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.     

基于Lorenz混沌同步系统的未知频率微弱信号检测

针对现有混沌类检测方法存在的不足,提出一种基于混沌同步系统测量强噪声背景下微弱信号频率值的新方法。该方法利用Lorenz混沌系统自身的初值敏感性、噪声免疫性和混沌系统的可同步性,采用驱动-响应法构建同步检测系统对微弱信号进行降噪处理,再结合多信号分类算法处理所得到的同步误差信号,最终实现微弱信号的频率测量。该方法有效解决了单Duffing振子参数设定复杂、运行状态转换时间长和状态判定困难的问题,也无需采用复杂的混沌系统阵列结构求解待测信号的频率值。仿真和实验结果表明新方法能够准确检测出微弱信号的频率,进一步完善了现有混沌类检测方法,为其应用于实际工程提供了新的思路。     

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。     

电磁信号检测的随机共振方法与应用研究

数字信息设备在工作时会产生微弱电磁泄漏信号,在电磁信号检测领域,应用随机共振方法将噪声的能量向信号转移,增强信号幅值。提高电磁泄漏信号的信噪比,实现从复杂噪声背景中提取微弱电磁波信号的特征信号。     

强噪声背景下的微弱信号检测新方法

提出了新的强噪声背景下的微弱信号检测方法,设计了一种硬件与软件相结合的实现方案。采用经典的仪表放大技术和单片机控制技术对数据进行检测和处理,并通过虚拟仪器技术仿真和显示,为解决热释电红外探测器中µA级微弱信号的检测提供了十分有效的方法。该系统通过实验对模拟低频微弱信号的检测,充分显示了它在微弱信号检测方面的实用性和优越性。     

基于耦合Van der Pol-Duffing系统的微弱信号检测研究

传统方法检测微弱信号具有一定的困难,利用混沌振子对微弱信号敏感以及对强噪声具有良好免疫力的特性,提出基于耦合Van der Pol-Duffing振子系统检测微弱信号的新方法。对比不同参数下耦合系统的动力学行为,通过分岔图和二分法确定临界阈值,保证阈值搜索速度和阈值精度。阐述基于相图的微弱信号检测原理,通过从混沌态到周期态的转变成功检测淹没在强噪声中的微弱信号,信噪比门限达到–30 d B。同时考察不同精度幅值下噪声对系统状态的影响,不同频率信号以及相移对检测的影响。仿真结果表明,该耦合系统在强噪声条件下对微弱信号敏感,用于检测微弱信号是可行的。     

基于非线性耦合双稳态随机共振的轴承微弱故障信号增强检测方法研究

针对滚动轴承微弱故障信号难以检测的难题,提出一种基于新型非线性耦合双稳态随机共振模型的轴承微弱故障信号增强检测方法。噪声背景下,随机共振可以实现微弱信号的增强输出,提高微弱信号特征的检测。提出的非线性耦合双稳态系统是由两个单一双稳态系统经非线性方式耦合而成,通过分析耦合系数、阻尼系数随着噪声强度改变的信噪改善比响应特性曲线图研究了不同参数对随机共振现象的影响。结果表明,耦合双稳系统比单一双稳态系统具有更强随机共振现象的产生。最后采用模型对轴承故障微弱信号进行了增强检测应用,所提出的非线性耦合双稳态随机共振能够实现在复杂的噪声背景下对微弱故障信号的检测。     

超导电阻测量系统设计

要本文通过对超导电阻特性的分析研究,提出了一种基于微弱信号检测的超导体电阻测量的新方案。论述了微弱信号检测应用于超导电阻测量的可行性。系统通过微弱信号检测中的相关检测方法实现超导电阻信号的提取,尽可能的去除噪声信号。并采用TMS320VC5509A进行信号处理,通过软件编程实现相关检测,提高信号质量。系统运行稳定,并充分显示出了自身在超导体电阻测量等微弱信号检测方面的优越性。     

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。     

杂乱背景中隐藏信号的三重相关检测技术

针对噪声中检测微弱信号难的问题,提出了一种实用的三重相关检测方法。该方法利用有信号和无信号噪声背景下,三重自相关集平均值的差异,排除噪声干扰,判断出信号的存在;采用似三维图形法计算峰值,实现杂乱背景中隐藏信号的检测,获得信号的确定位置。实验表明,采用三重相关峰值检测方法,在峰值信噪比为0.8702313、功率信噪比为-0.9257607dB时,可获得的信噪比改善约为23dB。在背景为随机噪声的二维图像序列中,也能判断和检测出微弱的点目标,为防伪机器识别提供了一种可供选择的方法。     

Real-Time Structural Health Monitoring Using a Novel Fiber-Optic Accelerometer System

This paper presents a novel fiber-optic accelerometer system to monitor civil engineering structures in real time and a successful application of the novel sensor system for damage detection of the concrete slab structure. This sensor system integrates the Moireacute fringe phenomenon with fiber optics to achieve accurate and reliable measurements. A signal processing unit implements unique algorithms to further enhance the resolution and increase the dynamic bandwidth of the sensors. The sensor system is immune to electromagnetic (EM) interference, making it suitable for difficult applications in such environments involving strong EM fields, electrical spark-induced explosion risks, and cabling problems, prohibiting the use of conventional electromagnetic accelerometers. Especially, this paper presents a unique real-time signal processing algorithm and applications to real-time damage assessment, demonstrating the uniquely high performance of the Moireacute fringe fiber-optic sensor system     

Low-power 2-D fully integrated CMOS fluxgate magnetometer

In this paper, we present a low-power, two-axis fluxgate magnetometer. The planar sensor is integrated in a standard CMOS process, which provides metal layers for the coils and electronics for the signal extraction and processing. The ferromagnetic core is placed diagonally above the four excitation coils by a compatible photolithographic post process, performed on a whole wafer. The sensor works using the single-core principle, with a modulation technique to lower the noise and the offset at the output. In contrast to traditional fluxgate approaches, the sensor features a high degree of integration and minimal power consumption at 2.5 V of supply voltage that makes it suitable for portable applications. A novel digital feedback principle is integrated to linearize the sensor characteristics and to extend the linear working range.     

Low Frequency Eddy Current Testing of Insulators and Composites

Eddy current testing (ECT), a non-destructive testing method widely used to evaluate defects within conductive materials, is explored in this study as it applies to insulators and non-uniformly conductive materials. Previous work has shown that at high frequencies, differences in electric permittivity can be detected with ECT. In this study, a new design of an ECT sensor that employs two resonance-tuned coils is evaluated. Results show that material inconsistencies in insulators are detectable due to spatial variations in permittivity and magnetic permeability, and that detection is possible at lower frequencies than previously demonstrated. In addition to determining signal dependence on individual electromagnetic parameters, sensitivity for defect detection in a carbon fiber-reinforced polymer (CFRP) composite is qualitatively determined. Although low signal-to-noise ratio is observed with a small-diameter coil, by increasing the coil diameter, the signal to noise ratio is increased while preserving adequate spatial resolution to detect defects in the sample. This study expands on previous studies of the application of ECT to insulators, and demonstrates that defect detection is possible in CFRPs.     

基于压电传感器的管道泄漏信号可靠性识别技术研究

管道泄漏检测的可靠性主要取决于泄漏信号的信噪比，泄漏信号信噪比的提高主要由传感器和对信号的处理方法决定。在定量分析的基础上，得出了基于压电传感器的管道泄漏检测方法具有比基于压力传感器的负压波法更高的泄漏信号信噪比。通过信号分析，论证了平滑滤波对于提高泄漏信号信噪比的必要性，提出了用区间信号能量来突出泄漏信号的方法。分析比较了实际检测信号幅值、区间信号能量和区间信号平均能量的平方3种方法下泄漏信号的信噪比，提出了用基于区间信号平均能量平方的顺序能量比率法进行管道泄漏信号识别的方法。结果表明该方法可以极大地提高泄漏信号信噪比和泄漏检测可靠性。     

频分多址法用于硐室盲炮检测与识别的试验

为探明硐室爆破中的盲炮,在高精度磁法、瞬变电磁法和瞬态电磁耦合法的研究基础上研究开发了频分多址法。该法是利用电磁波在大地中的传播规律,在不同装药硐室中预置发射不同频率的电磁信号发生器,在地面安装无线检测接收系统,通过接收到的不同频率信号来实现硐室盲炮检测与识别。试验结果表明,电场信号信噪比低、反应微弱,磁场信号的信噪比高,采用频率在1000Hz左右的磁场信号作为检测的信号源的实用性更好;频分多址法可以检测与识别出地下225m的盲炮,能满足地下硐室盲炮检测的距离要求;检测精度可达到2Hz,能同时有效地检测与识别地下单个及多个盲炮的存在。     

基于EEMD和分层阈值的磁记忆信号降噪方法研究

针对现有缺陷管道的磁记忆信号降噪效果不佳及信号完整性鲜有考虑等问题,提出了基于总体平均经验模态分解（ensemble empirical mode decomposition,EEMD）和分层阈值的磁记忆信号降噪方法。首先,设计了以STM32F407为控制核心的金属磁记忆检测系统,用于采集缺陷管道的磁信号;然后,对磁信号进行EEMD预处理,得到其本征模函数（intrinsic mode function, IMF）分量,并根据频谱分析和相似度计算选择最佳分解层数;最后,利用分层阈值降噪算法重构在最佳分解层数下的IMF分量,得到降噪后的信号。通过仿真分析和实验测试,对EEMD分层阈值降噪方法进行定量评价。结果表明：该方法适用于信噪比较小的含噪信号;与小波阈值降噪方法相比,其降噪后信号的信噪比和平滑度较高,均方根误差较小,缺陷特征信号完整,可更直观地显示缺陷位置。研究结果为金属管道磁信号降噪提供了一种切实可行的方法,为管道缺陷的在线检测奠定了基础。     

纳米Fe2O3-还原氧化石墨烯复合材料的制备及对双酚A的检测

双酚A（BPA）被广泛应用于食品包装材料中,它会引起人体内分泌失调,并导致免疫和生殖系统异常,因此对生活用水中BPA的检测十分重要。本文采用一步水热法合成纳米Fe₂O₃-还原氧化石墨烯（Fe₂O₃-rGO）复合材料并进行表征,基于Fe₂O₃-rGO复合材料构建电化学传感器Fe₂O₃-rGO/玻碳电极,用于检测水样中的BPA。通过FTIR、XRD和SEM分析,表明纳米Fe₂O₃粒子成功附着到rGO上;采用微分脉冲伏安法（DPV）进行BPA的电化学检测,结果显示BPA在0.1~100 μmol/L范围内呈现良好的线性关系,检出限为0.033 μmol/L（信噪比为3）。同时,Fe₂O₃-rGO/玻碳电极电化学传感器对电活性物质和常见金属离子具有良好的抗干扰能力,且实样检测结果理想。      

Passive 77 GHz millimeter-wave sensor based on optical upconversion

A passive millimeter-wave (mmW) sensor operating at a frequency of 77 GHz is built and characterized. The sensor is a single pixel sensor that raster scans to create an image. Optical upconversion is used to convert the incident mmW signal into an optical signal for detection. Components were picked to be representative of a single element in a distributed aperture system. The performance of the system is analyzed, and the noise equivalent temperature difference is found to be 0.5 K (for a 1 s integration time) with a diffraction limited resolution of ~8 mrad. Representative images are shown that demonstrate the phenomenology associated with this spectrum.     

Integrated optics magnetic sensor from 2 kHz to 9 GHz

A new type of integrated optical magnetic field sensor is presented in this paper. The proposed sensor consists of a Mach-Zehnder waveguide interferometer and a doubly loaded loop antenna. Such a structure can successfully avoid detection of the undesired electric field signal. The size of the sensor is 35 mm×6 mm×1 mm. The measurements show that the frequency response is from 2 kHz to 9 GHz, the dynamic range is 98 dB, and the minimum detectable magnetic field is 51.8 μA/m at 1 GHz. Therefore, this sensing system can be used in electromagnetic compatibility measurements.     

Surface plasmon resonance-based highly sensitive optical touch sensor with a hybrid noise rejection scheme

A surface plasmon resonance (SPR)-based optical touch sensor structure is proposed that provides high switch sensitivity and requires a weak activating force. Our proposed SPR-based optical touch sensor is arranged in a compact Kretschmann-Raether configuration in which the prism acting as our sensor head is coated with a metal nanofilm. Our optical-based noise rejection scheme relies on wavelength filtering, spatial filtering, and high reflectivity of the metal nanofilm, whereas our electrical-based noise reduction is obtained by means of an electrical signal filtering process. In our experimental proof of concept, a visible laser diode at a 655 nm centered wavelength and a prism made from BK7 with a 50 nm thick gold layer on the touching surface are used, showing a 7.85 dB optical contrast ratio for the first touch. An estimated weak mechanical force of <0.1 N is also observed that sufficiently activates the desired electrical load. It is tested for 51 operations without sensor malfunction under typical and very high illumination of 342 and 3000 lx, respectively. In this case, a measured average optical contrast of 0.80 dB is obtained with a +/-0.47 dB fluctuation, implying that the refractive index change in a small 3.2% of the overall active area is enough for our SPR-based optical touch sensor to function properly. Increasing optical contrast in our SPR-based optical touch sensor can be accomplished by using a higher polarization-extinction ratio and a narrower-bandwidth optical beam. A controlled environment and gold-coated surface using the thin-film sputtering technique can help improve the reliability and the durability of our SPR-based optical touch sensor. Other key features include ease of implementation, prevention of a light beam becoming incident on the user, and the ability to accept both strong and weak activating forces.