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Gas-insulated equipment such as GIS (Gas-Insulated Substation) and GIL (Gas-Insulated transmission lines) faces critical insulation failure challenges caused by particles inside. However, the particle traps, as key devices available to inhibit the movement of particles, lack theoretical basis and quantitative methodology for trap design especially with high voltage ratings. In this paper, a particle motion excitation and observation platform is established to physically simulate the actual online operating conditions of HVAC/HVDC GIS/GIL and study the capture mechanism of particle traps. Experimental results illustrate that, the collision motion style is a principal factor to affect the particle capturing capability, and the capture behavior of AC and DC particle traps can be classified into three separate modes, depending on variation of the collision process which can be characterized by random probability and the lognormal distribution rebound angle. A particle trajectory simulation model incorporating motion randomness is thereby presented to realize quantitative analysis and further optimize the trap parameters. A hazard index and minimum collision times are defined and calculated to quantitatively evaluate the particle collision effect on trapping capability. Further, a novel trap design topology is proposed to enhance the anti-motion efficiency of the particle traps. Targeted at high objective capture probability, the particle trap parameters are optimized to reduce the hazard index and improve the minimum collision times by the Monte Carlo scheme. The obtained results indicated that, the capture probability of AC traps can reach 86.5% at a gap spacing of 5 mm, while that of DC traps can reach 74.1% with an 8 mm-width slot and a 50-degree inclination angle. Verification of the novel article trap is implemented on a test rig, which gives an increased capture probability by 30% compared with the traditional trap design. The proposed new trap topology and corresponding methodology present quantitative guidance for particle traps optimization and render application potential for different voltage levels. [ABSTRACT FROM AUTHOR]

A novel integrated silicon micromachined diplexer-antenna module for compact terahertz (THz) heterodyne receiver is proposed. The module is composed of a radio frequency (RF) antenna, a local oscillator (LO) antenna, and a waveguide diplexer which are realized by using the silicon micromachining technology and stacking nine equal-thickness layers. The corrugated conical horn antenna and quasi-diagonal horn antenna are applied as the RF- and LO-antenna, respectively. The diplexer is composed of two third-order waveguide bandpass filters and an H-plane T-junction, providing the isolated RF and LO channels. An experimental study is carried out in the 340 GHz band, demonstrating its application potential in THz heterodyne receiver element and array. [ABSTRACT FROM AUTHOR]

A fully metallic partially open corrugated waveguide (CW) is employed to construct the Ka-band linearly polarized (LP) and circularly polarized (CP) frequency-scanning (FS) periodic leaky-wave antennas (PLWAs) with the spatial coverages from backward ($\theta < 0$) to forward ($\theta > 0$). The waveguide structure is obtained by cutting a conventional CW in half along its longitudinal symmetry plane. The $n =-1$ space harmonic is generated effectively by the half-wavelength radiating slots on the corrugations. The broadside frequency is about 31.5 GHz. The LP and CP radiations are realized by rotating the radiating slots to different angles. The measured scanning ranges of the LP and CP PLWAs are from −42.7° to 16.5° in the band of 26.5–33.5 GHz and from −48° to 22.7° in the band of 26.5–34 GHz, respectively. The measured axial ratio of the CP PLWA is below 3 dB in the mainlobe directions varied with frequency. The prototypes and experimental results make contributions to the polarization control, scanning rate improvement, and profile reduction in the frequency-controlled millimeter-wave imaging and radar systems. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the system outage probability of a simultaneous wireless information, and power transfer (SWIPT) based two-way amplify-and-forward (AF) relay network, where transceiver hardware impairments (HIs) are considered. The energy-constrained relay node processes the received signals based on a power splitting protocol, and the two terminals employ a selection combining (SC) scheme to exploit the signals from the direct and relaying links. Assuming independent but non-identically distributed Nakagami-m fading channels, we derive the system outage probability in a closed-form, which enables us to identify two crucial ceiling effects on the system outage probability caused by HIs in the high data rate regions, i.e., relay cooperation ceiling (RCC) and overall system ceiling (OSC). Specifically, the RCC prevents the relaying link from participating in cooperative communications, while the OSC leaves the overall system in outage. Furthermore, we derive the achievable diversity gain of the considered network, which shows that the diversity gain equals either the shape parameter of the direct link or zero. Computer simulations are provided to validate the correctness of our analytical results, and study the effects of various system parameters on the system outage performance and the optimal power splitting ratio, as well as the energy efficiency. [ABSTRACT FROM AUTHOR]

This article presents a Ka-band fully metallic crossover-in-antenna based on an anisotropic lens. The crossover-in-antenna is a multifunction device simultaneously acting as a waveguide crossover and a multibeam antenna. The anisotropic lens performs like a Maxwell fish-eye (MFE) lens and a Luneburg lens in different incident directions, supporting the transmission and radiation, respectively. The lens consists of a parallel plate waveguide (PPW) with gradient spacing loaded with periodic uniform cuboid posts, which can be treated as an array of anisotropic subwavelength unit cells with gradient equivalent refractive indices. The WR28 waveguides are employed as the input–output ports. A flare is added to improve the radiation and impedance matching of antenna channels. According to the experimental results, a waveguide crossover is well realized with the reflection coefficients lower than −15 dB and insertion losses mostly lower than 1.4 dB from 28.7 to 38.2 GHz. Meanwhile, a multibeam antenna with four independent beams is obtained in the whole Ka-band, showing the gains higher than 12.5 dBi and the radiation efficiencies higher than 87.8%. The results indicate that the proposed crossover-in-antenna has application potential in the high-density multifunction integration of millimeter-wave (mmW) systems. [ABSTRACT FROM AUTHOR]

This paper presents a Luneburg lens and a Luneburg reflector lens along with the corresponding compact and cost-effective multibeam antennas in the Ka-band. The Luneburg lens is composed of an air-filled parallel plate waveguide (PPW) loaded with equal-sized metallic posts. The upper plate of the PPW is designed to a curved surface to meet the requirement of the equivalent refractive index profile, meanwhile providing a transition between the lens and the feed waveguide. Also, based on the law of reflection, a reflecting wall is introduced to the Luneburg lens to achieve a Luneburg reflector lens. By employing the WR28 rectangular waveguides as the feeders, the Luneburg lens/reflector lens antennas with single beam and multiple beams are designed and experimentally verified in the whole Ka-band. The multibeam Luneburg lens antenna show the beam scanning from −45° to +45° with 0.6 dB scan loss. The multibeam Luneburg reflector lens antenna show the beam scanning from 30° to 60° with 0.7 dB scan loss. Besides, the acceptable performances of aperture efficiency, impedance matching and multiport isolation are achieved. The results indicate that the works in this paper have application potential in the millimeter-wave (mmW) wireless communications. [ABSTRACT FROM AUTHOR]

Cascading failures typically occur following a large disturbance in power systems, such as tripping of a generating unit or a transmission line. Such failures can propagate and destabilize the entire power system, potentially leading to widespread outages. One approach to mitigate impending cascading failures is through controlled islanding, in which a set of transmission lines is deliberately tripped to partition the unstable system into several disjoint, internally stable islands. Selecting such a set of transmission lines is inherently a combinatorial optimization problem. Current approaches address this problem in two steps: first, classify coherent generators into groups and then separate generator groups into different islands with minimal load-generation imbalance. These methods, however, are based on computationally expensive heuristics that do not provide optimality guarantees. This paper proposes a novel approach to controlled islanding based on weak submodularity. The new formulation jointly captures the minimal generator non-coherency and minimal load-generation imbalance in one objective function. The islanding problem is then relaxed to a formulation with bounded submodularity ratio and a matroid constraint. An approximation algorithm is proposed which achieves a provable optimality bound on non-coherency and load-generation imbalance. The proposed framework is tested on IEEE 39-bus and 118-bus power systems. [ABSTRACT FROM AUTHOR]

Voltage instability occurs when a power system is unable to meet the reactive power demand, and is typically corrected by switching on additional reactive power devices such as capacitor banks. Real-time monitoring and communication technologies can potentially improve voltage stability by enabling the rapid detection of low voltages and the implementation of corrective actions. These corrective actions, however, will only be effective in restoring stability if they are chosen in a timely, scalable manner. In this paper, we propose a submodular optimization approach for designing a control strategy that prevents voltage instability. Our key insight is that the voltage deviation from the desired level is a supermodular function of the set of reactive power injections that are employed, leading to computationally efficient control algorithms for stabilization with provable optimality guarantees. This submodular control framework is tested on the IEEE 300-bus transmission system. [ABSTRACT FROM PUBLISHER]

With the progressive exhaustion of fossil energy and the enhanced awareness of environmental protection, more attention is being paid to electric vehicles (EVs). Inappropriate siting and sizing of EV charging stations could have negative effects on the development of EVs, the layout of the city traffic network, and the convenience of EVs' drivers, and lead to an increase in network losses and a degradation in voltage profiles at some nodes. Given this background, the optimal sites of EV charging stations are first identified by a two-step screening method with environmental factors and service radius of EV charging stations considered. Then, a mathematical model for the optimal sizing of EV charging stations is developed with the minimization of total cost associated with EV charging stations to be planned as the objective function and solved by a modified primal-dual interior point algorithm (MPDIPA). Finally, simulation results of the IEEE 123-node test feeder have demonstrated that the developed model and method cannot only attain the reasonable planning scheme of EV charging stations, but also reduce the network loss and improve the voltage profile. [ABSTRACT FROM AUTHOR]

Some uncertainties, such as the uncertain output power of a plug-in electric vehicle (PEV) due to its stochastic charging and discharging schedule, that of a wind generation unit due to the stochastic wind speed, and that of a solar generating source due to the stochastic illumination intensity, volatile fuel prices, and future uncertain load growth could lead to some risks in determining the optimal siting and sizing of distributed generators (DGs) in distribution system planning. Given this background, under the chance constrained programming (CCP) framework, a new method is presented to handle these uncertainties in the optimal siting and sizing of DGs. First, a mathematical model of CCP is developed with the minimization of the DGs' investment cost, operating cost, maintenance cost, network loss cost, as well as the capacity adequacy cost as the objective, security limitations as constraints, and the siting and sizing of DGs as optimization variables. Then, a Monte Carlo simulation-embedded genetic-algorithm-based approach is employed to solve the developed CCP model. Finally, the IEEE 37-node test feeder is used to verify the feasibility and effectiveness of the developed model and method, and the test results have demonstrated that the voltage profile and power-supply reliability for customers can be significantly improved and the network loss substantially reduced. [ABSTRACT FROM AUTHOR]

Deep brain transcranial stimulation is used in both research and for the treatment of neuropsychological diseases. Ideally, such stimulation should be noninvasive and precisely controlled. We propose a temporal-spatial interference magneto-acoustic stimulation (TIMAS) method combining transcranial magneto-acoustic stimulation (TMAS) and temporal interference stimulation (TIS) to achieve such stimulations, using the characteristics of the response of brain neurons to modulated low-frequency oscillation. Ultrasonic waves with two frequencies can interfere with each other to produce a modulated low-frequency signal. The modulated signal with difference frequency characteristics can be used for deep brain electrostimulation by means of magneto-acoustic coupling effect. A focused difference frequency electric field with a millimeter focal spot, a lateral resolution of 1.2 mm, an axial resolution of 6.4 mm, and a frequency of 4.13 kHz was achieved in the experimental system. These parameters are much better than previously reported magneto-acoustic coupling stimulation parameters. The measured electric field intensity for nerve stimulation was 137.2 mV/m, which meets the stimulation standard and reaches the threshold for effective nerve stimulation. Simulation and experimental results showed that TIMAS has superior penetration and temporal-spatial resolution and can generate a low-frequency envelope modulated electric field with a definite direction. TIMAS can be used as a new noninvasive low-frequency envelope modulated electrical stimulation, which can obtain high spatial resolution and high focus even at deep stimulation depths, and has low envelope frequency compared with the traditional TMAS. The method proposed in this article provides a new direction for the development of TMAS and is expected to be applied in brain science research and the treatment of major neuropsychiatric diseases related to deep brain regions. [ABSTRACT FROM AUTHOR]

This communication proposes a novel fully metallic multibeam Luneburg lens antenna that can simultaneously support the radiation of horizontal polarization (H-pol) and vertical polarization (V-pol). The proposed Luneburg lens consists of a parallel plate waveguide with varying spacing and a series of loaded metallic nails with graded heights. Seven OMTs are employed as the feeder. The measured results show that H-pol/V-pol peak gain is higher than 10.9 dBi/13.8 dBi from 28 GHz to 32 GHz. The dual-polarized beam scan loss is lower than 1.1 dB from −48° to +48°. The results show its potential for application in the MMW multibeam and multipolarization system. [ABSTRACT FROM AUTHOR]

Detecting the vertical profile of optical properties is an important task in the remote sensing of the upper ocean, especially for 3-D reconstruction. Ocean color remote sensing can only provide surface information, while the light detection and ranging (lidar) technique can provide depth-resolved data. Lidar can provide global-scale observations of the upper ocean for days and nights with minimal atmospheric correction errors. Unfortunately, due to the strong multiple scattering effects that occur when light propagates in seawater, the simple lidar equation may cause some deviations between the actual measurements and the simulation of the lidar signals. In this paper, we present a shipborne oceanic lidar, which was developed to detect the optical properties of seawater. For evaluating the performance of the lidar system, a Monte Carlo (MC) model was established to simulate lidar signals based on the simultaneous in situ inherent optical properties of seawater. The lidar measurements and the MC simulation can provide both the lidar signals and the retrieved lidar attenuation coefficient $\alpha $. The results of the comparison indicate that the lidar-measured signals correspond well with the MC-simulated signals at different experiment stations in the Yellow Sea and at various receiving fields of view (FOVs). We also observed strong correlations between the lidar-measured $\alpha $ and MC-simulated $\alpha $ at different stations ($r = 0.95$) and at various FOVs ($r = 0.96$). The results indicate the reliability of the developed lidar system. [ABSTRACT FROM AUTHOR]

Acoustic and electrical characteristics of biological tissue are important factors in magnetoacoustic tomography with magnetic induction (MAT-MI). Acoustic inhomogeneity significantly affects the propagations of sound waves. Differences in sound speed lead to distortions of the sound sources in the reconstruction process. The objective of this study is to develop a novel algorithm to reconstruct the sound source distribution in an acoustically inhomogeneous medium. The proposed algorithm is developed on the basis of the finite-difference time-domain method and time-reversal acoustic theory; it combines the relationship among symmetrical transducers with the back-projection algorithm. An acoustically inhomogeneous model with different regions of variable sound speeds is established to validate the proposed algorithm. From the data collected by a rotated focused transducer, first, the sound speed distribution is reconstructed, and then, the sound sources of the model are reconstructed. The reconstructed sound sources are obviously distorted when the speed differences are not considered. In contrast, the proposed algorithm yields reconstructed sound sources that are consistent with the model in terms of shape and size. Thus, the proposed algorithm is capable of accurately reconstructing the acoustic sources distribution in an acoustically inhomogeneous medium. This method provides a solution reducing the influence of acoustic inhomogeneity in MAT-MI. The distributions of sound speed can be obtained during the process of reconstructing the sound source. Consequently, the imaging of the acoustic speed and the electrical conductivity of biological tissues can be implemented simultaneously in MAT-MI. [ABSTRACT FROM PUBLISHER]

In Geosynchronous SAR (GEO SAR), because of the increase of orbit height, the signal propagation delay time reaches up to hundreds of milliseconds, and the synthetic aperture time also reaches up to hundreds of seconds which will result in a curved synthetic aperture trajectory, thus the “Stop-and-Go” assumption and conventional imaging methods of low earth orbit SAR (LEO SAR) will lose effect in GEO SAR. In addition, because the angular velocity of earth rotation is approximately equal to that of satellite rotation, the Doppler parameter and resolution analysis in LEO SAR cannot be directly used too in GEO SAR either. In this paper, firstly, the accurate slant range model in GEO SAR is created based on the consideration of the error of “Stop-and-Go” assumption, and then the improved imaging method is proposed to compensate for the error of “Stop-and-Go” assumption and the effect of the curved synthetic aperture trajectory. Finally, based on the generalized ambiguity function (GAF) and projection theory, the accurate Doppler gradient vector is analytically obtained based on the consideration of earth rotation in GEO SAR, and the accurate resolution calculation in arbitrary direction is also derived in detail. All the simulation results verify the correctness and effectiveness of the proposed imaging method and resolution analysis method. [ABSTRACT FROM AUTHOR]