介质膜滤波器色散特性的研究

采用信号处理的方法,对介质膜滤波器的滤波特性进行了详细的研究。介质膜滤波器是最小相位滤波器,它的幅度响应与相位响应之间存在希尔伯特变换规律,因此可以通过它的幅度响应重构它的相位响应,进而可以得到它的色散特性。为了验证理论分析,设计了射频调制法测试介质膜滤波器群速度延时的实验装置。实验测试了一个100GHz33信道的介质膜滤波器的群速度延迟。通过对实验结果与理论计算结果的对比分析,发现实验数据与理论分析吻合得比较好。最后,对介质膜滤波器的色散的特点进行了分析。     

Novel miniature high power ring filter

The power handling capability of high temperature superconducting (HTS) filters is limited due to current concentration at the edges of the superconducting films. This problem can be overcome by using ring resonator, which employs the edge current free and reduces the current concentration. However, this kind of filter has large size. In order to reduce the cost and size and increase the power handling capability, in this paper a HTS photonic bandgap (PBG) structure filter is developed. The proposed pass band filter with PBG structure exhibits center frequency 12.23 GHz, steepness (about 35 dB/GHz), bandwidth (−3 dB bandwidth is 0.045 GHz), and low insertion loss (about −0.5 dB), and can handle input power up to 1 W (this value was limited by the measurement instrument used in the experiment). The size is reduced by 25%, insertion loss reduced by 37.5%, and steeper roll-off of the filter is also obtained compared with that in published literature.     

An investigation into EMI-induced noise in nanometer multi-quantum well InGaN LEDs

This study investigates the low-frequency noise induced by electromagnetic radiation interference (EMI) in a nanometer multi-quantum well InGaN LED (NMQLED). Theoretical models of the noise spectra and the EMI are constructed. In general, a good agreement is identified between the experimental and theoretical results. Both sets of results reveal that the magnitude of the EMI-induced noise is related to the pulse height, the output load, the parasitic capacitance, the interference frequency and the interference amplitude. It is shown that the harmonic noise increases with an increasing interference amplitude and frequency. The techniques presented in this study provide a systematic approach for obtaining the interference noise and signal-to-noise ratio (SNR) in LEDs and similar wavelength-based semiconductor devices.     

Relaxation in cooperative systems: Use of mixture virial coefficients

The coefficients in power series in the variable time that describe relaxation in a cooperative system can be calculated using a combinatorial approach where one considers how many ways one can introduce a given number of properly defined events in a system. The coefficients obtained in this manner can be related to the equilibrium virial coefficients for a mixture. If one assumes rapid internal equilibration, the relaxation process can be expressed completely in terms of the viral coefficients for a mixture with at most one solute particle, or, in some cases, just the virial coefficients for a single-component system. Thus, equilibrium virial coefficients can give useful information about the time evolution of processes in cooperative systems.     

Optimizing the performance of single-mode laser diode system using genetic algorithm

In this correspondence, micro-genetic algorithm (MGA) application results for optimizing the performance of electronic feedback of a laser diode are presented. The goal of optimization is to find the maximum bandwidth of the laser diode with electronic feedback used in fiber optic digital communication. A numerical analysis of the system theory of the single-mode laser diode to obtain numerical results of the gain, the pulse response, and the harmonic distortion for electronic feedback is also presented. The dependence of the system gain on the feedback gain and delay is examined. The pulse response is studied and it is shown that a transmission rate over 1 Gbyte/s can be achieved.     

An open volume, high isolation, radio frequency surface coil system for pulsed magnetic resonance

We present an open volume, high isolation, RF system suitable for pulsed NMR and EPR spectrometers with reduced dead time. It comprises a set of three RF surface coils disposed with mutually parallel RF fields and a double-channel receiver (RX). Theoretical and experimental results obtained with a prototype operating at about 100 MHz are reported. Each surface RF coil (diameter 5.5 cm) was tuned to f₀ = 100.00 ± 0.01 MHz when isolated. Because of the mutual coupling and the geometry of the RF coils, only two resonances at f₁ = 97.94 MHz and f₂ = 101.85 MHz were observed. We show they are associated with two different RF field spatial distributions. In continuous mode (CW) operation the isolation between the TX coil and one of the RX coils (single-channel) was about −10 dB. By setting the double-channel RF assembly in subtraction mode the isolation values at f₁ or f₂ could be optimised to about −75 dB. Following a TX RF pulse (5 μs duration) an exponential decay with time constant of about 600 ns was observed. The isolation with single-channel RX coil was about −11 dB and it increased to about −47 dB with the double-channel RX in subtraction mode. Similar results were obtained with the RF pulse frequency selected to f₂ and also with shorter (500 ns) RF pulses. The above geometrical parameters and operating frequency of the RF assembly were selected as a model for potential applications in solid state NMR and in free radical EPR spectroscopy and imaging.     

HT-7U等离子体位移快控电源设计

针对HT-7U装置等离子体位移快控电源大电流快速响应要求,提出了一种基于电流型变流器的快控电源(FCPS)设计新方案。该方案采用交-直-交拓扑结构,即网侧采用电流型PWP整流器设计。以获得稳定的直流电流及网侧单位功率因数正弦波电流控制;负载侧则采用电流型H桥逆变器设计以实现负载电流的快速跟踪控制。移相PWM控制策略在实现多组变流器并联运行的同时,提高了变流器的等效开关频率控制,从而改善了电流波形品质。模拟系统实验论证了方案的正确性。     

二甲醚/动力多联产系统初步研究

本文针对两步法二甲醚/动力多联产系统进行了研究。通过对两步法二甲醚生产和动力两个系统的分析整合,使用ASPEN对流程进行了模拟计算,考察了两步法DME和IGCC联产系统的特性。发现两步法DME-IGCC联产与两步法:DME和IGCC分产相比,折合热转功效率提高了5.66个百分点,折合合成能耗下降了26.05％,相对节能率为8.46％。     

提高大学物理实验教学效果的几种方法

本文阐述了提高大学物理实验教学效果的几种方法：提高认识、操作技术、故障排除、联系理论以及注重反馈。     

反馈调制型同轴虚阴极振荡器

 对反馈调制型同轴虚阴极振荡器进行了理论分析和数值模拟研究,结果表明:该器件通过增加同轴谐振腔结构并引入反馈可以对入射电子束形成明显的调制效果,从而使得器件具有高束波转化效率和频率单一稳定的特性;同时输出微波的频率被器件结构中的同轴谐振腔锁定,调节腔参数可以在一定范围内对输出微波频率进行调谐;在二极管电压约为600 kV,电子束功率26.2 GW条件下,可以得到平均功率3.6 GW的微波输出,转换效率达到13.7%,主频为5.5 GHz,模式为TM₀₂模。