Experimental investigation of the relativistic backward wave oscillator with a periodic guiding magnetic field

Experiment is carried out on the accelerator Sinus-700 to investigate the Relativistic Backward Wave Oscillator （RBWO） with a periodic guiding magnetic field. When the strength of the guiding magnetic field, whose period is 4.6 cm, is 0.54 T, a microwave output power of 0.95 GW at 9.1 GHz microwave frequency is achieved. It is shown that the RBWO with a periodic guiding magnetic field is feasible.     

A 12.1-W SESAM mode-locked Yb:YAG thin disk laser

Pumped by a 940 nm fiber-coupled diode laser, a passively mode-locked Yb:YAG thin disk oscillator was demonstrated with a semiconductor saturable absorber mirror(SESAM). 12.1 W mode-locked pulses were obtained with pulse duration of 698 fs at the repetition rate of 57.43 MHz. Measurement showed that the beam quality was close to the diffraction limit.     

Improvement of sintering,nonlinear electrical,and dielectric properties of ZnO-based varistors doped with TiO_2

The effects of TiO_2 on sintering and nonlinear electrical properties of(98.5-x)ZnO–0.5MnO_2–0.5Co_2O_3-0.5Bi_2O_(3–x)TiO_2(x = 0.3,0.5,0.7,0.9 mol%) ceramic varistors prepared by the ceramic technique are investigated in this work.The optimum sintering temperature of the prepared samples is deduced by determining the firing shrinkage and water absorption percentages.The optimum sintering temperature is found to be 1200℃,at which each of the samples shows a maximum firing shrinkage and minimum water absorption.Also minimum water absorption appears in a sample of x = 0.9 mol%.Higher sintering temperature and longer sintering time give rise to a reduction in bulk density due to the increased amount of porosity between the large grains of ZnO resulting from the rapid grain growth induced by the liquid phase sintering.The crystal size of ZnO decreases with increasing TiO_2 doping.The addition of TiO_2 improves the nonlinear coefficient and attains its maximum value at x = 0.7 mol% of TiO_2,further addition negatively affects it.A decrease in capacitance consequently in the dielectric constant is recorded with increasing the frequency in a range of 30 kHz–200 kHz.The temperature and composition dependences of the dielectric constant and AC conductivity are also studied.The increase of temperature raises the dielectric constant because it increases ionic response to the field at any particular frequency.     

Improved performance of near UV light-emitting diodes with a composition-graded p-AlGaN irregular sawtooth electron-blocking layer

We investigate the performances of the near-ultraviolet(about 350 nm-360 nm) light-emitting diodes(LEDs) each with specifically designed irregular sawtooth electron blocking layer(EBL) by using the APSYS simulation program.The internal quantum efficiencies(IQEs),light output powers,carrier concentrations in the quantum wells,energy-band diagrams,and electrostatic fields are analyzed carefully.The results indicate that the LEDs with composition-graded pAl_xGa_(1-x)N irregular sawtooth EBLs have better performances than their counterparts with stationary component p-AlGaN EBLs.The improvements can be attributed to the improved polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-AlGaN interface,which results in less electron leakage and better hole injection efficiency,thus reducing efficiency droop and enhancing the radiative recombination rate.     

基于CAN总线的振动试验智能监控系统软件设计

振动试验是为了保障航天及民用产品可靠性的重要试验手段,传统的振动试验对功放的操作繁琐,效率低下,已经越来越无法适应新型振动试验的发展。提出一种基于CAN总线控制器构建的振动试验功率放大器远程监控系统,使用Visual C++进行编程,实现了在计算上对功率放大器的远程操作,解放了操作人员,同时由于计算机的开放性,系统可以扩展出运行参数实时显示,配置本地存储、保护互锁、开机自检等功能,最后通过实验验证表明系统软件运行可靠,达到了预期的设计目的。     

光伏阵列伏安特性测试系统设计

基于对光伏电站控制和设计水平的要求,本文提出一种基于电容充放电的特性的光伏阵列伏安特性测试系统。本文阐述了测试系统的工作原理和系统关键的部分。当光伏阵列给电容充电时,得到当时环境中光伏阵列的电压、电流以及相应的功率特性曲线。同时对M*N的光伏组件进行建模,得出组件的相应的电性能参数,并对最大功率点进行分析。最后进行实验验证。本测试系统具有测量精度高、系统稳定性高、成本低廉,并且能更直观的测得光伏阵列的特性。     

高电子迁移率晶体管放大器高功率微波损伤机理

在TCAD半导体仿真环境中,建立了0.25 m栅长的AlGaAs/InGaAs高电子迁移率晶体管(HEMT)低噪声放大器与微波脉冲作用的仿真模型,基于器件内部的电场强度、电流密度和温度分布的变化,研究了1 GHz的微波从栅极和漏极注入的损伤机理。研究结果表明,从栅极注入约40.1 dBm的微波时,HEMT内部峰值温度随着时间的变化振荡上升,最终使得器件失效,栅下靠源侧电流通道和强电场的同时存在使得该位置最容易损伤;从漏极注入微波时,注入功率的高低会使器件内部出现不同的响应过程,注入功率存在一个临界值,高于该值,器件有可能在第一个周期内损伤,损伤位置均在漏极附近。在1 GHz的微波作用下,漏极注入比栅极注入更难损伤。     

多倍脉宽输出的螺旋重入脉冲形成线

提出了一种螺旋线重入结构的脉冲形成线,可实现多倍脉宽输出。该结构由储能外线和重入内线组成;重入内线的外屏蔽圆筒内表面呈阶梯状,内筒为均匀螺旋线结构,实现简单;储能外线与Tesla变压器一体化。结合采用螺旋重入和二级重入结构,给出了一组10 GW功率、百ns脉宽的重入型脉冲形成线设计,形成线采用Midel 7131合成酯绝缘介质,外筒内径1 m,长度2 m。     

L波段高功率波导缝隙阵设计与数值模拟

设计了一种基于宽边纵缝驻波阵的高功率射频微波辐射系统,系统由四路矩形波导以及聚四氟乙烯天线窗组成。天线内采用真空绝缘实现天线高功率容量,天线窗真空侧采用周期刻三角槽技术抑制高功率微波介质表面击穿。在波导缝隙阵与天线窗之间设计支撑板,除支撑天线窗外还可抑制表面波电流。采用HFSS数值模拟软件对辐射系统进行了优化设计。数值模拟结果表明,设计的辐射系统在频率为1.575 GHz时,增益为22.7 dBi,天线口径效率为98.3%,反射系数为-25 dB,带宽达到5%,带宽内天线增益波动小于等于0.4 dB、天线口径效率大于等于98%、主瓣指向偏差小于等于1.2。系统功率容量达到1.92 GW。     

双极结型晶体管的集电结反向雪崩击穿特性

通过气体放电产生更高浓度的低温等离子体要求具有纳秒上升沿和纳秒脉宽的高重频快脉冲,而目前被广泛使用的MOSFET和IGBT都无法满足这些参数要求,而双极结型晶体管(BJT）的集电极与发射极之间的雪崩击穿过程具有快导通、快恢复、高稳定性等优点,适合作为小型Marx发生器的自击穿开关。文中对用多种型号的BJT进行击穿特性比较测试实验,发现可以通过改变BJT的门极和发射极的并联电阻来调节其雪崩击穿电压,实现一定范围的工作电压。雪崩击穿恢复特性实验表明,当击穿电流衰减到低于维持电流时,BJT就会开始恢复绝缘而关断,通过改变电路中的参数以控制击穿电流的变化就可以控制BJT的雪崩击穿导通时间（即导通脉宽）。将这些结论应用到实际电路中,可获得上升沿5 ns、脉宽为10 ns、幅值2 kV、重复频率高达100 kHz的纳秒快脉冲,可用于激发高浓度低温等离子体。