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Besides transition radiation (TR) and synchrotron radiation (SR), Smith-Purcell radiation (SPR) is a simple method to generate powerful terahertz emission. Yet, as the distance from grating surface to electron trajectory increases, the SPR intensity decays exponentially due to the effective interaction range[1] ${h_{\operatorname{int} }} = \frac{\lambda }{{4\pi }}\beta \gamma $. The radiation efficiency is greatly reduced beyond the effective interaction range especially for large diameter beams. To increase the coupling efficiency, an inclined flat electron beam is used in this paper. Meanwhile, the Fabry-Perot resonator arrays take place of the ordinary grating to achieve higher radiation power. This new method of SPR reduces the requirement of electron beam and enhances the radiation intensity. To verify the theory, an electron gun from SJTU is used in experiment, the results of which agree with theoretical analyses and simulations..

The Terahertz (THz) traveling wave tube (TWT) is developed for demands of broad applications, such as broad bandwidth communications, biomedicine, security check, basic subject research, etc. Through solved and grasped key technologies of THz TWT, some THz TWTs has been designed, fabricated and measured at frequency W-band, G-band and J-band. In this paper, the research progresses of THz TWT in Aerospace Information Research Institute, Chinese Academy of Sciences (AIRCAS) will be described.

Folded Waveguide (FW) Traveling Wave Tubes (TWT) is a kind of high frequency, high power, and moderate bandwidth slow-wave structures. In many applications, FWTWT is a seductive choice. Such as radars, communication systems and electron counter measure. In this paper, a two-section folded waveguide at 0.108THz is designed to get 50W of average power. The structural parameters and dispersion characteristics of this folded waveguide are optimized through a detailed analysis. Influence of simulation parameters, angle dispersion, energy dispersion and roughness on output power are investigated using particle-in-cell (PIC) simulation. Analysis the phase velocity on the output power, and the results indicate that the output power can be increased by reducing the phase velocity. The simulation results shows that the maximum output power and gain are about 50W and 30dB at 0.108THz, and the bandwidth of this folded waveguide is about 10GHz, which is driven by an electron beam with operation voltage 13.2KV and current 0.08A.

In present work, we report a terahertz (THz) travelling wave tube (TWT) with two cascade sections, which has high power and broad-bandwidth. The operation voltage and operation current of electron beam are 17.18 kV and 71 mA, respectively. Using such electron beam, the peak power of TWT is 60 W at the frequency of 0.22THz. Besides, the gain is over 30 dB at over 6 GHz bandwidth. Such new THz TWT will be applicated in long-range radar and high-speed communication systems.

Printed electronics is a burgeoning additive manufacturing technique, which enabled extensive applications in micro/nano fabrication and flexible electronics. As a common printing material, metal oxide is employed in a variety of sensors and logic devices. However, synthesis of metal oxide ink with minimized particle size, uniform dispersion and appropriate rheological properties remains a challenge. In this study, we proposed two precursor-based inks for the printing of zinc oxide in nanoscale. The inks were tested using inkjet and dispensing printing method, respectively. The printed ZnO films showed porous nanostructures, which accommodates to the demands in sensor applications. Moreover, this study is also a demonstration of direct printing of metal oxide materials using precursor-based ink systems.

In this paper, we modelled a sub-Terahertz at the frequency of 0.108THz folded waveguide traveling-tube (FWTWT) by utilizing a 3-D particle-in-cell (PIC) in CST STUDIO SUITE., and we investigated the beam and electromagnetic field of 108GHz slow-wave structures (SWS). The process of the interaction for SWS are presented, including working voltage, the structural parameters, working frequency. The radiation power and gain of the SWS at 108GHz is 42.32W and 26.26dB. The output of the SWS changes only 1.2dB across the 7Ghz bandwidth ranging from 103Ghz to 110GHz., which is useful in many fields, such as communications, electronic countermeasures, radar.

We propose and investigate a coherent terahertz scheme, which uses a free-electron beam to drive a set of closely patterned sub-wavelength holes. Each hole is an independent electromagnetic resonator in the terahertz region and can emit coherent terahertz radiation. Detailed theoretical analyses are performed and the angular distributions of the radiation are obtained. We show that the proposed scheme can generate enhanced terahertz emission, which is insensitive to the moving direction of the electron beam, affording an efficient way of generating coherent terahertz radiation.

The vacuum electron device (VED) is one of the best devices to generate terahertz wave with its advantages of high power, high frequency and power synthesis. In order to obtain higher power terahertz wave, it is imperative to improve the output power and efficiency of VED. For this aim, we propose a novel THz rectangular grating slow wave structure (SWS). The SWS can make full use of the longitudinal electric field of the slot, so that the electromagnetic wave can interact with the electron beam efficiently, so as to improve the beam-wave interaction efficiency and output power. The field characteristics of the novel SWS are analyzed, and the “cold” dispersion equations are derived by the eigen-function method, and the dispersion characteristics and coupling impedance are calculated. The results show that the grating SWS with double holes embed sheet beams has higher working frequency and coupling impedance than the ordinary grating without any slot. These studies provide theoretical guidance for the design of the grating SWS with double holes embed sheet beams.

For the purpose of improving the whole efficiency of terahertz traveling wave tubes (TWT), multistage depressed collector is widely used during the design phase. It is tough to collect all the wasted electrons which undergo the beam wave interaction thus generating secondary electron emission in MDC. Emission will increase the back-streaming current that would damage the slow wave structure, effecting the whole microwave tube. In order to tackle this problem, an asymmetric model is proposed in this paper through detailed analysis of the spent beam. According to the simulation results, this asymmetric MDC maintains lower electron streaming backward while keeping high recovery efficiency which shed some light to the researchers.

Terahertz wave has been inspired great interests for its myriad applications, such as biochemical sensing and high-bandwidth communications, etc. THz sources are the key technology toward the wide applications. Therefore, THz sources are highly focused on developments, especial those with wide band, high power, room temperature operation. Vacuum electronic THz sources are important directions in THz sources. Institute of Electronics, Chinese Academy of Sciences (IECAS) with the history over 60 years has developed many kinds of vacuum electronic devices, such as klystrons, space traveling wave tube amplifier (TWTA), Gyrotron and extended interaction oscillator (EIO), etc. In this paper, we report the progresses of G-band traveling wave tube in IECAS.

In this article, we propose a classical optimization algorithm named L-BFGS to simulate the thermal behavior of electron gun for terahertz traveling-wave tubes. The L-BFGS algorithm, as a variation of Quasi-Newton optimization method, expert in dealing with the unconstrained optimization problems while keeping the stability of the calculation. Efficiency and accuracy of L-BFGS algorithm are verified by modeling the thermal behavior of an actual electron gun on MATLAB platform successfully with no breakdown. According to the simulation results, this method performs better than some reference methods in terms of computational memory usage and time cost. Our numerical conclusions indicate that it is promising for thermal analysis of electron gun, which would be useful for researchers during the design phase.

With the increasing types and functions of smart home devices, due to the lack of experience of users, they may cause unexpected errors and risks when configuring a large number of device linkage rules.In response to the above problems, in this paper, we propose an efficient conflict detection method to avoid unexpected situations.First, to reduce the complexity of subsequent rule conflict detection, we divide each rule into five categories according to its functions and characteristics. At the same time, we configure the priority, user rights, and execution area for each rule. Second, we filter out the rules of the same priority, user rights, and execution area. Third, we define five types of rule conflicts. Finally, the conflict detection algorithm is used to determine whether the filtered rules conflict with the rules in the corresponding database. We have created 379 non-conflicting rules in each type of rule storage database to detect whether the newly created rules conflict with them. Through experimental comparison, we find that our approach has more advantages than previous work in terms of performance and conflict detection types.

In this paper, the high frequency characteristics of Trapezoidal Staggered Grating Slow-wave Structure for 1THz Traveling Wave Tube has been studied. The transmission structure has been simulated, the reflection coefficient is less than -20dB in the frequency of 1015GHz to 1055GHz and the loss of the structure is over 58dB. The PIC simulation shows that the saturation output power is 405mW at the frequency of 1030GHz, and the corresponding gain is 19.08dB.

The Multi-stage depressed collector (MDC) is used as an essential efficiency enhancement technique in traveling-wave tubes (TWT). Two-third of the total power consumption of TWT is dissipated in the collector. In this paper, thermal and deformation analysis of MDC in G-band are implemented by using ANSYS. Temperature distribution of the MDC at given power supply are fully simulated, maximum deformations meanwhile in MDC at different ambient temperature are carefully compared with. The simulated prediction is in agreement with the experimental results.

In this paper, we modelled a sub-Terahertz at the frequency of 0.108THz folded waveguide traveling-tube (FWTWT) by utilizing a 3-D particle-in-cell (PIC) in CST STUDIO SUITE, and we investigated the beam and electromagnetic field of 108GHz FWTWT. The process of the interaction for FWTWT are presented, including working voltage, the structural parameters, working frequency. The radiation power and gain of the FWTWT at 108GHz is 42.32W and 26.26dB. The output of the FWTWT changes only 1.2dB across the 7Ghz bandwidth ranging from 103Ghz to 110GHz, which is useful in many fields, such as communications, electronic countermeasures, radar.

In vacuum electronic devices region, high power, compact, portable and miniaturized terahertz radiation source has always been the research goal. The core of vacuum electronic device is slow wave structure, which determines the beam wave interaction efficiency and output power. For the classical slow wave structure of rectangular grating, the field matching method is used to analyze the slow wave structure of rectangular grating with holes in the middle, and then the dispersion equation is obtained For the field treatment in the trough, the higher term is retained, which is expressed as the sum of an infinite standing wave [1].

A 0.67THz sheet electron beam traveling-wave tube based upon sine waveguide slow-wave structure is studied. In this paper, the high frequency characteristics and transmission characteristics are calculated by a 3-D high frequency simulation software. The beam-wave interaction is also simulated. From the simulation results, the peak output power is 1.7W ranging from 0.65THz to 0.69THz with synchronous voltage of 17kV, operation current of 10mA and input power of 3.2mW.

Although time-series data collected from users can be utilized to provide services for various applications, they could reveal sensitive information about users. Recently, local differential privacy (LDP) has emerged as the state-of-art approach to protect data privacy by perturbing data locally before outsourcing. However, existing works based on LDP perturb each data point separately without considering the correlations between consecutive data points in time-series. Thus, the important patterns of each time-series might be distorted by existing LDP-based approaches, leading to severe degradation of data utility. In this paper, we focus on real-time data collection under a honest-but-curious server, and propose a novel pattern-aware privacy-preserving approach, called PatternLDP, to protect data privacy while the pattern of time-series can still be preserved. To this end, instead of providing the same level of privacy protection at each data point, each user only samples remarkable points in time-series and adaptively perturbs them according to their impacts on local patterns. In particular, we propose a pattern-aware sampling method based on Piecewise Linear Approximation (PLA) to determine whether to sample and perturb current data point. To reduce the utility loss caused by pattern change after perturbation, we propose an importance-aware randomization mechanism to adaptively perturb sampled data locally while achieving better trade-off between privacy and utility. A novel metric-based w-event privacy is introduced to measure the privacy protection degree for pattern-rich time-series. We prove that PatternLDP can provide the above privacy guarantee, and extensive experiments on real-world datasets demonstrate that PatternLDP outperforms existing mechanisms and can effectively preserve the important patterns.

Autonomous flight through unknown environments in the presence of obstacles is a challenging problem for micro aerial vehicles (MAVs). A majority of the current state-of-art research assumes obstacles as opaque objects that can be easily sensed by optical sensors such as cameras or LiDARs. However in indoor environments with glass walls and windows, or scenarios with smoke and dust, robots (even birds) have a difficult time navigating through the unknown space.In this paper, we present the design of a new class of micro aerial vehicles that achieves autonomous navigation and are robust to collisions. In particular, we present the Tiercel MAV: a small, agile, light weight and collision-resilient robot powered by a cellphone grade CPU. Our design exploits contact to infer the presence of transparent or reflective obstacles like glass walls, integrating touch with visual perception for SLAM. The Tiercel is able to localize using visual-inertial odometry (VIO) running on board the robot with a single downward facing fisheye camera and an IMU. We show how our collision detector design and experimental set up enable us to characterize the impact of collisions on VIO. We further develop a planning strategy to enable the Tiercel to fly autonomously in an unknown space, sustaining collisions and creating a 2D map of the environment. Finally we demonstrate a swarm of three autonomous Tiercel robots safely navigating and colliding through an obstacle field to reach their objectives.

Massive integration of converter-based renewable energy sources into power systems through weak AC grid has become a dilemma in recent years. This paper investigates the design of a robust nonlinear multi-input-multi-output (MIMO) controller for voltage source converters (VSCs) connected to weak AC grids. Feedback linearization method is used to find the controller equations and design the inputs to regulate the active power and output voltage of the converter. With this approach, the controller is designed in a way that the grid impedance impact on the stability of the converter system is significantly reduced. The robustness of the proposed controller is evaluated using time-domain simulations of a grid-connected VSC enhanced with the nonlinear controller in various case studies. The results illustrate a significant improvement compared to existing approaches.

Electron optics system (EOS) for G-band traveling wave tube (TWT) is designed, and the design process of electron gun and permanent magnetic focusing system are described. Firstly, according to the particle-in-cell (PIC) simulation results of high frequency structure, we design an electron gun which can emit enough current whose quality is good. Secondly, combining with Piers theory, the structure of permanent magnetic focusing system which matches the electron gun is designed. The simulation results show that the passing rate of electron beam is high and its ripple is low. Basic parameters of EOS are as follows: the current emitted from the surface of cathode is greater than 70 mA when operating voltage is 17 kV. The length and radius of drift tube are 45 mm and 0.2 mm, respectively. Magnetic field (B) is about 6000 Gauss on the central axis. At last, the experimental results show that the passing rate of the electron beam is higher than 70%.

For meeting the myriad demands of high-bandwidth communications, biomedicine, material research and security check, the terahertz folded waveguide traveling wave tube (TWT) amplifier is developed. Through the solved key technologies of small electron gun cathode, miniature and low attenuation folded waveguide and assembly of THz TWT, it is tested through the setup of power and frequency experimental system. The measured results show that the power exceeds 5 W and bandwidth is greater than 5 GHz at frequency G-band. The higher output power THz TWT is being manufactured through the X-ray LIGA technology. On the other hand, the two-electron beam backward wave oscillator (BWO) is being developed. In this report, we will describe the progresses of THz vacuum electronic sources in institute of electronics, Chinese Academy of Sciences (IECAS).

Metasurfaces have shown extraordinary ability to manipulate the wavefront of electromagnetic wave and varieties of functional devices have been proposed. However, due to the dispersion of the phase accumulated in the light path, the metasurfaces suffer from large chromatic aberration and thus limit their usages in many domains. Here, a metasurface-based circularly polarized broadband reflective device is proposed, focusing on the directional reflectors and focusers constructed by metasurface elements, to eliminate the chromatic aberration. Utilizing the principle of the generalized Snell's laws and focusingcompensation, a one-dimensional deflector with 16 sub-arrays consisted of 19 geometricresonance combined phase shift elements is proposed. The reflector covers a continuous phase range from 90 to 360 and its efficiency remains over 50 percent in an expanded spectrum Compared with previously proposed structures, a much broader bandwidth and higher efficient achromatic aberration has been achieved, spanning from 0.37 THz to 0.5 THz, a relative bandwidth of 35 percent, which remains the fixed reflective angle of 20° stably, highly in consistent with the theory angle of 19.84°. Based on the one-dimensional achromatic sub-array, we further construct a two-dimensional wide-band parabolic-like focusing metasurface. The focal length is 40 mm fixed and its NA (numerical aperture) is 0.291. The simulation results are in good accordance with theoretical prediction. The proposed method to suppress the chromatic aberration paves an innovative way to control the phase dispersion at will and allow some advancement in optical systems, corrected imaging systems, and in full-color detection.

The 0.5THz backward wave oscillator, with Two-section rectangular gratings involving cylindrical electron beam, was developed. The length of the two-section backward-wave oscillator was determined by that of one section structure. The drift part linking the first section and second section, was located according to electron bunch. The output power of backward-wave oscillator is improved by introducing the floating part which can make the electron beam losing more energy and enhance the beam-wave interaction. The length of floating part was optimized by output power with particle-incell (PIC) simulations. When the length of floating part is 0.3mm, the maximum output power increases to 1.4W, comparing with that of one section structure (0.3W). Besides, the influences of conductivity, magnetic field, beam voltage and current on the output power are investigated through the CST simulation. The optimum results will be appeared in detailed abstract.

We reported the design of output window for 0.5THz backward wave oscillator. The initial parameters were determined by equivalent theories, then simulated and optimized by CST microwave studio. In this paper, sapphire was selected as the window material, and we obtained a pillbox output window with the voltage standing wave ratio of less than 1.1 in the frequency range of 0.502~0.519THz. The influences of structural parameter changes on the output performance were analyzed.