Generation and Analysis of Constrained Random Sampling Patterns

Random sampling is a technique for signal acquisition which is gaining popularity in practical signal processing systems. Nowadays, event-driven analog-to-digital converters make random sampling feasible in practical applications. A process of random sampling is defined by a sampling pattern, which indicates signal sampling points in time. Practical random sampling patterns are constrained by ADC characteristics and application requirements. In this paper, we introduce statistical methods which evaluate random sampling pattern generators with emphasis on practical applications. Furthermore, we propose a new random pattern generator which copes with strict practical limitations imposed on patterns, with possibly minimal loss in randomness of sampling. The proposed generator is compared with existing sampling pattern generators using the introduced statistical methods. It is shown that the proposed algorithm generates random sampling patterns dedicated for event-driven-ADCs better than existed sampling pattern generators. Finally, implementation issues of random sampling patterns are discussed.     

Decomposition and Analysis of Process Variability Using Constrained Principal Component Analysis

Process-induced variability has become a predominant limiter of performance and yield of IC products especially in a deep submicron technology. However, it is difficult to accurately model systematic process variability due to the complicated and interrelated nature of physical mechanisms of variation. In this paper, a simple and practical method is presented to decompose process variability using statistics of the measurements from manufacturing inline test structures without assuming any underlying model for process variation. The decomposition method utilizes a variant of principal component analysis and is able to reveal systematic variation signatures existing on a die-to-die and wafer-to-wafer scale individually. Experimental results show that the most dominant die-to-die variation and wafer-to-wafer variation represent 31% and 25% of the total variance of a large set of manufacturing inline parameters in 65-nm SOI CMOS technology. The process variation in RF circuit performance is also analyzed and shown to contain 66% of process variation obtained with manufacturing inline parameters.     

衍射微柱透镜聚集特性的严格电磁分析

利用时域有限差分(FDTD)方法作为严格电磁计算模式,分析了有限口径衍射微柱透镜衍射效率与透镜F数的关系.严格分析比较了在不同入射极化波(TE极化和TM极化)情况下,具有不同面型分布(连续面型和8台阶、2台阶量化面型)的微柱透镜衍射效率随透镜F数的变化,并且与传统标量理论进行了比较.结果表明,随着F数的减小,标量理论和严格矢量理论得到的透镜衍射效率之差逐渐加大;在大F数情况,TM极化波入射时微柱透镜的衍射效率要略高于TE极化波入射的情况.     

On Perfect Lenses and Nihility

The canonical problem of a perfect lens with linear bianisotropic materials is formulated. Its solution is shown to be directly connected with the concept of nihility, the electromagnetic nilpotent. Perfect lenses as well as nihility remain unrealizable.     

Orthorhombic Materials and Perfect Lenses

The potential of orthorhombic materials for perfect lenses is theoretically examined.     

波导短程透镜球差特性分析及其焦距精确测量方法的研究

本文研究短程透镜的焦点位于端面外的球差特性。对焦点位于波导外部（包括端面）的情况给出了一种精确测量焦距新方法，采用这种方法简单易行，测量精度取决于读数显微镜的读数精度（０．０１ｍｍ）。     

获取超大空域热像信息的凝视光学系统设计

论述超大空域凝视热像系统自动设计中的技术难点；运用Ａｉｔｋｉｎ插值方法于自动优化技术排除“溢出”光线；借助人的诱导，充分发挥像差渐晕的作用，改善像面照度的均匀性；给出了Ａｉｔｋｉｎ插值公式，误差分析公式和光阑边缘逼近公式。     

一种基于圆形区块随机增长的多样图约束纹理合成算法

本文提出了一种基于圆形区块随机增长的多样图纹理合成算法改善了扫描线算法所带来的锯齿效应。算法利用高斯分布约束各个输入样图在合成结果中的比例,采用基于梯度引导的泊松平滑处理相邻纹理块之间的过渡区域,并在合成匹配函数中引入结构特征约束。实验结果表明,算法在引入比例约束的同时有效地保持了视觉效果和纹理结构的连续性。     

高斯光束整形为平顶光束的非球面镜系统设计和面形参数分析

在将高斯光束整形为平顶光束的整形系统中,由两个非球面镜组成的系统是比较简单的结构形式,该系统由平凹镜和平凸镜组成.在实际生产加工中,非球面镜的非球面度直接反映加工的难度.在理论分析高斯光束整形为平顶光束的基础上,分析计算了几个特性参数对非球面截面曲线的影响,然后根据实际需要,在保证其紧凑性、尽可能地降低非球面度同时,按...     

Design Optimization of Multishell Luneburg Lenses

Guidelines are provided for designing multishell Luneburg lenses (LL) whatever the primary source is. Three different optimization problems that minimize three different norms of the discrepancy between the ideal relative permittivity and the reconstructed one with respect to the thickness and permittivity of each shell are detailed. The performances of the three so-optimized LL are compared by simulations with those of previously proposed approaches. The highest directivity is obtained for the minmax norm. An investigation of the influence of the number of shells on the lens antenna performances, directivity, sidelobe levels and aperture efficiencies for various lens diameters, is also proposed in order to better know how to choose these parameters. Finally, measurements done with a multishell Luneburg lens fed by a waveguide are compared with simulations to show, through excellent agreements between theory and measurements, the validity of this study     

衍射微柱透镜轴向光强分布特性的严格电磁分析

衍射聚焦器件轴向光强分布的焦深和焦移特性，直接决定着系统接收面的装配误差和获得最佳的能量利用率。当器件的口径和面型特征尺寸可与照射波长比拟时，必须考虑光波与衍射器件的电磁作用。利用严格电磁分析方法——时域有限差分法，对有限口径衍射微柱透镜的轴向光强分布进行了严格分析，并且与传统的标量分析方法进行详细比较。分析比较了TE和TM极化波入射情况下，不同面型分布(8台阶，16台阶量化面型和连续面型)的衍射微柱透镜焦深和焦移特性与透镜F数的关系。结果表明透镜轴向光强最大点向透镜面偏移，焦移量的严格计算结果要大于标量计算结果，表明透镜的快聚焦特性，而二者得到的焦深量基本一致，同时两种理论方法都表明透镜焦深和焦移随F数的增加而增加。     

原子物质波的聚焦及其原子透镜

介绍了原子物质波聚焦的基本原理，即原子透镜的工作原理，对几种类型的原子透镜及其对原子物质聚焦的优劣性进行了分析，描述了原子透镜在原子光学中的应用。     

Dual-Frequencies Diffractive Lenses at Millimeter Wavelengths

Diffractive lens have many advantages over refractive lens at millimeter waves band, such as thin, light and low dielectric loss and so on. However, diffractive lens have chromatic aberration, that is, focusing performance of diffractive lens is frequency dependent. In this report, a dual frequencies diffractive lens is developed, which can work at 8mm band and 3mm band, based on the harmonic diffractive lens techniques. Experiments show it has almost same focusing performance at 8mm band and 3mm band.     

多用户分集与能量受限非可信中继系统遍历安全性能分析

研究了一种能量受限的非可信中继与多用户分集技术相结合的两跳链路安全网络通信模型。为提升系统安全性能，本文采用混合时间-功率分配中继(time-power splitting-based relaying, TPSR)协议,并结合机会调度策略(opportunistic scheduling strategy, OSS)从多用户分集网络中选择一个最佳目的节点作为信息接收端。基于随机选择(random selection, RS)策略，该文中利用低复杂度的高斯Q函数分析系统的安全性能以及在协作中继上进行能量采集活动不中断的条件下推导了系统的遍历安全速率(ergodic secrecy rate, ESR)的近似闭合表达式。此外，将提出的OSS与RS通信方案下性能进行对比，证明本文所提出的OSS更适用于分布式多用户选择网络。      

Coverage and Association Bias Analysis for Backhaul Constrained HetNets with eICIC and CRE

Heterogeneous networks (HetNets) are envisioned as a key solution to address the ever increasing capacity demand in wireless networks. With the deployment of enhanced radio access technologies, the non-ideal backhaul will become a potential network bottleneck. However, the impact of backhaul capacities (BCs) on the network coverage and offloading are not well understood. To address these issues, using tools from stochastic geometry, we propose a tractable framework for analyzing the impact of BCs on the network coverage and the optimal offloading bias in HetNets with cell range expansion (CRE) and time domain enhanced inter-cell interference coordination (eICIC) techniques. Conditioned on guaranteeing the minimum quality of service (QoS) of serving users, the coverage probability is derived as a function of offloading bias and BC parameters. We show how non-ideal backhaul alters the network coverage and the optimal bias. Compared with the perfect backhaul case, the optimal coverage and the optimal bias exhibit different behaviors in the case of limited BC.     

激光聚焦非球面透镜设计

本文论述激光聚焦光学系统的设计特点，介绍用等光程原理设计激光聚焦非球面透镜的方法及实例。     

超短脉冲高斯光束经聚焦透镜的光场形式

考虑到激光腔模中光腰的频率依赖性 ,得到了超短脉冲高斯光束经消色差透镜聚焦后光场的解析形式 ,并讨论了此时透镜群速度色散对光束聚焦性质的影响。分析了单透镜色差和群速度色散对超短脉冲高斯光束聚焦的时间分布及脉冲波面的影响 ;比较了消色差透镜及单透镜中脉冲初始光腰尺寸对聚焦的影响。     

非线性锥形梯度折射率透镜的光学特征

本文对非线性锥形梯度折射率透镜进行了分析,根据稳态自聚焦理论以及ABCD定律,导出了高斯光束通过这种透镜光斑尺寸及其位置的公式。讨论了几种特殊的情况,得到了一些重要的结果。     

太赫兹3D打印透镜综述

太赫兹波由于其独特的电磁特性可应用于超高速率无线通信、生物化学物质检测以及高分辨率成像等领域。但由于太赫兹波的物理波长小,传统适用于低频的加工工艺难以满足其加工精度的要求;而微纳米加工工艺又具有加工复杂、成本高等缺点。3D打印技术的发展为太赫兹器件的加工提供了新的选择和更多的设计灵活度。文章介绍了香港城市大学太赫兹与毫米波国家重点实验室在3D打印太赫兹透镜方面的最新研究动态和实验研究新成果,包括基于3D打印的太赫兹高增益圆极化透镜、近场聚焦圆极化透镜、贝塞尔波束生成透镜的设计,高精度3D打印方法的探索以及太赫兹天线测试方法等。太赫兹3D打印透镜天线具有低成本、低损耗、能快速成型等特点,可应用于不同的太赫兹场景中。