Microwave imaging via space-time beamforming for early detection of breast cancer

A method of microwave imaging via space-time (MIST) beamforming is proposed for detecting early-stage breast cancer. An array of antennas is located near the surface of the breast and an ultrawideband (UWB) signal is transmitted sequentially from each antenna. The received backscattered signals are passed through a space-time beamformer that is designed to image backscattered signal energy as a function of location. The beamformer spatially focuses the backscattered signals to discriminate against clutter and noise while compensating for frequency-dependent propagation effects. As a consequence of the significant dielectric-properties contrast between normal and malignant tissue, localized regions of large backscatter energy levels in the image correspond to malignant tumors. A data-adaptive algorithm for removing artifacts in the received signals due to backscatter from the skin-breast interface is also presented. The effectiveness of these algorithms is demonstrated using a variety of numerical breast phantoms based on anatomically realistic MRI-derived FDTD models of the breast. Very small (2 mm) malignant tumors embedded within the complex fibroglandular structure of the breast are easily detected above the background clutter. The MIST approach is shown to offer significant improvement in performance over previous UWB microwave breast cancer detection techniques based on simpler focusing schemes.     

Distributed wireless communication system: a new architecture for future public wireless access

The distributed wireless communication system (DWCS) is a new architecture for a wireless access system with distributed antennas, distributed processors, and distributed control. With distributed antennas, the system capacity can be expanded through dense frequency reuse, and the transmission power can be greatly decreased. With distributed processors control, the system works like a software or network radio, so different standards can coexist, and the system capacity can be increased by coprocessing of signals to and from multiple antennas.     

超宽带无线技术标准之争

目前全球的宽带无线接入技术研究重点似乎已经向短距离传输技术转移.在WLAN和蓝牙技术逐渐成熟井走入商用市场的同时,对超宽带(UWB)无线传输技术的研究和产品研发投入在逐渐加大.本文在简要对UWB技术与其他短距离传输技术性能进行比较的基础上,对目前UWB技术标准化工作中两大阵营的纷争进行了介绍,最后分析了UWB技术的发展前景.     

CCP协议介绍及基于Matlab的CCP MCD实现

CCP协议是车载电子系统比较通用的一类匹配标定协议。文章介绍了该协议的基本原理和具体实现中的技术特征,重点讨论了CCP协议中采用数据采集模式进行匹配标定的机理和特点。结合协议介绍,文中还介绍了基于Matlab平台的CCP MCD设备的实现。实践证明,Matlab具有较好的开放性,并且可以方便地通过Simulink和Stateflow完成CCP协议中必须要求的时序机制。因此基于Matlab平台的CCP MCD设备具有一定的技术先进性和实用性。     

基于DirectSound的混音与放音实现

文中主要介绍了基于DirectSound的混音与放音的原理与实现的具体步骤,并对实现方法及用到的各API函数进行了具体的分析.     

基于平行因子四线性分解的二维角度和频率联合估计

该文提出了一种新的2维角度和频率联合估计方法.首先给出双平行线阵结构,将阵列天线输出的信号进行建模分析,表明此信号具有平行因子四线性模型特征,分析了该模型低秩分解的唯一性,从分解得到的矩阵中联合估计出信源的频率和到达角.该方法无需谱峰搜索,可实现参数的同时估计与配对,并与现有的算法进行了比较,具有更高的估计精度,而且在...     

叠层结构的手性液晶单元的反射谱特性

基于手性液晶的布拉格反射特性,设计了旋向相反的手性液晶所构成的红、绿、蓝三基色叠层级联结构,以达到增强单元反射率的目的。采用Berreman 4×4矩阵对其单元反射率进行了分析,比较了手性液晶的单旋向三基色叠层(三叠层结构)与双旋向三基色叠层(六叠层结构)单元的反射谱,给出了改变液晶材料参数和级联顺序进一步提高单元反射率的计算结果。在最佳参数与级联顺序下,六叠层单元的最大反射率达到98.91%,三叠层单元的最大反射率为64.95%。叠层结构单元的色度分析结果表明,三层单元的色温依级联液晶旋向而改变,范围为5 240.9～7 029.8K,在反射率最优的条件下,六叠层单元的色温为6 285.7K。     

机器视觉在TFT-LCD点缺陷检测系统中的应用

针对TFT-LCD点缺陷的特征和检测方法,介绍了机器视觉系统的基本构成,提出了一种基于Visual C＋＋6.0集成开发环境,以EURESYS的eVision作为机器视觉和图像处理核心软件的TFT-LCD点缺陷检测方法。实验结果表明,该方法能够快速高效地实现点缺陷的自动检测功能,具有良好的鲁棒性,并为后续复杂缺陷的检测应用提供了一条参考思路。     

Study of proton irradiation effects on AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors (HEMTs) were exposed to 3 MeV protons at fluences of 6 × 10¹³, 4 × 10¹⁴ and 1 × 10¹⁵ protons/cm². The drain saturation currents decreased by 20% and the maximum transconductance decreased by 5% at the highest fluence. As the fluence increased, the threshold voltage shifted more positive values. After proton irradiation, the gate leakage current increased. The Schottky barrier height changed from 0.63 eV to 0.46 eV, and the ideality factor from 2.55 to 3.98 at the highest fluence. The degradations of electrical characteristics of AlGaN/GaN HEMTs are caused by displacement damages induced by proton irradiation. The density of vacancies at different proton fluence can be calculated from SRIM. Being an acceptor-like defect, the Ga vacancy acts as a compensation center. While N vacancy acts as a donor. Adding the vacancies model into Slivaco device simulator, simulation results match well with the trends of experimental data. Hall measurement results also indicate the concentration and mobility of 2DEG decrease after proton irradiation. It is concluded that the Ga vacancies introduced maybe the primary reason for the degradation of AlGaN/GaN HEMTs performance.     

天津市邮政综合服务平台建设

结合中国邮政综合服务平台的建设现状，从综合服务平台的建设原则、方案思路、配套解决方案等几个方面分析和探讨了天津市邮政综合服务平台建设中的一些技术问题。