Hasil untuk "Electricity and magnetism"

Ma. Del Carmen Toledo-Pérez, Rodolfo Amalio Vargas-Méndez, Abraham Claudio-Sánchez et al.

In this article, a comprehensive review of electrical microgrids is presented, emphasizing their increasing importance in the context of renewable energy integration. Microgrids, capable of operating in both grid-connected and standalone modes, offer significant potential for providing energy solutions to rural and remote communities. However, the inclusion of diverse energy sources, energy storage systems (ESSs), and varying load demands introduces challenges in control and optimization. This review focuses on hybrid microgrids, analyzing their operational scenarios and exploring various optimization strategies and control approaches for efficient energy management. By synthesizing recent advancements and highlighting key trends, this article provides a detailed understanding of the current state and future directions in hybrid microgrid systems.

Jae-Gon Lee

In this paper, a dual-band circularly polarized (CP) shared-aperture microstrip patch antenna with a high frequency ratio of 4.1 is presented for S-/X-band satellite communications. The unit cell of the designed antenna is composed of a single perforated S-band trimmed patch and four X-band trimmed patches configured in a 2 × 2 array. The S- and X-band patches are interlaced, thus sharing their apertures within the same layer, which enhances isolation between the two bands and prevents the degradation of CP characteristics. The antenna was designed and optimized for the S-band frequency range of 1.9–2.05 GHz and the X-band frequency range of 7.8–9 GHz. To verify feasibility, the performance of the proposed antenna was measured in a full anechoic chamber. The measured results showed good agreement with the simulated results. The −10 dB impedance bandwidths of the S- and X-band antennas were 7.8% and 13.5%, respectively, while their measured 3-dB axial ratio bandwidths were 2% and 3.9%, respectively. Furthermore, the unit cell antenna achieved left-handed circularly polarized peak gains of 5.7 dBic at 2.02 GHz and 11.6 dBic at 8.28 GHz.

Haozheng WU, Chenguang SHI, Jianjiang ZHOU

Efficient Radio-Frequency (RF) stealth is crucial for Dual-Function Radar-Communication (DFRC) systems that detect radar stealth and con vert communication transmission. However, traditional beamforming schemes based on phased arrays and Multiple-Input Multiple-Output (MIMO) systems lack the ability to control the radiation energy in the range dimension, resulting in the facile interception of integrated transmission signals by enemy-owned passive detection systems. To address this issue, a joint transmit-receive beamforming design for Frequency Diversity Array MIMO (FDA-MIMO) DFRC systems is designed herein to achieve RF stealth. First, an integrated transmission signal model based on orthogonal waveform generation, frequency diversity modulation, and weighted transmission beamforming is constructed. The two-dimensional expression of the distance angle between the radar equivalent transmission beam pattern and the communication transmission channel is obtained through matched filtering and reception beamforming. Second, with communication information embedding and communication reachable rate as constraints, a joint optimization model for FDA-MIMO radar communication integrated transmission and reception beams for RF stealth is established. The model aims to simultaneously minimize the equivalent transmission beam power at the radar target and maximize the output signal-to-noise ratio. Finally, a joint optimization algorithm based on Weighted Mean-Square Error Minimization (WMMSE) and the Consensus Alternating Direction Method of Multiplier (C-ADMM) is proposed. Closed form expressions for each variable are derived and combined with convex optimization algorithms to achieve low-complexity solutions. The simulation results show that radar detection and communication transmission using the proposed method form a “point-to-point” pattern on the two-dimensional plane of range and angle, exhibiting good RF stealth capability. Simultaneously, this method can provide high clutter and interference suppression performance as well as a low communication bit error rate.

Jean de Dieu Nibigira, Richard Marchand

Predicting the behaviour of the Earth’s ionosphere is crucial for the ground-based and spaceborne technologies that rely on it. This paper presents a novel way of inferring ionospheric electron density profiles and electron temperature profiles using machine learning. The analysis is based on the Nearest Neighbour (NNB) and Radial Basis Function (RBF) regression models. Synthetic data sets used to train and validate these two inference models are constructed using the International Reference Ionosphere (IRI 2020) model with randomly chosen years (1987–2022), months (1–12), days (1–31), latitudes (−60 to 60°), longitudes (0, 360°), and times (0–23 h), at altitudes ranging from 95 to 600 km. The NNB and RBF models use the constructed ionosonde-like profiles to infer complete ISR-like profiles. The results show that the inference of ionospheric electron density profiles is better with the NNB model than with the RBF model, while the RBF model is better at inferring the electron temperature profiles. A major and unexpected finding of this research is the ability of the two models to infer full electron temperature profiles that are not provided by ionosondes using the same truncated electron density data set used to infer electron density profiles. NNB and RBF models generally over- or underestimate the inferred electron density and electron temperature values, especially at higher altitudes, but they tend to produce good matches at lower altitudes. Additionally, maximum absolute relative errors for electron density and temperature inferences are found at higher altitudes for both NNB and RBF models.

S. Polin, P. Laohana, Jirapat Kullapapinyokol et al.

The magneto-optical Kerr effect (MOKE) in monodomain bismuth ferrite (BiFeO3) thin films was investigated under applied electric fields and light irradiation. The field-swept MOKE measurements show that the Kerr rotation of BiFeO3 changes under applied electric fields or light irradiation. The piezoresponse force microscopy measurements found that the variation in electrical polarization at the BiFeO3 surface was similar under an applied electric field and ultraviolet irradiation, confirming that the Kerr rotation of BiFeO3 can be controlled using both electric fields and light irradiation. This paper presents a method to couple a magnetic field with an electric field or light irradiation via the Kerr angle measurements of BiFeO3, providing a concept for fabricating multifunctional devices in oxide electronics.

E. V. Glazunova, L. A. Shilkina, A. S. Chekhova et al.

The solid solutions of the (1-x)Na[Formula: see text]Bi[Formula: see text]TiO3-xNa[Formula: see text]K[Formula: see text]NbO3 system were produced by the conventional ceramic technology using mechanical activation of the synthesized product. It was found that in the (1-x)Na[Formula: see text]Bi[Formula: see text]TiO3-xNa[Formula: see text]K[Formula: see text]NbO3 system at room temperature, a number of morphotropic phase transitions occur: rhombohedral → cubic → tetragonal → monoclinic phases. The introduction of a small amount of Na[Formula: see text]K[Formula: see text]NbO3 leads to an increase in the temperature stability of the dielectric properties of ceramics. A change in the relaxor properties of the solid solutions of the (1-x)Na[Formula: see text]Bi[Formula: see text]TiO3-xNa[Formula: see text]K[Formula: see text]NbO3 system was shown. The increase in energy density and energy efficiency was found at additive 10[Formula: see text]mol.% of Na[Formula: see text]K[Formula: see text]NbO3.

Shixin Zhao, Xingbao Lyu, Aleksandr Astafiev et al.

Abstract The Gatchina discharge phenomenon holds significant promise as a laboratory model for simulating ball lightning. However, crucial aspects concerning the plasma components of the resulting afterglow remain unresolved. Notably, the measurement of the electron density, a critical parameter, has not been fully achieved thus far. In this study, microwave diagnostics and video recording were employed during a pulsed Gatchina discharge, along with synchronous measurement of discharge current and voltage. Distinct antennas were positioned at different heights to enable separate diagnosis of the discharge and the ensuing long‐lived afterglow. The findings revealed that during the active phase of the Gatchina discharge, the plasma density was substantial enough to cause reflection of an electromagnetic wave with a frequency of 20 GHz from this highly conductive object. In the afterglow, the signal experienced only a moderate weakening of 10–20 percent, facilitating the determination of the time dependence of average electron density during the afterglow's passage between the two antennas. These measurements verified the unusually slow plasma decay in the afterglow of the Gatchina discharge, suggesting the potential significance of chemi‐ionisation processes involving long‐lived (metastable) particles.

Lifang FENG, Lei HUANG, Hanfei ZHOU et al.

This paper proposes a radar signal transceiver framework that combines single-bit sampling and time division multiplexing receivers to satisfy the application requirements of low-cost lightweight radars. Firstly, this paper explains the advantages of saving the number of receivers by introducing the working principle of the framework. From the perspective of radar resource allocation, the importance of single-bit sampling in this framework was analyzed; additionally, the proposed framework can achieve better performance than a classical linear frequency modulation continuous wave radar using time and space exchange. Subsequently, the formulas for range, velocity and angle measurement were derived, along with the Cramér-Rao bound for estimating target parameters. Accordingly, the performance advantages of the proposed framework were verified, and the signal-to-noise ratio conditions for its stable operation were determined. Finally, this paper verifies the accuracy of the target acquisition principle of the proposed framework and the reliability of the performance analysis by using a velocity dimensional pairing algorithm based on single-bit two-dimensional multiple signal classification.

Haoran PAN, Hui MA, Dunfa HU et al.

Vortex Electromagnetic Waves (VEMWs) have unique wavefront phase modulation characteristics. As a new degree of freedom in the diversity of radar transmitters, the VEMW Radar (VEMWR) provides Radar Cross-Section (RCS) diversity and improves signal and information processing dimensions and performances. The detection and imaging performances of VEMWR have been verified in various radar systems. This article focuses on the applying background of forward-looking radar imaging and proposes a time-division multiplemode scanning imaging method based on a Uniform Circular Array (UCA) system with multiple transmitters and a single receiver at the UCA center. First, we establish the forward-looking VEMWR imaging mode and corresponding signal mode. Next, an improved three-Dimensional (3D) back-projection and range-Doppler algorithm is proposed, which utilizes the magnitude difference at various elevation angles of multimode VEMW, phase difference at different azimuth angles, and Doppler effect resulting from the relative motion of the radar and target to achieve 3D imaging of the target. As the elevation angle increases, the beam pattern gain of the high-mode VEMW decreases sharply due to the energy divergence of the VEMW. The proposed method can maintain stability at low or high elevation angles using the energy distribution of multiple modes in the spatial domain. Imaging results of point targets revealed that the normalized gain of target-imaging results is equivalent either at low or high elevation angles within the multimode VEMW field of view. The proposed method is validated through experiments with an aircraft target. Based on the imaging results, it is verified that the proposed method can accurately reconstruct the 3D structure of complex targets.

Zifan DONG, Jieshuai REN, Jiangang YIN et al.

Due to the breakdown of the test-side fracture during the non-outage voltage-withstand test, the double-fracture disconnect switch (DDS) with a common chamber structure has been exposed to the risk of affecting the insulation performance of the operating-side fracture. Therefore, it is necessary to study the electric field distribution and breakdown characteristics of the DSS during the design phase. In this paper, the newly developed 110 kV three-phase common box type GIS DDS was taken as an example. The finite element method was employed to simulate the electric field, as well as to obtain the internal electric field strength distribution during non-outage voltage-withstand test at the actual site. Based on the electric field calculation results and the breakdown criteria deduced by Thomson discharge theory, the breakdown characteristics of the two fractures were studied during non-outage voltage-withstand test. It was proven that the breakdown of the test-side fracture would not affect the insulation performance of the operating-side in the non-outage voltage-withstand testing process of the DDS. The results provide theoretical support for non-outage expansion and on-site insulation test during the second-phase expansion, and also provide a more detailed theoretical basis for insulation verification in the future development of the next-generation DDS equipment.

Zhongtao QIU, Yanming JIN, Shenzhi XU

Electricity emission factors are widely used in carbon accounting of different subjects such as industries, enterprises and products. Due to the different resource endowments in China, the differences of regional power emission factors are more significant. The use of national, regional and provincial emission factors will have greater impacts on the indirect carbon accounting of industrial enterprises and products. It directly affects the provincial "double carbon" indicator assessment, the payment of tariffs on the export of energy-consuming products and the costs of compliance in the domestic carbon market. This study takes the electrolytic aluminum industry as an example to measure the impacts of the selection of electricity emission factors on the carbon accounting of products in energy-consuming industries. The results show that the selection of electricity emission factors needs to be tailored to the application scenarios of the accounting subject. From the perspective of promoting fairness, the national carbon emissions trading market should adopt the national average electricity emission factor. While assessing the carbon emission intensity of provincial and sub-provincial administrative regions, compiling greenhouse gas inventories of provincial and sub-provincial administrative regions, and disclosing the voluntary greenhouse gas emission reports of enterprises, priority should be given to adopting the average emission factor of electricity corresponding to the provincial power grids.

DONG Hongchun, ZHANG Zhilan, WANG Ning et al.

Recently, multiple-cross polarization (multiCP) has attracted much interest owing to its favorable performance as a solid-state nuclear magnetic resonance quantitative method. Relating investigations revealed that the setup of multiCP parameters relies on the properties of the samples. Diverse types of samples require different parameters. To improve the tolerance to sample properties, an improved method named MLGCP-1 was proposed in this work, which employed Lee-Goldburg cross polarization technique. L-alanine, L-valine and their mixtures were chosen as model samples to evaluate the performance of MLGCP-1 method. multiCP experiments were also conducted for comparison. Based on the test of molecular group ratio, it was revealed that the range of contact time tp of MLGCP-1 was larger than that of multiCP, which improved from 1.0~1.3 ms to 0.8~2.0 ms. Moreover, according to the study of L-valine and mixtures, it was revealed that the range of tp was influenced by the difference of cross relaxation time TCH. Large TCH difference limited tp range for quantification. This manner was in accordance with multiCP. However, the tp range of MLGCP-1 was markedly enlarged in comparison with multiCP, presenting higher tolerance to the sample properties.

D. Sezer, D. Dai, T. F. Prisner

<p>In spite of its name, the solid effect of dynamic nuclear polarization (DNP) is also operative in viscous liquids, where the dipolar interaction between the polarized nuclear spins and the polarizing electrons is not completely averaged out by molecular diffusion on the timescale of the electronic spin–spin relaxation time. Under such slow-motional conditions, it is likely that the tumbling of the polarizing agent is similarly too slow to efficiently average the anisotropies of its magnetic tensors on the timescale of the electronic <span class="inline-formula"><i>T</i>₂</span>. Here we extend our previous analysis of the solid effect in liquids to account for the effect of <span class="inline-formula"><i>g</i></span>-tensor anisotropy at high magnetic fields. Building directly on the mathematical treatment of slow tumbling in electron spin resonance <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx14">Freed et al.</a>, <a href="#bib1.bibx14">1971</a>)</span>, we calculate solid-effect DNP enhancements in the presence of both translational diffusion of the liquid molecules and rotational diffusion of the polarizing agent. To illustrate the formalism, we analyze high-field (9.4 T) DNP enhancement profiles from nitroxide-labeled lipids in fluid lipid bilayers. By properly accounting for power broadening and motional broadening, we successfully decompose the measured DNP enhancements into their separate contributions from the solid and Overhauser effects.</p>

Takafumi D. Yamamoto, Pedro Baptista de Castro, Kensei Terashima et al.

We investigate the magnetic, thermal, and magnetocaloric properties of the intermetallic HoAl$_{3}$ compounds with two different crystal structures. The room-temperature equilibrium trigonal phase HoAl$_{3}$ undergoes an antiferromagnetic (AFM) transition at the Neel temperature $T^{\rm tri}_{\rm N} =$ 9.8 K. The AFM ordering of the compound is strong against the magnetic field, so that inverse magnetocaloric effect (MCE) is found even under a magnetic field change of 0-50 kOe. The high-pressure cubic phase HoAl3, prepared by a rapid-solidification process, is antiferromagnetically ordered below $T^{\rm cub}_{\rm N} =$ 15 K. Magnetic and specific heat measurements reveal that this long-range AFM state becomes unstable as the temperature drops and then it is replaced by a magnetic glassy state below a spin freezing temperature $T_{\rm f} =$ 11 K. The successive changes in magnetic state result in complicated temperature and field dependence of the MCE at low temperatures.

D. S. Aldar

For the efficient utilization of electromagnetic radio spectrum cognitive radio communication system is employed, which deals with the spectrum scarcity. An efficient antenna is essential for the appropriate selection of the available frequencies. This paper presents the design and implementation of frequency reconfigurable antenna for cognitive radio applications. Reconfigurable inverted U-shape microstrip patch antenna feeding by 50 W microstrip line is designed and implemented. The designed and implemented antenna applied for switching frequency between 3.25 GHz to 4.1 GHz by choosing a specific sub-band from the specified wideband.  The frequency reconfiguration was achieved by using twelve PIN diode switches by placing them on the slotted ground plane of the antenna. The PIN diodes were organized in such a way as to alter antenna bandwidth and to shift the operating band. The switching of PIN diodes controlled using the microcontroller to select the appropriate frequency. The performance of the simulated and fabricated antenna is investigated using different parameters.

Guozhu ZHANG, Juntai ZHANG, Yu WEN et al.

A fluegas waste heat and water recovery system for the coal-fired power plant is studied in this paper. Based on the material, energy balance and equivalent heat drop method, the water-saving and coal-saving capacity of the system were calculated. Off-design models of the system were developed, influences of environmental temperature and control strategy on system performance and state parameters were evaluated. Results show that the water-saving potential of the system is 15.34 kg/s under the design condition, and the energy-saving potential is 2.75 g/(kW·h). When the ambient temperature changes, the temperature of some state points of the system will decrease with the ambient temperature. The coal saving of the low-temperature economizer will be reduced to 1.44 g/(kW·h) when the ambient temperature is –20°C. To prevent low-temperature corrosion of the system, the operation strategy was proposed, the fluegas temperature entering the electrostatic precipitator is increased to 90°C, which can ensure the safe operation of the system. However, the coal saving of the low-temperature economizer is lower than that of the unadjusted by 0.2 g/(kW·h).

J. Maxwell

Lingxi MA, Xueqian FU

Under the background of vigorously developing energy internet and building facility agriculture in China, meteorology is an important factor affecting the seasonality of agricultural power load side and the uncertainty of agricultural new energy power generation side. In order to provide new ideas for the mutual promotion of new energy development and agricultural development, it is necessary to study the agricultural energy internet (AEI) of agriculture-meteorology-energy coupling. Based on an investigation of the research status of energy meteorology, agrometeorology and agricultural energy internet, the coupling mechanism of agriculture, energy and meteorology is summarized. The impact of their coupling is studied. The application scenarios of important technologies for dealing with the impact of energy meteorology and agrometeorology are elaborated under the framework of agricultural energy internet system. And the agricultural energy internet of agriculture-meteorology-energy coupling is analyzed from three levels. The results of this paper can provide a reference for the future research of agricultural energy internet.