激光多普勒测速仪中散射光特性的研究

后向散射光特性与多普勒信号的质量密切相关。为了设计高性能的激光多普勒测速仪,运用散斑理论详细分析了激光多普勒信号的强度与散射光斑大小的关系,结合泛函理论给出了计算多普勒电流的散斑表达式,并通过实验的方法研究了回波信号的偏振特性及其强度分布。理论分析与实验结果表明,激光多普勒信号的强度与接收器件光敏面的直径成正比,与光斑的直径成反比;选用光斑较小的圆偏振激光束,并用光敏面尺寸较小的探测器在镜面反射方向上接收信号光,可以大大提高多普勒信号的信噪比,增强系统的探测能力,为提高系统的测量精度创造有利的条件。     

Internal tissue displacement measurement based on ultrasonic wave Doppler signal digital detection and its application to fetal movement monitoring

We have developed a fetal movement monitoring system based on small displacement measurement of internal tissues. When ultrasonic pulses are transmitted to the fetus, the reflected ultrasonic waves which have a Doppler frequency shift due to the fetal movements are detected by using an ultrasonic pulsed Doppler technique. In this paper, we propose a displacement measurement method for internal tissues which is based on the Doppler signal digital detection technique. In the method, the received ultrasonic RF signals are sampled with a sampling frequency of four times higher than the centre frequency of the ultrasonic waves; the Doppler frequency shift signals are derived using digital signal processing. From the detected signals, the internal displacements are estimated using the arc-tangent method. The basic algorithm of the detection method has already been used in the area of blood flow sensing, however, we apply the algorithm to the displacement measurement of internal tissues. The comparison between the proposed method and the conventional method is presented. The fetal movement quantitative monitoring system based on the method which has been constructed is shown.     

Doppler angle and flow velocity mapping by combined Doppler shift and Doppler bandwidth measurements in optical Doppler tomography

Accurate estimation of flow velocity requires measurement of Doppler angle, which is not available in general clinical applications. We describe a novel method of direct Doppler angle and flow velocity mapping that uses a conventional single-beam optical Doppler tomography system. The Doppler angle is estimated by combination of Doppler shift and Doppler bandwidth measurements, and flow velocity is calculated from the Doppler shift and the estimated Doppler angle. In vivo study of lip microvascularization demonstrates that this method is capable of providing both flow speed and flow direction information.     

Wideband signal detection based on high-speed photonic analog-to-digital converter

This Letter demonstrates the effectiveness of a high-speed high-resolution photonic analog-to-digital converter(PADC) for wideband signal detection. The PADC system is seeded by a high-speed actively mode locked laser,and the sampling rate is multiplied via a time-wavelength interleaving scheme. According to the laboratory test,an X-band linear frequency modulation signal is detected and digitized by the PADC system. The channel mismatch effect in wideband signal detection is compensated via an algorithm based on a short-time Fourier transform. Consequently, the signal-to-distortion ratio(SDR) of the wideband signal detection is enhanced to the comparable SDR of the single-tone signal detection.     

CT-6B托卡马克等离子体角向转动的光谱测量

利用高分辨光谱测量系统，根据杂质离子谱线ＯⅡ４６４.２ｎｍ，ＣⅢ４６４.７ｎｍ和氢Ｈα谱线的多普勒位移，测量了ＣＴ-６Ｂ托卡马克等离子体角向转动速度的径向分布．结果表明：杂质离子的角向转动速度的方向在等离子体内部为电子逆磁漂移方向，其线速度在小半径约９ｃｍ处达到极大值３.５ｋｍ／ｓ；在接近孔阑ｒ＝１０ｃｍ处，反转为离子逆磁漂移方向．由此导出等离子体内部的径向电场向里，其最大值为１８Ｖ／ｃｍ．中性氢原子只存在其方向为电子逆磁漂移方向的角向转动分量，其数值较杂质离子谱线所得结果要低．最后对所得的结果作了初步的讨论 关键词：     

光学平台微角振动激光探测方法研究

 设计了精密动态测角实验系统，该系统利用扩束镜正向和逆向不同的光学变换性质，将共孔径双向传输的倍增式角敏光学系统与光电精密位置传感器（PSD）相结合，并从理论上分析了高灵敏光学测角的基本原理，给出了被测角与传感器信号的关系。为消除光电噪声对探测分辨率的影响，信号处理引入了相关检测模式。通过压缩系统噪声信号的等效带宽，从频域中滤除干扰信号的频率成分，实现了从噪声中提取高分辨角度信息。     

任意复包络信号的匀速运动目标回波脉间补偿及相干积累

现代声呐、水下制导等水声探测系统常常使用窄带脉冲、调制、编码、伪随机等种类繁多的发射信号波形来满足低信噪比检测、高分辨估计、抗干扰、主动隐蔽探测的应用需求.针对这一情况,本文研究了任意信号的长时间积累问题,给出了一种任意复包络信号的匀速运动目标回波脉间补偿及相干积累检测方法.通过构建任意发射信号波形的广义模糊函数,将匹配滤波器输出表示为所构造的广义模糊函数,使得任意复包络信号的脉压波形不仅能够用统一的数学模型来表述和计算,而且能够提供多脉冲回波的距离走动信息和多普勒频移信息,为多脉冲距离位置对齐和Fourier变换(FFT)积累提供了依据.对于用广义模糊函数表示的匹配滤波器输出,采用Keystone变换将复包络对齐,消除了距离走动,采用FFT补偿多普勒频移项,实现了任意复包络信号的长时间相干积累.对于水下探测中使用的连续波信号、线性调频信号以及复杂的m序列编码信号、Costas跳频编码信号波形进行了信号积累及检测的计算机仿真,验证了任意复包络信号的匀速运动目标回波脉间补偿及相干积累的正确性.消声水池实验验证了该方法的有效性.     

自适应滤波技术在激光多普勒测速仪中的应用

激光多普勒测速仪检测系统提取的光电信号中存在较大的噪声信号。为了消除这些噪声干扰, 提高激光多普勒测速仪的测量精度,提出一种新的信号处理方法,将最小均方差自适应滤波技术应用于激光多普勒测量中,利用多普勒信号和噪声信号的统计特性,以最小均方误差估计为准则,最大程度地滤除噪声信号。阐述了最小均方差自适应滤波算法的基本原理,在MATLAB平台上将其应用于理想正弦信号进行仿真,并将其应用于实测多普勒信号的处理中。仿真和实验均表明,该技术可以有效抑制激光多普勒测量中的多频率噪声的干扰,大大提高多普勒信号的信噪比和测量精度,为设计高精度的激光多普勒测速仪创造了条件。     

改进的经验模态分解法分离超声多普勒血流与管壁信号

超声多普勒血流信号常包含管壁信号的干扰,准确分离二者对提高血流检测的精度具有重要作用。本文提出两种改进的经验模态分解(EMD)方法,先将含管壁信号的超声多普勒信号分解成多层本征模态函数(IMF),然后根据血流信号与管壁信号的不同特性,对既含管壁信号又含血流信号的IMF分量进行分离处理,最后将各层IMF分量中的管壁成分叠加得到管壁信号的估计,而血流信号可通过原信号减去估计的管壁信号而得到。将本方法用于计算机仿真信号和人体实测的超声多普勒信号,并与高通滤波器法、空间选择性降噪法和原EMD法进行比较,结果表明:本文提出的两种方法能在较大的管壁搏动速度范围内准确地分离血流信号和管壁信号,其平均相对误差比高通滤波器的结果降低了约52%和57%。可见,本文提出的两种方法有望用于血流信号与管壁信号的准确分离。      

Magnetic resonance imaging and pulsed Doppler sonography of poststenotic jets: Correlation between signal void and flow velocity distribution

To correlate the appearance of poststenotic jets on gradient echo images with features of localized Doppler spectra of the jets, we studied an in vitro model of steady flow-through stenoses of 86, 96, and 99% area reduction. As fluids, water and a 40% glycerol solution in water were used. MRI was performed with a 1.5 T whole body imager and gradient echo images were obtained in planes parallel to the direction of flow. Doppler spectra were acquired separately from the MR measurements at 1 cm intervals for a distance of 10 cm downstream from the stenosis. Poststenotic signal void was observed for water and for the 40% glycerol solution only if the mean velocity within the stenosis exceeded a limit of 50–60 cm/sec. On the MR images, the jets could be divided into two segments: A proximal jet segment of uniform width equal to the diameter of the stenosis, followed by a distal jet segment which was characterized by broadening and then dissipating signal void. Except for the 99% stenosis, a high signal intensity core was present within the proximal jet segment. In the proximal jet segment, the Doppler measurements showed a low temporal fluctuation of the maximal flow velocity and only little flow opposite to the main flow direction. In the distal jet segment, the velocity fluctuation and the intensity of reverse flow increased sharply. The high signal intensity core of the jet was associated with a poststenotic zone of constant maximal flow velocity. The results demonstrate a close relationship between characteristic features of poststenotic jets in MRI and pulsed Doppler sonography.     

超声波流速测量的多普勒频移提取方法研究

为了提高超声波多普勒法测量复杂流体流量的精度,针对流体的超声回波频率的复杂性,本文研究多普勒流速测量中的频偏提取方法。以傅里叶分析为理论基础,设计了硬件电路并获得代表回波平均频率的信号,然后以该信号作为输入,以数字鉴频法获得回波多普勒频移。基于该方法设计了一种超声多普勒流量测量系统,实验结果显示:油水混合流体流量的测量误差在3%以内,从而证实了此频偏提取方法的有效性。     

固体沿光轴方向的极缓慢速度和微小位移的激光多普勒测量

为了实现目标极缓慢速度和微小位移的实时、准确监测,消除各种干扰对微弱多普勒信号的影响,设计了一套激光多普勒测速(LDV)系统。该系统采用迈克尔逊干涉光路和调幅解调、相敏检测技术,具有较强的抗干扰能力。实验结果表明,该系统可实现固体目标沿光轴方向μm/s级速度和μm级位移的实时、准确测量。该系统光路结构简单,对目标的表面状况无特殊要求,可用于滑坡、地陷等地质灾害的监测,及桥梁、大坝等工程结构变形状况的检测,该方案对相关科学实验和工件精密测量也有重要意义。     

Pulsatile flow measurement in hydraulic systems using a laser velocimeter

Servo valves find their major application in high performance hydraulic control systems where the accurate control of position, velocity and load is essential. Because of this, it is important to determine the dynamic characteristics of the servo valve (i.e. flow rate as a function of input command signal) more precisely.Previous techniques for this evaluation depended on monitoring spool position using linear transducers, since flow measurement techniques capable of following fast transients and oscillating (or pulsating) flows were not easily applied. The introduction of the laser Doppler anemometer changes this. Steady state flow measurement, using the dual beam scatter system, is now common but since it needs a spectrum analyser to measure the Doppler frequency it is not suitable for unsteady flow. Since hydraulic systems are relatively particle free, the Doppler signals are dreceived intermittently. Because of this, a signal processing system has been developed which measures the period of one or more oscillations in the frequency burst caused by a scattering particle passing through the control volume.Using this technique steady and unsteady laminar flow profiles have been measured in order to assess its effectiveness in the performance testing of hydraulic servo systems.     

Acoustic measurements of boundary layer flow and sediment flux

Results are reported on an assessment of the application of coherent Doppler and cross-correlation techniques to measure nearbed boundary layer flow. The approaches use acoustic backscattering from sediments entrained into the water column from the bed, to obtain high-resolution profiles of the nearbed hydrodynamics. Measurements are presented from a wave tunnel experiment in which sediment was entrained by unidirectional, oscillatory, and combined flows. The data collected have been used to evaluate the capability of the two flow techniques to measure boundary layer mean, turbulent, and intrawave velocity profiles. Further, the backscattered signal has been used to measure suspended sediment concentration profiles, which have been combined with the velocity profiles to obtain high-resolution measurements of boundary layer sediment flux.     

空间多普勒激光雷达地面散射信号分析

为了扩展空间多普勒激光雷达地面散射信号的应用范围,采用多个机载多普勒激光雷达飞行实验数据,对地面散射信号的强度、海拔高度、速度等特征进行了数据分析,并利用地面散射信号与上层大气信号强度的比值,可以等效体现地面反射率特征,即地面散射信号解算的海拔高度与数字海拔高度模型数据相吻合,两者平均值偏差小于20 m,标准偏差小于100 m;使用地面散射信号实现飞机速度校正,与使用飞机平台数据解算的结果具有较好的一致性,采用直接探测手段时,标准偏差小于1.5 m/s,采用相干探测手段时,标准偏差小于0.5 m/s,验证了利用地面散射实现空间平台速度校正的可行性。另外,针对云散射信号的存在和影响,提出了一种利用海拔高度数据比对的方法,实现云散射和地面散射的识别。     

激光—声通信研究

通过对多普勒相干检测方法的研究,开发了一套激光测振系统,可以通过对水面质点振动速度进行非浸入式的探测,进而获取水下声信息。本文对水面平静和波动两种情况下的激光声通信进行了研究,通过水池实验证明了探测和通信原理的正确性和可行性,给出了系统最小可探测声压级,对波动水面下的数据丢失情况进行了分析,并提出了可能的解决途径。     

Passive component based multifunctional Jones matrix swept source optical coherence tomography for Doppler and polarization imaging

We present a fiber based multifunctional Jones matrix swept source optical coherence tomography (SS-OCT) system for Doppler and polarization imaging. Jones matrix measurement without using active components such as electro-optic modulators is realized by incident polarization multiplexing based on independent delay of two orthogonal polarization states and polarization diversity detection. In addition to polarization sensitivity, this system measures Doppler flow without extra hardware for phase stabilized SS-OCT detection. An eighth-wave plate was measured to demonstrate the polarization detection accuracy. The optic nerve head of a retina was measured in vivo. Detailed vasculature and birefringent structures were investigated simultaneously.     

Detecting Doppler ultrasound embolic signals using the wavelet-based feature extraction algorithm

The non-invasive detection of circulating emboli with the Doppler ultrasound technique is of active significance in clinical applications. In order to eliminate drawbacks of artifacts brought by the movement of probes or patients and detect emboli accurately, relevant feature parameters are extracted from two angles of the wavelet transform of Doppler signals. The singularity of the signal waveform is analyzed based on its wavelet scalogram; then transverse and longitudinal parameters are extracted to represent the scalogram characteristics. A novel method is proposed based on the adaptive wavelet packet basis, from which several parameters such as the energy, the scale, etc. are extracted to represent the optimized signal approximation features. With all feature parameters in two aspects, a classification system is established for Doppler Ultrasound embolic signals by solving the generalized Fisher discriminant plane. From experiments on 300 simulated and 298 clinical Doppler ultrasound signals of cerebral arteries, it is shown that the proposed system can achieve the emboli detection rates of 99.0% and 98.5% for the training set and the testing set respectively. Therefore this method makes an improve- ment of emboli detection compared to traditional in the automatic detection of clinical emboli. methods and has the possibility to be applied     

A new synthetic detection technique for trackside acoustic identification of railroad roller bearing defects

The detection of railroad roller bearing defects is of great importance for railway traffic. The acoustic defective bearing detector (ADBD) via a trackside acoustic detection system (TADS) is a popular and reliable tool for trackside identification of railroad bearing incipient defects. However, the defective trackside acoustic signal of bearing is confronted with three challenges: demodulation of acoustic signal, removal of Doppler effect and enhancement of defect frequency. This paper proposes a synthetic detection technique to overcome these difficulties successively. In the technique, the signal envelope is first extracted by a new variable-resolution ridge demodulation (VRRD) method. Then the Doppler effect is removed in the envelope via a dynamic signal resampling method. Finally, the rectified defect frequency is enhanced through the means of logarithmic transformation and piecewise linear detrending. The VRRD technique extracts the envelope from the signal time–frequency distribution (TFD) along the Doppler shift curve of resonance frequency traced by an improved ridge extraction algorithm. The resampling method is carried out on the envelope according to the Doppler shift curve of defect frequency obtained by the same ridge extraction algorithm. The sidebands around defect frequency can be suppressed by the logarithmic transformation and the low-frequency non-linear trend can be removed by the detrending method. The signal amplitude is unified at the same time. Two practical bearing signals with inner-race and outer-race defects separately verify the effectiveness of proposed technique.