基于FPGA的增益可调微弱信号采集系统设计

针对以往采集电路中放大倍率固定,适用的采集环境单一,不可灵活调理实际微弱信号的现状,设计了基于FPGA的增益可调微弱信号采集系统,该系统以FPGA为核心,以集成运算放大器OP37G,模拟开关DG611DY组成增益可调放大电路,具备了×0.5,×2,…,×100,×200等10种放大倍率可编程控制的功能,以高精度模数转换芯片AD7865为采集芯片,实现了高精度微弱信号的采集。试验结果表明:系统在多种微弱信号环境下经增益电路放大后,各通道采样精度均能达到0.1%。系统可灵活应用于多种微弱信号采集环境,稳定可靠,已成功应用于某微弱信号测试场合。     

基于虚拟仪器的植物电位信号测量系统的设计

采用U12数据采集卡和微弱信号放大器、以LABVIEW为软件开发平台,设计了植物电信号采集虚拟仪器试验系统,利用该试验系统可以对植物电位信号进行数据采集,初步建立了“植物-电信号获取-电信号的调理-计算机信息数据处理-数据波形显示-数据分析”系统.     

局部放电超声信号监测及数字降噪

设计了基于超声法的局部放电监测系统,并对信号进行了数字降噪研究。系统的硬件设计主要包括超声传感器、放大电路、滤波电路和数字电路,其中放大电路设计为两级四档可调放大电路,滤波电路采用四阶高通滤波器和二阶低通滤波器级联而成。对采集的信号综合运用FIR滤波器、FFT降噪、小波包降噪等数字降噪方法进行降噪。实验和仿真表明,系统可以清晰地采集局放信号,数字降噪算法可以有效地抑制干扰。     

光电式甲醛监测系统中信号调理电路的设计

根据光电式甲醛检测原理和探测光束的特点，设计了光电式甲醛浓度测量传感器信号调理电路，该调理电路主要由光电探测器前置放大电路、窄带有源滤波器和精密交流信号-直流信号转换电路3部分组成。基于OP07运算放大器设计的交流信号-直流信号转换电路等效净输入信号小于0．3μV，降低了甲醛测试系统检测限，提高料测试精度。以此信号调理电路构成的系统，实验标定的甲醛浓度的检出限低于2μg／L．     

放大器非线性失真测量装置的设计与实现

该文设计了一种放大器非线性失真测量装置,以晶体管放大电路作为基本电路,采用STM32F103RET6作为控制器,控制器输出电平给电压转换电路控制模拟开关,通过液晶触摸屏按钮使放大器输出无明显失真波形和4种非线性失真波形。控制器采集被测信号进行傅里叶变换得到基波和各谐波对应的幅值,计算信号总谐波失真THD值并显示。该系统可以准确测量频率为0.1 Hz～10.0 kHz、峰峰值为20 m V～5 V的信号。实测结果表明系统稳定可靠,精度高,具有较好的实用价值和应用前景。     

EOG眼电信号检测与特征识别

近年来,应用眼电信号实现无障碍人机交互是国内外的研究热点。设计了一套眼电信号采集检测系统,详细介绍了其中的信号放大模块、电缆驱动电路以及带通滤波模块。对采集的眨眼信号和眼球上下左右扫视运动信号进行特征分析,根据眼电信号脉冲波形的幅值和脉宽特征,提出了有意识眨眼信号和上下左右扫视运动信号的识别算法,并给出了具体的程序流程。     

高温200℃测井仪器微弱电压信号放大电路设计

针对高温(200℃)测井仪器中的微弱电压信号检测问题,设计一种测量放大电路,包括由并联仪用放大器组成的主放大器、带通滤波器和差分输出电路。实验表明:该电路输入信号幅度范围为40 n V~10μV,频带为500 k Hz~1 MHz,接收电路增益为92 d B,可在环境温度为200℃时可靠工作,信号频带内增益随温度变化小于0.5 d B,满足实际测量要求。实验结果与理论分析和数值计算相符合,可以为高温(200℃)测井仪器中的微弱电压信号测量技术领域的研究工作提供参考。     

井下地层流体NMR分析仪微弱信号放大电路设计

针对井下地层流体核磁共振分析仪器回波信号的频率高、强度弱、信噪比低的特性,以及测井仪器工作环境的特殊性,设计了一种低噪声的微弱信号放大电路。电路以低噪声双极性晶体管MAT02为核心的负反馈放大电路作为第一级放大,采用低噪声集成运放AD8130作为第二、三级放大,改善了微弱信号放大电路的噪声性能。实验表明:该电路对于频带4~5 MHz微弱信号,增益可达70 d B,且其等效输入噪声电压为槡2.1 n V/Hz,同时在环境温度0~150℃时有良好的线性度、较平坦的带宽和优良的低噪声性能,可为测井仪器中较高频率的微弱信号测量研究提供参考。     

基于MEMS矢量水听器微弱信号提取电路的设计与测试

文中介绍了一种基于纤毛式MEMS矢量水听器微弱信号提取电路。该电路采用两级信号放大,两级之间设计二阶巴特沃斯低通滤波器。该电路设计经电路仿真软件进行仿真和水下测试。测试结果表明:该微弱信号提取电路可以很好地对水听器采集到的信号进行放大,表现为水听器的接收灵敏度为-160 dB(0 dB=1 V/μPa)。采用这种电路设计的MEMS矢量水听器不仅具有令人满意的"8"字形方向特性,而且具有良好的低频特性,可以满足低频声学测试需要。     

窝点接触力自动测试仪数据采集系统的设计

实现了一种用于自动测量弹性臂窝点接触力的新型测试仪.主要介绍了该仪器数据采集系统的硬件和软件设计.其中硬件电路的设计包含了信号调理电路和信号采集电路,前端使用了仪用放大器调理传感器输出的微弱信号,后端使用了AVR单片机完成AD转换和数据串行传输.上位机软件主要负责仪器的运动控制、视觉测量和数据的采集和处理.软件的数据处理部分采用了Matlab6.5与VC6混合编程来实现窝点接触力的求解.     

Note: Quantitative (artifact-free) surface potential measurements using Kelvin force microscopy

The measurement of local surface potentials by Kelvin force microscopy (KFM) can be sensitive to external perturbations which lead to artifacts such as strong dependences of experimental results (typically in a ～1 V range) with KFM internal parameters (cantilever excitation frequency and/or the projection phase of the KFM feedback-loop). We analyze and demonstrate a correction of such effects on a KFM implementation in ambient air. Artifact-free KFM measurements, i.e., truly quantitative surface potential measurements, are obtained with a ～30 mV accuracy.     

Kelvin probe force microscopy in application to biomolecular films: Frequency modulation,amplitude modulation,and lift mode

Kelvin probe force microscopy (KPFM) is a powerful technique to visualize the differences of work function in metals and lateral surface potential distribution in thin organic films. Earlier we have shown that frequency modulated-Kelvin probe force microscopy has significant advantages in both sensitivity and resolution when applied to metal and inorganic interfaces in vacuum. High resolution, high sensitivity, and performance in ambient conditions are required in order to study biologically relevant samples. In this work we compared the resolution of frequency modulation (FM-KPFM), amplitude modulation (AM-KPFM), and lift modes KPFM for imaging the local electrical surface potential of complex biomolecular films and demonstrated that FM-KPFM mode has superior resolution for biological applications. The power of the method was illustrated on pulmonary surfactant films, revealing nm spatial resolution and mV potential sensitivity in ambient air. At this level of resolution this method can provide critical insight into the molecular arrangement and function of complex biosystems in a way that other KPFM modes cannot do. Based on the observed changes in the local surface potential we discovered that excess cholesterol produces nm size electrostatic domains and change the electric fields.     

Photoacoustic detection of CO2 based on LABVIEW at 10.303 μm

A detailed study on a photoacoustic carbon dioxide detection system, through sound card based on virtual instrument, is presented in this paper. In this system, the CO(2) concentration was measured with the non-resonant photoacoustic cell technique through measuring the photoacoustic signal caused by the CO(2). In order to obtain small photoacoustic signals buried in noise, a measurement software was designed with LABVIEW. It has functions of Lock-in Amplifier, digital filter, and signal generator; can also be used to achieve spectrum analysis and signal recovery; has been provided with powerful function for data processing and communication with other measuring instrument. The test results show that the entire system has an outstanding measuring performance with the sensitivity of 10 μv between 10-44 KHz. The non-resonance test of the trace gas analyte CO(2) conducted at 100 Hz demonstrated large signals (15.89 mV) for CO(2) concentrations at 600 ppm and high signal-to-noise values (～85:1).     

Interpretation and implementation of an ion sensitive probe as a plasma potential diagnostic

An ion sensitive probe (ISP) is developed as a robust diagnostic for measuring plasma potentials (Φ(P)) in magnetized plasmas. The ISP relies on the large difference between the ion and electron gyroradii (ρ(i)/ρ(e)～60) to reduce the electron collection at a collector recessed behind a separately biased wall distance ～ρ(i). We develop a new ISP method to measure the plasma potential that is independent of the precise position and shape of the collector. Φ(P) is found as the wall potential when charged current to the probe collector vanishes during the voltage sweep. The plasma potentials obtained from the ISP match Φ(P) measured with an emissive probe over a wide range of plasma conditions in a small magnetized plasma.     

有杆泵井管杆材料电化学腐蚀行为实验研究

为探讨电化学腐蚀对抽油井中管杆磨蚀的影响,选取油田常用的4种管杆材料分别在不同污水环境下进行了电极电位和电偶腐蚀实验研究。结果表明被试验钢样电位差异不大,多数情况下不超过20 mV;有氧、短期电偶腐蚀试验表明,材料配对的电偶腐蚀现象很轻微或可忽略。     

Confocal imaging of glutathione redox potential in living plant cells

Reduction–oxidation-sensitive green fluorescent protein (roGFP1 and roGFP2) were expressed in different sub-cellular compartments of Arabidopsis and tobacco leaves to empirically determine their performance as ratiometric redox sensors for confocal imaging in planta . A lower redox-dependent change in fluorescence in combination with reduced excitation efficiency at 488 nm resulted in a significantly lower dynamic range of roGFP1 than for roGFP2. Nevertheless, when targeted to the cytosol and mitochondria of Arabidopsis leaves both roGFPs consistently indicated redox potentials of about –320 mV in the cytosol and –360 mV in the mitochondria after pH correction for the more alkaline matrix pH. Ratio measurements were consistent throughout the epidermal cell layer, but results might be attenuated deeper within the leaf tissue. Specific interaction of both roGFPs with glutaredoxin in vitro strongly suggests that in situ both variants preferentially act as sensors for the glutathione redox potential. roGFP2 targeted to plastids and peroxisomes in epidermal cells of tobacco leaves was slightly less reduced than in other plasmatic compartments, but still indicated a highly reduced glutathione pool. The only oxidizing compartment was the lumen of the endoplasmic reticulum, in which roGFP2 was almost completely oxidized. In all compartments tested, roGFP2 reversibly responded to perfusion with H₂O₂ and DTT, further emphasizing that roGFP2 is a reliable probe for dynamic redox imaging in planta . Reliability of roGFP1 measurements might be obscured though in extended time courses as it was observed that intense irradiation of roGFP1 at 405 nm can lead to progressive photoisomerization and thus a redox-independent change of fluorescence excitation ratios.     

用于注浆成形的钡铁氧体粒子的浆料制备

原始钡铁氧体粒子经过行星磨磨细后 ,粒子平均尺寸由 8.2 9μm减小为 3.6 6 μm ,而比表面积由 2 .5 8m2 /g增大到 5 .84m2 / g ,相应地零电位点 (IEP)由pH6 .2～pH6 .5提高到 pH8～pH9。结果使得磨细粉制成的水基悬浊液 ,在酸碱度被调节到pH3.5或更低时 ,获得最高的Zeta电位。采用磨细的钡铁氧体粉末 ,添加非离子型高分子表面活性剂PEG和蒸馏水 ,并调低pH值 ,经高速混合、机械搅拌后 ,可以制备成用于注浆成形的稳定的钡铁氧体水基浆料。研究表明 ,粒子间的静电排斥力对钡铁氧体粒子在水中的分散仍起主导作用 ;而吸附在粒子表面的PEG只相当于一个绝缘层 ,从而机械地隔开了粒子 ,改进分散性能。通过对浆料粘性的测定 ,优化了浆料的配比。     

基于单片机的AFM纳米机械性能测试系统

摘要：目的：为解决采用AFM系统进行纳米机械性能测试中存在的不能够直接获得载荷——压深曲线以及不能够随意改变加载、保载、卸载时间等问题,对AFM系统进行改造。方法：开发了一套基于单片机的信号输入输出模块。将该模块与AFM控制系统相联,形成新的纳米机械性能测试系统。结果：该系统可以实现动态改变垂直载荷,并依据相应算法,可以实现载荷——压深曲线的实时获得。通过单片机设置模拟信号的输出速率可以实现加载、保载和卸载速率的改变。并结合二维微动精密工作台,可以实现较大范围内点阵的压痕测试。结论：通过在聚碳酸酯、聚二甲基硅氧烷等材料表面进行试验测试表明：该系统可以进行高速高精度的测量样品的纳米机械性能参数,包括对样品进行纳米压痕测试和对样品的纯弹性变形过程进行检测如聚二甲基硅氧烷或者各种微梁等微小构件。     

Practical and simple circuitry for the measurement of small capacitance

Practical and cost-effective circuitry with high sensitivity has been developed to measure a small capacitance using current compensation method. The circuitry uses an electronic switch to periodically connect or separate the capacitor under test (C(x)) from a reference capacitor (C(r)). When C(x) is connected in parallel with C(r) the total capacitance becomes C(x)+C(r). On the other hand, as C(x) is separated from C(r), the total capacitance is only C(r). This periodic change of the capacitance generates a periodic square-wave output with an amplitude in proportion to the capacitance of C(x). A high sensitivity of DeltaV/DeltaC=202.2 mV/pF has been achieved, making the circuitry a powerful tool in measuring small capacitances. Three applications have been performed to present its capability: (a) displacement, (b) height of liquid, and (c) angle of tilt. The experimental results demonstrate the performance of the circuitry.     

Peculiarities of imaging one- and two-dimensional structures in an emission electron microscope. 1. Theory

Local changes in work function cause deviations of the electrical microfield near a sample surface as a result of the uniform accelerating field distribution between the sample (cathode) and the extractor electrode (anode). This results in a change in the electron trajectories. As a consequence, the microscope image shows remarkable changes in position, size, intensity and lateral resolution of distinct details, which can be quantitatively described by the calculations presented here. Analysing these effects in the image gives an opportunity to determine the real lateral size of the observed structures and the distribution of local contact potentials.