MHD角速度传感器预处理电路的低噪声设计方法研究

为改善磁流体动力学(MHD)角速度传感器的噪声性能,研究预处理电路的低噪声设计方法.采用3个并联的SSM-2220双极型晶体管对作为输入级,级联低噪声集成运放构成差分放大电路,作为前置放大器,后级加入低通滤波、交流耦合和单端转差分电路.建立了预处理电路的噪声模型,并进行了噪声测量实验,电路的输入噪声电压谱密度约为0.6 nV/Hz(1 kHz).提出的低噪声预处理电路将MHD角速度传感器等效输入噪声水平降低至nV/Hz量级.     

基于JFET的低噪声感应式磁传感器设计

在航空瞬变电磁（TEM）大深度测量时,由于飞行过程中共模噪声和天电噪声的引入,致使传统感应式磁传感器（IMS）探测灵敏度降低,无法满足地质探测深度的需要。为了增加IMS探测微弱磁场信号的能力,通过理论分析IMS的物理结构和前置放大电路的机理,研究了噪声引入的主要来源,建立了基于结型场效应晶体管（JFET）的IMS等效模型,设计了一种低噪声IMS。通过在屏蔽室内对所研制的IMS性能进行测试,结果表明：其输入噪声为2nV/Hz1/2@10 kHz,3 dB响应带宽达到42 kHz,较3D—3磁传感器信噪比提高了10.04dB,为其在实际项目应用提供了可靠的性能保障。     

基于磁通负反馈的低噪声宽频带感应式磁传感器设计

感应式磁传感器（IMS）是频率域电磁法（FEM）中使用最广泛的磁传感器,通常由感应线圈和前置放大器组成.为了增加IMS探测深度和微弱磁场信号的能力,基于磁通负反馈技术,获得其在低频段平坦的灵敏度曲线,拓宽了其观测频带.采用斩波前置放大技术,降低了1/f噪声对IMS的影响,对IMS的输出噪声进行了压制.通过在屏蔽室内对所研制的IMS性能进行测试,结果表明：其频带范围为0.001Hz ～10 kHz,输入噪声为3 nV/Hz1/2,较3D-3磁传感器等效输入噪声提高了10.04dB,为其在实际项目应用提供了可靠的性能保障.     

Terfenol-D/SAW谐振器/Terfenol-D复合磁传感器

设计了一种由超磁致伸缩材料Terfenol-D和SAW谐振器构成的复合磁传感器,在磁场作用下,Terfenol-D沿长度方向伸缩,并将应力应变传递至SAW谐振器,使其产生应变,造成谐振频率改变,通过测量SAW谐振器谐振频率的变化来测量磁场强度.分析了该磁传感器的传感原理,建立了该复合磁传感器的静态模型,对弹性敏感元件进行了受力分析,根据压磁方程和受力平衡得到该磁传感器的静态特性.实验结果表明:该复合磁传感器灵敏度可达341.6Hz/Oe,较Terfenol-D/SAW谐振器结构灵敏度提高了3倍;测量谐振频率的分辨率为1Hz,SAW谐振器频率稳定度为0.1×10-6时,该磁传感器对磁场的分辨率为10-6T.     

采用面向低噪声的运放进行设计

物理过程的现实使我们无法获得具有完美精度、零噪声、无穷大开环增益、转换速率和增益带宽乘积的理想运放.但是,我们期待一代又一代连续面市的放大器可比前一代的放大器更好.那么,低频噪声运放的下一步会怎么样呢? 回到1985年,ADI的George Erdi设计了LT1028.30多年过去了,该器件依然是市面上低频条件下电压噪声最低的运放,其在1 kHz时的输入电压噪声密度为0.85nV/√Hz,在0.1～10 Hz时的输入电压噪声为35 nVP-P.直到最近,一款新型放大器LT6018才对LT1028的地位提出了挑战.LT6018的0.1～10 Hz输入电压噪声为30 nVP-P,并具有一个1Hz的拐角频率,但是其宽带噪声为1.2nV/√Hz.结果是,LT6018是适合较低频率应用的较低噪声选择,而LT1028则可为很多宽带应用提供更好的性能,如图1所示.     

高灵敏度弱磁传感器研究

磁传感器在生物医学、资源探测和航空航天等领域有巨大的应用价值,基于原子自旋的弱磁传感器拥有目前最高的磁场测量灵敏度。但通常的方案采用射频场调制或远离共振的激光检测,前者增加了磁力仪的线宽,而后者对激光频率的锁定带来了困难。为了解决以上问题,提出了一种基于激光强度调制和圆二向色性检测的原子弱磁传感器方案,详细描述了其工作原理和系统构成,并对原子弱磁传感器的性能进行了测试。实验结果表明:原子弱磁传感器的磁共振线宽为22 Hz,在对恒定磁场进行30 min连续测量时,峰峰值抖动小于9 pT,灵敏度达到了0.12 pT/Hz1/2。     

FS-4型锁定分析器

FS-4型锁定分析器能迅速、方便地同时测量微弱信号的同相与正交分量或振幅与相位分量,测量频率范围为1Hz到100kHz,满刻度灵敏度范围为100mV到10nV。而且,它有在宽带噪声或其他干扰中检测信号频率的能力,即使信号频率作缓慢变化也能进行检测。本文介绍了它的原理与特点。     

用于空间弱磁场检测的自旋阀型GMR传感器

采用离子束溅射及光刻工艺,在衬底硅片上制备了结构为Ta/NiFeCoCu/NiFeCo/FeMn/Ta的自旋阀型多层膜磁阻单元,然后采用四个磁阻单元构成惠斯通电桥,形成磁敏感元件,进而研制GMR传感器.介绍了自旋阀GMR传感器的结构和工作原理,研究了该传感器的特性,实验结果表明：该自旋阀线性度好、灵敏度高,可作为航天器进行宇宙空间微弱磁场测量的重要仪器.     

磁阻式传感器电学特性测试仪的研制

针对现有的锑化铟一铟磁阻式传感器的灵敏度、噪声等电学特性的测量过程所存在的不足之处,本文提出一种改进的测量方法,并且在此基础之上设计了一个自动测试仪,采用ADS744型A／D转换器和CH365型专用PCI接口芯片,达到高的采样速率与传输速率,实现对此种传感器的电学特性的快捷、精确的测量。     

测振传感器的低频特性补偿研究

现有的大多数测振传感器不能满足超低频振动测量的需要,有必要扩展其工作频带以满足需要。研究了零极点配置法在941B型测振传感器的应用。通过此方法,拓展了测振传感器的工作频带,尤其是其低频特性得到了拓展,其工作频带由补偿前的0.7~105Hz拓展为补偿后的0.08~109 Hz。在此基础上,利用MATLAB进行了数值仿真,输入不同持续时间的单个半正弦波以及正弦叠加信号,系统在补偿前后的响应表明:低频特性得到明显改善。     

Call for Papers The 6^th International Conference on Grid and Cooperative Computing

Recent years have seen rapid advances in various grid-related technologies, middleware, and applications. The GCC conference has become one of the largest scientific events worldwide in grid and cooperative computing. The 6th international conference on grid and cooperative computing (GCC2007) Sponsored by China Computer Federation (CCF),Institute of Computing Technology, Chinese Academy of Sciences (ICT) and Xinjiang University ,and in Cooperation with IEEE Computer Soceity ,is to be held from August 16 to 18, 2007 in Urumchi, Xinjiang, China.     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

法律信息库系统

本文分析了法律数据库的结构和特点，介绍了采用面向对象设计方法和超文本数据库技术开发和实现法律信息库系统将作为重要网络资源之一为不同用户进行法律咨询服务。     

View-based model-driven architecture for enhancing maintainability of data access services

In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times.     

International Journal of Automation and Computing Table of Contents

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Information for authors

正SCIENCE CHINA Information Sciences(Sci China Inf Sci),cosponsored by the Chinese Academy of Sciences and the National Natural Science Foundation of China,and published by Science China Press,is committed to publishing highquality,original results of both basic and applied research in all areas of information sciences,including computer science and technology;systems science,control science and engineering(published in Issues with odd numbers);information and communication engineering;electronic science and technology(published in Issues with even numbers).Sci China Inf Sci is published monthly in both print and electronic forms.It is indexed by Academic OneFile,Astrophysics Data System(ADS),CSA,Cabells,Current Contents/Engineering,Computing and Technology,DBLP,Digital Mathematics Registry,Earthquake Engineering Abstracts,Engineering Index,Engineered Materials Abstracts,Gale,Google,INSPEC,Journal Citation Reports/Science Edition,Mathematical Reviews,OCLC,ProQuest,SCOPUS,Science Citation Index Expanded,Summon by Serial Solutions,VINITI,Zentralblatt MATH.     

Erratum to: Fast global kernel fuzzy c-means clustering algorithm for consonant/vowel segmentation of speech signal

正Erratum to:J Zhejiang Univ-Sci C(ComputElectron)2014 15(7):551-563doi:10.1631/jzus.C1300320The original version of this article unfortunately contained mistakes.Algorithm 6 should be as follows:Algorithm 6 FGKFCM-F clustering Input:(1)X={x_1,x_2,…,x_N},,x_iR~d,i=1,2,…,N,the dataset;(2)C,1C≤N,the number of clusters;(3)ε0,the stopping criterion;     

Journal of Zhejiang University-SCIENCE C (Computers & Electronics) Total contents

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A pragmatic multi-method investigation of discrepant technological events: Coping,attributions, and ‘accidental’ learning

Discrepant technological events or situations that entail a problem, a misunderstanding or a difficulty with the Information Technology (IT) being employed, are common in the workplace, and can lead to frustration and avoidance behaviors. Little is known, however, about how individuals cope with these events. This paper examines these events by using a multi-method pragmatic approach informed by coping theory. The results of two studies – a critical incident study and an experiment – serve to build and test, respectively, a theoretical model that posits that individuals use a variety of strategies when dealing with these events: they experience negative emotions, make external attributions, and adopt engagement coping strategies directed at solving the event, eventually switching to a disengagement coping strategy when they feel they have no control over the situation. Furthermore, users’ efforts may result in ‘accidental’ learning as they try to overcome the discrepant IT events through engagement coping. The paper ends with a discussion of the results in light of existing literature, future opportunities for research, and implications for practice.