Performance of new signal‐to‐noise ratio estimation for SEM images based on single image noise cross‐correlation

A new technique for estimation of signal‐to‐noise ratio in scanning electron microscope images is reported. The method is based on the image noise cross‐correlation estimation model recently developed. We derive the basic performance limits on a single image signal‐to‐noise ratio estimation using the Cramer–Rao inequality. The results are compared with those from existing estimation methods including the nearest neighbourhood (the simple method), the first order linear interpolator, and the autoregressive based estimator. The comparisons were made using several tests involving different images within the performance bounds. From the results obtained, the efficiency and accuracy of image noise cross‐correlation estimation technique is considerably better than the other three methods.     

一种基于波信号能量谱相关系数的损伤定位方法

基于波信号能量谱的相关系数,采用了两种策略分别计算传感线路的损伤特征参数(Damage index,DI),策略一:计算一条传感线路的感应波信号能量谱在基准和检测两种状态下的相关系数,并把该系数作为该条传感线路的DI。策略二:首先计算一条传感线路的激励波与感应波信号的相关系数,并把检测状态的相关系数相对于基准状态的相关系数的变化量作为该条传感线路的DI。在检测一个具有加强筋的复合材料板结构时,结合所计算的DI和损伤定位方法获取锥形孔损伤的概率分布图。试验结果表明策略二比策略一定位损伤的精度更高。这是由于策略二有效地避免了基准状态和检测状态的激励波信号的微弱差异所导致的损伤识别误差。     

斜拉桥健康监测信号改进小波相关降噪

为提高斜拉桥健康监测动态信号的降噪效果,针对传统小波相关降噪算法的缺陷,提出一种改进小波相关降噪算法。该算法将各层小波系数的主要能量周期作为相关检测邻域范围,并根据斜拉桥动态响应信号特征设置降噪阈值,最后采用一种全新的信号重构算法,得到降噪后的信号。将该算法与传统小波相关降噪和小波默认阈值降噪算法进行仿真试验比较,结果表明,改进小波相关降噪算法具有较好的降噪效果,能够应用于斜拉桥健康监测动态响应信号的降噪处理。     

一种用于混沌信号去噪的循环相关算法

基于局部相关原理,提出了一种可以有效实现混沌信号和噪声分离的方法。通过分析混沌信号在一定维数的相空间中存在的局部相关性,阐明了混沌信号内在的局部特征,引入循环相关算法对相空间中的相点进行有限次相关迭代以重新估计各个相点的值,利用相空间重构技术从这些新的相点中恢复出原始信号序列。试验仿真结果表明,该方法具有良好的噪声抑制能力和计算收敛性,算法简洁等优点。滤波效果与背景噪声类型无关。     

自动跟踪相关滤波在电主轴动平衡中的应用

根据动不平衡信号的信息特征和信号的相关性,给出了自动跟踪相关滤波原理和算法;基于Labview开发系统,依据自动跟踪相关滤波原理开发了动不平衡信号提取图形化程序,应用此程序对含有不同倍频谐波和噪声的振动信号进行仿真处理,并在电主轴动平衡中进行现场试验.结果表明,通过自动跟踪相关滤波,能够准确提取不同转速的动不平衡信号;能够满足电主轴高精度动平衡测试的要求.     

基于小波降噪与分形理论的滚动轴承故障诊断

为了识别滚动轴承振动信号中包含的故障类型,运用小波对采集到的信号进行降噪,通过计算降噪后振动信号的关联维数,判断信号中是否包含故障。并以关联维数为特征量,通过计算各工况之间的距离函数,判断属于何种故障的信号。结果表明,运用分形理论进行故障诊断具有很强的实用价值。     

Spurious pulse rejection in a photon correlation experiment

A method has been developed to significantly suppress the effect of spurious pulses on the correlation spectrum in photon correlation experiments. When the correlation experiment is operated at a low count rate (<2 true pulses per total measured correlation time), the circuit rejects an incoming pulse stream whenever more than two pulses are detected in that interval. Details of this spurious noise pulse rejection circuit are presented. This circuit has been incorporated into an existing correlation computer system as an option selected by the operator. Application of this circuit to a test case where the spurious pulse correlations were excessive compared with the signal events yielded very accurate signal correlation spectra.     

基于互相关检测和混沌理论的弱信号检测方法研究

本文简术了互相关检测的原理及混沌理论,在此基础上,提出了将互相关检测与混沌理论相结合检测微弱正弦周期信号的瓣方法。给出了原理框图、仿真模型及仿真实验结果。研究结果表明,此方法是目前信噪比门限较低的时域信号处理方法,因而具有广泛的应用前景。     

基于相关自适应器的EM-MWD信号检测系统设计

经EM-MWD(electromagnetic method measurement while drilling)电磁通道传输至地表的信号很微弱并且极易受到白噪声、奇异噪声、工频噪声及其谐波等干扰,导致信号特征参数提取的准确度降低,为了解决这一难题,通过对电磁波传输信道的研究,根据接收初始信号强度以及自适应检测和相关检测的特点,研究并设计了相关自适应器,并基于此设计了电磁随钻地表信号检测系统。然后用Hilbert变换求信号包络,完成了数据拟合和残差分析,并计算了信噪比、均方根误差和误码率,最后做了实验。仿真和实验结果表明,利用该检测系统,能够提高信号特征参数的准确度,达到有效降噪目的,对后续分析和研究提供了保证。     

铝合金电阻点焊多信息融合与质量分类

采用分布式多传感器同步采集系统实现铝合金点焊质量实时监测,并利用LABVIEW图形化语言编制相关数据处理软件。研究发现：焊点内喷溅与点焊电压和电极位移信号波形“下榻”现象相关联;电极压力所产生的高频脉冲强度和持续时间与内喷溅强弱有关,三种特征信息根据内喷溅严重程度,同时发生或个别出现。所提取的9种特征信息能够反映点焊质量,信噪比高,可为实现铝合金点焊质量分类奠定基础。采用主成分分析可进一步实现信息融合和数据压缩,点焊质量判断准确率达98 %。     

Application of Hilbert-Huang Decomposition to Reduce Noise and Characterize for NMR FID Signal of Proton Precession Magnetometer

The parameters in a nuclear magnetic resonance free induction decay (FID) signal contain information that is useful in magnetic field measurement, magnetic resonance sounding and other related applications. A real time sampled FID signal is well modeled as a finite mixture of exponential sequences plus noise. We propose to use the Hilbert-Huang transform (HHT) for noise reduction and characterization, where the generalized Hilbert-Huang represents a way to decompose a signal into so-called intrinsic mode function (IMF) along with a trend, and obtain instantaneous frequency data. First, acquiring the actual untuned FID signal by a developed prototype of proton magnetometer, and then the empirical mode decomposition is performed to decompose the noise and original FID. Finally, the HHT is applied to the obtained IMFs to extract the Hilbert energy spectrum of the signal on the frequency axis. By theory analysis and the testing of an actual FID signal, the results show that, compared with general noise reduction methods such as auto correlation and singular value decomposition, combined with the proposed method can further suppress the interfered signals effectively, and can obtain different components of FID signal, which can be used to identify the magnetic anomaly, the existence of groundwater etc. This is a very important property since it can be exploited to separate the FID signal from noise and to estimate exponential sequence parameters of FID signal.     

基于伪随机序列自相关的多传感器测距系统

针对单脉冲回拨方式的超声测距方法存在抗干扰能力差和不能全方位检测环境信息等缺陷,开发了一种多传感器测距系统。该多传感器超声测距系统基于伪随机序列自相关原理,通过对发射信号和回波信号进行相关运算精确的捕捉其相位差来计算渡越时间。以现场可编程门阵列(FPGA)为核心器件,结合超声回波的特点设计了能抑制和隔离电路中噪声的回波微弱信号接收电路、多路模数转换电路和相应的软件系统;提出了适用于该系统的误差校正方法。FPGA仿真结果表明,在误码存在的情况下,设计的基于自相关的回波信号识别系统可以很准确的消除超声串扰和计算出渡越时间。     

Experimental study on acoustic vector tomography of 2-D flow field in an experiment-scale furnace

An experiment study is performed on acoustic measurement of 2-D dynamic fields in a cold experimental scale furnace. By the acoustic method, the velocity field is restored with the vector tomography from the reciprocal acoustic travel time data measured. Regarding the measuring system, piezoelectric speakers and pickups are used as transmitters and receivers, which can stimulate powerful acoustic signal resource and receive the acoustic signal stimulated from long distance respectively. A high-pass digital FIR filter is designed for the signal filtering, and the signal correlation analysis by correlation coefficient is performed to obtain accurate acoustic transit time data from the filtered simulated and received acoustic signals. In the experiments, two different cases are tested, respectively symmetric and asymmetric flow fields. To validate the flow field recovered by the acoustic method, under the same conditions, the symmetric velocity field is measured by a hot-wire anemometer at some points and simulated with CFD software, and the asymmetrical velocity field is simulated. It is proved that the flow fields recovered by the acoustic method are reasonable and reliable. As a whole, from the experiment results, the acoustic measuring system and method developed in this paper is applicable in measuring the 2-D flow field in a cold experimental set-up and similarly in cold large-scale industrial furnaces. Additionally, the extension of the method to hot furnaces is discussed too.     

基于相关性的钢丝绳断丝特征提取

断丝信号与正常信号的非相关性是断丝信号的重要时域特征。以相关分析理论为指导,研究钢丝绳检测信号的相关性,提出一种获取断丝相关特征的方法。利用检测信号的相关运算,通过选择时延,提取断丝信号与股波信号在特定时延点的相关特征。研究相关窗长度和时延对结果的影响,提出确定相关窗长度和最佳时延的方法。最后针对一段检测信号,验证提取断丝相关性特征的过程。相关性是时域信号的重要特征,基于该特征的相关性识别方法对于提高断丝自动识别的可靠性和准确性具有一定的应用价值。     

Design of new sound metric and its application for quantification of an axle gear whine sound by utilizing artificial neural network

The gear whine sound of an axle system is one of the most important sound qualities in a sport utility vehicle (SUV). Previous work has shown that, because of masking effects, it is difficult to evaluate the gear whine sound objectively by using only the A-weighted sound pressure level. In this paper, a new objective evaluation method for this sound was developed by using new sound metrics, which are developed based on the increment of signal to noise ration and the psychoacoustic parameters in the paper, and the artificial neural network (ANN) used for the modeling of the correlation between objective and subjective evaluation. This model developed by using ANN was applied to the objective evaluation of the axle-gear whine sound for real SUVs and the output of the model was compared with subjective evaluation. The results indicate a good correlation of over 90 percent between the subjective and objective evaluations. This paper was recommended for publication in revised form by Associate Editor Yeon June Kang Professor Sang-Kwon Lee received a Ph.D. degree in ISVR (Institute of Sound and Vibration Research) from Southampton University in 1998. He joined Hyundai Motor Research Center in Korea, working with the Automotive Noise and Vibration Control Group from 1985 to 1994. He has been the Professor at the Department of Mechanical Engineering, Inha University, Inchon, Korea, since March 1999. His research interests are the digital signal processing, NVH (noise vibration harahness), condition monitoring, product sound quality design and active control.     

基于灰色准则与EEMD的滚刀振动信号降噪方法

工程现场采集的滚刀振动信号掺杂噪声,致使信号特征难以提取。提出一种基于灰色准则与集合经验模态分解(EEMD)的滚刀振动信号降噪方法。首先将原信号进行EEMD分解得到若干个特征模态函数(intrinsic mode function,IMF),再根据提出的灰色准则对IMF分量进行极性一致化处理、均值化处理,计算出IMF1与其他IMF分量的灰色关联度,并按照灰色关联度将IMF分量降序排列,然后选择降序排列中前一半IMF分量进行软阈值处理,最终将处理后的IMF分量、未处理的IMF分量及余项进行重构,得到降噪后的信号。通过不同初始信噪比的仿真信号和实际加工中的滚刀振动信号验证了本方法的可行性和有效性,同时与EEMD结合相关系数降噪法、小波软阈值降噪法进行了比较,结果表明本方法的降噪效果更优。     

金属材料小缺陷超声反射信号建模及识别

为了能从含噪声金属材料超声检测信号中有效识别出微小缺陷回波,建立了金属材料超声反射信号模型并提出了基于相关系数的微小缺陷回波识别方法。对含微小缺陷金属材料超声脉冲反射信号的成分进行分析,建立了基于散射声场与高斯回波理论的优化超声回波模型。设计了超声缺陷回波位置识别方法。该方法对超声脉冲反射信号去噪后,取探头发射脉冲信号为参考信号;然后与去噪后的信号逐段求解相关系数;最后对该相关系数序列进行阈值化处理,获得缺陷回波在超声回波信号中的位置。将利用上述优化超声回波模型生成的超声反射信号及其频谱与实验获得的金属材料超声反射信号及其频谱进行了对比,结果表明:两者的时频域特征具有一致性。当将阈值设定为相关系数序列最大值的60%时,能够有效从超声背散射信号中识别出金属材料微小缺陷回波。     

AltBOC navigation signal quality assessment and measurement

In order to ensure that Chinese BeiDou satellite navigation system runs smoothly,the assessment of signal quality has become a significant task.Alternative binary offset carrier （AltBOC） is BeiDou B2 frequency signal.The acquisition of BeiDou signal is processed in off-line mode and the evaluation is performed by taking signal power spectrum,eye diagram,constellation,correlation,loss and s-curve deviation on AltBOC as signal quality evaluation parameters.The results illustrate that the new system signal,namely AltBOC signal,has the best performance in code tracking precision,anti-jamming and anti-multipath.     

Airborne particles detection and sizing at single particle level by a novel electrical current pulse sensor

A novel method for detecting and sizing airborne particles at single particle level is presented in this paper. When a particle hits a metal electrode which is grounded, electrostatic charges will be transferred between the particle and the electrode. As a result, an electrical current pulse will be generated in the measurement system. The number of the signal pulse represents the number of particles in the sample. To determine the effect of the particle size on the magnitude of the signal, the correlation between the magnitude of the signal and the size of particle was experimentally investigated. The results show that the magnitude of the measured signal is linearly proportional to the square of particle’s diameter. Such a correlation can be used to evaluate particle size from the measured signal. The airborne particle detection method presented in this paper can be used for counting and sizing airborne particles at single particle level.     

基于SG算法的MEMS加速度传感器信号恢复研究

针对信号恢复前期存在局部干扰噪声,导致信号恢复质量较差和恢复速率较慢的问题,提出基于 SG 算法的 MEMS 加速度传感器信号恢复方法.将小波 SG 设定为传感器的预滤波单元,降低白噪声和局部强干扰对信号恢复产生的影响,同时结合 EEMD 抑制模式的特性剔除无利用价值的信号,提取有效的信号.将经过去噪处理信号的时间域平滑特性和空间平滑特性相结合,组建联合图模型.通过联合图模型中传感器信号的关联特性设计迭代恢复算法,最终完成 MEMS 加速度传感器信号恢复.实验结果表明,基于 SG 算法的 MEMS 加速度传感器信号恢复方法,可获取高质量和高效率的信号恢复结果.