激光光栅多普勒效应微小振动测量

为了提高测量微小振动的精度和动态范围，提出一种基于激光光栅多普勒效应的微振动测量系统。通过对差拍信号的频率分析，以峰值频率比值的方法可以排除干扰获得被测振动频率，找到振动的翻转点并判断振幅的大小；推导了在翻转点附近的微小位移与电压值的关系，对于小于计数当量值的位移由测量电压得到，提高了微小振动位移的测量精度以及系统测量的最小分辨率、动态范围。实验系统的频率范围为0．5～500Hz，振幅为20～10mm，相对误差小于1％，其动态范围大于100dB。     

激光多普勒微振动信号的直接强度解调

在传统的激光多普勒测振方法中,频移信号的检测通常需要具有比较复杂的频率或相位解调系统。从激光多普勒频移和干涉理论出发,提出了一种测量振幅小于纳米量级的方法———直接强度解调法。分析了直接强度解调法的适用范围。实验中利用了迈克尔逊干涉仪结构,采用了直接强度解调的方法。对振幅约为1nm的振动信号来说,其信噪比为23dB。     

半导体激光微小振动实时干涉测量仪

设计了一种半导体激光干涉测量仪,可以实时测量物体的微小振动。通过信号处理电路对干涉信号进行分析,得到实际振动的振幅和频率。给出了具体的理论分析,实验结果验证了该干涉仪的实用性。     

频率扫描干涉仪漂移误差正反向扫描补偿法

频率扫描干涉仪对测量过程中光程差的漂移非常敏感,目标镜的微小位移会被放大几千倍,使得测量结果严重失真,因此必须消除或减弱漂移误差。针对现场测量中目标镜的低频振动或缓慢漂移,根据光频连续正反向扫描测量值漂移误差放大项大小近似相等、符号相反的特性,提出了一种光频连续正反向快速扫描的漂移误差补偿方法,并进行了频率扫描干涉仪漂移误差补偿实验,分析对比补偿前后的实验结果,验证了该方法的可行性。实验结果表明,在测量距离约1543.3mm处,目标镜振动频率为4.7Hz,振幅为1μm,采用补偿后,连续40次采样测量的标准差由补偿前的51.9μm下降到8μm。     

目标物材料特性对激光语音获取的影响研究

为了扩大激光语音检测系统的应用场景,分析目标物材料参数对系统语音获取的影响,在完善语音获取中,语音信号从产生到与目标物作用的信号流程基础上,对目标物进行声致振动建模,以Sewell-Sharp-Cremer模型为基础,提出目标物声致振动幅度计算方法,并根据Matlab分析计算和实验对比了铁、铝、塑料、纸4种目标物的振幅及其对激光语音获取的影响。仿真及实验结果表明:目标物振幅在300 Hz～1 000 Hz呈指数型衰减,在1 000 Hz以上衰减趋于平缓;300 Hz处非金属材料振幅为69 nm和62 nm,高于金属材料的30 nm和10 nm。金属材料较非金属材料动态范围小,频率敏感度低,更适合作为语音获取的目标物。     

THz干涉测量用于障碍物后振动传感的研究

为探索THz干涉技术用于障碍物后振动传感的可行性,采用工作波长214.58 μm(对应频率约1.4 THz)的CO2激光器泵浦气体太赫兹源搭建了一套基于迈克尔逊干涉仪结构的THz干涉测量装置,实验研究了薄纸板遮挡后敲击目标镜产生的微小振动,利用相位分析法和频谱分析法对振动干涉信号进行处理,得到了振动位移随时间的变化以及...     

THz干涉测量用于障碍物后振动传感的研究

为探索THz干涉技术用于障碍物后振动传感的可行性,采用工作波长214.58 μm （对应频率约1.4 THz）的CO2激光器泵浦气体太赫兹源搭建了一套基于迈克尔逊干涉仪结构的THz干涉测量装置,实验研究了薄纸板遮挡后敲击目标镜产生的微小振动,利用相位分析法和频谱分析法对振动干涉信号进行处理,得到了振动位移随时间的变化以及不同时段振动频率的分布情况,测得的峰峰值振幅最小为7.98 μm,最大为17.54 μm,振动峰值速度为2.7 mm/s,振动频率最小21 Hz,最大58 Hz.研究结果表明THz干涉测量技术能有效克服传统振动传感技术无法穿透障碍物的缺点,是一种简便有效的障碍物后振动传感的新型手段,预示了THz技术在振动检测相关领域的广阔应用前景.     

一种结合两类相位调制激光多普勒频移测量的方法

提出了一种新的激光多普勒频移测量方法,该方法以相位调制拍频信号振幅和相位作为自变量定义新函数,并以该函数作为多普勒频移鉴频参量,将两类相位调制激光多普勒频移测量方法结合.理论上将该方法的鉴频曲线、灵敏度曲线以及误差曲线等与两类相位调制方法的相应曲线进行比较,发现该方法不但继承了相位调制拍频信号振幅方法的工作方式,能够对小频移量进行测量,而且吸收了相位调制拍频信号相位方法的测量能力,具有更高的测量灵敏度和动态范围.通过实验对硬目标反射的频移可控信号光进行测量,证明了理论的正确性,而且通过调整平移参数,可以使该方法的测量动态范围提高约26.8%,更适合对高多普勒频移量进行测量.     

水下声辐射激励水表面声波的特征参数测量

采用激光干涉方法对水下声辐射激励水表面声波的特征参数频率和振幅进行了测量研究。从理论上对水表面声波激光相干测量信号的频谱构成进行了分析,在此基础上提出了水表面声波两个重要声学参数频率和振幅的解算方法,并通过数值仿真进行了验证。搭建了一套简单的激光干涉测量实验系统,对不同频率和声压激励的水表面声波进行了测量实验,验证了水表面声波频率和振幅解调方法的准确性。对水表面声波横向传播的振幅衰减现象进行了初步的实验研究,结果表明水表面声波的频率越高,振幅的横向衰减越快。研究表明激光相干检测方法能够准确地实现水表面声波振幅和频率的测量。      

三光路结构的调频连续波重采样测距方法

调频重采样是一种绝对测距技术。这种方法采用的光源波长随时间变化,形成一束宽光谱激光。激光在各时刻的波长通过辅助干涉装置进行测量,并对其中频率间隔相同的部分进行重采样,使调频测距系统具有较大的线性光谱带宽,较高的分辨率及精度。在实际测量过程中,测量装置本身及待测物都容易受到振动的影响,导致待测距离及辅助光纤长度发生变化,引入测距误差。针对这个问题,分析了振动对重采样测量结果产生的误差:(1)待测物的移动引入一个多普勒频移分量;(2)辅助光纤的振动使重采样频率也发生变化。为了弥补这两种误差,提出了一种三光路结构的补偿方法,在辅助光路中,使用一种光路结构简单小巧,且测量速度更快的全光纤马赫泽德干涉仪等效代替光谱仪,实时的监测信号光的瞬时频率。在测量光部分,在测量光路中引入两个部分反射镜产生两路补偿光信号,并通过FFT算法产生频谱。频谱的三个峰值分别与三路信号相对应。通过测量信号与其中一路补偿信号的峰值相减即可补偿多普勒误差,通过两路补偿信号的频率差与相对距离的比值即可得出实际的辅助光纤长度。实验证明,传统的重采样测距方法精度为23.6μm,三光路测距方法的精度可达到11μm,可见这种方法能够对系统的振动误差进行有效补偿。     

Application of Hilbert–Huang transform to laser Doppler velocimeter

A new method based on Hilbert–Huang transform is proposed to analyze the laser Doppler signal with a large acceleration. The Doppler signal is decomposed into several Intrinsic Mode Functions (IMFs) via empirical mode decomposition (EMD). And the Hilbert transform is used to compute the instantaneous frequency. The vehicle velocity parameter is estimated by taking linear fitting on the instantaneous frequency of the relevant IMF. The simulation results show that the HHT-based method is quite useful for the LDV that offers velocity parameter to the vehicle self-contained navigation system when the vehicle moves at a large acceleration.     

Sinusoidal modeling for nonstationary voiced speech based on a local vector transform

A voiced speech signal can be expressed as a sum of sinusoidal components of which instantaneous frequency and amplitude continuously vary with time. Determining these parameters from the input, the time-varying characteristics are crucial error sources for the algorithms, which assume their stationarity within a local analysis segment. To overcome this problem, a new method is proposed, local vector transform (LVT), which can determine instantaneous frequency and amplitude for nonstationary sinusoids. The method does not assume the local stationarity. The effectiveness of LVT was examined in parameter determination for synthesized and naturally uttered speech signals. The instantaneous frequency for the first harmonic component was determined with an accuracy almost equal to that of the time-corrected instantaneous frequency method and higher accuracy than that of spectral peak-picking, autocorrelation, and cepstrum. The instantaneous amplitude was also determined accurately by LVT while considerable errors were left in the other algorithms. The signal reconstructed from the determined parameters by LVT agreed well with the corresponding component of voiced speech. These results suggest that the method is effective for analyzing time-varying voiced speech signals.     

回转件弯扭测量系统及其不确定度分析

为了准确诊测轴系振动特性,基于激光多普勒的频移原理,提出一种能同时测量旋转轴系弯曲振动、扭转振动和轴系旋转速度的方法。设计了能分离弯扭振动的多普勒外差干涉光路,结合光学差拍及参考光技术,构建了测量系统数学模型。对影响激光多普勒弯扭振动测量的主要因素进行了分析,讨论了各参量对测量结果的影响,并给出了相应的测量不确定度。在置信水平为95%时,瞬时转速的不确定为0.079 r/min,弯曲振动速度分量的不确定为0.001 4 mm/s,其精度能满足旋转状态下轴系振动的综合测量要求。     

基于Hilbert变换的水下多源声信号频率的相干探测

为实现水下中低频声信号的探测识别,通过研究水下多声源相干探测信号的特征,理论上给出了相干探测信号频谱混叠情况下的特征表达式,并提出了一种基于Hilbert变换的信号解调处理方法,实现了水下多声源相干探测信号频谱混叠情况下各声源发声频率的解调.该方法将探测信号经过滤波平滑处理之后进行Hilbert变换,得到信号的解析形式,然后对解析信号模值的平方进行二次滤波平滑等处理,分离混叠在一起的频带,将得到的信号进行频谱分析,根据频移值计算得到水下各个声源的发声频率.在光学暗室下搭建激光相干探测系统,对2~6kHz的水下声信号进行实验,实验结果表明,该方法可以有效分离探测信号中混叠在一起的信号频带,并准确提取各水下声信号的发声频率,频率提取重复性不大于2.5Hz.     

Review of LDA and PIV applied to the measurement of sound and acoustic streaming

A review of laser Doppler anemometry (LDA) and particle image velocimetry (PIV) with their application to the measurement of sound is presented. The fundamental principles behind LDA and PIV are discussed and extended to the application of sound measurement. Special attention is paid to analysis of LDA signals including the Hilbert transform, which enables amplitude information to be obtained about various frequency components of a signal and wavelet analysis, which allows non-stationary signals to be accurately analysed. The influence of the refractive index variations in a medium due to a sound wave on the laser beams of an LDA signal is discussed. Attention is also paid to acoustic streaming which arises due to high-intensity sound, and PIV results are presented to demonstrate the effect.     

Effect of noise and vibration on the performance of a particle concentration laser meter and optimization of its parameters

Spurious illumination penetrating into a gas duct adversely affects the performance of a laser gage measuring the concentration of solid particles dispersed in the air flow. The noise and gas duct vibration caused by the noise and vibration of the flow driver and other sources mechanically connected to the gas duct modulate the spurious radiation so that it may generate a signal that is perceived as a useful one by a photodetector. The noise-and vibration-modulated spurious illumination, as well as its optical-to-electric conversion with consideration for the spectral characteristics and the connection of the photodetector to the laser gage, is analyzed. From the amplitude and frequency properties of real noise and vibration sources causing the gas duct walls, on which the laser gage is mounted, to vibrate, the effect of the parasitic illumination is estimated. The operating parameters of a laser gage with double amplitude modulation and subsequent double synchronous detection, which make it possible to considerably improve its noise immunity, are proposed.     

可调谐半导体激光器的瞬时光谱测量方法研究

可调谐半导体激光器在调谐过程中的瞬时光谱特性,如瞬时的波长、调谐率、功率、线型和线宽等参数影响着以激光器为光源的光学测量和光相干通信系统的精度。然而,能够同时测量这些瞬变参数的技术至今未见报道。提出了一个基于时频分析的测量半导体激光器在调谐过程中瞬时光谱参数的方法,利用一个短时延外差测量系统,利用激光器瞬时光谱参数与差拍信号瞬时参数的关系,最终获得了半导体激光器在连续电流调谐过程中的瞬时光谱。测量系统采用了10 cm光程差的Mach-Zehnder干涉仪,调谐电流是幅度为20~120 mA、频率是1 kHz的锯齿波,差拍信号可视为直流信号、载波信号与噪声的叠加,按照短时延相干光测量原理,差拍信号中的直流分量幅度的大小反映了激光器输出光信号的功率;载波信号是一种多项式相位信号,由其频率可以推算激光器输出光谱的中心频率或波长;噪声信号则与激光器输出光谱的线型和线宽相关,通过对噪声信号进行时频分析,可以获知激光器在连续电流调谐过程中每一时刻或每个电流下的瞬时线型、线宽。采用了趋势局部均值分解方法对差拍信号进行了准确分离,并对分离信号分别进行处理,同时获知了半导体激光器在调谐过程中的瞬时输出光功率、光波长、调谐率及线型、线宽。在去掉弛豫部分后截取的整周期差拍信号对应的调谐电流60~115 mA变化范围内,半导体激光器(FRL15DDR0A31-18950, Furukawa)瞬时输出光功率变化范围是5.16~10.6 mW,瞬时光波长变化范围为1 579.2~1 579.6 nm;激光器的瞬时调谐率在0.004 8~0.011 5 nm·mA-1范围内单调变化;线宽是852.55~954.95 kHz,呈非线性随机分布。基于短时延、局部均值分解和时频分析方法的瞬时光谱参数测量系统可以准确得到各瞬时光谱参数,测量结果与激光器的静特性相符,且测量系统结构简单,使我们更深入地理解激光器的工作原理,具有广阔的应用前景。     

Hilbert transform for processing of laser Doppler vibrometer signals

A first application of the digital Hilbert transform for processing of laser Doppler vibrometer signals is considered. The possibility of vibration amplitude measurement with a relation errors less than 1% in the amplitude interval 0.1-10Λ, where Λ is the fringe spacing, and the linear velocity measurement of the examined object has been proved. The analysis of the amplitude measurement errors is given. The applications of the method under review are discussed.     

Parameter estimation of underwater moving sources by using matched Wigner transform

According to the acoustical Doppler effect, an improved narrow-band technique is proposed to estimate underwater source’s motion parameters including speed, closest distance, rest frequency, and closest point of approach (CPA) time, by using a single receiving sensor. First, the matched Wigner transform (MWT), which produces a time–frequency distribution (TFD) with optimal energy concentration and without inner artifacts for a high-order polynomial phase signal, is defined. On the basis of the MWT, a method is developed for the accurate instantaneous frequency (IF) estimation of Doppler signal. Moreover, we deduce that the Wigner–Ville distribution of the Doppler signal has a peak at the center of the TFD. Thereafter, the CPA time is directly estimated. When the CPA time is obtained, the other motion parameters can be easily estimated by using a simplified amplitude weighted nonlinear least-squares method, which fits the IF estimates to the predicted Doppler shift. Finally, the effectiveness of the proposed scheme is validated by using underwater acoustic data.