伪随机码测距及其在故障检测定位中的应用

伪随机码测距已在雷达、导航等方面得到广泛应用，本文针对用脉冲反射法进行故障检测定位存在的问题，提出了将伪回机码测距技术应用于故障检测定位，这种方法不仅能提高故障定位槽度，而且还适用于故障的无损检测和在线检测．     

一种明显提高相位测距分辨率的方法

本文从原理和实验两方面提出了一种明显提高相位测距分辨率的方法.应用差频模拟锁相环(APLL)专用集成电路KD080H,作者设计制作出一种环路噪声带宽小于1Hz的晶体分频APLL,并成功用于相位检测频率1.5kHz的相位测距系统.实验表明,在光电信号频率为15MHz,晶体滤波器带宽500Hz,所得信号信噪比仅为40dB的条件下,测距分辨率可优于0.5mm,比应用中心频率1.5kHz带宽50Hz的有源滤波器测距系统的分辨率提高约7倍.该方法还具有结构简单,成本低,使用方便等优点.     

混沌理论在车载超声测距系统中的应用研究

利用混沌系统敏感依赖于初始条件的特性,通过判断系统运动状态的变化,实现车载噪声环境下的微弱超声波信号的提取。系统的仿真实验结果表明混沌振子检测理论在抑制噪声、检测微弱信号方面具有很高的先进性,可以大大提高超声波测距的精度和性能。     

相位法测距误差分析

介绍了相位法测距的基本原理,对信号相位变化及噪声干扰引起的相位测量误差进行了详细分析,给出了减少测量误差的有效技术措施.     

基于AT89S51单片机的超声测距

介绍一种基于AT89C51单片机的脉冲式超声波反射测距系统。该系统以空气中超声波的传播速度为确定条件,利用反射超声波测量待测距离。概述了超声波测距基本原理,对影响测量系统的主要参数进行讨论;并在介绍超声波测距基本功能的基础上,提出系统的总体构成,论证系统发射、接收、检测、显示部分的设计方案,分析系统软硬件的实现方法。     

红外主动式PSD测距系统

主动式ＰＳＤ测距系统是一种远运动机构、结构简单、精度较高的实用型测距系统。介绍了该系统原理,给出了测距系统的计算公式及计算结果。讨论了控制电路原理和电路设计中的关键问题,并应用此电路进行了测距实验,得出了实验数据和结论。     

基于单片机的超声波测距系统设计

利用超声波测量距离是一种有效的非接触式测距方法,本文结合超声波精确测距的需要,分析了超声波测距的工作原理和系统构成,给出了软件控制流程,并在数据处理中采用了温度补偿修正,来有效提高超声波测距系统的精度。     

潜艇双通道测距测速方法

本文主要叙述在潜艇辐射噪声测量中应用双通道测距测速方法测量潜艇运动要素,并在此基础上扩展双通道测距测速功能,将其应用于声速和海流流速的测量,从而能够提高声速测量精度,也能够确定艇速受流速影响的程度。最后将单通道与双通道测距测速方法作了一般性比较。     

对高精度激光脉冲测距技术的分析

高精度激光测距技术在现代社会生产中的应用非常的广泛,主要的介绍激光脉冲测距技术的原理,分析影响脉冲激光测距的主要原因,以及针对原因给出解决的措施,介绍提高测量精度的几个方法及其工作原理。     

同步钟式水下测距技术研究

水下运动体辐射噪声测试必需建立相应的海上测试手段,其诸多手段中,实现不影响水下噪声目标辐射噪声特性研究的水下实时精密测距是极为重要的。本文就此给予了一般性的论述。文中重点对各种同步钟式水下测距技术结合我们多年的工作实践进行了较为详尽的讨论。     

AlPbOAg as a solid electrolyte cell

Thin film AlPbOAg sandwich solid electrolyte cells are obtained by vacuum evaporation on glass substrates; PbO is grown thermally by oxidizing vapour-deposited lead at 150 °C on the bottom aluminium electrode. A.c. and d.c. conductivity studies on symmetrical AlPbOAl sandwich cells indicate that PbO is an ionic conductor. The AlPbOAg sandwich cell is seen to generate a short-circuit current of few nanoampères and a dark voltage in the range 400–800 mV in air ambient, silver being the positive electrode. The discharge characteristics of the cells are studied and a cell reaction is proposed. The variation in cell voltage with temperature and white light illumination is also studied. The photovoltage of the cell is found to add to its dark voltage. The short-circuit current of the cell is also observed to increase with illumination.     

基于PSD的强背景下光点位置探测技术研究

目前基于PSD的光电探测应用大多是以激光入射,有效信号远强于背景,为了满足更大的测量需求,本文提出了一种基于PSD的强背景下探测闪光点空间位置的方法.设计了预处理电路将PSD产生的微弱电流信号转换为电压信号并经过高速AD转换为数字信号,分析了背景信号对PSD测量结果的影响,提出了在软件中减去背景和暗电流以提取有效信号并对其进行精确计算的方法.用LED做闪光点在不同室外背景下进行了相关实验,结果表明:该方法可以实现200 kHz的高速测量,有效去除了不同背景和暗电流的影响,强背景下测量线性误差在±1.2％以内.     

Characterization of the Input Noise Sources of a dc SQUID

From the theory of the intrinsic noise in a dc SQUID by Tesche and Clarke, we derive the expressions of the current and voltage input noise spectral densities in a dc SQUID current amplifier operated in a flux locked mode. The expected current and voltage noises are compared, at audio frequencies, with the experimental results obtained with a low noise dc SQUID in which the input load (resonant and not) and the operating temperature (1–4 K) are changed. In order to evaluate the input voltage noise, which is directly related to the current noise around the SQUID loop and is usually neglected, we have used as the input circuit a LC resonator with a very high quality factor (10⁶). Both the voltage and current input noises exceed the expected values by the same factor of about 8. This means that the modulus the optimum source impedance of the SQUID amplifier is still in agreement with the value expected from the theory, which is approximately given by the product of the input coil inductance and the angular frequency. To explain the excess noise results, we propose a model in which the voltage and current input noises are due to a thermal magnetic noise source which is present near the SQUID.     

A novel logarithmic response CMOS image sensor with high output voltage swing and in-pixel fixed-pattern noise reduction

A novel logarithmic response CMOS image sensor fabricated by 0.25-/spl mu/m CMOS logic process is proposed. The new cell has an output voltage swing of 1 V in the targeted illumination range, which makes it less susceptible to noises in the readout system. Furthermore, the proposed new cell with in-pixel CDS control drastically reduces the fixed pattern noise in logarithmic mode CMOS APS. Comparing with a conventional pixel, a reduction of 10 times in fixed-pattern noise is demonstrated in the new logarithmic response CMOS image sensor.     

Noise characterization in circular dichroism spectroscopy

Circular dichroism (CD), defined as the difference in absorption between left and right circularly polarized light, is used to spectroscopically study the structures of chiral materials. In this article, various methodologies are presented for characterizing the performance of CD spectrometers to determine (1) experimental conditions for optimal data collection, (2) noise characteristics dependent on machine parameters, (3) the relative significance of spectral data as a function of detector gain, and (4) stray light and dark current as a function of wavelength. The results of case studies of two commercial CD spectrometers (specifically, Jasco J810 and J815) are described. The analyses show that the variation of CD signal is Poisson distributed and hence can be considered shot noise. Also, optimum scan parameters are established and a weighting function of CD data significance is produced so that wavelength-dependent gain (as determined by the high tension, HT, voltage applied to the photomultiplier tube, PMT, detector) can be accommodated. Lastly, the amount of stray light and dark current for the photomultiplier tube is determined. Though specific to the Jasco CD spectrometers characterized in this study, it is expected that all CD spectrometers exhibit similar behavior and the methodology described here can be usefully applied to characterize CD spectrometers independent of manufacturer.     

Single-stage photodiode op-amp solution suited for a self-mixing FMCW system

The current delivered by the photodiode in a self-mixing frequency modulated continuous wave or optical frequency domain reflectometry system consists of a dc-current resulting from the local oscillator, the reflected signal, dark current in the photodiode, and current generated from background light. The current also contains the useful harmonic signal with a beat frequency corresponding to the range and radial velocity of a target. To avoid saturation and clipping due to the dc current generated in the photodiode, it is desirable to minimize the gain at dc while maintaining a high gain in the beat frequency region. We have investigated some different solutions and present a modified current-to-voltage converter using bootstrapping and added voltage gain, which addresses this problem using only one OP-amp and no dc shorting inductors.     

Electrothermal Characterization of Single-Walled Carbon Nanotube (SWCNT) Interconnect Arrays

Electrothermal characterization of a metallic single-walled carbon nanotube (SWCNT) interconnect array is performed in this paper. The array is biased by a high voltage or under the impact of an electrostatic discharge pulse current. Using both time-dependent and -independent finite-difference methods, 1-D longitudinal heat conduction equation of SWCNT in the array is first solved, with CNT length-dependent temperature distribution, breakdown voltage, power handling capability, as well as transient thermal response captured and compared. Two modified equivalent electrothermal circuit models of a single SWCNT and an SWCNT array are proposed to accurately characterize hybrid effects of the biasing voltage, CNT length, and maximum rise in temperature. Their electrothermal circuit models are further implemented for investigating self-heating impact on signal integrities of SWCNT interconnect arrays, in particular, time-delay-induced crosstalk and noise. It is theoretically demonstrated that self-heating effect should be considered carefully in the design of local SWCNT interconnects when a high biasing signal voltage is applied.      

Control of a converter system for an asymmetrical parameter type two-phase induction motor drive operating in motoring and generating modes

The control of a converter system is presented and discussed for an asymmetrical parameter type two-phase induction machine drive that is operating in motoring and generating modes. The proposed system consists of back-to-back voltage source converters. For a machine side, a three-leg voltage source converter provides both unbalanced and balanced two-phase output voltages with a scalar V/F control based on a carrier space vector pulse width modulation (SVPWM) technique. For a front end, a single-phase AC/DC doubled voltage converter with hysteresis current control is used to keep DC-link voltage constant, thus resulting in a bi-directional power flow operation for the motoring and generating modes. A closed-loop design for the DC-link voltage is fully given and also included is a review of carrier-based SVPWM for two-phase three-leg VSI. The proposed drive system was both simulated using MATLAB/SIMULINK and implemented on digital microcontrollers. The comparative performance evaluation of the whole system between balanced and unbalanced two-phase voltages for the machine is given. The simulation and experimental results show that the unbalanced phase voltage offers better performance for the whole system.     

Digital frame averaging and dark mapping for a video-based underwater imaging spectrometer system

A solid-state video camera is used as the focal plane detector in an underwater spectrometer system to acquire multiple spectra simultaneously within the water column. Signal-to-noise enhancement of the spectra is accomplished by use of a combination of frame averaging and dark field mapping so that the dynamic range of the individual frame can be increased from approximately 7 bits to > 13.5 bits. This method also removes the need for shuttering to determine the dark background or device cooling to reduce the dark current noise. The dark mapping algorithm is shown to be valid over a range of device temperatures so that the detector can vary freely with the ambient water temperature without loss in mapping accuracy. Despite observation times that can be up to an order of magnitude greater than cooled devices, the use of frame averaging and dark mapping eliminates the need for additional detector cooldown time and can provide a smaller, simpler, more power efficient, and robust design.     

Range accuracy limitation of pulse ranging systems based on Geiger mode single-photon detectors

Geiger mode single-photon detectors have been used in pulse ranging system and three-dimensional imaging systems due to high sensitivity and easy integration. The ranging accuracy and precision is influenced by many factors. Based on statistical theory, five main factors are discussed in this article, namely, echo signal intensity, pulse width, detector quantum efficiency, target position, and background noise. An analytical relationship among the ranging accuracy, precision, and these factors is obtained for a Q-switched laser pulse. Through this relationship, it is shown that the echo signal intensity and pulse width are more important than other factors and higher echo signal intensity and narrower pulse width can result in better accuracy and precision.