Hasil untuk "Electricity and magnetism"

Yuhao Gu, Yu-Hui Song, Yihao Wang et al.

The altermagnetism with antiparallel spin alignment exhibits anisotropic spin splitting and may possess an insulating state with a high Neel temperature, while the charge-order-induced ferroelectricity has ultrafast electric polarization switching. Considering that altermagnetism requires breaking space inversion,, the physical foundation for exploring ultrafast electrically controlled magnetism in altermagnetic ferroelectric materials is thus established. In this Letter, based on symmetry analysis and first-principles electronic structure calculations, we predict that LiV$_2$F$_6$ is a material that simultaneously hosts altermagnetism and charge-order-induced ferroelectricity. Since both the altermagnetism and ferroelectricity originate from charge order, LiV$_2$F$_6$ should exhibit strong magnetoelectric coupling. Our calculations indeed demonstrate that electric polarization reversal can induce band spin-polarization switching in LiV$_2$F$_6$. Moreover, time-dependent density functional theory calculations show that the electric polarization reversal in LiV$_2$F$_6$ occurs in 15 femtoseconds. Consequently, ultrafast electrically controlled magnetism can be realized in LiV$_2$F$_6$. Given that LiV$_2$F$_6$ has already been experimentally synthesized, our work provides a promising material platform for achieving ultrafast electrically controlled magnetism, which might have significant implications for the design of future electronic devices.

Liyuan Huang, Yuanxun Li, Yanfeng Shang et al.

With the rapid development of electronic integration technology, highly integrated chips are in urgent need of packaging materials that are thermally matched to printed circuit boards. Here, [Formula: see text]CoxAl2O4 (ZCAO, x= 0.00–0.20) ceramics are synthesized using the solid-state reaction method. The phase composition, microstructure, microwave dielectric properties and CTE of [Formula: see text] in the ZnAl2O4 ceramic substituted by [Formula: see text] are systematically revealed. An appropriate amount of [Formula: see text] substitution promotes a more homogeneous grain growth to form a dense microstructure. The average grain size, bulk density and relative density of ZCAO ([Formula: see text]) ceramic are 1.59[Formula: see text][Formula: see text]m, 4.472[Formula: see text]g/cm3 and 97.4%, respectively. The optimal microwave dielectric properties ([Formula: see text], [Formula: see text],701[Formula: see text]GHz, [Formula: see text][Formula: see text]ppm/∘C) of the ZCAO ([Formula: see text]) ceramic sintered at 1450∘C are achieved. More importantly, the ZCAO (x = 0.10) possesses a CTE = 11.59[Formula: see text]ppm/∘C that is nearly thermally matched to the printed circuit boards (PCB, CTEPCB = 12[Formula: see text]ppm/∘C). This ceramic has great potential for application in the electronic packaging of PCB devices.

Hang Wang, Haoran Zhang, Lei Li et al.

ABSTRACT Partial discharge (PD) is the indicator of the insulation defect in cables. However, the pulse current method, which is widely adopted in land cables, cannot obtain PD signals of high‐voltage direct current (HVDC) submarine cables due to attenuation and installation position. To detect the PD of the HVDC submarine cable, a PD vibration diagnosis methodology using the embedded fibre based on the heterodyne interferometric phase‐sensitive optical time‐domain reflectometry (φ‐OTDR) and Hilbert demodulation is proposed. The proposed method is verified by a PD experiment with preset defects in 220 kV submarine cables under DC voltage. The results show that the PD can be detected by fibre using the proposed method. Among the three types of PD generated in preset defects in 220 kV submarine cables under DC voltage, the inception voltage of corona discharge, internal airgap discharge and surface discharge is 18, 14 and 14 kV, respectively. The peak value of the phase difference in corona discharge is the smallest, and the peak value of the phase difference in surface discharge is close to that in internal airgap discharge. A recommended parameter configuration is provided through statistical analysis, where a modulation frequency of 10 kHz and a pulse width of 100 ns achieve a 10% detection probability at 2.25 km fibre length and 10 m spatial resolution.

Xinyang ZHAO, Hongsen ZOU, Chen YANG et al.

The traveling wave method is currently a common approach for fault distance measurement in grounding electrode line, but it generally relies on simulation in terms of threshold setting, and cannot determine the type of grounding electrode line fault. To address the above issues, this paper adopts an active traveling wave injection method, and through analytical calculations, obtains the time-domain expression of the modulus-backward traveling wave at the measuring point at the first end of the ground electrode line after a single-line ground fault, a cross-line fault, a single-line open-circuit fault and a double-line open-circuit fault. A grounding electrode line fault type recognition and localization method is proposed based on modulus backward traveling wave. The proposed injection wave method has a clear expression of distance measurement threshold setting, then can accurately identify the type of line fault. The reliability and robustness of this method is verified in PSCAD/EMTDC simulations. Simulation results show that this method can achieve accurate fault distance measurement, and reliably identifies grounding electrode fault type, demonstrating strong tolerance to transition resistance and resistance to noise interference.

Qingzhen Liu, Yadong Liu, Yingjie Yan et al.

ABSTRACT Accurate and timely insulator defect detection is crucial for maintaining the reliability and safety of the power supply. However, the development of deep‐learning‐based insulator defect detection is hindered by the scarcity of comprehensive, high‐quality datasets for insulator defects. To address this gap, the synthetic insulator defect imaging and annotation (SYNTHIDIA) system was proposed. SYNTHIDIA generates synthetic defect images in a 3D virtual environment using domain randomisation, offering a cost‐effective and versatile solution for creating diverse and annotated data. Our dataset includes 22,000 images with accurate pixel‐level and instance‐level annotations, covering broken defect and drop defect types. Through rigorous experiments, SYNTHIDIA demonstrates strong generalisation capabilities to real‐world data and provides valuable insights into the impact of various domain factors on model performance. The inclusion of 3D models further supports broader research initiatives. SYNTHIDIA addresses data insufficiency in insulator defect detection and enhances model performance in data‐limited scenarios, contributing significantly to the advancement of power inspection.

G. M. Wysin

A chain of dipole-coupled elongated magnetic islands whose long axes are oriented perpendicular to the chain is studied for its magnetization properties. With a magnetic field applied perpendicular to the chain, the competition between dipolar energy, shape anisotropy, and field energy leads to three types of uniform states with distinct magnetizations: (1) oblique to the chain, (2) perpendicular to the chain, and (3) zero due to having alternating dipoles. The response of these states to a slowly varying field is analyzed, focusing on their stability limits and related oscillation modes, and the dependencies on the dipolar and anisotropy constants. Based on identifiable transitions among the three states and their instability points, the theoretically predicted zero-temperature magnetization curves show significant dependence on the anisotropy. The model suggests a path for designing advanced materials with desired magnetic properties. Different geometries and magnetic media for the islands are considered.

Hang RUAN, Jiahao CUI, Xiuhua MAO et al.

Deep Neural Network (DNN)-based Synthetic Aperture Radar (SAR) image target recognition has become a prominent area of interest in SAR applications. However, deep neural network models are vulnerable to adversarial example attacks. Adversarial examples are input samples that introduce minute perturbations within the dataset, causing the model to make highly confident yet incorrect judgments. Existing generation techniques of SAR adversarial examples fundamentally operate on two-dimensional images, which are classified as digital-domain adversarial examples. Although recent research has started to incorporate SAR imaging scattering mechanisms in adversarial example generation, two important flaws still remain: (1) imaging scattering mechanisms are only applied to SAR images without being integrated into the actual SAR imaging process, and (2) the mechanisms achieve only pseudo-physical-domain adversarial attacks, failing to realize true three-dimensional physical-domain adversarial attacks. This study investigates the current state and development trends in adversarial attacks on SAR intelligent target recognition. First, the development trajectory of traditional generation technologies of SAR-image adversarial examples is meticulously traced and a comparative analysis of various technologies is conducted, thus summarizing their deficiencies. Building on the principles and actual processes of SAR imaging, physical-domain adversarial attack techniques are then proposed. These techniques manipulate the target object’s backscattering properties or emit finely adjustable interference signals in amplitude and phase to counter SAR intelligent target recognition algorithms. The paper also envisions practical implementations of SAR adversarial attacks in the physical domain. Finally, this paper concludes by discussing the future directions of SAR intelligent adversarial attack technologies.

Christopher J. Fischer, Jennifer Delgado, Sarah LeGresley et al.

We assessed changes in calculus proficiency and calculus self-efficacy in a second semester course of introductory physics focused on electricity and magnetism. While all students demonstrated an increase in calculus proficiency, including a possible improvement in calculus transfer to physics, women displayed larger gains than men. Conversely, men showed larger gains in calculus self-efficacy. When combined, these data suggest that student identity modulates the correlation between a student's calculus abilities and their perception or self-evaluation of those abilities. These data highlight a potential contributing factor to gender-related differences in physics self-efficacy as well as the complexity of addressing those differences.

Emil Siuda, Piotr Trocha

In this work, we study thermally-generated spin current in the system consisting of a quantum dot connected to two magnetic insulators. The external leads are kept at different temperatures which leads to an imbalance of magnon populations in two magnetic insulators resulting in the flow of the magnon (spin) current. We take into account many-body magnon interactions and incorporate energy-dependent density of states of the magnetic insulators. Both features can strongly affect magnon distribution in the magnetic insulators and the coupling strengths between the leads and the dot, and thus, the thermally generated spin current. All the calculations are carried out in the weak coupling regime. We show, that results obtained with a density of states being a function of energy differ significantly from the ones obtained with a density of states taken as a constant. In turn, magnon interactions in the leads proved to be important at high temperatures and large values of energy of transported spin waves.

Sangwoon Youn, Byung-jun Jang, Hosung Choo

This paper proposes a single circular radiator with a multi-port (SRMP) antenna that can estimate the direction-of-arrival (DoA) in the azimuth and elevation directions. The proposed SRMP antenna is designed to minimize the size of the ultra-wideband system by using only one patch radiator. To verify the feasibility, the proposed antenna is fabricated, and the reflection coefficient and boresight gain are measured (−13.3 dB and 3.4 dBi at 8 GHz). Then, to observe the direction-finding performance, the DoA estimation results using the Bartlett beamformer are compared with the typical array. At all incident angles, a root-mean-square error of less than 1° is observed when the signal-to-noise ratio is higher than 6 dB.

Gunnar Gidion, Taimur Aftab, Leonhard M. Reindl et al.

The theory and application of resonances and vibrational modes are part of the foundation of science. In this contribution, examples of acoustical resonators are highlighted, and compared to electromagnetic modes. As an example from architecture, we describe the phenomenon of whispering galleries; such modes are nowadays known in dielectric and optical resonators. A specimen of a semicircular whispering bench in Park Sanssouci in Potsdam is acoustically investigated and demonstrated to show low losses for sound propagation. A special acoustical bug is discussed which was used for the espionage of the U.S. ambassador in Moscow. The Sovyets could interrogate this passive device by radio waves. Its working principle was based on the electromagnetic resonance of the cavity that the sound-sensitive membrane was part of. The underlying relation between excitation and resonance is compared to the sound production in flue organ pipes. A stopped flue organ pipe was investigated using a piezoelectric film sensor inside the pipe body. The results show that even-numbered modes, which are usually suppressed in the radiated sound of a stopped pipe, are still present in the vibrations inside the resonator.

Lan DU, Xiaoyang CHEN, Yu SHI et al.

As a biometric technology, gait recognition is usually considered a retrieval task in real life. However, because of the small scale of the existing radar gait recognition dataset, the current studies mainly focus on classification tasks and only consider the situation of a single walking view and the same wearing condition, limiting the practical application of radar-based gait recognition. This paper provides a radar gait recognition dataset under multi-view and multi-wearing conditions; the dataset uses millimeter-wave radar as a sensor to collect the time-frequency spectrogram data of 121 subjects walking along views under multiple wearing conditions. Eight views were collected for each subject, and ten sets were collected for each view. Six of the ten sets are dressed normally, two are dressed in coats, and the last two are carrying bags. Meanwhile, this paper proposes a method for radar gait recognition based on retrieval tasks. Experiments are conducted on this dataset, and the experimental results can be used as a benchmark to facilitate further research by related scholars on this dataset.

Shiho Nakamura, Nobuyuki Umetsu, Michael Quinsat et al.

The exchange stiffness of magnetic materials is one of the essential parameters governing magnetic texture and its dynamics in magnetic devices. The effect of single-element doping on exchange stiffness has been investigated for several doping elements for permalloy (NiFe alloy), a soft magnetic material whose soft magnetic properties can be controlled by doping. However, the impact of more practical multi-element doping on the exchange stiffness of permalloy is unknown. This study investigates the typical magnetic properties, including exchange stiffness, of permalloy systematically co-doped with Mo and Cu using broadband ferromagnetic resonance spectroscopy. We find that the exchange stiffness, which decreases with increasing doping levels, is proportional to a power of magnetization, which also decreases with increasing doping levels. The magnetization, $M_{\rm s}$, dependence of the exchange stiffness constant, $A$, of all the investigated samples, irrespective of the doping levels of each element, lies on a single curve expressed as $A\propto M_{\rm s}^n$ with exponent $n$ close to 2. This empirical power-law relationship provides a guideline for predicting unknown exchange stiffness in non-magnetic element-doped permalloy systems.

Zaid Hamid Abdulabbas Al-Tameemi, Tek Tjing Lie, Gilbert Foo et al.

Microgrids (MGs) are capable of playing an important role in the future of intelligent energy systems. This can be achieved by allowing the effective and seamless integration of distributed energy resources (DERs) loads, besides energy-storage systems (ESS) in the local area, so they are gaining attraction worldwide. In this regard, a DC MG is an economical, flexible, and dependable solution requiring a trustworthy control structure such as a hierarchical control strategy to be appropriately coordinated and used to electrify remote areas. Two control layers are involved in the hierarchy control strategy, including local- and global-control levels. However, this research focuses mainly on the issues of DC MG’s local control layer under various load interruptions and power-production fluctuations, including inaccurate power-sharing among sources and unregulated DC-bus voltage of the microgrid, along with a high ripple of battery current. Therefore, this work suggests developing local control levels for the DC MG based on the hybrid particle swarm optimization/grey wolf optimizer (HPSO–GWO) algorithm to address these problems. The key results of the simulation studies reveal that the proposed control scheme has achieved significant improvement in terms of voltage adjustment and power distribution between photovoltaic (PV) and battery technologies accompanied by a supercapacitor, in comparison to the existing control scheme. Moreover, the settling time and overshoot/undershoot are minimized despite the tremendous load and generation variations, which proves the proposed method’s efficiency.

Junfeng TAN, Ping YANG, Fan ZHANG et al.

Under the goal of “carbon peaking and carbon neutrality”, construction of the new power system with new energy as the mainstay will surely promote the user-side participation in the real-time energy balance. In the integrated energy system (IES) with multi-energy operation of cooling, heating, electricity and gas, the real-time balance of power system through coordinating internal operation strategies combined with the auxiliary adjustment of various internal flexible resources can promote the economic energy use of industrial park and the regional renewable energy consumption. A multi-time scale IES optimization dispatch model is thus proposed with consideration of energy-auxiliary services. The energy cost of industrial park is optimized through providing such auxiliary services as peak-shaving and frequency regulation to power grid, and the equivalent linearization method is used to solve nonlinear programming problem. The case study shows that with the proposed optimization model, the park can not only realize the economic energy use through multi-energy coordination and complementation, but also can effectively promote regional renewable energy consumption and real-time energy balance through participating in peak shaving and frequency regulation auxiliary services.

Morteza Ghaderi Aram, Hadi Aliakbarian, Hana Dobšíček Trefná

Abstract Antennas are the building block of radiative hyperthermia (HT) applicators. This study proposes a compact UWB antenna specifically tailored to meet the requirements for deep HT array applicators. The proposed Open Ridged‐Waveguide (ORWG) antenna, which is an adaptation of a double‐ridged horn antenna, operates over the frequency band of 400–800 MHz. It was experimentally assessed as a single element. The quality metrics considered were reflection coefficient, penetration depth, effective field size (EFS), and mutual coupling. The design shows a 75.5% fractional bandwidth with a reflection coefficient measured to be below −10 dB from 367 up to 820 MHz. The EFS is greater than the physical dimensions of the 3‐by‐4 cm aperture. The mutual coupling between two adjacent elements in the array, measured in a flat phantom arrangement, is lower than −30 dB throughout the entire band. The antenna's performance was further tested in two deep HT scenarios in order to assess the mutual coupling and focussing abilities while in the array configuration. To this end, phased array applicators consisting of 10 and 16 ORWG antennas were simulated in CST, and the results are presented for a homogeneous cylindrical muscle phantom and a realistic patient model, respectively. The good agreement between the simulated and measured results suggests that the antenna can be successfully used for HT.

Qiao Zhang, Chang Chen, Weidong Chen et al.

Abstract A new strategy for designing single‐band and dual‐band balanced bandpass filters (BPFs) based on a circular patch resonator is proposed in this study. By altering the output balanced ports of the balanced BPFs to inhibit or transport the TM31 mode of the circular patch resonator under the differential‐mode (DM) excitation, a single‐band or dual‐band balanced BPF can be realized. As the odd modes could be restrained under the common‐mode (CM) excitation, the balanced BPFs could feature high CM suppression in the DM passbands. Meanwhile, several perturbing tactics are introduced to improve the performance of the balanced BPFs. Specifically, perturbation vias are presented to disturb the electric field distribution to enhance the CM suppression in the DM passbands, and slots are applied on the circular patch resonators to perturb the current distribution to amend the second DM passband of the dual‐band balanced BPF. The proposed single‐band and dual‐band balanced BPFs are fabricated and characterized. Good agreement can be achieved between the simulated and measured results of the fabricated balanced BPFs, which validates the feasibility of the proposed design method.

Lihua ZHAO, Lan YANG, Weiwei LI et al.

In order to study the crossed-linked polyethylene (XLPE) insulation material in thermal decomposition activation energy, electrical and mechanical properties changing with thermal aging degree, accelerated thermal aging tests were carried out at 110 ℃ on XLPE insulation material for AC cables. The thermal decomposition behavior of XLPE at 20~600 ℃ was studied by thermogravimtric analyzer (TGA) test. The electrical properties of the aged XLPE samples were studied by AC breakdown testing, broadband dielectric spectrum testing and volume resistivity testing; and the mechanical properties of the aged XLPE samples were studied by tensile test. The results show that the crosslinking structure and crystalline state of XLPE are destroyed by thermal aging, and the activation energy of XLPE tends to decrease. Due to the rapid oxidation reaction, the XLPE molecular chain breaks and the cross-linking structure weakens, resulting in serious deterioration of XLPE insulation materials. The activation energy, breakdown strength, volume resistivity, elastic modulus and elongation at break tend to decrease with the increase of aging time, while the dielectric constant, dielectric loss and conductivity tend to increase.

A. R. Celik, M. B. Kurt

Detection of the breast cancer tumors at an early stage is very crucial to be successful in the treatment. Microwave measurement systems have gained much attention for this aim over last decades. The main principle of these systems is based on the significant difference in the dielectric properties of the malignant tumor and normal breast tissue in the microwave frequencies. In this paper, firstly several breast cancer detection techniques are mentioned. Then the advantages of the using microwaves in the detection systems are given. After that, some simulation and experimental studies of the radar-based ultra-wideband microwave measurement system are presented to detect tumor. The main purposes of these measurements are comparing the performance of a previously designed planar monopole antenna (PMA) with a dual-ridge horn (DRH) antenna and demonstrating a simple microwave breast cancer detection system. In the system, a planar breast phantom which is consisted of low dielectric constant material to represent the healthy tissue and high dielectric constant material to represent the tumor is used. Firstly, the measurements are made without tumor in the phantom. Then, the tumor-mimicking object is located to the phantom. In the measurements, both the PMA and DRH antennas are used respectively. These antennas are ultra-wideband and directional. They have narrow beamwidth and stable directional pattern at the interval of 3-10 GHz. According to the return loss results, the reflected energy increases when the antenna gets close to the tumor. Therefore, it can be said that the scattering parameters give important information about the tumor. According to the obtained results in this study, it can be said that the performance of the compact-sized PMA is better than the DRH antenna having larger size.

Firdaus firdaus, Rivanol Chadri, Nasrullah Nasrullah

PWM is widely used in the fields of automatic control, power electronics and cellular communications. Previous research designed a PWM generator using the OMAP-L138 chip to produce a simple, high-precision, flexible and portable circuit. Another generator uses a single board computer FEZ Panda III and an Arduino board for power inverters. While the FPGA Spartan 3 is also used to generate PWM signals that can vary the duty cycle. In this paper, the PWM signal generator is made using the AVR ATmega8535 microcontroller where the frequency parameters and the output signal duty cycle can be adjusted via the keypad. The signal is tested using a measuring instrument for its accuracy. The ATmega AVR microcontroller family has a timer / counter with one of its operating modes, namely fast PWM. In order to change the frequency and duty cycle as desired, the ICR register is used to store the TOP value and the OCR register for the MAX value. The OCR value determine the duty cycle and the ICR value specify the frequency. The results are the higher the PWM frequency, the greater the value of the measured and desired frequency difference, this is because the large frequency makes ICR register value becomes small even though the frequency divider at minimum value. The difference between measurements and calculations on the Duty Cycle gives the result under 1%. This difference also occurs due to the rounding of the ICR and OCR values, but at a frequency of 20 kHz and a 25% Duty Cycle where the ICR value is 599 and OCR is 116 resulting in the minimum difference in frequency and Duty Cycle. From the experiments that have been carried out, the design of the PWM generator based on the AVR ATmega microcontroller has been successfully realized