基于数字锁相技术的微弱光信号检测系统设计

详细分析利用数字锁相进行微弱光电信号检测系统的基本原理以及各个组成部分.     

采用数字微镜的共焦显微镜的研制

研究了基于数字微镜器件(DMD)的多路并行共焦显微镜.利用DMD产生特定的图案对光源进行调制,形成多路并行共焦检测工作模式,其作用相当于虚拟针孔阵列,可以代替现有的并行扫描方式.采用DMD作为共焦系统的并行横向扫描方式,在不损失分辨率的前提下,大大提高了测量速度.系统中虚拟针孔的大小和周期等关键参数具有程序可控制性,能...     

原子磁力仪中的检测光强噪声补偿方法研究

为解决原子磁力仪检测光强残余噪声问题,提出了检测光强噪声数字补偿方法。首先根据原子自 旋进动检测基本理论,通过光弹调制器和锁相放大器进行线偏光的光旋角检测,利用噪声衰减器对检测光功率 进行正弦调制拟合得到补偿系数,然后使用光弹调制器调制频率的二倍频信号对一倍频信号进行后处理修正, 实现检测光强噪声压制。得到补偿系数后可将用于幅度调制的硬件甚至前级稳光强装置移除,仅利用数字补偿 技术即可实现光强噪声抑制。搭建基于K?Rb?21Ne气室的磁力仪实验装置,在无自旋交换弛豫态（Spin?Exchange Relaxation?Free, SERF）下开展检测光强噪声补偿实验, 结果显示光旋角检测信号的噪声被压制了 13. 2 dB@3 Hz。应用此噪声补偿方法,避免了不同光路所引入的非共模噪声,并在前级稳光强的基础上实现了 二次稳光强。此补偿方法可进行补偿系数的定期校准,减小系统状态改变及不稳定性带来的影响,对于提升原 子磁力仪灵敏度具有重要意义。     

WMS温度测量中谐波信号锁相放大器的设计

在波长调制光谱技术(Wavelength Modulation Spectroscopy, WMS)温度测量中,传统的锁相放大器测量谐波信号的振幅必须对被测信号及参考信号的相位单独进行调整。针对这一问题,设计了一种基于高精度平衡调制器AD630进行同步相敏检测的谐波信号的双锁相放大器。与传统的锁相放大器相比,所提双锁相放大器利用正交双通道的平方和检测,可以避免被测信号与参考信号进行严格的相位匹配问题。利用Multisim软件构建仿真模型,包括前置高通滤波器、正交双通道的相敏检波器、低通滤波器等部分。理论计算和仿真结果表明,所提方法能够准确检测微弱一次、二次、四次谐波信号的幅度,检测误差小于5%,具有电路简单、运行速度快、线性度高等优点,能够满足WMS温度测量工程应用。     

基于SOPC的8通道地震数据采集系统设计

针对多通道地震仪在并行数据采集和降低功耗方面所面临的问题,提出基于可编程片上系统(system on a programmable chip,SOPC)的多通道数据并行采集方案。该采集系统包括前端采集电路、以太网通信电路以及FPGA主控制系统,采集电路包括模拟开关、程控放大器、前端调理电路以及A/D、D/A转换器。基于FPGA控制系统开发符合AMBA(advanced microcontroller bus architecture)总线标准的多通道并行采集控制器IP核。通过对采集系统进行测试,证明该采集系统能够稳定可靠运行,可实现并行数据同步采集,有效降低地震仪功耗,整机功耗为2.38 W。     

声相关计程仪检测技术

声相关计程仪(Acoustic Correlation Log,ACL)检测技术用于对ACL在陆上进行功能检测。阐述了检测技术原理、检测方案以及检测平台的设计与实现。采用声呐阵对接检测的方案,可以连续对ACL完成一系列的检测。为了对70k Hz ACL进行功能检测,使用快速多通道并行的A/D、D/A模块,基于运行在PXI控制器的WINDOWS平台,开发了微软基础类库(Microsoft Foundation Classes,MFC)框架下的检测软件,搭建了完整有效的可视化检测平台。该检测平台可以完成对70 k Hz ACL的在载体功能检测,包括发射通道检测、接收通道检测以及串口输出检测等主要功能检测。检测平台使用便捷,性能稳健。经实验室测试证明,检测方案具备可行性,检测平台具有实用性。     

光谱吸收式光纤甲烷气体传感器及其信号处理方法

基于气体在其特征吸收波长下光的吸收随浓度变化的机理,通过对甲烷气体吸收光谱的分析,提出了一种光谱吸收式全光纤甲烷气体传感器及其系统。该系统以1300nm波段的DFBLD作为光源,波长响应范围为1100~1900nm的高灵敏度、低噪声的InGaAsPIN作为光电探测器,利用锁相放大器对传输信号进行相敏检波,采用一次谐波反馈光源注入电流、二次谐波与一次谐波的比值作为系统输出的谐波检测技术对微弱信号进行处理,使得系统达到很高的灵敏度。研究表明,该传感器的灵敏度达到10ppm,精确度和稳定性等性能指标均可满足甲烷气体检测要求。     

光弹调制器式多通道反射差分光谱技术

反射差分光谱术（RDS）是研究材料表面和薄膜光学各向异性属性的重要手段.现有的技术以光弹调制器（PEM）式单通道测量模式为主,可以实时监测单个波长的反射差分信号,但全光谱测量则需要采用扫描波长的方式完成,耗时长,不适合在线监测等时效性强、全光谱测量的应用.在研究基于光弹调制器的多通道反射差分光谱仪的技术实现的基础上,结合虚拟仪器技术、高速多通道同步采集卡和数字锁相放大算法,提出一种新的多通道测量构架.实验表明,新方法在全光谱范围内测量信号的标准偏差小于10-3,在仪器开发上具有组合灵活、扩展性好等优点.     

一种基于DSP的测量微弱光电信号的方法

采用相关检测原理设计并基于DSP的双相位锁相放大技术,设计了一种光电信号检测的方法,特别是针对背景噪声比较大的微弱光电信号,它具有很高的灵敏度。从应用的角度研究了微弱光电信号的检测原理,讨论其应用于DSP技术的双重锁相结构的优点,消除了参考信号和待测信号相位差不确定性的影响。实现了对微弱光电信号的实时在线检测。     

一种强噪声背景下微弱信号检测系统的设计与实现

<正>本文针对工程应用领域微弱信号检测的实际需要,提出了一种基于锁相放大器的微弱信号检测通用方案,设计实现了一种基于AD630和Cypress PSoC4蓝牙低功耗(Bluetooth Low Energy,BLE)微处理器的微弱信号检测系统。系统由AD630、微处理器、A/D采集电路和智能终端等部分组成,可用于对淹没于强噪声背景中特定频率信号的检测,具有通用性强、可扩展     

Detection of Magnetic Fields Highly Attenuated by the Skin Effect Through a Ferrous Steel Boundary Using a Super Narrow-Band Digital Filter

A complete instrumentation system is described that is capable of launching alternating magnetic fields through a large mild steel plate that is 2 mm in thickness and detecting them on the face opposite from the transmitter with remarkable signal-to-noise ratios. Results for signal frequencies ranging between 4.5 and 13 kHz are reported. The skin depth at 9 kHz for the steel used is approximately 137 mum. The detection of the minute fields arriving at the receiving coil is made possible by the use of digitally synthesized input signals, low-noise amplification, and, in particular, the use of a powerful real-time digital signal processing system that isolates the signal of interest using a super narrow-band filter and very high levels of distortion-free gain. Although traditional methods of weak signal detection, such as lock-in amplification, may also be applied in this context, the digital approach discussed here is both more cost effective and flexible, allowing the simultaneous detection of multiple frequencies.     

微弱电信号检测方法回顾

系统分析了微弱电信号检测的理论和技术,着重讨论了强噪声背景下微弱电信号现有检测方法的优缺点及应用.以线性和非线性为主线,将线性分析法按时域(相关检测法、锁定放大、取样积分、数字式平均、时域平均)、频域(功率谱法)以及时频域(小波变换谱分析、分数谱分析)检测方法进行梳理归类,而对于非线性分析法主要分析了高阶谱、神经网络、支持向量机、经验模式分解、混沌理论、差分振子以及随机共振方法.最后认为,多种理论与技术的结合以及借助软件技术,如LabVIEW,是弱信号检测的发展趋势.     

A Study on the Weak Signal Detection System Applied to the High Field Research Based on the Digital Lock-In Technique and Wavelet Filter

An improved digital lock-in technique with a wavelet filter is developed for the weak signals detection. A simulated signal modulated with a frequency of 40 kHz and contaminated by white noise is constructed to estimate the performance of the system. In this study, the selection of the wavelet filter parameters, such as the decomposition level, the wavelet basis and the threshold strategy is discussed. Finally, the performance of the system in different conditions is presented.     

一种基于摄影手段的检测方法

利用摄影手段，来实现机械加工、设备制造领域的质量检测和加工控制是一种多学科相结合的新途径。微距摄影检测有准确、即时、非接触等特点，可实现在线即时非接触测量和加工控制，能大幅提高加工效率、减少报废，在机械加工、设备制造等众多领域都有广阔的应用前景。     

锁定放大技术在参量接收阵中的应用

为抑制泵波影响,提取参量接收阵中的微弱差频信号,根据微弱信号探测原理,设计了一个基于锁定放大技术的参量接收阵系统。简要介绍了参量接收阵原理,详细描述了锁定放大技术,以及所设计的参量接收阵系统的工作过程,给出泵波比差频高130 dB时的仿真数据。结果表明,采用锁定放大技术后的参量接收阵系统可对接收的差频信号优化约5 dB。     

基于变尺度多稳随机共振的微弱信号检测研究

针对强噪声背景下微弱信号难以检测的难题,提出基于变尺度多稳随机共振的微弱信号检测方法。多稳随机共振系统比双稳随机共振系统具有更好的微弱信号检测能力,为强噪声背景下微弱信号的检测提供了新方法。首先对大频率信号进行尺度变换使之满足随机共振条件,将频率压缩后的信号通过多稳系统,调整参数使其发生随机共振得到信号的频谱特征,并与双稳随机共振方法得到的特征频率进行比较,仿真和实例结果均表明:相同条件下,多稳随机共振方法比双稳随机共振方法得到的频率准确,可以增强信号的幅值,有效地检测出被噪声淹没的微弱信号。     

Multiple Pedestrian Detection and Tracking in Night Vision Surveillance Systems

Pedestrian detection and tracking are vital elements of today’s surveillance systems, which make daily life safe for humans. Thus, human detection and visualization have become essential inventions in the field of computer vision. Hence, developing a surveillance system with multiple object recognition and tracking, especially in low light and night-time, is still challenging. Therefore, we propose a novel system based on machine learning and image processing to provide an efficient surveillance system for pedestrian detection and tracking at night. In particular, we propose a system that tackles a two-fold problem by detecting multiple pedestrians in infrared (IR) images using machine learning and tracking them using particle filters. Moreover, a random forest classifier is adopted for image segmentation to identify pedestrians in an image. The result of detection is investigated by particle filter to solve pedestrian tracking. Through the extensive experiment, our system shows 93% segmentation accuracy using a random forest algorithm that demonstrates high accuracy for background and roof classes. Moreover, the system achieved a detection accuracy of 90% using multiple template matching techniques and 81% accuracy for pedestrian tracking. Furthermore, our system can identify that the detected object is a human. Hence, our system provided the best results compared to the state-of-art systems, which proves the effectiveness of the techniques used for image segmentation, classification, and tracking. The presented method is applicable for human detection/tracking, crowd analysis, and monitoring pedestrians in IR video surveillance.     

微弱信号检测方法研究现状分析

强噪声背景下微弱特征信号检测一直是工程应用领域的难题。本文系统的研究了基于线性理论的时域、频域、时频域和基于非线性理论的微弱信号检测方法,分析了各检测方法的基本原理和特点。时域检测法中主要分析了相关检测、取样积分与数字式平均、时域平均检测法;频域检测法中分析了最为常用的频谱分析法;时频分析法中主要分析了应用范围最广的短时Fourier和小波变换;基于非线性理论的检测法中重点分析了随机共振。分析认为基于非线性理论的微弱信号检测法、多种检测方法的结合是未来微弱信号检测的研究方向。     

Simultaneous and continuous multiple wavelength absorption spectroscopy on nanoliter volumes based on frequency-division multiplexing fiber-loop cavity ring-down spectroscopy

We demonstrate a method for measuring optical loss simultaneously at multiple wavelengths with cavity ring-down spectroscopy (CRD). Phase-shift CRD spectroscopy is used to obtain the absorption of a sample from the phase lag of intensity modulated light that is entering and exiting an optical cavity. We performed dual-wavelength detection by using two different laser light sources and frequency-division multiplexing. Each wavelength is modulated at a separate frequency, and a broadband detector records the total signal. This signal is then demodulated by lock-in amplifiers at the corresponding two frequencies allowing us to obtain the phase-shift and therefore the optical loss at several wavelengths simultaneously without the use of a dispersive element. In applying this method to fiber-loop cavity ring-down spectroscopy, we achieve detection at low micromolar concentrations in a 100 nL liquid volume. Measurements at two wavelengths (405 and 810 nm) were performed simultaneously on two dyes each absorbing at mainly one of the wavelengths. The respective concentrations could be quantified independently in pure samples as well as in mixtures. No crosstalk between the two channels was observed, and a minimal detectable absorbance of 0.02 cm(-1) was achieved at 405 nm.     

基于 FPGA 的电磁金属探伤系统及其微弱信号处理

本文介绍了一种基于FPGA的电磁金属探伤系统,该系统用于研究电磁无损检测技术在金属板损伤探测上的应用。在该电磁金属探伤系统中,传感系统提供的测量感应信号为强噪声背景下的微弱信号。为了提高信号的检测精度,本文采用信号调理电路结合FIR数字滤波的方法,将基于FPGA的电磁成像金属探伤系统中微弱的测量感应信号从噪声中提取出来,仿真实验证明,该方案能为后续信号处理环节提供一个低噪声背景下的较强的感应信号。