复眼透镜在激光二极管阵列光束整形中的应用

在回顾复眼透镜对单光束光源的均匀化机制基础上,分析了复眼透镜对激光二极管(LD)阵列光源的光束均匀化机制。即对子光束分割叠加破坏相似性,对所有分割叠加后的子光斑进行叠加获得均匀性。在此基础上,以抽运薄片或者板条激光器需要高功率密度的均匀抽运光为需求,设计了基于复眼透镜的LD阵列光束整形系统,并给出了其中复眼透镜和积分透镜这两个关键部件的结构形式和相关参数。最后根据所设计的复眼透镜LD光束整形系统搭建了相应的实验光路并测试了整形后光斑不均匀性,测试表明不均匀性为9.8%,验证了对复眼透镜LD阵列光束整形的分析。     

航空用三相电压型PWM整流器并联控制技术

本文分析了双路三相电压型PWM整流系统并联原理,基于航空270V高压直流并联系统,提出了一种以三相电压型PWM整流器为整流方式的均流策略.在MATLAB中建立了系统的等效仿真模型,并进行了系统的硬件电路试验,仿真与试验均证明了此均流方法的可行性.     

EPON_EOC统一网管拓扑发现功能的设计和实现

针对目前大部分以太网无源光网络(EPON)与以太数据通过同轴电缆传输(EOC)设备都是使用相对独立的网管方式,在研究EPON_EOC系统结构与特点的基础上,提出了一种可以实现EPON和EOC设备统一管理的方案,并进行了EPON与EOC设备的拓扑发现功能的设计与系统实现.实际测试结果表明,该方案能较好地实现EPON_EO...     

SGDBR型激光器的波长自动控制系统

根据取样光栅分布布拉格反射器(SGDBR)型激光器的波长调谐原理,设计出用于SGDBR型激光器的波长自动控制系统.利用该系统对自行研制的SGDBR型激光器进行了准确、快速的波长扫描,为器件的动态性能研究奠定了测试基础.     

YF3:Eu3+的水热合成和发光性质

采用水热法合成了Eu3+单掺YF3荧光粉.分析了样品的结构与形貌,结果表明,所合成的样品为单相,颗粒粒度分布均匀.测定了YF3:Eu3+的激发和发射光谱,结果显示,激发光谱峰值分别为320,365,386,397,418和467 nm,激发主峰峰值位于397 nm;发射光谱由位于591 nm(5D0→F1)和612 n...     

一种C/S网络的FPGA/CPLD实验系统设计

通过分析虚拟实验室和远程实验室存在的优缺点和FPGA/CPLD实验的特殊需要,提出了C/S网络的FPGA/CPLD实验系统的设计方案.本文主要描述了实验系统的客户端、C/S网络、服务PC机、数字IC测试系统和FPGA/CPLD实验板五部分,介绍了解决多用户共享问题的方法,客户端的服务PC机的软件设计.本设计在解决贵重实...     

Effect of rapid thermal annealing on pentacene-based thin-film transistors

The bottom contact pentacene-based thin-film transistor is fabricated, and it is treated by rapid thermal annealing (RTA) with the annealed temperature up to 240 °C for 2 min in the vacuum of 1.3 × 10⁻² torr. The morphology and structure for the pentacene films of OTFTs were examined by scanning electron microscopy and X-ray diffraction technique. The thin-film phase and a very small fraction of single-crystal phase were found in the as-deposited pentacene films. While the annealing temperature increases to 60 °C, the pentacene molecular ordering was significantly improved though the grain size only slightly increased. The device annealed at temperature of 120 °C has optimal electrical properties, being consistent with the experimental results of XRD. The post-annealing treatment results in the enhancement of field-effect mobility in pentacene-based thin-film transistors. The field-effect mobility increases from 0.243 cm²/V s to 0.62 cm²/V s. Besides, the threshold voltage of device shifts from −7 V to −3.88 V and the on/off current ratio increases from 4.0 × 10³ to 8.7 × 10³.     

Thermoelectric Performance of Poly(3,4-Ethylenedioxy-thiophene)/Poly(Styrenesulfonate) Pellets and Films

The thermoelectric performance of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) pellets and free-standing PEDOT/PSS films, prepared from PEDOT/PSS solution containing the additives dimethyl sulfoxide or ethylene glycol, have been systematically investigated. It has been found that the electrical conductivity of free-standing PEDOT/PSS films is invariably much higher than that of PEDOT/PSS pellets, while there is no distinct change in the Seebeck coefficient. The highest electrical conductivity of a free-standing PEDOT/PSS film can be up to 300 S cm⁻¹, five to six times higher than that of PEDOT/PSS pellets (55 S cm⁻¹). The thermal conductivity was measured over a wide temperature range, indicating that PEDOT/PSS has extremely low thermal conductivity. The figure of merit (ZT) of free-standing PEDOT/PSS films with good environmental stability can be up to 10⁻², an order of magnitude higher than that of pressed PEDOT/PSS pellets (10⁻³).     

Analysis of microwave MESFET power amplifiers for digital wireless communications systems

The analysis of microwave MESFET power amplifiers (PAs) for digital wireless communications by using the hybrid Volterra-series method is presented in this paper. Compared with the traditional approach in the pure frequency-domain operation, the hybrid method has the advantage of fast computation for the continuous spectral signals with the same accuracy. The major modification is the equivalent baseband formulations in the time domain for the digital modulation signal, and the frequency-domain treatment with the nonlinear system via Volterra-series expansion. The MESFET two-dimensional current model is utilized and detailed current expressions are given to account for the gate-drain cross-term effects, while the nonlinear capacitors are also considered to describe the MESFET nonlinear characteristics completely. Circuit-level simulation yields the output modulation signal parameters with the measured data confirmation. System performance degradations due to nonlinear distortions of the MESFET PA are also performed for the communication link with the additive white Gaussian noise channel model. These results would be very useful in PA designs for digital wireless communications systems.     

Minimum cost localization problem in wireless sensor networks

Localization is a fundamental problem in wireless sensor networks. Current localization algorithms mainly focus on checking the localizability of a network and/or how to localize as many nodes as possible given a static set of anchor nodes and distance measurements. In this paper, we study a new optimization problem, minimum cost localization problem, which aims to localize all sensors in a network using the minimum number (or total cost) of anchor nodes given the distance measurements. We show this problem is very challenging and then present a set of greedy algorithms using both trilateration and local sweep operations to address the problem. Extensive simulations have been conducted and demonstrate the efficiency of our algorithms.