Hasil untuk "Electricity and magnetism"

Xinchun Xie, Dapeng Song, Yulu Ding et al.

A new three-layer Aurivillius phase piezoceramic, Bi[Formula: see text]Na[Formula: see text]Ti[Formula: see text]NbxO[Formula: see text] ([Formula: see text], 0.03, 0.05 and 0.10), was prepared by the traditional solid-state sintering method. All samples display a uniphase orthorhombic structure and plate-shaped grains. The introduction of Na/Nb inhibits the generation of oxygen vacancies, enhances dielectric stability and resistivity and reduces dielectric loss. Increasing the Na/Nb amount could increase the activation energy [Formula: see text] and enhance the dc resistivity. The dc resistivity of Bi[Formula: see text]Na[Formula: see text]Ti[Formula: see text]NbxO[Formula: see text] ([Formula: see text]) ceramics has increased to above [Formula: see text] [Formula: see text]cm at [Formula: see text]C and [Formula: see text] [Formula: see text]cm at [Formula: see text]C. The conduction mechanisms of the Bi[Formula: see text]Na[Formula: see text]Ti[Formula: see text]NbxO[Formula: see text] ceramics are also sufficiently explored. The conducting carriers are mainly oxygen vacancies, and their migration exhibits temperature-dependent relaxation characteristics. The Bi[Formula: see text]Na[Formula: see text]Ti[Formula: see text]Nb[Formula: see text]O[Formula: see text] ceramics obtain the excellent properties of high [Formula: see text]C, small [Formula: see text]C, low [Formula: see text], large [Formula: see text]cm and better [Formula: see text] [Formula: see text]pC/N. This work presents a valid tactic to design Aurivillius phase piezoceramics with enhanced resistivity and piezoelectricity for the field of high-temperature piezoelectricity.

Qihang XU, Lan LAN, Guisheng LIAO et al.

When radar and communication systems share the same frequency spectrum on the same platform, mutual interference may occur. In addition, mainlobe deceptive interferences pose a serious threat to radar target detection. To address these issues, we devise a Frequency Diverse Array Multiple-Input Multiple-Output (FDA-MIMO) radar and MIMO communication spectral coexistence system and propose a radar-centric joint transceiver design scheme. In this respect, the radar transmission waveform, radar receive filter, and communication transmission codebook are optimized to maximize the Signal-to-Interference-plus-Noise Ratio (SINR) of the radar system, thereby enhancing the target detection probability while ensuring MIMO communication throughput. During the optimization process, the Alternating Optimization (AO) strategy is employed to decompose the problem into multiple subproblems, which are solved in an iterative way. Specifically, the radar receive filter is obtained using the Lagrange multiplier method. In addition, the communication transmission codebook is approximated using an inequality theorem, and the radar transmission waveform is optimized using Taylor expansion and relaxation algorithms. Simulation results reveal that this joint design method can effectively improve the SINR of the radar system while ensuring communication throughput, thereby considerably enhancing the performance of the FDA-MIMO radar and MIMO communication spectral coexistence system under mainlobe jamming conditions.

Éric Djekounyom, Eric Verney, Didier Vincent

In this paper, we propose a tunable isolator based on coplanar waveguide (CPW) realized on yttrium iron garnet substrate, in which one of the ground planes of the CPW is periodically loaded with short-circuited slots. With an in-plane DC magnetic field perpendicular to the direction of the propagation, the structure achieves nonreciprocal propagation at a resonant frequency that can be tuned in the Ku-band. The resonant frequency can be tuned either magnetically by tuning the DC magnetic bias field, or mechanically by putting a copper plate at an adjustable distance above the structure. By applying a low magnetic bias field of only 70 Oe, the operating frequency could be tuned mechanically from 13.6 to 15.15 GHz, with the tuning frequency range being 2 GHz. The benefits of choosing mechanical tuning over magnetic tuning are also highlighted. The proposed tunable isolator exhibits immense potential for radio frequency (RF) applications and can be easily implemented in different microwave devices for reconfigurable RF applications.

L. M. Ramos, M. Schmidt, F. M. Zimmer

We investigated the isotropic spin-1/2 Heisenberg model on an anisotropic square lattice with competing exchange interactions, motivated by the unconventional magnetic behavior observed in the verdazyl-based compound (o-MePy-V)PF6. Using a cluster mean-field approach, we explore a field-induced phase stabilized by the interplay between frustration and quantum fluctuations, focusing on the role of exchange interactions. We identify: (i) the formation of spin singlet pairs, signaled by enhanced spin-spin correlations in specific field regimes; and (ii) a one-half magnetization plateau, emerging from a subtle balance between competing exchange couplings and field-enhanced quantum fluctuations. Our results reveal that an enhancement of frustration, achieved by tuning small variations in the spatially anisotropic exchange interactions of the compound (o-MePy-V)PF6, can stabilize a field-induced quantum phase where ferromagnetism coexists with antiferromagnetic dimers. Our results provide microscopic insight into the mechanisms driving these nontrivial phases and offer theoretical support for interpreting experimental observations in this class of low-dimensional quantum magnets.

Yang Zhang, Lan Gao, Hantao Ji et al.

Laser-driven capacitor coils are widely used to generate intense magnetic fields for various applications in high-energy-density physics research. Accurate measurement of the magnetic fields is essential but challenging, due to the overlapping contributions from magnetic and electric fields in proton radiography, which is the primary tool diagnosing the field generation around the coils. In this study, we systematically analyze proton radiographs obtained from laser-driven capacitor-coil targets along two orthogonal axes under various electromagnetic field conditions, including magnetic field only, electric field only, and combined electromagnetic fields. By analyzing key features in the radiographs, we distinguish and characterize the respective contributions from magnetic and electric fields. Using detailed simulations validated by experimental benchmarks, methods to isolate and quantify the magnetic field and electric field are given. The methods are successfully applied to determine the electric current and charge distribution in a double coil configuration. Our findings provide insights into improving the diagnostic capability of proton radiography, potentially leading to more accurate measurements of electromagnetic fields and enhancing the utility of laser-driven capacitor coils in high-energy-density experiments.

Zhishu Qu, Yihua Zhou, James R. Kelly et al.

Abstract In this paper, a reconfigurable transmitarray unit cell using liquid metal is presented. It consists of three conducting layers where the geometries of the resonators, on the different layers, differ and consist of an arrow shape together with rotated split rings. The arrow‐shaped conducting layer has the capability to convert the polarization of the incoming waves by 90°. The split ring resonators, on the upper and lower conducting layers, have the same dimensions but different orientations (horizontal and vertical polarization). Several fluidic channels are placed beneath/above the conducting layers. The transmission behaviour of the unit cell can be changed by altering the geometrical parameters which is achieved by injecting the liquid metal into the channels. More than 300° phase shift range with a maximum S21 of ∼ −1.5 dB at 3.3 GHz is obtained. It exhibits 3 dB of insertion loss over a bandwidth ranging from 3.2 to 3.43 GHz. It is the first time that a transmitarray unit cell, reconfigured employing liquid metal, provides a combination of low insertion loss and large phase shift range. The proposed prototype was fabricated and measured within an open‐ended waveguide and the measured results agree well with the simulations and verify the effectiveness of the design. The reconfigurable transmitarray unit cell can be used to design beam‐scanning arrays, as well as for applications in wireless communications.

David Barranco, Şengül Kuru, Javier Negro

Electric and magnetic waveguides are considered in planar Dirac materials like graphene as well as their classical version for relativistic particles of zero mass and electric charge. In order to solve the Dirac-Weyl equation analytically, we have assumed the displacement symmetry of the system along a direction. In these conditions we have examined the rest of symmetries relevant each type, magnetic or electric system, which will determine their similarities and differences. We have worked out waveguides with square profile in detail to show up some of the most interesting features also in quantum and classical complementary contexts. All the results have been visualized along a series of representative graphics showing explicitly the main properties for both types of waveguides.

Alexander Pukhov, Nikolay E. Andreev, Anton A. Golovanov et al.

The phase velocity of a laser-driven wakefield can be efficiently controlled in a plasma channel. A beatwave of two long laser pulses is used. The frequency difference between these two laser pulses equals the local plasma frequency, so that the slow resonant excitation of the plasma wave is possible. Because the driver energy is spread over many plasma periods, the interference pattern can run with an arbitrary velocity along the channel and generate the wakefield with the same phase velocity. This velocity is defined by the channel radius and the structure of laser transverse modes excited in the channel. The wake velocity can be matched exactly to the witness velocity. This can be the vacuum speed of light for ultra-relativistic witnesses, or subluminal velocities for low-energy, weakly relativistic witnesses such as muons.

Masaya Ishida, Toshiaki Watanabe

Abstract A phase‐shifted circularly polarised ring microstrip antenna (PS‐CP‐RMSA), which can switch between three different phases, is proposed. The phase of a circularly polarised antenna can be shifted by changing the angle of rotation. Taking advantage of this property, the proposed PS‐CP‐RMSA comprises a circularly polarised ring microstrip antenna (CP‐RMSA) with three groups of feed lines and perturbation elements; phase shift can be achieved by switching their groups. Thus, the phase of a circularly polarised antenna can be electronically shifted without phase shifters, which has been difficult in the past. Therefore, the PS‐CP‐RMSA array can perform beam tilt electronically. In this study, PS‐CP‐RMSA and its four‐element array were designed, fabricated, and measured. The maximum circular polarisation gain of the prototype PS‐CP‐RMSA was 6.3 dBic with an axial ratio of 1.1 dB at 5.7 GHz. The maximum gain of the boresight directional beam of the four‐element array was 11.3 dBic with an axial ratio of 0.4 dB at 5.67 GHz. The proposed antenna can be a candidate for a new beam‐control method for array antennas.

Sushrisangita Sahoo, K. P. Andryushin, P. K. Mahapatra et al.

The present investigations mainly focused on the colossal dielectric response and complex impedance analysis of LaFeO3 ceramics. The studied sample was prepared by a citrate gel method. Structural and microstructural properties are analyzed from the XRD pattern and SEM micrograph. The anomalies in the dielectric constant versus temperature plots are analyzed on the basis of polarization induced by the Maxwell-Wagner mechanisms and ferromagnetic interaction between the Fe[Formula: see text] ions driven by the oxygen vacancy mediated Fe[Formula: see text]–V[Formula: see text] –Fe[Formula: see text] exchange interaction A giant dielectric permittivity in the order of [Formula: see text]105 was observed in the sample even at the room temperature for 100 Hz. The colossal dielectric constant in LaFeO3 is mainly driven by the internal barrier layer capacitor (IBLC) formation. The formation of IBLC was explained on the basis of highly insulating grain boundary and less resistive/semiconducting grain, which was confirmed from both the resistance and capacitance of grain and grain boundary from the impedance analysis. The non-Debye-type relaxation process associated with the grain and grain boundary effect was investigated from the broad and asymmetric relaxation peak. The relaxation time for both the grain and grain boundary effect was also calculated. In addition to this, we have also analyzed the normalized bode plot of imaginary part of impedance and electrical modulus which suggests the relaxation process dominated by the short-range movement of charge carriers.

Yanqiang HE, Ying WANG, Xiaoqiang CHEN et al.

Aiming at the problems of energy saving, efficiency improvement and harmonic control of electric railways, a control strategy of railway traction network-side energy storage system is proposed with consideration of characteristic harmonic control. Firstly, the access scheme of the traction network-side energy storage system is analyzed and its working modes are classified. Secondly, according to the distribution of characteristic harmonics of traction load, a novel method is deduced for peak load shaving and characteristic harmonics control by using the energy storage system at the grid side. And then, a control strategy of supercapacitor energy storage system is proposed, which takes into account the grid-side characteristic harmonic suppression. Finally, the feasibility of the proposed strategy is verified by simulation tests under multiple working conditions. The results show that the proposed strategy can effectively recover the regenerative braking energy, reduce the power fluctuation, and suppress the characteristic harmonics at the grid side.

Akane Inda, Satoru Hayami

An electric toroidal dipole (ETD) moment is one of the fundamental dipole moments as well as electric and magnetic ones. Although it directly couples to neither an electric nor magnetic field due to its spatial inversion and time-reversal parities, its ordered state leads to unconventional transverse responses of the conjugate physical quantities. We here theoretically investigate nonlinear transverse magnetic susceptibility under the ETD ordering. By performing a self-consistent mean-field calculation for a five $d$-orbital model under a tetragonal crystalline electric field and using the nonlinear Kubo formula, we show that a third-order transverse magnetic susceptibility corresponding to a uniform magnetization perpendicular to the external magnetic field becomes nonzero once the ETD moment is ordered under tetragonal crystalline electric field. Moreover, we find that spin-orbital entanglement and a low-lying first excited crystal-field level are important for realizing large transverse responses.

Casper Floris Schippers, Michał J. Grzybowski, Km Rubi et al.

Recent demonstrations of the electrical switching of antiferromagnets (AFs) have given an enormous impulse to the field of AF spintronics. Many of these observations are plagued by non-magnetic effects that are very difficult to distinguish from the actual magnetic ones. Here, we study the electrical switching of thin (5 nm) NiO films in Pt/NiO devices using magnetic fields up to 15 T to quantitatively disentangle these magnetic and non-magnetic effects. We demonstrate that these fields suppress the magnetic components of the electrical switching of NiO, but leave the non-magnetic components intact. Using a monodomainization model the contributions are separated, showing how they behave as a function of the current density. These results show that combining electrical methods and strong magnetic fields can be an invaluable tool for AF spintronics, allowing for implementing and studying electrical switching of AFs in more complex systems.

Hongmei Liu, Yan Zhang, Yao Wang et al.

Abstract Here, a circular polarized (CP) patch antenna with a wide 3‐dB axial ratio beamwidth (ARBW) and suppressed backward cross‐polarized radiation is proposed. A narrow slot is inserted into the ground to widen the 3‐dB ARBWs of the CP antenna. An annular metal strip loaded with a circular row of L‐shaped bent metal branches is etched around the circular radiation patch to reduce backward cross‐polarized radiation, as well as to further increase the 3‐dB ARBW. To validate, a prototype is designed at 1.575 GHz and fabricated. The experimental results show that the 10‐dB impedance matching bandwidth of the fabricated prototype is 25.8%, and the 3‐dB CP bandwidth is 5.1%. Besides, 3‐dB ARBWs of 238° and 259° are obtained at the two principal planes, respectively, with the front‐back ratio of more than 26 dB. Satisfactory agreement is achieved between measurement results and simulated ones.

Ju Tang, Fuping Zeng

Amjad Iqbal, Mohamed I. Waly, Amor Smida et al.

Abstract This study presents a simple and low‐profile cylindrical dielectric resonator antenna (CDRA) for the fifth‐generation (5G) band (3.5 GHz) with switchable polarization. The antenna can operate with linear or circular polarization (right‐handed circular polarization [RHCP] or left‐handed circular polarization [LHCP]) by changing the states of the PIN diodes below the CDRA, while keeping the same operating frequencies. The antenna operates at three modes (Mode 1, Mode 2, and Mode 3). It exhibits linear polarization in Mode 1, RHCP in Mode 2, and LHCP in Mode 3. The 10‐dB bandwidths of 750 MHz (3.1–3.85 GHz), 950 MHz (3.03–3.98 GHz), and 960 MHz (3.03–3.99 GHz) are noted for Mode 1, Mode 2, and Mode 3, respectively. The 3‐dB axial ratio bandwidth of 22.2% (3.09–3.86 GHz) and 21.4% (3.08–3.82 GHz) is achieved for Mode 2 and Mode 3, respectively. The reported antenna has high gain ( >5.25 dBi for all operating modes) and high radiation efficiency ( >79.8% for all operating modes). The proposed antenna is suitable for use in polarization diversity applications.

Yuxiang JIA, Jiafu WANG, Wei CHEN et al.

At present, research on metamaterials is continuously advancing to engineering applications, and great progress is being achieved in the areas of physical mechanisms and effects, design theory and methods, and fabrication and measurement. However, traditional metamaterials design mainly relies on artificial design and optimization. In the face of large-scale engineering applications, it is impossible to realize the rapid overall design of a large number of metamaterial structural units. In recent years, the proportion of intelligent algorithms covering traditional heuristic algorithms and neural network algorithms in metamaterials design has increased gradually. Metamaterials design based on intelligent algorithms can surpass the limitation of traditional methods in different substrate systems, frequency variation, and different performance indicators, offering the unique advantages of rapid design and architectural innovation. This paper summarizes the application of several typical intelligent algorithms, including the genetic algorithm, Hopfield network algorithm, and deep learning algorithm in metamaterials design, which include forward designs and an inverse design. The use of intelligent algorithms can achieve the rapid design of frequency selective surfaces under different performance indexes, multi-mechanisms composite absorber metamaterials, flat focusing, and abnormal reflection metasurfaces, providing the necessary support for design methods while promoting the engineering applications of metamaterials.

Wenjian ZHANG, Geng LIANG, Gengda LI et al.

Although the traditional digital power plant technology can attain the digital mode of enterprise construction and management, it still lacks the conditions and features of high intelligence in the aspects of the breadth of information collection and the depth of information utilization. In this paper, by taking the production characteristics of power plant into consideration, an intelligent all-digital technology system applicable for power plant is proposed on the basis of the technology of digital power plant, and the concept, composition and basic relationship between the elements of intelligent all-digital technology is aslo proposed, expounds the basic structure and principle of intelligent all-digital system, elaborates the intelligent operation mode of intelligent subject, and explores the application scheme of intelligent all-digital technology in power plant. In this system, the intelligent subject and digital technology are organically combined to increase and expand the breadth and depth of data information usage, i.e., expand the paths and means of information acquisition and collection to increase the breadth of information, and conduct in-depth analysis, mining and reutilization of data information by introducing more intelligent calculation algorithms and analysis methods. At the same time, the new data and knowledge generated by the system can be fed back to the existing all-digital system continuously to achieve the self-adjustment and self-organization of the system, in which the traits of intelligence are fully exhibited.

Shunsuke Murai, Gabriel W. Castellanos, T. V. Raziman et al.

We demonstrate an enhanced emission of high quantum yield molecules coupled to dielectric metasurfaces formed by periodic arrays of polycrystalline silicon nanoparticles. Radiative coupling of the nanoparticles, mediated by in-plane diffraction, leads to the formation of collective Mie scattering resonances or Mie surface lattice resonances (M-SLRs), with remarkable narrow line widths. These narrow line widths and the intrinsic electric and magnetic dipole moments of the individual Si nanoparticles allow to resolve electric and magnetic M-SLRs. Incidence angle- and polarization-dependent extinction measurements and high-accuracy surface integral simulations show unambiguously that magnetic M-SLRs arise from in- and out-of-plane magnetic dipoles, while electric M-SLRs are due to in-plane electric dipoles. Pronounced changes in the emission spectrum of the molecules are observed, with almost a 20-fold enhancement of the emission in defined directions of molecules coupled to electric M-SLRs, and a 5-fold enhancement of the emission of molecules coupled to magnetic M-SLRs. These measurements demonstrate the potential of dielectric metasurfaces for emission control and enhancement, and open new opportunities to induce asymmetric scattering and emission using collective electric and magnetic resonances.

Chu ZHANG, Yi YANG, GE JIN et al.

The unstable vibration on the 2nd harmonic has been existing in the pump-motor system, and the way to cool the motor has a significant effect on its vibration characteristics. Therefore, the field testing for this fault has been taken to diagnose and verify the failure of dynamic mirror plate warping of the motor under certain conditions. The analysis on the mechanism of the mirror warping failure concludes that it is the axial misalignment that leads to double frequency vibration. The concentration of the axial misalignment determines the dominant frequency of the operating equipment. The low-frequency vibration signal is amplified into the vibration displacement during the integration of the vibration velocity. At the end, it is suggested that the vibration velocity should be used to evaluate the vibration of the non-rotating parts of the low-speed equipment.