Hasil untuk "Electricity and magnetism"

Yulong Liu, Hongcheng Zhou, Tianhao Han et al.

This study introduces a high-sensitivity magnetoelectric (ME) sensor featuring a novel multi-electrode, series-connected configuration for ultra-weak magnetic field detection. The sensor design integrates segmented electrodes on a PZT-5H piezoelectric layer, connected in series to allow constructive voltage accumulation through serial connection. A comprehensive theoretical framework is developed to derive the ME voltage coefficient (MEVC) and analyze the sensor’s electromechanical behavior. Theoretical predictions are verified through finite element simulations and experimental measurements. Results show that the MEVC increases significantly with the number of electrode pairs, reaching up to 41.67[Formula: see text]V/Oe, compared to 15.72[Formula: see text]V/Oe for a single-electrode configuration. The sensor’s limit of detection (LOD) has been reduced from 940[Formula: see text]fT to 234[Formula: see text]fT without enlarging the sensor volume. Moreover, the mechanical quality factor increases by 1.8 times. The equivalent magnetic noise decreased to 37.14[Formula: see text]fT/Hz[Formula: see text] in the four-electrode configuration. These results demonstrate that the proposed sensor design not only improves sensitivity and noise performance but also retains compactness and low power operation, making it a promising candidate for applications in biomagnetic imaging and low-field magnetic sensing.

Gian Carlo Montanari, Sukesh Babu Myneni, Grazia Berardi et al.

ABSTRACT This paper focuses on the energisation of high voltage DC (HVDC) and medium voltage DC (MVDC) insulation systems, referring mainly to cables for both theoretical development and validation testing. Cable system energisation can be frequent during its lifetime, and it can possibly be affected by partial discharges (PD), because of manufacturing, laying, ageing, interfaces or structural cavities (as butt gaps). A theory‐driven and measurement‐based procedure is presented in this paper, having the purpose to minimise PD inception risk. This procedure is based on stepwise voltage application during cable energisation. The fundamental idea behind the proposed approach stems from considering that the jump voltage is the trigger of PD occurrence. Indeed, the jump voltage, and the consequent electric field variation, directly relates to AC PD inception voltage (PDIVAC). In addition, the electric field distribution in an insulation system is driven by insulation permittivity (capacitance) during voltage transients, and by conductivity in DC, thus the PDIVAC is generally smaller than DC PD inception voltage (PDIVDC). Hence, energising a DC cable by an initial step lower than PDIVAC, and then increasing the voltage in steps smaller than PDIVAC, would minimise the risk of PD inception during transients and the relevant degradation rate. However, this does not change, the risk of occurrence (if any) of low‐repetition partial discharges at DC steady state. Effectiveness of the proposed technique is proved by the help of tests performed on cables with artificial surface and internal defects. It is shown that compared with the conventional energisation consisting of rapidly increasing voltage, the stepwise approach can reduce the risk of PD inception and related extrinsic ageing, even for the steady state voltages larger than PDIVDC.

Xupeng SONG, Xiaoyang YANG, Zhengzhen FAN

During the fault ride-through process of the doubly-fed wind farms, the short-circuit current provided by the wind farm side exhibits frequency deviation, which leads to errors in the Fourier algorithm based phasor extraction. Additionally, the second harmonic restraint element may act incorrectly, leading to longterm blockage of the differential protection. This paper proposes a novel time-domain protection scheme based on the characteristics of the current synthesis vector trajectory. Based on the intrinsic differences between internal faults and external faults of transformers, two current synthesis vectors are constructed accordingly, and corresponding protection schemes are designed according to the trajectory characteristics of each synthesis vector. A simulation model of the control and protection of the delivery system of doubly-fed wind farms is constructed in PSCAD/EMTDC. Experimental results show that the proposed scheme can identify various internal faults and is not affected by the interference of magnetizing inrush current, current transformer (CT) saturation accompanying external faults and CT measurement errors accompanying external faults. The proposed scheme can operate in 15ms at the fastest and the average operation time is less than a fundamental frequency cycle.

Xutao Han, Haotian Wang, Jie Cui et al.

Abstract Gas‐insulated switchgear (GIS) plays a critical role in ensuring the reliability of power systems, but partial discharge (PD) is a primary cause of failures within GIS equipment. Traditional PD diagnostic methods rely heavily on laboratory data, which differ significantly from that under the complex conditions of field data, leading to a marked drop in recognition accuracy when they are applied to field PD diagnosis. This study addresses the challenge by integrating field data into the training process, utilising a deep transfer learning approach that combines laboratory and field data to improve diagnostic accuracy for GIS PD. The research collected PD data from laboratory models representing five defect types and field data gathered from operational GIS equipment. A deep residual network (ResNet50) was pretrained using laboratory data and fine‐tuned with field data through deep transfer learning to optimise the recognition of PD in field conditions. The results show that the proposed model achieves a significantly higher recognition accuracy (93.7%) for field data compared to traditional methods (60%–70%). The integration of deep transfer learning ensures that both low‐dimensional general features from laboratory data and high‐dimensional specific features from field data are effectively utilised. This research significantly contributes to improving the diagnostic accuracy of PD in GIS under field conditions, providing a robust method for defect detection in operational equipment.

Anurag Yadav, Anuj Kumar

We report here the structural, micro-structural/morphological and detailed magnetic properties of RECrO3 (RE = La, Nd, Sm, Eu and Gd) Orthocromites. A series of RECrO3 (RE = La, Nd, Sm, Eu and Gd) Orthocromites polycrystalline samples with uniform particle size were synthesized via standard solid-state reaction method. LaCrO3 (LCO), NdCrO3 (NCO), SmCrO3(SCO), and EuCrO3 (ECO) crystallizes in single phase of orthorhombic structure with Pnma (No.62) space group while GdCrO3 (GCO) found to crystallize in orthorhombic phase with Pbnm space group. SEM images confirms the systematic growth of all studied samples grain growth takes place during the sintering process and images shows the polyhedral shape with varying average grain size ranging from approximately 1.0μm to 3μm confirm the bulk synthesis of studied RECrO3. Lowest average grain size (~ 1.1μm) was observed for LaCrO3 and maximum (~ 2.8μm) for EuCrO3. The shapes of the grain size changes because of crystal lattice distortion induced by various rare earths (La, Nd, Sm, Eu and Gd) at A site. Energy dispersive X-ray Analysis (EDAX) reveals the elements confirmation in different studied RECrO3 samples. Within the detection limit of EDAX no impurity elements were observed in different as synthesized RECrO3 samples. Temperature dependent DC magnetization (M-T) studies showed an antiferromagnetic transition (TN) attributed to Cr3+ spins in all samples at different temperature. At low temperature spin-reorientation (TSR) of rare earth ion was also observed in NCO, SCO at around 50K and the same is observed at around 30K in ECO and the same was missing in GCO because of large moment of Gd3+ ions attributed by ground state spectroscopic term 8S7/2 by external applied magnetic field. The magnetization versus applied magnetic field (M-H) loops exhibited ferromagnetic like behavior at 10K and 100K and paramagnetic at 300K for GCO.

Shalaka A. Kamble, Sanket Jangale, Somnath Bhopale et al.

Thermal plasma is one of the upcoming powerful tools used for materials processing. It covers a wide range of technological applications such as synthesis of various refractory ceramic materials, metals and alloys, deposition of coatings, high temperature processing of materials as well as disintegration of waste materials. Representative technologically important material systems viz rare earth hexaboride (e.g. GdB6) and carbonaceous materials are focus of the present manuscript. Both the material systems have been processed using DC thermal plasma route and characterized thoroughly for structural, morphological, surface properties using XRD, TEM, XPS respectively. Morphology of GdB6 has been tailored by varying plasma parameters during synthesis. Further, these GdB6 powder were investigated for electron emission performance using Field Electron Emission and maximum current density of 0.5 mA/cm2 was noted for the nanocrystalline GdB6 sample. Feasibility of thermal plasmas for production of nanocrystalline GdB6 and processing of a bio-waste to obtain technologically important carbonaceous materials has also been explored.

S. K. H. Auluck, R. Verma, R. S. Rawat

This paper explores a recently proposed scalable z-pinch-based space propulsion engine in greater detail. This concept involves a “modified plasma focus with a tapered anode that transports current from a pulsed power source to a consumable portion of the anode in the form of a hypodermic needle tube continuously extruded along the axis of the device”. This tube is filled with a gas at a high pressure and also optionally with an axial magnetic field. The current enters the metal tube through its contact with the anode and returns to the cathode via the plasma sliding over its outer wall. The resulting rapid electrical explosion of the metal tube partially transfers current to a snowplough shock in the fill gas. Both the metal plasma and the fill gas form axisymmetric converging shells. Their interaction forms a hot and dense plasma of the fill gas surrounded by the metal plasma. Its ejection along the axis provides the impulse needed for propulsion. In a nonnuclear version, the fill gas could be xenon or hydrogen. Its unique energy density scaling could potentially lead to a neutron-deficient nuclear fusion drive based on the proton-boron avalanche fusion reaction by lining the tube with solid decaborane. In order to explore the inherent potential of this idea as a scalable space propulsion engine, this paper discusses its theoretical foundations and outlines the first iteration of a conceptual engineering design study for a proof-of-concept experiment based on the UNU-ICTP Plasma Focus facility at the Nanyang Technological University, Singapore.

Junying WU, Xin LU, Hong LIU et al.

To improve the prediction accuracy of multi-region power load, an ultra-short-term multi-region power load forecasting model based on Spearman-GCN-GRU is proposed with focus on the spatial-temporal correlation analysis of multi-region power data. Firstly, the Spearman correlation coefficient is used to analyze the spatial-temporal correlation of power load in different regions and construct the Spearman adjacency matrix. And then, the graph convolutional network (GCN) and gated recurrent unit (GRU) are used to respectively extract the spatial and temporal features from the data. Finally, the multilayer perceptron (MLP) is used to decode and output the prediction results. Through comparison with the distance adjacency matrix-based models, the Spearman-GCN-GRU model is proved to be feasible. In terms of prediction accuracy, the Spearman-GCN-GRU model are optimal in common evaluation indexes compared with traditional statistical models and neural network models. Specifically, in terms of the root mean square error (RMSE), the Spearman-GCN-GRU model exhibits a respective decrease of 13.90%, 11.66%, and 8.36% compared to the GRU, GCN and deep neural network (DNN) models, demonstrating its superior predictive performance.

Hanning SU, Jiameng PAN, Qinglong BAO et al.

Interrupted Sampling Repeater Jamming (ISRJ) falls within the category of intrapulse coherent deception interference. ISRJ employs the principle of undersampling to engender multiple spurious target peaks on the range profile, thereby disrupting the detection and tracking of genuine targets. To address this challenge, this study introduces a novel method grounded in the waveform domain to mitigate ISRJ before matched filtering. First, considering the partial matching attributes of ISRJ, an expanded domain, specifically the waveform domain, is incorporated into the matched filtering. This augmentation enables the investigation of local features within the interference signals and components of authentic target echo signals. Moreover, adaptive threshold functions are defined for each waveform domain. Subsequently, the introduction of the Kalman filter enables the state estimation of waveform domain signals. Additionally, valid and invalid integral elements are discriminated within the waveform domain signals via adaptive threshold detection, and a state space estimation is formulated, specifically concerning the valid integral elements. In conclusion, by suppressing the invalid integral elements within the waveform domain signals, the proposed approach simultaneously supplements the estimated state space of valid integral elements with their corresponding length components. This preservation of residual valid integral elements, coupled with integration operation, yields a range profile outcome devoid of deceptive interference artifacts. Importantly, the approach proposed herein operates independently of any prior information regarding the interference device parameters, thereby substantially reducing the effect of ISRJ. Simulation experiments illustrate that, in comparison with traditional methodologies, the method proposed in this study exhibits remarkably superior resistance against the ISRJ interference challenges.

Bogdan R. Bułka

We simulated the radiative response of the cavity quantum electrodynamics (QED) inductively coupled to the ring pierced by magnetic flux, and analyzed its spectral dependence to get insight into persistent current dynamics. Current fluctuations in the ring induce changes in the microwave resonator: shifting the resonant frequency and changing its damping. We use the linear response theory and calculate the current response function by means of the Green function technique. Our model contains two quantum dots which divide the ring into two arms with different electron transfers. There are two opposite (symmetric and asymmetric) components of the persistent current, which interplay can be observed in the response functions. The resonator reflectance shows characteristic shifts in the dispersive regime and avoided crossings at the resonance points. The magnitude of the resonator frequency shift is greater for coupling to the arm with higher transparency. Fluctuations of the symmetric component of the persistent current are relevant for a wide range of the Aharovov-Bohm phase $φ$, while the asymmetric component becomes dominant close to $φ\approx π$ (when the total persistent current changes its orientation)

J. E. Hirsch, F. Marsiglio

In Nat Commun 13, 3194 (2022) [1], Minkov et al. reported magnetization measurements on hydrides under pressure that claimed to find a diamagnetic signal below a critical temperature demonstrating the existence of superconductivity. Here we present an analysis of raw data recently released [2] by the authors of [1] that shows that the measured data do not support their claim that the samples exhibit a diamagnetic response indicative of superconductivity. We also point out that Ref. [1] in its original form omitted essential information that resulted in presentation of a distorted picture of reality, and that important information on transformations performed on measured data remains undisclosed. Our analysis also calls into question the conclusions of Minkov et al's trapped flux experiments reported in Nat. Phys. (2023) [3] as supporting superconductivity in these materials. This work together with earlier work implies that there is no magnetic evidence for the existence of high-temperature superconductivity in hydrides under pressure.

Jiahang SUN, Xiaohua WANG, Jingguang HUANG et al.

In a high proportion of new energy islanded microgrids, the reduction in the proportion of conventional synchronous generator (SG) will lead to a gradual decrease in their overall inertia. The conventional control strategy cannot effectively coregulate the frequency and voltage in microgrid under low inertia conditions. To simultaneously improve the dynamic stability of the frequency and voltage in the islanded microgrid, this paper proposes a model predictive control (MPC) based frequency-voltage control strategy for energy storage virtual synchronous generator (VSG). By developing a predictive model of VSG, a cost function of frequency and power is designed, and the power reference value of VSG is dynamically corrected after calculating the required active and reactive power increments. Considering that the interaction between SG and VSG reduces the transient voltage stability of the system, the voltage control loop is improved by reducing the angular difference between SG and VSG during transients, and the reactive power reference value is further adjusted. The dynamic stability control of the system frequency and voltage is achieved based on the power reference value. Finally, the simulation results verify the effectiveness of the strategy and the superiority.

Yan Lu, Yunlong Wang, Linghan Zhu et al.

Single magnetic molecules may be the smallest functional magnets. An electric-field controllable spin state of magnetic molecules is of fundamental importance for applications while its realization remains challenging. To date the observed spin-electric interaction based on spin-orbit coupling or spin dipole coupling is useful to tune fine spin structures but too weak to flip the spin state. In this work, we propose a new mechanism to realize enhanced spin-electric coupling and flip the spin states by tuning the spin superexchange between local spins. Using first-principles calculations and Heisenberg Hamiltonian, we demonstrate this effect in a family of magnetic molecules, transition metallic Porphyrins. We show that their d-π and π-π spin superexchange couplings are determined by the relative energies of d and π electronic states, which are sensitive to the applied electric field. Therefore, applying electric field can tune a wide range of magnetic ground states, including ferromagnetic, ferrimagnetic, and antiferromagnetic configurations. This spin-electric coupling may provide a new approach for designing and controlling molecular spintronics.

Avishek Singh, Jayita Chakraborty, Nirmal Ganguli

We investigate the electronic structure and magnetic properties of a $J_\text{eff} = 1/2$ iridate Ca$_4$IrO$_6$ and the implications of doping electrons and holes using ab initio density functional theory. Our calculations considering spin-orbit interaction reveal that although the Mott-insulating parent compound transforms into a conductor upon doping, antiferromagnetism sustains in the doped system, albeit with a grossly noncollinear arrangement of the spins. We find a strong spin-orbit interaction and magneto-crystalline anisotropy, causing frustration in the system, possibly leading to the highly noncollinear arrangement of spins upon non-magnetic doping. Our results may be important from the viewpoint of spintronics using iridates or other $5d$ materials.

Andrea Droghetti

The understanding of the Physics underlying the performances of organic spin-valve devices is still incomplete. According to some recent models, spin transport takes place in an impurity band inside the fundamental gap of organic semiconductors. This seems to be confirmed by recent experiments performed with La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/AlO$_x$/Co devices. The reported results suggest a possible correlation between the magnetoresistance and the variable oxygen doping in the Alq$_3$ spacer. In this paper we investigate by means of first-principles calculations the electronic and magnetic properties of O$_2$ molecules and ions in Alq$_3$ films to establish whether oxygen plays any important role for spin transport in La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/AlO$_x$/Co devices. The conclusion is that it does not. In fact, we show that O$_2$ molecules do not form an impurity band and there is no magnetic interaction between them. In contrast, we suggest that spin-transport may be enabled by the direct exchange coupling between Alq$_3^-$ ions.

Marco Landini, Giovanni Mazzanti, Riccardo Mandrioli

The verification of the limits of the population’s exposure to the magnetic field generated by double-circuit power lines from field measurements carried out on site is not trivial. It requires knowledge of the power line current instant values during the measurement period, the determination of the relationship between current and field at the measurement points (made more complex by the double-circuit overhead line configuration) and the use of that relationship to extrapolate the field values. Nevertheless, the verification of exposure limits for double-circuit power lines from on-site measurements is often conducted with rough, or not particularly stringent, procedures. A practical and straightforward procedure of general validity for non-optimized double-circuit lines is proposed here. No specific measurement position or conductors disposition knowledge is required as well as no complex three-dimensional finite element method code is necessary. The procedure, potentially also applicable to high- and extra-high-voltage lines, is validated on a medium-voltage (15 kV) double-circuit overhead power line study case. Exposure limits assessment suggests that if the line is operated at its rated capacity (230/285 A), the 3 μT quality target is missed. Results are provided with a 95% confidence interval ranging from ±100 nT to ±140 nT in all the cases.

Jonas K. H. Fischer, Hiroki Ueda, Tsuyoshi Kimura

The electric field effect on magnetism was examined in the multiferroic conical magnet Mn$_2$GeO$_4$, which shows a strong coupling between ferromagnetic and ferroelectric order parameters. The systematic evaluation of the electric polarization in the multiferroic phase below 5.5 K under various field cooling conditions reveals that small magnetic fields of 0.1 T significantly reduce the required electric fields needed to reach saturation. By applying electric fields during magnetic field dependent hysteresis measurements of magnetization M and polarization P an electrically controllable exchange bias was observed, a phenomenon exceedingly rare in single phase multiferroics. Furthermore, non-reversible electric switching of P and M domains was achieved under specific magnetic field conditions.

Chengxi Huang, Jingtong Guan, Qiongyu Li et al.

Electrical control of magnetism in a two-dimensional (2D) semiconductor is of great interest for emerging nanoscale low-dissipation spintronic devices. Here, we propose a general approach of tuning magnetic coupling and anisotropy of a van der Waals (vdW) 2D magnetic semiconductor via a built-in electric field generated by the adsorption of superatomic ions. Using first-principles calculations, we predict a significant enhancement of ferromagnetic (FM) coupling and a great change of magnetic anisotropy in 2D semiconductors when they are sandwiched between superatomic cations and anions. The magnetic coupling is directly affected by the built-in electric field, which lifts the energy levels of mediated ligands' orbitals and enhances the super-exchange interactions. These findings will be of interest for ionic gating controlled ferromagnets and magnetoelectronics based on vdW 2D semiconductors.

Peerasan Khamsalee, Piyaporn Mesawad, Rangsan Wongsan

This paper proposes the gain enhancement of dual-band and dual-polarized asymmetric horn antenna for the secondary radar system using hybrid metamaterial techniques. The hybrid metamaterial is comprised of the structures of woodpile electromagnetic bandgap (EBG) for gain enhancement of the primary main beam of the radar system at the operating frequency of 1,300 MHz with horizontal polarization; and the wire medium structure that is placed beside the EBG structure for gain improvement of the identification friend or foe (IFF) main beam, which is operated at the center frequency of 1,060 MHz with vertical polarization. Meanwhile, the cooperated structures have to function to control the directions of the primary and IFF main beams retaining at 0° and 6°, respectively, too. When the hybrid metamaterial structure is placed at the front of an asymmetric horn’s aperture, with suitable parameters and optimized spacing, it is found to increase the gains of the two beams compared to the single asymmetric horn around 3 dB and retain the directions of original main beams. The comparison of the results between simulation and measurement, such as the reflected power (S11), gain, and radiation patterns, are in good agreement.

Haisheng Guo, Kexin Song, Zhenrong Li et al.

Pb(In1∕2Nb1∕2)O3-Pb(Mg1∕3Nb2∕3)O3-PbTiO3 (PIN-PMN-PT) relaxor ferroelectric crystals in 5″ diameter by 5″ length were grown by the Bridgman (BR) method for the first time. Typical issues in the crystal growth concerning large volume of the melt, high density of the crystal and corrosion of the melt on the wall of Pt crucible are discussed.