Hasil untuk "Electricity and magnetism"

W. Panofsky, M. Phillips

E. Shire

Rongqing WANG, Jingyang XIE, Biao TIAN et al.

Interrupted Sampling Repeater Jamming (ISRJ) is a type of intra-pulse coherent jamming that can easily generate false targets resembling real ones, thus posing a severe threat to radar systems. Traditional methods for countering ISRJ techniques are relatively passive and often fail to adapt to evolving jamming techniques, leading to residual jamming effects and signal loss. To improve radar’s anti-jamming capabilities, a novel scheme integrating “jamming perception, parameter estimation, and jamming suppression” has been developed in this study. This method begins by using a bidirectional double sliding window pulse edge detector and a sliding truncated matched filter. These devices are used to extract the ISRJ components of received radar signals and accurately estimate the parameters such as sampling duration and period. The jamming components are then reconstructed and eliminated, allowing for effective target detection. Simulation experiments demonstrate that the proposed method effectively overcomes ISRJ across different modulation modes with almost no loss of signal energy. When the jamming-to-noise ratio is 9 dB, the method boosts the signal-to-jamming ratio by over 33 dB after jamming suppression, ensuring robust anti-ISRJ performance.

Murilo Eduardo Casteroba Bento

The load margin is an important index applied in power systems to inform how much the system load can be increased without causing system instability. The increasing operational uncertainties and evolution of power systems require more accurate tools at the operation center to inform an adequate system load margin. This paper proposes an optimization model to determine the parameters of a Physics-Informed Neural Network (PINN) that will be responsible for predicting the load margin of power systems. The proposed optimization model will also determine an optimal location of Phasor Measurement Units (PMUs) at system buses whose measurements will be inputs to the PINN. Physical knowledge of the power system is inserted in the PINN training stage to improve its generalization capacity. The IEEE 68-bus system and the Brazilian interconnected power system were chosen as the test systems to perform the case studies and evaluations. Three different metaheuristics called the Hiking Optimization Algorithm, Artificial Protozoa Optimizer, and Particle Swarm Optimization were applied and evaluated in the test system. The results achieved demonstrate the benefits of inserting physical knowledge in the PINN training and the optimal selection of PMUs at system buses for load margin prediction.

Guoming QIAN, Jie MENG, Haidong ZHU et al.

In order to take full advantages of the new PV-Storage power station participating in power grid multi-time scale frequency modulation while considering the operation economy. First of all, according to the characteristics of photovoltaic modules, flywheel energy storage and lithium iron phosphate energy storage, their life cycle models are established respectively, and a coordinated operation strategy is proposed to reduce energy storage battery attenuation and improve frequency modulation performance. Second, on the basis of the primary and secondary frequency modulation mechanism, the model of PV-Storage power station participating in power grid frequency modulation capacity planning is established with the maximization of the frequency modulation revenue as the optimization objective function. Finally, a simulation model of PV-Storage system is built by virtue of Matlab software. The simulation results show that, as it is guaranteed that the requirements are fully met for second-level primary frequency modulation and minute-level secondary frequency modulation, the hybrid energy storage combined with photovoltaic reserve capacity can make resource planning more reasonable and improve both the economy and reliability of frequency modulation. Moreover, the reduction of flywheel cost will allow more capacity allocation so as to increase the frequency modulation income, hence the investment return period can be shortened.

Dong Zhu, Qiang Zhao, Lixia Yang et al.

Abstract In this paper, a novel deep learning (DL) approach is developed to solve the electromagnetic inverse scattering (EMIS) problems. Many challenges, such as ill‐posedness, high computational cost, and strong non‐linearity, are encountered when solving the EMIS problems. To surmount these difficulties, a multi‐model fusion convolutional neural network architecture is proposed, termed here as Amplitude‐Phase scheme. To the best of our knowledge, it is the first time that the multi‐model fusion DL approach is employed to solve the EMIS problems. Amplitude data and phase data of the measured scattering data are applied to train the proposed scheme. Furthermore, we compare APs with three different training schemes, including Amplitude‐Only scheme, and Phase‐Only scheme, and Complex‐Value scheme. The performance of the proposed DL schemes has been validated by numerical simulations. The results demonstrate that the proposed multi‐model fusion approach outperforms other DL schemes in terms of accuracy and is able to achieve a better performance in reconstructing homogeneous and heterogeneous scatterers.

Dimitrios Kontogiannis, Dimitrios Bargiotas, Aspassia Daskalopulu et al.

Accurate electricity demand forecasting is vital to the development and evolution of smart grids as well as the reinforcement of demand side management strategies in the energy sector. Since this forecasting task requires the efficient processing of load profiles extracted from smart meters for large sets of clients, the challenges of high dimensionality often lead to the adoption of cluster-based aggregation strategies, resulting in scalable estimation models that operate on aggregate times series formed by client groups that share similar load characteristics. However, it is evident that the clustered time series exhibit different patterns that may not be processed efficiently by a single estimator or a fixed hybrid structure. Therefore, ensemble learning methods could provide an additional layer of model fusion, enabling the resulting estimator to adapt to the input series and yield better performance. In this work, we propose an adaptive ensemble member selection approach for stacking and voting regressors in the cluster-based aggregate forecasting framework that focuses on the examination of forecasting performance on peak and non-peak observations for the development of structurally flexible estimators for each cluster. The resulting ensemble models yield better overall performance when compared to the standalone estimators and our experiments indicate that member selection strategies focusing on the influence of non-peak performance lead to more performant ensemble models in this framework.

Xiao Yang, Yi Zhang, Zhuodong Yang et al.

Abstract The current continuity equation is usually applied to solve DC electric field distribution when there is inhomogeneous material conductivity due to temperature gradient or multi‐layer dielectrics. However, in the presence of charge accumulation, which may result from the process of electrode injection, impurity ionisation or charge trapping, the material conductivity is in tangled relationship with local field strength, and the current continuity equation can be hardly applied due to the ignorance of conductivity distribution. Thus, quantitative analysis on the effect of space (surface) charge for DC apparatus with inhomogeneous material conductivity has been a difficult problem, which requires a complicated physical model to solve. This paper has proposed a simple method to compute the synergetic influence of inhomogeneous conductivity and the space charge on the DC field distribution; through assigning bulk (interface) charge as functions of local material conductivity and field strength, the effect of inhomogeneous conductivity can be incorporated in Gauss' law and the space charge accumulation can be further included in the equation. The effect of space (surface) charge on electric field distribution in DC apparatus with temperature gradient as well as multiple‐layer dielectrics is simulated through the proposed method, which shows that the method has offered a convenient approach for investigating the effect of charge accumulation on DC field distribution under various insulation structure and working conditions.

Shahriar Hasan Shehab, Jiewei Feng, Nemai Karmakar et al.

Abstract In this paper, an eight‐way substrate integrated waveguide unequal power divider with an enhanced co‐phase bandwidth is presented, and demonstrated a potential application for the Ku‐band radiometer antennas. The proposed divider design is based on the −35 dB Chebyshev beam‐shaping algorithm to achieve at minimum −25 dB of antenna side‐lobe level (SLL) and high beam efficiency (>90%). Investigations on different unequal power splitting techniques are discussed, and an efficient method for the unequal power division is proposed, exhibiting improved co‐phase bandwidth and wideband matching. The proposed unequal eight‐way power divider demonstrates a wider co‐phase bandwidth of 10% within 10° phase error and the −15 dB return loss bandwidth of 36.8%. Furthermore, the proposed unequal divider is integrated with eight longitudinal slot radiators, designed at 18.7 GHz and exhibits low radiation loss (better than −1.3 dB). The antenna measurement results exhibit a symmetrical fan beam radiation pattern and satisfied the goal of −25 dB SLL, resulting high beam efficiency of 97% and gain of 13.45 dBi. Therefore, the proposed unequal power divider technique shows the potential to be utilised in the low SLL antenna array designs for an accurate brightness temperature measurement of radiometer systems. The application of this technique can be further extended to radar and satellite/wireless communications.

Saeed Barzegari, Keyvan Forooraghi, Bijan A. Arand

Abstract In the present study, a novel periodic planar leaky‐wave antenna (PLWA) was designed, simulated, and fabricated based on the substrate integrated waveguide (SIW) technology. The antenna can scan the main beam from around −60° to +20° continuously with complete suppression of open stopband (OSB) by the sweeping frequency from 9.2 to 14.1 GHz. The proposed structure was designed to have circular polarisation (CP) in the entire operating frequency range, where the broadside or centre frequency is 12.25 GHz. Antenna gain in the broadside frequency is around 13 dBi. The radiation efficiency of the structure is improved and equalised through broadside, which is around 80% in the frequency band of operation. Also, series and shunt analysis was applied to the proposed periodic PLWA in the fundamental TE10 mode. In the next step, the asymmetric was applied longitudinally and transversely to the proposed structure to achieve OSB elimination combined with circular polarised radiation simultaneously. The equivalent circuit of the proposed structure was extracted and, finally, the antenna was fabricated. Based on the results, excellent agreement was observed between the measured, modelled, and simulated results.

Bin CAO, Liqiang WANG, Yongfei ZHAO et al.

As the large-scale new energy is connected into the grid, the electromagnetic transient characteristics of traditional power grid have been greatly changed owing to the access of the massive power electronic components. Therefore, new requirements of the power grid simulation have been put forward from both the algorithm and the calculation scale. The electromagnetic transient model of Inner Mongolia power grid with new energy access is built based on PSCAD software to realize the accurate simulation of the electromagnetic transient of the whole network. Based on cluster parallel simulation technology, the problem that the computing scale is too large to be computed or the simulation efficiency is low is solved. Furthermore, a network equalization integration method based on the size of the node matrix is proposed, which reduces the occupancy rate of computing resources. The simulation results show that the cluster parallel technology can effectively improve the simulation efficiency of the new energy grid-connected electromagnetic transient model. At the same time, under the premise of ensuring the simulation speed, the proposed network equalization integration method can optimize the utilization efficiency of computing resources.

Xuan LI, Kun LIU, Xichao LIU et al.

In view of the fact that the supply voltage of power voltage transformer varies with load, this paper introduces a method of supply voltage compensation based on series compensation technology of auxiliary transformer. Taking a single-phase power supply voltage transformer with rated primary voltage of 110 / 3 kV and rated capacity 60 kV·A as an example, this paper calculates the variation rate of power supply voltage and capacity with load capacity and power factor. According to the rate of change, an automatic compensation circuit of power supply voltage is designed based on auxiliary transformer, which can realize the compensation of power supply voltage (+4.4 V, +8.8 V, +13.2 V, +17.6 V, +22 V, +26.4 and +30.8 V). The power factor cosφ=1 and cosφ=0.89 (inductive) are used to verify the power supply voltage compensation effect under different load capacities. The experimental results show that the power supply voltage change rate of the power supply voltage transformer increases from –1.8% ~ + 11.36% to –3% ~ + 0.045% after adding the automatic series compensation circuit of the auxiliary transformer, and the requirements for the quality of single-phase 220 V power supply voltage can be satisfied. The automatic series compensation technology of auxiliary transformer can be used to compensate the supply voltage of power supply voltage transformer, which solves the problem of low power factor of rural load and low supply voltage in peak load period, and can provide a guarantee for improving the voltage quality of users.

Jung-Hwan Lim, Jae Wook Lee, Taek-Kyung Lee et al.

The performance of synthetic aperture radar (SAR) antenna determines the quality of images obtained from the spaceborne SAR system, and thus, SAR antenna should be designed to satisfy the target performance of SAR system. The performance indicators of a SAR system, such as ambiguity-to-signal ratio and resolution, also depend on the SAR operation mode. Therefore, it is important to consider the operation mode when designing an SAR antenna. In this paper, we analyzed the SAR antenna’s effect on ScanSAR (scanning synthetic aperture radar) which is a representative wide-swath mode and its quadrature-polarimetric (quad-pol) mode. In addition, we confirmed that the optimal reflector antenna for the C-band quad-pol ScanSAR system can be designed by analyzing the relation between the antenna size and the system performance.

Teguh Wijaksana Isma, Milda Yuliza, Tuti Angraini et al.

Smartphones are electronic devices that are widely used in the current modern era. Ranging from children to adults are using smartphones. Lack of knowledge from smartphone users makes the use of smartphones improperly exceeding the body's limits. This makes a variety of negative impacts of using a smartphone. One way to overcome this problem is to use an electrocardiograph (ECG) sensor. The use ECG is to determine the fatigue of smartphone users based on heart rate rhythm. The sensor used as fatigue detection is the type AD8232. The result of this process is a secure or insecure condition for using a smartphone. When BPM is worth 60 <BPM <120, the condition of smartphone users is safe, whereas when BPM <60 or BPM> 120, the condition of smartphone users is unsafe. Based on the results that have been tested, the longer the use of a smartphone, the value of the BPM will sharply be reduced.

H. Marhadi, L. Lazim, N. Hermita et al.

This article reports on the implementing a four-tier test diagnostic instrument on electricity magnetism concept, which has not been defined in the literature. It is an enhanced understanding of the two-tier test substances. The four-tier diagnostic test was focused on electricity magnetism concept. It was measured to 40 elementary school students. They were correctly trained on the preceding topics. The substantial corporate of the respondents was established to have an unfortunate kind and misconceptions of the subjects tested. We have already described that the test was able to investigate and categorize students into student conception of electricity magnetism concepts. Research result with four tier tests showed scientific conception 8.85%, which was likely to have misconceptions 63.4%, and the students were lack of knowledge the concept of 25.2%, and had an error amounted to 2.55%. The elementary school students’ inclined to be unwell aware among what they diagnosed and what they do not diagnosed. It might be determined that a Four-Tier Diagnostic Test which has previously been established be able to assess elementary school students’ conception on electricity magnetism concept. The constructed test has shown effectively to identify primary students’ conception

L. Gunther

Jinfeng Lin, Xiao Wu, Cong Lin et al.

Photochromic (PC) luminescent ferroelectric materials have aroused great interest because of their potential applications in optical information memories, optical switches and bio-imaging. However, those materials are basically opaque. In this work, we prepared a PC luminescent K0.5Na0.5NbO3-based ferroelectric transparent ceramic by modifying with Eu3+, Ba2+, Ti4+ and Sr2+, which not only have good optical transmittances (∼60% at 900nm), moderate ferroelectric properties and down-conversion photoluminescence (PL) properties, but also exhibit reversible PC behavior. After the illumination by xenon lamp, the colors of the ceramics change from pale green to gray, and then reversibly recover to their initial state via thermal stimulus (200∘C for 10min). Interestingly, both the optical transmittances and PL intensities can be effectively tailored by controlling the PC reaction process. The results suggest that the ferroelectric transparent ceramics are promising for the modulation of photoenergy and the design of optoelectronic devices.

Yang Wei, Chen WeiJiang, Zhou Yuan et al.

A saturable reactor is one of the important components of converter valves in high-voltage direct current transmission systems. With the ever-increasing capacities of converter valves, the heat losses generated by saturable reactors are also increasing. Thus, a thermal–fluid mechanics coupled heat dissipation model for saturable reactors is proposed. In order to study the factors affecting the thermal dissipation in the saturable reactor, the epoxy resin insulating layers with different thermal conductivity were considered in this work. The simulation results showed that the hot spots in the saturable reactor are on the iron core and close to the pipe inlet that most of the generated heat can be extracted by a cooling pipe and that the effect of heat dissipation can be improved by raising the thermal conductivity of the epoxy resin. The thermal conductivities of the epoxy resin used in the two reactors were 0.8 and 1.2 W/mK, respectively. The time dependence of the iron core temperature was in accordance with the simulation results and the maximum temperatures of the saturable reactor were also consistent with the simulation results. By increasing the thermal conductivity of the epoxy insulation layer, the temperature of the iron core could be significantly reduced.

J. Katyal

The localized surface plasmon resonance of homo-dimer nanostructures is studied using FDTD simulations. The calculated LSPR wavelength of Au, Ag and Al nanosphere forming a homo-dimer configuration is compared and the results reveal a larger LSPR shift in Ag and Al homo-dimer than in Au homo-dimer. Taking the sensitivity of LSPR shape to the size and interparticle spacing of nanoparticle along with a surrounding refractive index, parameters like refractive index sensitivity have been determined. The spherical homo-dimer over the whole range of particle size, studied here shows the index sensitivity order as Ag>Al>Au. Hence, the use of plasmonic material towards the refractive index sensing applications is useful in this order.  The average refractive index sensitivities of Ag, Al and Au are 287.09 nm/RIU, 210.21 nm/RIU and 192.47 nm/RIU in DUV-Visible-NIR region. Apart from LSPR shift, the highly confined near-field intensity enhancement of homo-dimer nanostructures for SERS has also been studied. The interacting homo-dimer nanoparticles reveals intensity enhancements in the junction. Comparing the field enhancement for Au, Ag and Al homo-dimer nanostructure 10^8-10^9  have been theoretically predicted in DUV-UV-visible region which can be used to strongly enhance the Raman scattering of molecules.

D. Mandal, K. S. Kola, J. Tewary et al.

In this paper a pattern synthesis method based on Evolutionary Algorithm is presented. A Flat-top beam pattern has been generated from a concentric ring array of isotropic elements by finding out the optimum set of elements amplitudes and phases using Differential Evolution algorithm. The said pattern is generated in three predefined azimuth planes instate of a single phi plane and also verified for a range of azimuth plane for the same optimum excitations. The main beam is steered to an elevation angle of 30 degree with lower peak SLL and ripple. Dynamic range ratio (DRR) is also being improved by eliminating the weakly excited array elements, which simplify the design complexity of feed networks.