In this article, a folded waveguide with two coupling grooves is proposed for high-power and high-frequency traveling wave tubes (TWTs). The structure allows a modified TE20 high-order mode interact ...with two sheet electron beams. The transmission characteristics of this novel structure were simulated and measured. A good <inline-formula> <tex-math notation="LaTeX">{S}_{{21}} </tex-math></inline-formula> of −10 dB and <inline-formula> <tex-math notation="LaTeX">{S}_{{11}} </tex-math></inline-formula> of less than −15 dB were achieved in the 218-230-GHz range. Moreover, simulations of the beam-wave interaction in this structure predicted an output power of 930 W at 220 GHz, with a small signal gain of 58 dB and a 3-dB bandwidth of 1.3 GHz.
Traveling wave tube (TWT) is an attractive solution for wideband and high-power sources or amplifiers in the terahertz (THz) band. In this article, a novel slow-wave structure (SWS) for TWT, named ...double tunnel sine waveguide (DTSW), which is based on sine waveguide (SW), is proposed. The following key technologies are adopted: 1) the rectangular holes, at which the operating mode is cutoff, are alternately opened on the sine-shaped ridges to form two electron beam tunnels and 2) the lower surface of rectangular holes is flush with the top of sine-shaped ridges. Compared with the SW-SWS, DTSW-SWS has the wider operating band and higher interaction impedance under the condition that the phase velocity of the two SWSs is at the same level. In addition, DTSW-SWS is simple in structure and easy to fabricate. The particle-in-cell simulation results reveal that DTSW-TWT has an output power of more than 202 W in the frequency range of 202-255 GHz with the maximum power of ~405 W and electron efficiency of ~9.8% at 215 GHz, under the operating voltage of 23 kV and beam current of 180 mA. Therefore, the DTSW should be considered as a promising SWS for the high-power and wideband THz traveling wave amplifier.
This letter presents the research progress of a pulsed G-band 50 W traveling wave tube (TWT) with pencil beam focused by periodic permanent magnet (PPM). Three approaches have been combined to ...improve the tube's operation performances including setting the operating point near the cutoff frequency, using the folded waveguide (FWG) slow wave structure (SWS) with modified circular bends (MCBs), and adopting phase velocity tapering (PVT) technique. The measured output power can be over 50 W at 5% duty cycle with a bandwidth of 3.6 GHz when the beam voltage is 24.25 kV and the beam current is 59 mA. Corresponding electronic efficiency and gain are higher than 3.5% and 35 dB, respectively. The results provide a demonstration of a compact terahertz amplifier with high power, high electronic efficiency and significant bandwidth.
Abstract
In order to solve the difficult problem of fault branch determination in multi-branch distribution networks, the transmission characteristics of fault traveling waves in the distribution ...line are analyzed. The variation law of fault traveling wave amplitude with fault distance and frequency is deduced theoretically, and the reasons for the difficult determination of fault branch in the distribution line are revealed. A fault branch determination method based on the energy spectral density of the amplitude of the first wave head of the fault initial traveling wave is proposed. The reference node and the reference end of distribution networks are defined. The ratio of the intrinsic amplitude matrix to the real fault matrix before offline is calculated. The fault branch determination matrix is established to realize the reliable determination of the fault branch. PSCAD is used to build a 10 kV multi-dominant network model to simulate various fault conditions to verify the fault branch determination method. The simulation results show that the method can effectively identify the fault branch and has strong reliability.
We present the results of experimental investigations of multifrequency oscillations in a Formula Omitted-band gyrotron traveling-wave tube (gyro-TWT) with double-disk external reflector. The system ...operation in multifrequency regime was tested for a prolonged period of time with temperature monitoring by an infrared camera. Based on the measurement results, the possibility of stable generation for a period of several tens of minutes at the output power level of more than 2 kW is demonstrated.
This article proposes an end-to-end framework for solving multiobjective optimization problems (MOPs) using deep reinforcement learning (DRL), that we call DRL-based multiobjective optimization ...algorithm (DRL-MOA). The idea of decomposition is adopted to decompose the MOP into a set of scalar optimization subproblems. Then, each subproblem is modeled as a neural network. Model parameters of all the subproblems are optimized collaboratively according to a neighborhood-based parameter-transfer strategy and the DRL training algorithm. Pareto-optimal solutions can be directly obtained through the trained neural-network models. Specifically, the multiobjective traveling salesman problem (MOTSP) is solved in this article using the DRL-MOA method by modeling the subproblem as a Pointer Network. Extensive experiments have been conducted to study the DRL-MOA and various benchmark methods are compared with it. It is found that once the trained model is available, it can scale to newly encountered problems with no need for retraining the model. The solutions can be directly obtained by a simple forward calculation of the neural network; thereby, no iteration is required and the MOP can be always solved in a reasonable time. The proposed method provides a new way of solving the MOP by means of DRL. It has shown a set of new characteristics, for example, strong generalization ability and fast solving speed in comparison with the existing methods for multiobjective optimizations. The experimental results show the effectiveness and competitiveness of the proposed method in terms of model performance and running time.
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Hundreds of piezoelectric ultrasonic motors (PUSMs) have been proposed for scientific researches and developed for commercial applications in the past decade. They are surveyed and ...mainly classified into three types: standing wave motor (SWM), traveling wave motor (TWM) and hybrid modes motor (HMM), according to their operating principles. These different types of PUSMs are discussed in detail, in terms of their operating principles, structures, features and performances. The methods to realize the multi-degree-of-freedom (multi-DOF) motions of the PUSMs are also investigated based on the basic operating principles of the SWM, TWM and HMM. Some practical applications and representative designs of the PUSMs are introduced briefly. Finally, further efforts and research perspectives of the PUSM are summarized. This review contributes to a comprehensive understanding of the state of arts of the PUSM.
This paper addresses the task scheduling and path planning problem for a team of cooperating vehicles performing autonomous deliveries in urban environments. The cooperating team comprises two ...vehicles with complementary capabilities, a truck restricted to travel along a street network, and a quadrotor micro-aerial vehicle of capacity one that can be deployed from the truck to perform deliveries. The problem is formulated as an optimal path planning problem on a graph and the goal is to find the shortest cooperative route enabling the quadrotor to deliver items at all requested locations. The problem is shown to be NP-hard. A solution is then proposed using a novel reduction to the Generalized Traveling Salesman Problem, for which well-established heuristic solvers exist. The heterogeneous delivery problem contains as a special case the problem of scheduling deliveries from multiple static warehouses. We propose two additional algorithms, based on enumeration and a reduction to the traveling salesman problem, for this special case. Simulation results compare the performance of the presented algorithms and demonstrate examples of delivery route computations over real urban street maps.
Differential protection is widely used for transmission lines, but its performance is affected by distributed capacitance current and current-transformer (CT) saturation. Travelling-wave (TW) ...differential protection is immune to these factors and can achieve ultra-high-speed operation. These characteristics are essential for long-distance extra/ultra-high-voltage transmission-line protection. However, the contradiction between sampling frequency and communication traffic makes it hard to ensure high sensitivity and high reliability at the same time. To solve this problem, a new TW differential protection based on equivalent travelling wave (ETW) is proposed in this paper. Wavelet transform is adopted to extract wavelet-transform modulus maxima (WTMM) of TW, which are used to reconstruct ETW. Only several WTMMs need to be exchanged with the opposite terminal, so the amount of communication is largely reduced. Current energy ratio is defined and used for operation criterion to enhance the sensitivity during faults with large fault resistance and a small fault inception angle. Detailed discussions on the selection of setting value ensure the reliability of the proposed protection scheme. Extensive simulations are conducted to test the performance of the protection. Simulation results verify that the protection can correctly discriminate between internal and external faults with high sensitivity and reliability.
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