impact of overvoltage will cause the local field strength in the air gap to exceed the breakdown field strength, which will eventually cause the discharge ablation. The results of the full text review summarized the causes of buffer layer failures and proposed corresponding preventive measures, which can provide as references for future research on buffer layer failures.

Zibo ZHOU, Chaowei ZHANG, Saiqiang XIA et al.

As a stable and widely covered signal resource, a Global Navigation Satellite System (GNSS) plays an important part in micro-Doppler extraction in a near field. This paper aims at the problems associated with rotor blade target recognition and proposes a novel solution based on phase compensation. First, the mathematical mechanism of flicker distribution in a time-frequency field is analyzed, and phase compensation is used to achieve the Doppler focusing, and then the blade number can be estimated. Second, according to the that the minimum delta frequency principle between the center frequency and standard frequency, the rotation velocity of the rotor blade is obtained. Next, blade lengths can be calculated through the flicker bandwidth in the time-frequency domain. Finally, the simulation experiments validate the effectiveness of the proposed method.

Xiaolong CHEN, Weishi CHEN, Yunhua RAO et al.

Flying birds and Unmanned Aerial Vehicles (UAVs) are typical “low, slow, and small” targets with low observability. The need for effective monitoring and identification of these two targets has become urgent and must be solved to ensure the safety of air routes and urban areas. There are many types of flying birds and UAVs that are characterized by low flying heights, strong maneuverability, small radar cross-sectional areas, and complicated detection environments, which are posing great challenges in target detection worldwide. “Visible (high detection ability) and clear-cut (high recognition probability)” methods and technologies must be developed that can finely describe and recognize UAVs, flying birds, and “low-slow-small” targets. This paper reviews the recent progress in research on detection and recognition technologies for rotor UAVs and flying birds in complex scenes and discusses effective detection and recognition methods for the detection of birds and drones, including echo modeling and recognition of fretting characteristics, the enhancement and extraction of maneuvering features in ubiquitous observation mode, distributed multi-view features fusion, differences in motion trajectories, and intelligent classification via deep learning. Lastly, the problems of existing research approaches are summarized, and we consider the future development prospects of target detection and recognition technologies for flying birds and UAVs in complex scenarios.

LI Xiaofeng, ZHANG Biao, YANG Xiaofeng

Spaceborne Synthetic Aperture Radar (SAR) can observe the ocean surface with high spatial resolution and wide swath under all-weather conditions, day and night. Thus, it is a crucial microwave sensor for obtaining information on sea surface wind and wave fields. This paper reviews various geophysical model functions for wind and wave retrieval and SAR applications in studies of marine atmospheric boundary layer phenomena, offshore wind energy resource development, typhoon monitoring/forecast. The use of traditional SAR and new types of interferometric and polarized SAR data in ocean research are discussed. With the advance of radar satellite technology, the constellation of SAR satellites has become a new trend in the global ocean observations. Many SAR research algorithms have become mature enough to be implemented operationally to provide sea surface wind and wave fields to the scientific communities for ocean dynamic environment monitoring.

YUN Ye, LÜ Xiaolei, FU Xikai et al.

In recent years, spaceborne Interferometric Synthetic Aperture Radar (InSAR) technology has shown increasing application potential in the field of geohazard monitoring. In this article, we first introduce the principle of InSAR technology, then systematically review the development of InSAR technology and analyze the technical characteristics and applicable scope of methods such as differential InSAR and time-series InSAR. We then discuss the application status and development trend of InSAR technology in geohazard monitoring with respect to earthquakes, landslides, hydropower projects, and ground subsidence. Finally, to guide future work in the dynamic monitoring and prevention of geohazards, we summarize the key issues and scientific problems faced by the application of InSAR to geohazard monitoring, which include atmospheric correction, complex-area deformation data acquisition, and the acquisition of multidimensional deformation data. Judging from the current applications of geological hazard monitoring, this technology is now at the point of extensive application. With the development of future spaceborne SAR satellite systems and the driving force of industry application, InSAR technology will develop into a sophisticated high-precision ground observation technology that will have a huge impact on geological hazard monitoring.

Zhenghong LI, Xiaobing DING, Baocheng FENG et al.

In the petal-shape regional distribution network, the fast power recovery cannot be realized with the traditional auto transfer system when a power failure occurs at the non-standby-switch room. To solve this problem, based on the idea of real-time sampling, real-time data exchange, real-time judge, and real-time control, a regional power grid auto transfer system is proposed in the paper based on the high-availability seamless redundancy (HSR), which can be used in various complicated regional distribution network structures. The composition, communication structure and logic control strategies of the regional power grid auto transfer system are discussed in the paper. The field application of the developed devices of the regional power grid auto transfer system shows that the system can effectively realize the rapid recovery of power supply after failure of the petal-shape distribution network.

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