宽带高功率谐波雷达发射机的设计与实现

近年来雷达探测技术在各个领域发展取得了飞跃发展，广泛应用于军事、民用等方面，谐波雷达由于其非接触性、穿透性和便携性等优点而引发人们关注。为了提高发射机的探测距离分辨率和抗电磁干扰能力，提出了一种宽带高功率谐波雷达发射机的设计方案，对发射前端的功放、天线等关键器件给出了具体的设计过程。通过对谐波雷达发射前端系统的仿真与分析，实物制作与测试，验证了方案的可行性。     

交流稳压电源谐波对电气参数测量影响的分析

针对电路实验中电气参数测量出现的问题 ,在对其输出电压谐波含量进行测试分析的基础上 ,研究分析了电源两端并联电容对电路测量造成的干扰 ,进而提出了解决的方法。     

矿用变频器谐波测试系统设计

矿用电气设备尤其是矿用变频器对井下电网电能质量污染的问题,越来越受研发厂家、安全准入、各工矿企业的重视;简述了矿用变频器的结构、原理,研究其谐波产生机理,阐述了其谐波的危害;设计了一套基于FLUKE1760的带负载性能测试系统,该系统主要由测试样机、陪试变频器、对拖电机、电能质量分析仪、上位机等单元组成;使用该系统对变频器进行了谐波加载性能测试,并对采集到的电压电流数据进行了谐波分析;实测结果证明:被测变频器的电压电流中均含有较大的5次7次谐波及高次谐波。     

变电站谐波测试和分析

对选定回路进行谐波测试,分析变流设备产生谐波的原因,并提出抑制方案.     

基于并联型APF的变频设备谐波治理容量的选择与验证

变频器在工程中的应用越来越广泛,已成为电力系统中重要的谐波源。针对谐波治理通常采用并联型有源电力滤波器(APF)。实践中发现按谐波电流选择有源滤波器的容量,补偿效果往往不理想,但补偿容量过高又增加不必要的投资。如何选择适合的谐波治理容量成为困扰设计人员的一个难题。本文以某再生水厂变频设备为研究对象,采用并联型APF就地治理的方案,根据参考文献资料并结合工程经验选择APF容量,通过测量负载侧和电网侧在谐波治理前后的电气参数验证治理效果。治理后电网侧和负载侧的谐波指标均降至国标GB/T14549允许范围之内,取得理想的治理效果。该结果对工程设计中有源电力滤波器容量的选择具有一定的借鉴和指导意义。     

有源电力滤波器在工业供电系统中的应用

目前我国工业供电系统中越来越多地使用电力电子设备,这些设备会导致供电系统谐波含量增多,电能质量下降,并对其他用电设备造成不良影响。鉴于此,本文阐述了电网谐波抑制的重要性、紧迫性及谐波抑制方法,分析了有源滤波器的工作原理,并通过具体实例介绍其应用情况。     

基于NCP1014的4W LED驱动电源设计

采用NCP1014作为主控制器,设计一款输出电压10V,输出电流320mA隔离式、节能高效的4W LED驱动电源,并分析所设计电路的基本工作原理,给出外围电路及变压器参数的详细设计过程.所设计的驱动电源通过赛宝实验室相关的电气测试,并达到量产,具备进入小功率LED照明市场的能力,且对开发低成本、高性能的小功率LED驱动电源具有一定的参考价值.     

柱栅传感器数学模型

柱栅传感器是一种新型数字式直线位移传感器。它具有许多优良的电气和机械特性。柱栅传感器是在感应同步器的基础上提出来的新型位移传感器，其具有与感应同步器相似的数学模型。但是由于柱栅的绕组是空间螺旋结构，因此它们的数学模型也就不尽相同。本文在电磁场理论指导和感应同步器的数学模型引导下，推导柱栅传感器数学模型。其理论将有利于柱栅绕组的结构尺寸设计。使用频谱分析仪对感应输出进行分析，验证数学模型。     

移动电站动态负载测试的仿真与特性分析

在移动电站供电的独立电力系统中,负载的冲击会造成电能质量的恶化,因此动态负载下的电气特性是移动电站的关键性能指标.针对目前测试平台评估指标不全面,测试方法落后的问题,建立了移动电站仿真系统,对中小功率移动电站常采用的谐波无刷同步发电机励磁系统与电子调速系统进行了建模,并对两类动态负载下移动电站的动态特性进行仿真分析.仿真结果表明所建模型可以用于移动电站动态特性的研究,采用的评估指标可以较好的评估移动电站性能,为研制移动电站测试用电子负载提供了依据,对于进一步优化电站试验平台检测技术具有重要意义.     

滤除零序谐波的建模与仿真研究

在数字化机房中产生的零序谐波对设备有损害,造成大电网能量耗散.传统滤波设备能耗高,不适宜在数字化设备为主的机房中使用.为滤除数字化机房中设备产生的3、9次等零序谐波,减少能耗,提高大电网的能效,提出了仅使用无源纯感性线圈绕组来设计滤除机房内3、9次等零序谐波装置的新思路.根据零次谐波的数学特性,运用三角函数及矢量分析等...     

电气设备谐波干扰性检测与评估方案

针对风力发电、光伏发电新能源出现的谐波干扰性问题,提出了电气设备谐波干扰性检测与评估方案,设计了电气设备谐波检测系统,包含六大部分：主控电路、电压采样电路、波形转换电路、同步锁相倍频电路、A/D转换电路和液晶显示电路;实现了电气设备信号的采集、波形的转换、信号的倍频放大和信号的显示功能;并且还采用了基于改进DFT和时域准同步算法进行电气设备谐波的检测,实现对谐波精准、稳定的检测;此外还研究了对电气设备谐波评估的方法,采用非干预式估计法对电气设备谐波进行评估,实现了对负荷运行没有影响的情况下进行电气设备谐波的评估;试验表明,本研究电气设备谐波检测的误差在±0.5%范围内,具有高精准度和稳定性。     

基于谐波的乐纹提取和音乐检索

提出了一种基于节拍内音乐谐波特性的乐纹特征提取方法,首先求得每帧音乐的谐波信息,再利用跟踪得到的节拍,计算节拍内所有帧的谐波信息的均值,构成此节拍的乐纹特征矩阵。为了提高音乐检索的效率,设计了一个二级音乐检索算法：根据节拍信息,将与查询音乐片段的每分钟节拍数相近的音乐作为候选音乐,再逐节拍计算所查询音乐的乐纹和候选音乐乐纹的相似度,选择相似度最高的音乐作为检索结果。实验结果表明,提出的乐纹特征和音乐检索算法有效地提高了检索准确率和检索效率。     

西安北环线牵引供电系统谐波测试与分析

随着我国电气化铁路的飞速发展,交直交型电力机车普遍被运用的同时,由其产生的谐波问题对电网的影响也日益凸显。为更好的研究分析牵引供电系统谐波特性规律,对西安北环线牵引供电系统某供电区段的牵引变电所和分区所主要电气量参数进行了同步测量,并在测试数据一时间段内选取了多个典型时刻。通过对典型时刻数据的分析,结果表明该供电区段的谐波特性呈现一定规律,并对其抑制方式提供了合理建议。     

Power‐saving primary design for displays enclosing a target color gamut

Abstract— Display primaries are optimized for the trade‐off between the total primary power and color gamut under the requirement that a target color gamut is enclosed by the color gamut of the display. LED displays and HDTV color gamut are taken as examples. Compared to the display using a set of typical commercial RGB LEDs, it was found that a total optical (electrical) power of 23.6% (15.6%) can be saved for the display using optimal RGB LEDs. Although the size of the display color gamut is sacrificed, the color gamut of the display using optimal RGB LEDs still encloses the HDTV color gamut. The combined effect of the LED luminous efficiency and white‐point condition on the determination of the optimal LED wavelengths and bandwidths is also studied.     

Microstrip phase inverters with different harmonic waves

The structure of the microstrip phase inverters with different harmonic waves is presented. The orders of the harmonic wave can be easily changed through the displacement of slot line in the ground. Theoretical equations for the relationship among the displacement of slot line and the orders of suppressed harmonic waves are derived. A picture is used to figure out the distribution modes of the electrical field of the slot line. For demonstration, three kinds of phase inverter with different harmonic waves are simulated, fabricated, and measured, respectively. The theoretical results, simulated results, and measured results show good agreement in this design, which proved the correctness of the proposed structure.     

Enhancement of the light output of GaN-based light-emitting diodes using surface-textured indium-tin-oxide transparent ohmic contacts

InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) with indium tin oxide (ITO) as widow layers were fabricated. The ITO surface was textured utilizing the natural lithography combined with the inductively coupled plasma (ICP) etching technology by use of polystyrene spheres as the etching mask. The morphologies of the textured ITO surface were characterized by a scanning electron microscope (SEM) and an atomic force microscope (AFM). The electrical and optical properties of surface-textured ITO/GaN LEDs were measured and analyzed. The influence and dependence of ICP etching time on the light output of the fabricated LEDs was investigated. Experimental results indicated that ITO/GaN LEDs with nano-islands with a depth of about 120 nm and a diameter about 320 nm on the surfaces exhibited a 60% or more enhancement in the output power. The typical 20 mA driven forward voltage is only 0.2 V higher than that of conventional planar ITO/GaN LED. The fabricated surface-textured GaN LED chips from the whole 2″ wafer presented a quite good conformance in electrical and optical characteristics, and the proposed method demonstrated a good reliability. The results indicate that the surface-textured ITO method utilizing the natural lithography combined with the inductively coupled plasma (ICP) etching technology has high potential in future large-area high-power GaN LED applications.     

Optimizing angular placements of the LEDs in a LCD backlight module for maximizing optical efficiency

This study aims to optimize angular placements of the LEDs with novel cone-shaped caps for achieving high optical efficiency in an ultra-thin, directly-lit RGB LED backlight unit (BLU) for large-sized LCD-TVs. This novel lens cap is used as a diffuser with the purpose to gain higher efficiency and provide satisfactory uniformity over a display panel. To this aim, the outer surface of the novel lens is coated with aluminum for mirroring effects to reflect most of the LED emitted light horizontally and then reflect the light at the BLU boundaries, finally to the output plane. Since the emitted white light from LEDs result from color-mixing of three individual RGB chips in a LED package, the addition of the LED cap however deteriorates the aforementioned expected color mixing. The optimal design on angular placements of LEDs presented in this study for satisfactory color-mixing and emission uniformity is achieved by necessary optics simulations via TracePro, followed by utilizing an intelligent numerical optimization technique, genetic algorithm (GA). The design parameters for GA optimization are different combinations of LED placement angles in a backlight module. Favorable color balance is shown achievable in terms of high low color difference resulted. Finally, experiments are conducted, which successfully validate the expected performance of color balance and emission uniformity for a novel cone-shaped LED lens with optimized angular placements in a large-area backlight module.     

On the individuality of fingerprints

Fingerprint identification is based on two basic premises: (1) persistence and (2) individuality. We address the problem of fingerprint individuality by quantifying the amount of information available in minutiae features to establish a correspondence between two fingerprint images. We derive an expression which estimates the probability of a false correspondence between minutiae-based representations from two arbitrary fingerprints belonging to different fingers. Our results show that (1) contrary to the popular belief, fingerprint matching is not infallible and leads to some false associations, (2) while there is an overwhelming amount of discriminatory information present in the fingerprints, the strength of the evidence degrades drastically with noise in the sensed fingerprint images, (3) the performance of the state-of-the-art automatic fingerprint matchers is not even close to the theoretical limit, and (4) because automatic fingerprint verification systems based on minutia use only a part of the discriminatory information present in the fingerprints, it may be desirable to explore additional complementary representations of fingerprints for automatic matching.     

Non‐polar‐oriented InGaN light‐emitting diodes for liquid‐crystal‐display backlighting

Abstract— This article addresses spontaneously polarized light emission from GaN‐based light‐emitting diodes (LEDs) fabricated on electrically non‐polar crystallographic orientations and application of spontaneously polarized emission for backlighting of liquid‐crystal displays (LCDs). The first half of the article describes polarized light emission from GaN‐based LEDs and its role in solid‐state lighting technology. The second half reports on our experimental work to explore the potential of non‐polar LEDs for LCD backlighting applications. Optical transmission of non‐polar LED emission was characterized through a liquid‐crystal layer. Extinction ratios of 0.21 were measured between zero and an applied bias voltage to the liquid‐crystal cells. These extinction ratios are not particularly high yet; nevertheless, the experiment has demonstrated the potential of such non‐polar LEDs for LCD backlighting.     

Fast fingerprint identification for large databases

Fingerprint matching has emerged as an effective tool for human recognition due to the uniqueness, universality and invariability of fingerprints. Many different approaches have been proposed in the literature to determine faithfully if two fingerprint images belong to the same person. Among them, minutiae-based matchers highlight as the most relevant techniques because of their discriminative capabilities, providing precise results. However, performing a fingerprint identification over a large database can be an inefficient task due to the lack of scalability and high computing times of fingerprint matching algorithms.In this paper, we propose a distributed framework for fingerprint matching to tackle large databases in a reasonable time. It provides a general scheme for any kind of matcher, so that its precision is preserved and its time of response can be reduced.To test the proposed system, we conduct an extensive study that involves both synthetic and captured fingerprint databases, which have different characteristics, analyzing the performance of three well-known minutiae-based matchers within the designed framework. With the available hardware resources, our distributed model is able to address up to 400 000 fingerprints in approximately half a second. Additional details are provided at http://sci2s.ugr.es/ParallelMatching.