Hasil untuk "Electricity and magnetism"

Agostina Lo Giudice, Augusto Román, Laura Beatriz Steren

Interest in planar Hall effect (PHE) sensors has re-emerged in recent years due to their promising potential for a wide range of applications, particularly in biotechnology. Sensor sensitivity can be enhanced by lowering the effective anisotropy field; however, this favors magnetic domain formation during magnetization reversal, leading to hysteretic responses. Therefore, precise control of magnetic anisotropy and magnetization reversal is essential to balance sensitivity and stability in PHE sensors. In this work, we investigate the magnetic anisotropy and magnetization reversal mechanisms of Ni-Fe- and Co-Fe-based multilayers grown on various metallic buffer layers and deposited with and without an external magnetic field, in order to evaluate the effects of the buffer layers and field-assisted deposition on the resulting magnetic anisotropy. NiFe films exhibit a dominant uniaxial anisotropy mainly determined by the applied field during growth, with an anisotropy constant of approximately $3,\mathrm{kerg,cm^{-3}}$, largely independent of the buffer layer. In contrast, the magnetic anisotropy of CoFe films is dominated by the buffer layer, resulting in a biaxial magnetic response. In particular, Ag-buffered films deposited under an external magnetic field exhibit a biaxial anisotropy with values up to $14.88,\mathrm{kerg,cm^{-3}}$. The magnetization reversal mechanism of each system was deduced from the analysis of the angular dependence of the coercive field.

Hao Wang, Li Zhang, Youliang Sun et al.

ABSTRACT The internal component structure of the converter transformer plays an extremely important role in the generation and propagation of vibration noise. In order to comprehensively reveal the influence of the component structure on the vibration and noise of converter transformers, this paper conducted vibration and noise experiments on different combinations of three iron core structures, four winding structures, two oil tank structures, two foot insulation structures and three positioning structures under different frequency harmonic excitations in a semi‐anechoic chamber environment. The results show that the optimal configuration for minimising noise in converter transformers comprises the following components: an entanglement internal screen winding within the coil assembly, a 7.2 mm six‐step‐123 iron core, a cross‐shaped reinforced oil tank, bottom foot insulation, an upper eccentric circle design and lower pouring positioning.

Zhiqiang HU, Yuanyu YE, Lingang YU et al.

In order to solve the problems of increased losses and reduced power supply quality caused by unbalanced three-phase loads, an automatic equalization method for three-phase load unbalance in low-voltage stations involving active loads is proposed. Based on the high-speed carrier technology of the power Internet of Things, the meter load data of the low-voltage station area is collected, and the load data is monitored and collected in real time. A three-phase load imbalance equalization control terminal is designed and the objective function is established. The pigeon swarm algorithm is used to solve the function to achieve automatic balancing control of three-phase load imbalance in the low-voltage station area, which has good control effects.

Xue WANG, Lin LIU, Wendi LIU et al.

The power system, traditionally dominated by synchronous generators, is evolving into a new power system where virtual synchronous generators (VSGs) take the lead. This transition results in significant changes in the system's dynamic characteristics. Currently, most literature focuses on analyzing the dynamic behaviors of standalone or multi-machine grid systems based on an assumption of infinite power supply, with limited research on the dynamic characteristics of new power systems dominated entirely by VSGs. Therefore, this study first builds a model of a three-machine, nine-node system where VSGs are the primary controllers and conducts transient simulations using differential equations. Subsequently, the crisscross optimization (CSO) algorithm is employed to optimize the inertia delay in the new power system. A comparison is made between the optimized control system and the non-optimized system. The results demonstrate that the optimized system exhibits reduced oscillation amplitude and shorter adjustment times after disturbances occur. Through simulations, the validity of the conclusions is verified.

Joonhyeon Jun, Jongsung Kang, Jaehyun Park et al.

This paper tackles the low-angle target tracking problem caused by surface-reflected multipaths through successive interference cancelation (SIC) and single-tone frequency (STF) estimation. The coherent specular multipath component in the received radar signal is canceled through SIC, after which the angle-of-arrival (AoA) of the direct path is accurately estimated by applying STF estimation to the interference-suppressed signal. To further improve estimation accuracy, we develop an iterative process where SIC and STF are sequentially repeated. Drawing on the AoA of the direct path estimated using STF, a more accurate AoA of the specular path is obtained by exploiting their geometrical relationship between the two paths, which is then used to suppress the specular multipath in the received radar signal more precisely during the next SIC process. Computer simulations verify that the proposed angle estimation method using SIC and STF (AE-SICSTF) outperforms conventional angle estimation methods. Furthermore, while computational complexity analysis shows that the complexity of each iteration in AE-SICSTF is comparable to that in three-dimensional beam-domain maximum likelihood, it is also found that the former requires less than 10 iterations to converge the root mean square error performance, resulting in considerably less computing time than the refined maximum likelihood and root-MUSIC algorithms.

Jianhao Ma, Yi Liu, Jingnan Qin et al.

Polystyrene (PS) microspheres have the advantages of good stability, corrosion resistance and low density, which have a broad application prospect. In this paper, PS composite microspheres with 20% silver plating content were prepared by chemical plating method and incorporated into polydimethylsiloxane (PDMS) flexible matrix to prepare Ag@PS/PDMS flexible wave-absorbing materials. The electromagnetic parameters were adjusted to optimize the dielectric and wave-absorbing properties by varying the additional amount of Ag@PS composite microspheres in Ag@PS/PDMS composites. The X-ray diffraction (XRD) results proved the successful preparation of Ag@PS composite microspheres. The SEM and EDS images indicated that the Ag particles were attached to the external surface of PS. The presence of Ag particles in the Ag@PS composite microspheres enhances their electrical conductivity and enables the formation of a conductive network. This, in turn, improves the composites’ dielectric constant. The optimal wave-absorbing capability of the composites was achieved when the Ag@PS composite microspheres were added at a weight percentage of 50%. When the sample attains a thickness of 1.8[Formula: see text]mm, a reflection loss of at least −39.8[Formula: see text]dB is attained at 10.4[Formula: see text]GHz, along with a bandwidth of 1.6[Formula: see text]GHz (9.1–10.7[Formula: see text]GHz) for the effective absorption bandwidth (EAB). The pressure-sensitive properties of the pliable composites were investigated as well. The optimal pressure-sensitive performance of Ag@PS/PDMS composites was achieved with a 60[Formula: see text]wt.% addition of Ag@PS composite microspheres. The resistance undergoes significant changes when subjected to pressure with a sensitivity of 9.7. The results indicate that the flexible composites’ wave-absorption and pressure-sensitivity properties can be modulated by adjusting the amount of Ag@PS composite microspheres added.

Xavier Batlle, Carlos Moya, Mariona Escoda Torroellla et al.

Some of the synthesis methods and physical properties of iron-oxide based magnetic nanoparticles such as Fe3-xO4 and CoxFe3-xO4 are reviewed because of their interest in health, environmental applications, and ultra-high-density magnetic recording. Unlike high crystalline quality nanoparticles larger than a few nanometers that show bulk-like magnetic and electronic properties, nanostructures with increasing structural defects yield a progressive worsening of their general performance due to frozen magnetic disorder and local breaking of their crystalline symmetry. Thus, it is shown that single-crystal, monophasic nanoparticles do not exhibit significant surface or finite-size effects, such as spin canting, reduced saturation magnetization, high closure magnetic fields, hysteresis-loop shift or dead magnetic layer features which are mostly associated with crystallographic defective systems. Besides, the key role of the nanoparticle coating, surface anisotropy, and inter-particle interactions are discussed. Finally, the results of some single particle techniques -- magnetic force microscopy, X-ray photoemission electron microscopy, and electron magnetic chiral dichroism -- that allow studying individual nanoparticles down to sub-nanometer resolution with element, valence and magnetic selectivity, are presented. All in all, the intimate, fundamental correlation of the nanostructure (crystalline, chemical, magnetic) to the physical properties of the nanoparticles is ascertained.

Samuel Wagner, Ababil Hossain, Stephen Pancrazio et al.

Abstract Currently, no publicly available comprehensive set of specifications exists for the design of ground‐penetrating radar antennas. Specifications are presented and derived for the design of a ground‐penetrating radar antenna based on the antenna's interaction with the rest of the radar system. Typically, ground‐penetrating radar antenna engineers are given basic parameters such as gain and bandwidth to design an antenna. An antenna can be designed to meet those specifications but may not perform well in a ground‐penetrating radar imaging system. By considering the whole system, including the operation parameters, expected targets, and signal processing algorithms, we can constrain the less‐commonly considered performance aspects of an antenna to perform more reliably in a deployment. We propose quantitative specifications for the antenna's coupling, beamwidth, boresight radar cross‐section, pulse integrity, residual ringing, and front‐to‐back ratio. Meeting these antenna specifications will decrease the probability that a deficiency in the antenna design impacts the radar's image output. Finally, a summarised design equation table that will be helpful in the ground‐penetrating radar antenna community at large is offered.

Jia ZHU, Feng WANG, Yiquan LI et al.

As one of the important transformer protections, zero sequence differential protection has the advantages of high sensitivity and strong anti-interference ability. The comparison object of its protection criterion is the self-generated zero sequence current and neutral zero sequence current obtained by the sum of three phase currents on the side of the three-phase incoming line. The difference of saturation characteristics between the three phase incoming-line side CT and the neutral side NCT will cause errors of zero sequence current transmission. The zero sequence current waveform after CT transmission will produce distortion in different degrees, which leads to the generation of false differential current, and then causes the misoperation of zero sequence differential protection. To solve this problem, on the basis of an analysis of the magnitude and phase characteristics of zero sequence current on both sides after CT transmission under various working conditions, a Tanimoto similarity-based constraint scheme for transformer zero-sequence differential protection is proposed, and the effectiveness of the proposed constraint scheme is verified by simulation.

Zhirui WANG, Yuzhuo KANG, Xuan ZENG et al.

This study proposes a Synthetic Aperture Radar (SAR) aircraft detection and recognition method combined with scattering perception to address the problem of target discreteness and false alarms caused by strong background interference in SAR images. The global information is enhanced through a context-guided feature pyramid module, which suppresses strong disturbances in complex images and improves the accuracy of detection and recognition. Additionally, scatter key points are used to locate targets, and a scatter-aware detection module is designed to realize the fine correction of the regression boxes to improve target localization accuracy. This study generates and presents a high-resolution SAR-AIRcraft-1.0 dataset to verify the effectiveness of the proposed method and promote the research on SAR aircraft detection and recognition. The images in this dataset are obtained from the satellite Gaofen-3, which contains 4,368 images and 16,463 aircraft instances, covering seven aircraft categories, namely A220, A320/321, A330, ARJ21, Boeing737, Boeing787, and other. We apply the proposed method and common deep learning algorithms to the constructed dataset. The experimental results demonstrate the excellent effectiveness of our method combined with scattering perception. Furthermore, we establish benchmarks for the performance indicators of the dataset in different tasks such as SAR aircraft detection, recognition, and integrated detection and recognition.

Daniela Freyer, Melanie Pannach, Wolfgang Voigt

For geochemical calculations of solubility equilibria between Sorel phases, Mg(OH)2, and oceanic salt solutions, the polythermal THEREDA dataset (based on the HMW model at 25°C) was extended. With both models, H+ solution concentrations in equilibrium with Mg(OH)2(s) and the 3-1-8 Sorel phase at 25°C can be calculated in good agreement. In contrast, calculated OH− solution concentrations do not agree. Using the solubility constants (lg Ks) determined up to 60°C in Part I of this work, together with available solubility isotherms up to 120°C, temperature functions for the 3-1-8 phase (25°C–100°C), 2-1-4 phase (60°C–120°C), and 9-1-4 phase (100°C–120°C) were derived. In order to accurately model the OH− solution concentrations, it was necessary to implement the solution species Mg3(OH)42+ (∆RGm° temperature function) in addition to the MgOH+ already contained in the previous model. Finally, fitting Pitzer mixing coefficients for both species now allow the calculation of the solubility equilibria of Mg(OH)2(s) and the Sorel phases in agreement with the experimental data in the Mg-Cl-OH-H2O and Na-Mg-Cl-OH-H2O systems.

Yanhui XU, Yijia XU

In order to smooth the output power of wind farms and reduce the influence of wind power fluctuations on power grid, a hybrid energy storage system consisting of energy-based energy storage element electrolyzer and power-based energy storage element supercapacitor is adopted to smooth wind power fluctuations. Firstly, the energy storage output in a large number of time slots is analyzed by probability statistics, and the smoothing effect of wind power fluctuation is evaluated by the probability change of the grid-connected power fluctuation within the limit of wind power fluctuation, and the power at a given confidence level is taken as the rated power of the hybrid energy storage. On this basis, the hybrid energy storage power is decomposed by the adaptive sliding window algorithm considering the economy, and the rated capacity of the supercapacitor and the rated power of the electrolyzer are determined, so as to realize the capacity allocation which takes into account the economy and fluctuation stability effect. Secondly, based on the charging state of the supercapacitor, the rated power of the electrolytic cell and the overall power command of the energy storage system, the operation control strategy of the hybrid energy storage system is formulated. Finally, the simulations results show that this method can effectively reduce the fluctuation of wind power while realizing the power distribution and ensuring the normal operation of each energy storage module.

Xiao-ming CHEN, Xiu-chao ZHAO, Xian-ping SUN et al.

Due to the detection sensitivity provided by the high nuclear spin polarization, hyperpolarized 129Xe has been employed in animal and human magnetic resonance imaging (MRI). However, during the accumulation-thawing process of hyperpolarized 129Xe, multiple factors lead to the relaxation of spin polarization and would hinder the wider application of 129Xe. In this research, the spin relaxation mechanism of hyperpolarized 129Xe during the accumulation-thawing process is investigated by both theoretical model analysis and experimental measurements. Meanwhile, the stability of the homebuilt device for the accumulation-thawing is measured. Our results demonstrate that the thawing mode and the cold trap material significantly affect the polarization loss; the automatic device is very stable during long-term operation and shows a high degree of automation, resulting in a polarization recovery ratio of 85.6% ± 4.7%. This research greatly helps to improve the efficiency of hyperpolarized 129Xe in animal and human MRI.

Wen Li, Stewart Barnes

It is of considerable technological importance to achieve an electrical control of magnetism of sufficient magnitude. To overcome the in-plane shape anisotropy, needed is the electrical control of a perpendicular magnetic anisotropy (PMA). It is known, within a free electron model, the Rashba spin-orbit coupling provides such a control. Surprisingly, this same Rashba PMA is enhanced by two to three orders of magnitude when a periodic potential is added. Usually spin Berry phase physics reflects time dependent magnetic fields. Here it is shown, within a time independent model, such physics arises because the Rashba effective magnetic field has texture within the unit cell. Predicted are electrical controllable band-structure gaps, linear in the applied electric field $E$, that can result in a truly giant linear PMA. Also possible is a Peierls mechanism, in which the magnetisation tilts from the vertical, shifting these gaps to the Fermi level. As a consequence there are low dissipation electric field driven dynamics, an alternative to the more dissipative spin torque transfer (STT) effect. The theory requires the introduction of an intrinsic spin Berry connection $\vec A_s$, an effective vector potential, and is incompatible with current density functional theories (DFT).

Zhengdong Qi, Xinggan Zhang, Yechao Bai et al.

Abstract An approach for the synthesis of sum and difference patterns in monopulse antennas is described. The proposed approach provides a significant reduction in the complexity of the beam‐forming network that is fulfilled by reducing the number of array elements and keeping the elements at the edges of the array that share common excitations for both sum and difference modes. An iterative constrained optimisation method is used where the non‐convex lower‐bound constraints on the beam pattern are cast as an equivalent multi‐convex optimisation problem while concurrently minimising a reweighted l1‐norm of the magnitudes of the elements in the beam‐forming weight vector. Thus, better radiation performance of beam pattern (e.g. narrower beamwidth, lower peak sidelobe level), a much narrower spatial aperture and a smaller number of elements can be achieved compared with the case of uniformly spaced arrays. To compensate for array imperfection in practice, robust beam pattern constraints are derived in the optimisation stage using a worst‐case performance optimisation technique. Numerical examples show the effectiveness and advantages of the proposed synthesis approach.

Yanqing Liu, Lichun Shu, Qin Hu et al.

Abstract The flashover problem of ice‐covered insulators has seriously affected the safe operation of transmission lines. Numerous researches have shown that the high conductivity water film on the surface is determined by the conductive ions distribution in the icicle which is the key factor affecting the flashover voltage of ice‐covered insulators. In our previous work, the conductive ions distribution in the icicle has been obtained through experiments and simulation analysis. In order to calculate the conductivity of the water film, the conductive ion‐specific content at different positions in the icicle has been calculated mathematically. In addition, based on the simulation of icicle melting process, the icicle melting process is analysed, and the melting water conductivity of the icicle is calculated. Moreover, melting ice test is carried out in artificial climate chamber to verify the validity of the calculation method. The calculated results are in good agreement with the test results. The conclusion obtained here would provide theoretical basis for establishing a flashover model of ice‐covered insulators.

Xingang YANG, Peng ZHANG, Yang DU et al.

With the rapid development of the power Internet of Things, clarification of user load status are significant for improving the quality of power supply service, power price decision-making, demand-side response, and paid precise services. The classification and identification of industrial power equipment based on non-intrusive methods is faced with the challenges of poor prior knowledge of industrial loads and low sampling frequency of the used data. Using the power quality monitoring data of large industrial users, this paper proposes a classification and identification method of power equipment for industrial users based on the level of harmonic emission. Firstly, a detection method is proposed for industrial equipment switching events based on bilateral cumulative sum algorithm. Secondly, the typical characteristics of each event is extracted to construct a feature matrix for industrial user equipment, and a feature screening method with high contribution rate is proposed to reduce the number of features. A classification and identification method of power equipment for industrial users based on k-means algorithm and silhouette coefficient is proposed. The 14-day power quality monitoring data of a rolling mill user under the 10 kV voltage level in Shanghai area was used to verify the proposed method. The result proves that the proposed method has high accuracy in classification of industrial user equipment with unknown equipment conditions, and has significant practical and promotion values.

Vadym Zayets

The parametric torque presents a promising recording mechanism for MRAM, complementing Spin Transfer Torque and Spin Orbit Torque, enabling magnetization reversal in a nanomagnet using a DC electrical current. Its resonance nature allows for optimization of magnetization reversal at a lower current, presenting an opportunity for a lower recording current and, therefore, for efficient and high-performance operation in modern MRAM technology. The in-plane magnetic field generated by spin accumulation serves as the driving force behind this torque. Experimental measurements of the current-induced in-plane magnetic field in the FeB nanomagnet reveal its magnitude to be around 40 Gauss at a current density of 25 mA/$μm^2$, a value adequate for facilitating parametric magnetization reversal. The parametric torque is analytically calculated by solving the Landau-Lifshitz equation. Analytical calculations demonstrate its potential in advancing modern MRAM technology.

Zhuodong Yang, Xuebao Li, Xiangrui Meng et al.

In this study, the surface discharge current pulses of polyetheretherketone (PEEK) material under positive repetitive square voltage in a nitrogen atmosphere are measured. The influences of different voltage amplitudes and frequencies on the detail parameters of forward discharge and backward discharge current pulses are statistically analysed. The results show that as the square voltage amplitude increases, the current pulse amplitude, fall time and pulse width of both forward and backward discharge current increase, and the rise time does not change significantly. As the voltage frequency increases, current pulse amplitude, fall time and pulse width of both forward and backward discharge current decrease, and the rise time does not change significantly. Due to the independence of the discharge at different repetitive cycles, the specific discharge process in one cycle is analysed in detail to explain the influence mechanism of the voltage amplitude and frequency on the discharge current. By mean of the Richardson–Schottky and the Cavallini relaxation model, the relationship between discharge voltage ratio and surface charge, and the decay process of surface discharge are analysed. Furthermore, the influences of amplitude and frequency of the positive repetitive square voltage on the PEEK surface current pulses are explained qualitatively.