钛扩散铌酸锂矩形波导中的双折射耦合对传播常数的影响

 从亥姆霍兹方程出发，得到了各向异性光波导在弱导近似下的耦合模理论。耦合系数包括偏振耦合项和双折射耦合项。并用马卡提里近似下的模式作为零级近似。用一级微扰法计算了折射率渐变分布的钛扩散铌酸锂矩形波导的传播常数。在给定参数的情况下，得到双折射项引起的传播常数的改变约为主微扰项的3%，因此双折射耦合对钛扩散铌酸锂矩形波导的性能影响不可忽略，这对设计和分析与它相关的光波导器件具有指导意义。     

混合矢量有限元法分析高温超导微带线的传输特性

采用混合矢量有限元方法结合唯象二流体模型,对高温超导微带线的复电导率表达式做了推导,经Helmholtz方程弱形式变换,得到了适用于HTS微带线的方程,对高温超导(HTS)微带线的传输特性(包括损耗、色散等)进行了全波分析,与谱域法计算比照后可以发现,两者曲线在0.1GHz~1000GHz吻合很好,并采用该方法计算分析了HTS微带传输线中模式色散的影响。     

Time-domain Wave Propagation in Dispersive Media^①

The equation of time-domain wave propagation in dispersive media and the explicit beam propagation method are presented in this paper.This method is demonstrated by the short optical pulses in a directional coupler with second order dispersive effect and shows to be in full agreement with former references.This method is simple,easy and practical.     

基于三维空间特征库的MR定位系统

测量报告(MR)是由网管系统收集的终端上报的测量信息,包括RSRP,PCI等信息,MR能够最真实地反馈用户在无线网络中的体验。但是由于隐私问题,MR中不包含用户的位置相关信息,这就导致运营商无法确定用户感知差的情况究竟发生在哪里。本文提出一种基于三维空间特征库的MR定位系统,利用确定性传播模型,建立三维空间接收场强特征库,并以此对MR进行精确定位,确定MR中每条记录发生的空间位置。这样就可以帮助运营商对网络的盲点、热点等进行精准定位,进而有目的地进行网络规划和优化。     

Behaviour of CPW and TFMS lines at high temperature for RF applications in sub-45 nm nodes

Coplanar waveguide (CPW) and thin film microstrip (TFMS) lines integrating porous ultra low-k as inter-metal dielectric layers (k = 2.5) and copper as metal, are for the first time experimentally measured up to 110 GHz and under different temperature conditions, up to 200 °C. The extracted attenuation and propagation coefficients of those transmission lines are compared to simulations performed with MAGWEL software, a frequency domain 3-D Maxwell solver. Based on the characterization results some guidelines related to interconnect design are presented for future applications.     

On the Cramer-Rao lower bound for RSS-based positioning in wireless cellular networks

An accurate position of a mobile user's location is substantial in wireless cellular networks with respect to location based services (LBS) implementation. Among the available parameters used to estimate a desired location, low cost measurement of received signal strength (RSS) makes it suitable for outdoor and indoor positioning. Our aim here is to look at the performance of a theoretically optimal user's position estimator. We examine the Cramer-Rao lower bound (CRLB), which sets the lowest variance of any unbiased estimator. Due to the oversimplification with respect to reliance on detailed cognizance of environment, we deploy theoretical free-space and empirical COST-231-Hata, Stanford University Interim (SUI) and ECC-33 path loss models that are dominantly used in real scenarios aiming to form the system model equations. The findings show that the CRLB on estimation precision depends on the underlying path loss exponents (PLE) and the relative positions of the mobile and base stations. The calculated bounds provide a benchmark against which it is possible to evaluate different positioning algorithms, techniques and estimators relying on the specified path loss models.     

Introduction of a new technique for simultaneous reduction of the delay and leakage current in digital circuits

By the reduction in the size of transistors and the development of submicron technology, as well as the construction of more integrated circuits on chips, leakage power has become one of the main concerns of electronic circuit designers. In this article, we first review techniques presented in recent years to reduce leakage power and then present a new technique based on the gate-level body biasing technique and the multi-threshold CMOS technique to minimize leakage power in digital circuits. Afterward, we develop another new method by improving the first proposed technique to achieve higher efficiency and simultaneously reduce leakage power and propagation delay in digital circuits. In the proposed technique, we use two dynamic threshold MOSFET transistors to reduce leakage current. In this paper, the body biasing generator structure is applied to reduce propagation delay. The proposed technique has been successfully validated and verified by post-layout simulation with Cadence Virtuoso based on the 32 nm process technology.We evaluate the efficiency of the proposed techniques by examining factors including power, delay, area, and the power delay product. The simulation results using HSPICE software and performance analysis to process corner variations based on the 32 nm process technology show that the proposed technique, in addition to having proper performance in different corners of the technology, significantly reduces leakage power and propagation delay in logic CMOS circuits. In general, the proposed technique has a very successful performance compared to previous techniques.     

Effects of aggregation on the electromagnetic resonance scattering of dielectric spherical objects

Summary The effects of aggregation on the electromagnetic resonance scattering by small, strongly reflecting spheres are studied. Two or more spheres are allowed to cluster together to form rather complicated anisotropic scatterers whose extinction cross-section is calculated as a function of the wave number of the incident field in the neighbourhood of the lowest resonance of the individual spheres. The macroscopic absorption coefficient of a low-density random dispersion of clusters is also calculated in the same range of wave number. The results for two-, three- and four-sphere clusters are discussed. Work supported in part by C.N.R. through the G.N.S.M. and in part by the U.S. Army European Research Office through grant DAJA45-84-C-0005 and contract DAJA37-81-C-0895.     

TextInsight: A new text visualization system based on entropy and GMap

In recent years, text visualization has been widely acknowledged as an effective approach for understanding the structure and patterns hidden in complicated textual information. In this paper, we propose a new visualization system called TextInsight with two of our contributions. Firstly, a textual entropy theory is introduced to encode the semantic importance distribution in the corpus. Based on the proposed multidimensional joint probability histogram in vector fields, the improved algorithm provides a novel way to position valuable information in massive short texts accurately. Secondly, a map-like metaphor is generated to visualize the textual topics and their relationships. For the problem of over-segmentation in the layout and clustering procedure, we propose an optimization algorithm combining Affinity Propagation （AP） and MultiDimensional Scaling （MDS）, and the im- proved geographical representation is more comprehensible and aesthetically appealing. Our experi- mental results and initial user feedback suggest that this system is effective in aiding text analysis.     

典型微区环境下信道特性的仿真结果

多径效应产生的扩散效应一直是无线信道研究的主要问题。作者利用自行开发的无线信道仿真软件对微区环境下的主要信道特性进行了大量的仿真，得到了典型微区环境下的传播损耗，时延扩展和角度扩散等主要信道特性的描述。