多传感器特征决策融合的钢轨裂纹识别方法

随着高速铁路的快速发展,钢轨裂纹的有效检测对于铁路安全运行具有重要的意义.针对基于漏磁信号的钢轨裂纹识别问题,采用多传感器特征决策融合技术,在对漏磁信号进行了时域和频域的多特征提取与融合的基础上,同时对多传感器信号进行决策融合,设计了一种基于支持向量机(SVM)的多传感器信息融合分类器.利用人工裂纹的实测漏磁信号进行实验,相比于提取单一特征和利用单一传感器信号进行识别,提出的方法取得了更好裂纹识别效果,平均识别率达到98％.     

基于视觉的零部件振动裂纹在线监测系统研究

金属零部件的质量检测是劳动密集型工作,一般通过疲劳测试评价金属零部件质量,对金属零部件质量进行准确评估的依据,能够指导设计合理的机械结构并有效减少安全事故和经济损失。为了快速筛选质量合格、抗振性较强的金属零部件,针对疲劳测试中快速振动的金属零部件,提出了一种基于计算机视觉的振动疲劳裂纹在线检测算法。该算法首先基于前后帧对齐方法消除振动产生的位移和运动模糊,然后利用帧间差法检测零部件表面变化,最后根据裂纹的纹理特征和几何特征通过分割算法得到裂纹形态和长度参数。实验结果表明,与静态条件下的裂纹检测算法相比,提出算法能够在振动台不停机的情况下,自动地获取零部件裂纹的位置、长度及形状等信息,记录裂纹的延展过程,可以大大提高振动裂纹检测的工作效率。     

基于多频平衡电磁技术的管道内外缺陷检测与全角度表面裂纹识别方法EI北大核心CSCD

缺陷和裂纹是管道安全运行的潜在隐患。因管道表面裂纹方向各异,漏磁方法对表面裂纹敏感性低,而交变电磁方法受限于趋肤效应,无法检测管道外缺陷。该文提出多频平衡电磁技术,解决了管道内外缺陷检测与全角度表面裂纹识别难题。根据电磁平衡技术的电磁场传播特点,分析管道缺陷与裂纹的检测原理。采用有限元方法,研究激励频率对裂纹偏角与内外缺陷响应信号的影响,优化得到20Hz和400Hz的最佳频率组合,并对预制内外缺陷和裂纹的管道进行实验验证。结果表明:多频平衡电磁信号的峰值随内外缺陷深度的增加而近似线性增大;当裂纹偏角由0°增至90°时,平衡电磁信号的峰值逐渐增大。平衡电磁信号峰值与缺陷深度和裂纹角度的关系可用于缺陷深度的量化与裂纹偏角的识别,从而为管道完整性评估奠定良好的基础。     

基于金属磁记忆技术的微裂纹检测仿真分析

鉴于金属磁记忆检测技术对微裂纹的早期预判上有独到优势,基于金属磁记忆检测机理,考虑磁性材料磁导率的各向异性,运用COMSOL有限元分析软件对起重机导轨常用材料Q235B钢进行磁记忆检测有限元仿真,定量分析了被检测钢块在裂纹宽度、裂纹深度、拉伸载荷、提离高度及外加地磁场变化时材料磁记忆信号的变化规律。结果表明,随微裂纹尺寸的增大,磁记忆检测信号增强;随外加应力的增高,磁记忆检测信号先增大后减小;随提离高度的增加,磁记忆检测信号减小。     

高Q值超低功耗谐振式磁传感器的设计与实现

针对现有谐振式磁传感器原理不能同时实现高品质因数(Q)和低功耗的缺点,利用双端固定石英音叉谐振器与铁镓磁致伸缩合金片复合,设计了一种隔离磁机阻尼的高Q值、数字频率输出的超低功耗谐振式磁传感器。利用音叉谐振器结构的解耦特性,设计应力耦合传递结构,隔离了磁致伸缩材料磁机阻尼,从而保证复合传感器Q值与音叉谐振器Q值相当。在磁场作用下,磁致伸缩力传递到音叉谐振器,由于音叉力敏感特性,实现磁-力-频率转换。制备了铁镓合金/石英音叉谐振器复合敏感结构,测试表明,在低气压封装条件下的品质因数约为16 764,门振荡电路功耗约为124.8μW,在线性区灵敏度为3.05 Hz/Oe,分辨率为6 mOe。     

单向CFRP表面缺陷的涡流检测与有限元仿真研究

针对目前钢制拉索耐腐蚀性差，寿命周期短，同时无法满足当前工程应用中超大跨距的要求，碳纤维复合材料因具有优异的机械性能和稳定的化学性能，为寻找替代钢拉索的新材料拉索提供了新的研究方向。本研究利用实验与数值仿真相结合的方法，开展CFRP裂纹损伤结构的涡流场分析与检测。结果表明，当激励频率为1 250 kHz时，线圈对碳纤维板索裂纹损伤检测最为敏感。裂纹处信号幅值随裂纹深度的增加而增加；随裂纹宽度的增加呈现先增加后减小的趋势，在裂纹宽度为1.5 mm时幅值达到最大值。通过CFRP涡流场有限元仿真，能够有效地验证实验结果。涡流检测技术可以有效应用在CFRP的损伤缺陷检测当中，为今后利用电磁涡流技术实现CFRP拉索的在役缺陷检测提供参考依据。     

波导谐振环微带阵列多裂纹检测传感器设计

针对飞行器机翼的大面积壁板等金属结构的多形态裂纹分布难以同时检测、检测精度低等问题,设计了一种互补开口波导谐振环微带阵列多裂纹检测传感器。该传感器群阵列中不同尺寸的互补开口波导谐振环微带传感器能够检测直裂纹、针孔、星型3种裂纹的特征参数。实验结果表明,传感器对3种裂纹的参数变化的最大检测灵敏度达到了150 MHz/mm,传感器可检测出的最小直裂纹尺寸为10 mm×1 mm×0.1 mm。该传感器结合了互补开口谐振环辐射能力强、易于表面共形和基片集成波导低损耗、品质因数高、尺寸小的特性,能够实现对金属材料上多形态裂纹的同时检测,具有灵敏度高、检测范围大等优点。     

锈蚀铁磁材料表面的极微裂纹信号的聚类与提取

表面生锈的铁磁材料的微裂纹检测是个难点。当微裂纹深度与表面腐蚀深度接近时，表面腐蚀凹陷所造成的噪声几乎淹没裂纹信号，造成深度在0．6mm以下的裂纹检测数据相互覆盖。基于LabWindows／CVI的虚拟微裂纹信号分析仪，利用三种模糊聚类算法(模糊C-均值聚类算法、“max-min”准则下的模糊聚类算法、基于遗传算法的模糊C-均值算法)对采样数据进行分类，再通过小波变换与信号分形技术，有效地从噪声中提取了0．6mm以下的极微裂纹信号，同时成功的对0．6mm以下、不同深度的裂纹进行分形识别，从而改善了硬件检测系统对这种极微裂纹的分辨率，提前了材料寿命的预报时机。     

基于编解码的超声导波轨底裂纹识别方法研究

超声导波在针对钢轨小裂纹检测时由于利用高频信号，会导致信号衰减明显，对于小裂纹的检测灵敏度降低，针对细小裂纹难以识别，为提高缺陷信号识别度，本文将barker码作为编码方式，并用类BPSK作为解码方式，利用到导波检测钢轨小裂纹的信号处理中。通过实验将对钢轨轨底上深度6 mm宽度0.5 mm的人工裂纹进行验证，为衡量算法效果分别用未经过任何信号处理的原始收发导波信号和经过barker码-匹配滤波编解码处理的导波信号与实验方法进行对比。结果表明，利用barker码-类BPSK编解码处理的导波信号在处理钢轨轨底小裂纹的识别上有着明显的增强作用，效果优于另外两种方法，可以为以后的导波钢轨小裂纹检测提供支持。     

花萼状涡流阵列传感器裂纹扰动半解析模型构建

针对金属螺栓连接结构中螺栓孔位置处的裂纹损伤定量监测需求,在已有研究成果的基础之上,提出一种具有柔性平面特点的花萼状涡流阵列传感器,构建花萼状涡流阵列传感器裂纹扰动半解析模型,得到在三维结构裂纹下的传感器各感应通道扰动电压,并通过搭建实验装置验证裂纹扰动半解析模型的准确性。在模型构建过程中,通过对结构三维裂纹表面进行网格划分,以网格中心点处的自由电荷密度为未知待定系数,根据自由电荷边界条件以及扰动模型假设得到网格单元中心点处自由电荷密度所满足的线性方程组,并最终得到三维裂纹周围的自由电荷密度分布。裂纹扩展模拟实验结果表明,在3 MHz和6 MHz两种激励频率下,2A12-T4铝合金和不锈钢的扰动模型计算结果与实验测量结果比较吻合,传感器4个感应通道的扰动模型计算误差都在25%以内。     

仅利用零序电流的谐振接地系统接地故障方向算法

由于多数终端难以获得零序电压或三相电压信号,限制了暂态功率方向法在小电流接地故障定位、多级保护、分界技术的应用。分析了谐振接地系统单相接地时故障点上游与下游的零序电流工频分量、暂态主谐振分量以及衰减直流分量与故障初相角的关系,发现可利用零序电流工频分量作为零序电压的极化相量,进一步识别故障方向。当零序电流工频分量初相位分别在(-45°,75°)或(135°,255°)以内,暂态主谐振分量初相位分别在(-30°,30°)或(150°,210°)以内时,或者衰减直流分量与工频分量幅值之比大于预设门槛时,故障方向为正,否则故障方向为负。仿真和现场实际故障数据验证了算法的正确性。     

Cantilever beam temperature sensors for biological applications

This review presents two types of cantilever beams employed as highly sensitive temperature sensors. One type is fabricated from composite materials and is operated in the deflection mode. The second type, used as a temperature sensor and presented in this review, is a resonant cantilever beam. The materials used for the fabrication of the bimaterial cantilever beam are silicon or silicon nitride and thin metallic films such as gold or aluminum. When the temperature changes, the different coefficients of thermal expansion of the metal and silicon cause the sensor to deflect. Considering the models of temperature measurement for biological cells, the heat should be applied locally at the tip of the cantilever beam. Formulas for the calculation of the deflection as a function of incident power applied at the free end of the cantilever beam operated in a liquid are presented in this review. The natural convective heat transfer coefficient was estimated by using the mathematical model and experimental values. For biological applications, the cantilever beam temperature sensor was operated in a liquid, and the heat transfer coefficients were between 381 and 642 W/m²K when the temperature applied to the cantilever's free end varied from 28 to 71.8 °C. The resonant cantilever beam was also demonstrated as a sensitive temperature sensor for biological applications. As a thermogenic sample, brown fat cells (BFCs ), which are related to metabolic heat production, are employed. The working principle of the resonator cantilever beam temperature sensor is based on the shift in resonant frequency in response to temperature changes. The resonant frequency and the temperature coefficient were 960 kHz and 22.0 ppm/K, respectively. The measurements were performed by stimulating the activity of BFCs by flowing a norepinephrine (NE ) solution (1 µM ).     

基于磁轭结构的脉冲涡流热成像激励效果比较

针对目前脉冲涡流感应热成像无损检测中激励线圈加热不均匀、受提离影响大的问题,将导线缠绕在磁轭装置上加载电流,分析其激励效果。为确定线圈缠绕位置对激励效果的影响,比较了不同装置激励时裂纹两端和底部的涡流分布及温度分布。结果表明,引入磁轭装置后系统的能量传递效率得到很大提高,同时激励的不均匀性减弱。激励线圈均匀分布在磁轭装置横梁及两极靴时激励效果最好。利用最优激励模型对不同方向的裂纹进行检测,结果表明,铁磁材料表面各个方向角的裂纹都可以被检测到,非铁磁材料方向角较小的裂纹不能被检测到。根据试件表面最高温度随裂纹方向角增大而线性增加的特点可以识别裂纹的方向角。     

硅微机械谐振式压力传感器闭环方法

提高硅微机械谐振式压力传感器的性能指标有很多方法,如何对已知敏感结构的输出量程范围内所有谐振频率点进行实时闭环跟踪是其中之一。对几种比较常用硅微机械谐振式压力传感器的激励-拾振方式进行介绍,对所调研的国内外文献给出的谐振式微结构传感器闭环控制方法进行比较分析,提出一种新的针对电热激励-压阻拾振方式的复合敏感结构进行闭环控制的方法,同时给出了提高该类型传感器性能的有效手段和研究方向。     

A Novel Wireless Passive Temperature-Pressure SAW-based Sensor

A novel wireless and passive surface acoustic wave (SAW) sensor is developed for measuring temperature and pressure. The sensor has two single-port resonators on a substrate. One resonator, acting as the temperature sensor, is located at the fixed end without pressure deformation, and the other one, acting as the pressure sensor, is located at the free end to detect pressure changes due to substrate deformation. Pressure at the free end bends the cantilever, causing a relative change in the acoustic propagation characteristics of the SAW traveling along the surface of the substrate and a relative change in the resonant frequency of the resulting signal. The temperature acts on the entire substrate, affecting the propagation speed of the SAW on the substrate and directly affecting the resonant frequency characteristic parameters. The temperature and pressure performance of this new antenna-connected sensor is tested by using a network analyzer, a constant temperature heating station, and a force gauge. A temperature sensitivity of 1.5015 kHz/°C and a pressure sensitivity of 10.6 kHz/gf at the ambient temperature have been observed by wireless measurements. This work should result in practical engineering applications for high-temperature devices.     

小波分析在管道螺纹缺陷超声波检测中的应用

油管螺纹区由于其工作和结构上的特殊性,螺纹区内易产生螺纹内断裂,根部裂纹,应用通常的检测方法很难对螺纹区缺陷进行检测.这些缺陷如不及时发现,将影响到油井作业的安全.本文介绍的是采用超声波技术研制油管螺纹区裂纹检测的传感器,检测出螺纹区内的缺陷信号;并提出了一种采用小波技术对超声波检测信号进行初步降噪;然后采用基于快速傅里叶逆变换(IFFT)小波矩的快速算法进行插值处理的方法,对超声波信号图像细节特征进行了提取检测,通过比对模极大值点捕捉缺陷位置,获得了良好的检测效果.     

横波声场中倾斜平面反射特征的研究

与入射波束成一定角度的面状缺陷的声场反射特征和垂直入射时的反射特征不同。通过对横波声场中一系列不同宽度的 ４５°模拟裂纹的反射回波特征进行研究,得出了主波束入射、扩散波束入射时端角反射、面反射、端部反射的声压、声程落点的规律。     

Non-destructive Testing Method for Crack Based on Diamond Nitrogen-vacancy Color Center

Magnetic field measurement plays an extremely important role in material science, electronic engineering, power system and even industrial fields. In particular, magnetic field measurement provides a safe and reliable tool for in-dustrial non-destructive testing. The sensitivity of magnetic field measurement determines the highest level of detec-tion. The diamond nitrogen-vacancy (NV) color center is a new type of quantum sensor developed in recent years. The external magnetic field will cause Zeeman splitting of the ground state energy level of the diamond NV color center. Optical detection magnetic resonance (ODMR), using a microwave source and a lock-in amplifier to detect the resonant frequency of the NV color center, and finally the change of the resonant frequency can accurately calcu-late the size of the external magnetic field and the sensitivity of the external magnetic field change. In the experiment, a diamond containing a high concentration of NV color centers is coupled with an optical fiber to realize the prepara-tion of a magnetic field scanning probe. Then, the surface cracks of the magnetized iron plate weld are scanned, and the scanning results are drawn into a two-dimensional magnetic force distribution map, according to the magnetic field gradient change of the magnetic force distribution map, the position and size of the crack can be judged very accurately, which provides a very effective diagnostic tool for industrial safety.     

Fabrication and characterization of piezoelectric driven microdiaphragm resonating sensor for a biosensing application

The detection capability of microresonating sensors is decided by the resonant properties (mass sensitivity and quality factor) because the microresonating sensors have detection principle that the target material of small amount quantitatively detect by measuring the resonant properties change of microresonators. Mass sensitivity is important factor to evaluate minimum detectable mass of microresonating sensors. For the biomolecule detection in liquid, microresonaotrs have to keep the quality factor that can discriminate small frequency change when the liquid sample injected on the microresonating sensors. In order to study mass sensitivity and quality factor of the fabricated microdiaphragm sensors, Pt thin film with different thicknesses are deposited on the our Pb(Zr_0.52Ti_0.48)O₃ layer-embedded microdiaphragm sensors. Increasing the mass sensitivity ranging from 1.68 to 36.61 Hz/ng which is found with the decreasing the width of squared microdiaphragms ranging 900 to 300 μm. The mass sensitivity of our microdiaphragm sensor stands comparison with microcantilever sensor of length scale of 200?~?300 μm. Moreover, we find that the quality factor is kept on more than 23 that was ten times better than microcantilever resonating sensor with length scale of 200 μm.