太赫兹通信芯片关键技术与系统发展浅析

[目的]现代无线通信低频频谱资源越来越紧张,但太赫兹频段具有丰富的频谱资源,太赫兹通信兼具大带宽、高保密性等优势,故成为下一代无线通信技术的重要候选技术,而其关键在于太赫兹芯片.[方法]本文主要介绍太赫兹芯片技术及基于芯片的通信技术,对其从基于肖特基二极管芯片的混频、倍频分立式器件到太赫兹芯片的现有成果和未来发展趋势到...     

太赫兹技术应用进展

近年来太赫兹技术的高速发展为太赫兹技术应用提供了基础。太赫兹以其高频率高穿透性以及低光子能量等优势,在多个领域受到了重点关注,并在多个具体的应用方向上实现了初步的探索。着重讨论用于高速率高带宽通信的太赫兹无线通信技术、用于生物化学物质检测研究以及用于医学领域的太赫兹光谱成像技术、用于无损探测系统的光谱成像以及谱分析技术、用于安全检查领域的太赫兹人体成像技术等太赫兹技术应用领域的进展,并对应用中存在的挑战进行了简要总结。     

太赫兹通信智能抗干扰技术研究

太赫兹通信是一种新型无线通信技术,具有通信速率高、抗干扰、抗截获等优势,在国防和军事领域具有广阔的发展潜力。随着现代战争逐渐向智能化方向发展,战场电磁环境愈发复杂,智能化干扰技术种类繁多且层出不穷,给太赫兹通信的实际应用带来了严峻挑战,迫切需要相应的智能化抗干扰技术来加以应对。本文针对太赫兹通信中的信息发送端和接收端,讨论了自适应波形设计、智能信号检测技术的抗干扰原理与实现过程,最后对太赫兹通信智能抗干扰技术进行了总结与展望。     

MEMS技术在THz无源器件中的应用

太赫兹技术将在未来高精度频谱探测技术、高分辨率成像和高性能通讯等应用前景良好.太赫兹技术处于电子学与光子学领域的交叉领域,太赫兹器件的尺寸在数十微米到毫米量级,传统的机械加工技术很难达到加工精度要求,甚至无法加工.MEMS技术在太赫兹器件的加工方面具有巨大的优势.总结了目前采用DRIE,LIGA等工艺加工太赫兹器件的研...     

太赫兹通信中MIMO信道建模与容量分析

随着纳米技术的不断发展与新型纳米材料石墨烯研究的不断深入,作为纳米网络通信技术的太赫兹通信成为无线通信的研究热点,然而现阶段对太赫兹通信中多输入多输出( MIMO)机制的研究较少。为此,采用离散化的数学方法,以接收端获取信道信息的遍历容量模型为基础,结合太赫兹信道的分子吸收噪声与传输路径损失,提出一种适用于太赫兹通信的MIMO信道模型。对建立的MIMO信道模型进行仿真与分析,结果表明,与单一太赫兹信道相比,太赫兹通信中的MIMO信道具有更高的信道容量与传输比特率。     

基于真空电子学方法的太赫兹源

太赫兹技术因其在医疗诊断,安全检查等领域具有很大的应用价值,使其成为当前各国争先研究的领域。太赫兹源则是太赫兹技术研究中极为关键的器件之一,而基于真空电子学方法的太赫兹源又是当前太赫兹源研究领域的重要分支之一。综述行波管、返波管以及回旋管这几类真空电子太赫兹源的结构、原理,结合器件的频率、功率等问题进行了重点讲解,同时对纳米速调管这一极具发展潜力的技术进行了展望。     

无线纳米网中太赫兹电磁波传输特性分析

针对基于太赫兹通信的电磁纳米网络,深入分析太赫兹电磁波路径传输特性以及大气分子吸收特性,从能耗的角度构建太赫兹信道传输的数学模型。分别针对不带反射路径的传输场景和带有反射路径的传输场景来分析路径传输特性;利用大气辐射原理来分析大气分子吸收特性。在不同传输距离和传输频率下,结合路径传输和大气分子吸收对太赫兹电磁波传输能量损耗进行仿真。结果表明:分子吸收损耗是太赫兹电磁波传输能量损耗的重要组成部分,大气分子吸收损耗与传输介质分子组成有关;路径传输损耗受到传输频率和距离的影响。分析结果对太赫兹通信频段的选择以及纳米节点能耗设计有重要参考价值。     

基于太赫兹时域光谱技术的煤岩界面识别

为了研究基于太赫兹时域光谱的煤岩界面识别可行性,首先应用太赫兹时域光谱技术,以气煤和砂岩粉末压片作为实验样本进行了相关实验,得到了太赫兹脉冲穿过不同样本时所产生的时间延迟和衰减幅度。然后采用Hilbert-Huang变换对煤岩样的太赫兹光谱进行了时频域分析,并与由传统快速傅里叶变换方法获得的样品频谱进行了对比,结果表明,在时频域内太赫兹光谱信号具有更高的分辨率,可以更好、更直观地分析太赫兹脉冲在任意时刻的频率、能量成分,研究任意频率在不同时刻对吸收谱线的作用。最后介绍了基于太赫兹时域光谱技术的煤岩界面识别过程,通过实验验证了采用Hilbert谱和边际谱提取出的光谱特征值可以很好地区分煤岩介质。     

浅析石墨烯对空间传输波的调控作用

石墨烯(Graphene)是一种由碳原子紧密堆积的二维晶体,其优异的电学性能引起了研究者的广泛关注,并有望应用微纳米器件,微波毫米波和太赫兹等领域。本文评估石墨烯在微波器件领域未来的应用,对石墨烯应用于天线和频率选择表面的可行性进行探讨。     

基于LabVIEW的太赫兹二维扫描成像系统设计

采用LabVIEW语言设计的透射式单频太赫兹二维扫描成像系统,选择基频为140 GHz的太赫兹源发射连续的太赫兹波,调用平移台驱动器和锁相放大器的LabVIEW功能函数,实现了待成像样品的逐点二维移动和太赫兹信号的幅值数据读取,对样品位置及其对应的幅值信息进行图像重构与灰度处理,完成了太赫兹二维快速扫描成像的设计。使用基频140 GHz和3倍频420 GHz作为太赫兹成像源,对网孔钢板和十字板两个样品进行成像实验,验证了所设计本系统的成像效果的有效性和可行性。实验结果表明:420 GHz辐射源的成像分辨率高,成像分辨率主要与样品的扫描步进和太赫兹源波长有关。     

Rain generated ring-waves: Measurements and modelling for remote sensing

We present an analysis of ring-wave and scatterometer data from a water surface that was agitated by simulated rain. Water droplets of 2.8mm diameter impacted the water surface at almost terminal velocity, and the rain rates cover a wide range of conditions (5 to 200mm hr^?1). Both the ring-wave energy and backscattered power from the GHz scatterometer increase as R increases, but the growth rates slacken at higher rain intensities. Ring-wave frequency spectra and wavenumber spectra are well represented by log-Gaussian spectral models. The results can be used to guide development of microwave scattering models.     

高动态扫频仪的设计与实验

针对现有的扫频仪动态范围小、应用范围受限等问题,基于若干集成电路设计了一款高动态扫频仪。该扫频仪利用2个DDS芯片产生正交信号,利用MC1496模拟乘法器作为零中频检测器,利用LTC2440完成高精度采样及数字滤波。该系统中,一路DDS相位0/90可变,另外一路DDS相位保持不变,由此构造了消除直流偏置的零中频算法且信号处理及显示在PC机完成。实验测试结果表明,其动态范围接近120 dB。利用该扫频仪能够完成滤波器、放大器等器件幅频特性的测量,可广泛应用到高频器件生产及测试中。     

Noncontact test signal acquisition

An arrangement of electrostatic pickups for logic signals is described; this allows data over a wide range of repetition rates to be acquired from insulated wires or from insulation-covered printed circuits. Minimum coupling capacities are of the order of 1 pF and it is shown that 5 V pulses from 0.5 Hz to 5 MHz can be detected and reproduced. Preliminary results are also reported for an electrostatic pickup system for audio frequency analogue signals. Applications are suggested in high voltage DC isolation of analogue or digital circuits, noncontact computer bus couplers and diagnostic probes.     

Configurable symbol synchronizers for software-defined radio applications

In many synchronous receivers, symbol timing synchronization is achieved through implementation of an analog phase locked loop (PLL). A phase detector and voltage-controlled oscillator drive a reference signal to be in phase with the received training sequence. Due to the quick phase convergence this option is attractive; however, limitations in pre-packaged hardware make this approach infeasible at times. Changes in the received symbol rate in software radio applications can further complicate the hardware implementation by requiring additional control signals to alter the frequency of the reference signal. This paper examines a configurable symbol synchronizer for software-defined radio (SDR) architecture with a predefined RF front end. In this scenario, we implement a typical method for digital phase locking and make it adaptable to different data rates. A pre-synchronization step is used to provide a reasonable initial estimate for the received symbol period for lower, over-sampled data rates. This decreases the synchronization time while maintaining a constant sampling period at the ADC. It also maintains the down-conversion stage at the receiver. The paper shows the feasibility of this architecture to support wide range of symbol rates.     

G-tree: a new data structure for organizing multidimensional data

The author describes an efficient data structure called the G-tree (or grid tree) for organizing multidimensional data. The data structure combines the features of grids and B-trees in a novel manner. It also exploits an ordering property that numbers the partitions in such a way that partitions that are spatially close to one another in a multidimensional space are also close in terms of their partition numbers. This structure adapts well to dynamic data spaces with a high frequency of insertions and deletions, and to nonuniform distributions of data. We demonstrate that it is possible to perform insertion, retrieval, and deletion operations, and to run various range queries efficiently using this structure. A comparison with the BD tree, zkdb tree and the KDB tree is carried out, and the advantages of the G-tree over the other structures are discussed. The simulated bucket utilization rates for the G-tree are also reported     

基于小波变换的多源图像数据融合与边缘检测方法

提出基于小波变换的多源图像数据融合和边缘检测的方法,对多源图像进行分解,将高频区域中的绝对值较大的系数作为重要小波系数;在低频区域,对逼近系数进行加权平均得到新的逼近系数,然后进行小波重构实现多源图像数据融合。应用小波变换对融合图像进行多尺度边缘检测,获取多源图像边缘,或对多源图像进行小波多尺度边缘检测,然后融合边缘。     

Use of a hydrologic model as a flood control policy statement

For Southern California watersheds, as is the case for most watersheds in the United States, rainfall-runoff data are relatively sparse such that the calibration of a hydrologic model is uncertain. With the large number and types of hydrologic models currently available, the choice of the “best” hydrologic model to use is not clear. Because of the limited data, the hydrologic model must be simple in order to validate parameter values and submodel algorithms. Due to the uncertainty in stream gage data frequency analysis, a level of confidence (e.g., 85%) should be chosen to provide a level of protection against a specified flood return frequency (e.g., 100-year). Due to the calibrated model range and distribution of possible outcomes caused by uncertainty in modelling parameter values, the use of a regionally calibrated model at an ungaged catchment needs to address the probability that the hydrologic model estimate of flood quantities (e.g., peak flow rates) achieves the level of protection for a specified flood level. In this paper, a design storm unit hydrograph model is developed and calibrated with respect to model parameter values and with respect to runoff frequency tendencies (design storm) in order to address each of these issues.     

合成孔径声纳频率变标成像算法

对小距离幅宽场景成像时,可以采用解线频调技术降低回波信号的带宽,从而降低距离向的采样率.线频调变标算法要求回波信号在距离向是线性调频的,因此无法直接处理这一数据形式.文中采用频率变标(FS)算法对解线频调后的回波信号进行处理,应用频率变标技术,在消除回波信号剩余视频相位项的同时校正距离徙动,整个成像过程不需要插值处理.最后用该算法处理了合成孔径声纳斜侧视工作模式下的仿真点目标的解线频调回波数据,得到了良好的成像结果.     

A numerical investigation on AC electrowetting of a droplet

We numerically analyze the AC electric field around a droplet placed on an insulator-covered electrode. The time-averaged effective electrical wetting tension, which is a function of AC frequency, is computed by integrating the Maxwell stress. The computed wetting tension is compared with the experimental result converted from the separately obtained contact-angle data. There is a good agreement between the two results at a low-frequency range and a qualitative agreement at a high-frequency range. Interestingly, the numerical results show that the electric-field strength decreases remarkably in the insulating layer near the TCL as the AC frequency increases. This decrease may account for the delay of the dielectric breakdown of an insulating layer in the AC case, which could be related to the contact-angle saturation phenomenon.     

三维离散余弦变换的分形视频编码方法

由于视频数据是时间轴上的二维图像序列,提出了利用分形和三维离散余弦变换相结合的视频编码方法。利用三维离散变换把三维视频数据从时空域变换到频域中,再利用分形技术在频域中来寻找对应每个可变三维频域值域块的最佳定义域块匹配。由于频域中DCT系数的强相关性和分形的高压缩性能,能够实现视频数据的高压缩。试验证明对于非实时处理低比特流视频,有一些应用前景。