Application of a six-port wave-correlator for a very low velocity measurement using the Doppler effect

A new radar system based on a six-port wave-correlator is proposed for measuring the Doppler frequency of a moving object. The six-port wave-correlator is operated as a two-channel wave receiver and the vector relation, both amplitude and phase, between the two input signals is determined directly by measuring the power levels. By using the six-port wave-correlator, no circulator or mixer is needed for the phase measurement. The proposed system has been applied for the measurement of an object moving at a very low velocity. The experiment and simulation results at 10 GHz show that the target velocity around 0.2 mm/s has been successfully inferred, which proved the validity of the proposed scheme.     

Synthesis of a Distributed Recording Circuit for a Time-of-Flight Velocity Meter with Adapation of the Setting Intervals of Sensors

A systematic technique is proposed for synthesizing a distributed recording circuit for a time-of-flight type of velocity measuring system. The technique is based on the criterion of minimum sum of methodic error in the indirect determination of the instantaneous velocity and the error of measurement of the average velocity along a portion of the path. The expressions obtained can be used to determine the optimal value of the intervals between neighboring sensors and to estimate the errors of measurement. It is shown that the interval between sensors should be variable, with an adaptation to the results of the measurement on the preceding interval along the path.     

Speckle-based three-dimensional velocity measurement using spatial filtering velocimetry

We present an optical method for measuring the real-time three-dimensional (3D) translational velocity of a diffusely scattering rigid object observed through an imaging system. The method is based on a combination of the motion of random speckle patterns and regular fringe patterns. The speckle pattern is formed in the observation plane of the imaging system due to reflection from an area of the object illuminated by a coherent light source. The speckle pattern translates in response to in-plane translation of the object, and the presence of an angular offset reference wave coinciding with the speckle pattern in the observation plane gives rise to interference, resulting in a fringe pattern that translates in response to the out-of-plane translation of the object. Numerical calculations are performed to evaluate the dynamic properties of the intensity distribution and the response of realistic spatial filters designed to measure the three components of the object's translational velocity. Furthermore, experimental data are presented that demonstrate full 3D velocity measurement.     

Bidirectional axial transmission can improve accuracy and precision of ultrasonic velocity measurement in cortical bone: a validation on test materials

The axial transmission technique uses a linear arrangement of ultrasonic emitters and receivers placed on a same side of a cortical bone site in contact with the skin, involving ultrasonic propagation along the axis of bone. The velocity of the waves radiated from bone has been shown to reflect bone status. The thickness and composition of soft tissue may vary along the length of the bone, between different skeletal sites, or between subjects. Hence, accurate estimates of velocity require first to eliminate the effect of the overlying soft tissue that is traversed by the ultrasound wave. To correct for such bias without measuring soft tissue properties, we designed new ultrasonic probes in the 1-2 MHz frequency range. It is based on propagation along the bone surface in two opposite directions from two sources placed on both sides of a unique group of receivers. The aim is to obtain an unbiased estimate of the velocity without any intermediate calculation of soft tissue properties, such as thickness variation or velocity. Validation tests were performed on academic material such as Perspex or aluminium. We found that head wave velocity values could be biased by more than 10% for inclination of a few degrees between the test specimen surface and the probe. On test materials, the compensation procedure implemented in our probe led to a relative precision error on velocity measurement lower than 0.2 to 0.3%. These results suggest that the correction procedure allows measuring in vivo velocities independently of soft tissue properties.     

Detection of relative and uniform motion

We measured the lowest velocity (velocity threshold) for discriminating motion direction in relative and uniform motion stimuli, varying the contrast and the spatial frequency of the stimulus gratings. The results showed significant differences in the effects of contrast and spatial frequency on the threshold, as well as on the absolute threshold level between the two motion conditions, except when the contrast was 1% or lower. Little effect of spatial frequency was found for uniform motion, whereas a bandpass property with a peak at approximately 5 cycles per degree was found for relative motion. It was also found that contrast had little effect on uniform motion, whereas the threshold decreased with increases in contrast up to 85% for relative motion. These differences cannot be attributed to possible differences in eye movements between the relative and the uniform motion conditions, because the spatial-frequency characteristics differed in the two conditions even when the presentation duration was short enough to prevent eye movements. The differences also cannot be attributed to detecting positional changes, because the velocity threshold was not determined by the total distance of the stimulus movements. These results suggest that there are two different motion pathways: one that specializes in relative motion and one that specializes in uniform or global motion. A simulation showed that the difference in the response functions of the two possible pathways accounts for the differences in the spatial-frequency and contrast dependency of the velocity threshold.     

Radiation and dynamics of a nanoparticle in equilibrium background radiation upon translational–rotational motion

We have obtained general expressions for the intensity of radiation and tangential force of a small polarizable particle in the process of translational–rotational motion in equilibrium radiation background (thermalized photon gas) of a certain temperature at an arbitrary relative orientation of the linear and angular velocity vectors. It is shown that, in a cold vacuum background, the translational velocity of particle is independent of time and the intensity of its spontaneous emission is determined by the angular velocity and imaginary part of the particle polarizability.     

MEMS微结构旋转角度的快速测量方法

可运动的微结构是MEMS器件的重要单元,其运动特性与器件的性能和可靠性是密切相关的.针对频闪成像技术获得的微结构运动图像序列,提出一种微结构旋转角度的快速测量方法.该方法利用运动微结构上普遍存在的释放工艺孔结构作为目标特征,对其中两个释放工艺孔的图像特征分别求取质心和两质心连线的斜率,最后比较运动图像序列中质心斜率的变化,得到各运动状态下的旋转角度.实验结果表明,该测量方法的运算时间小于0.5s,角度测量分辨率可达到0.01°.     

First-order algorithm with three clusters of optical flow vectors

The first-order algorithm is an algorithm for recovering the motion parameters from a single optical flow field. It compares the spatial derivatives, to first order, of the optical flow field obtained from two different parts of the field of view and obtains a linear constraint on the direction of the translational velocity. We modify this algorithm to incorporate the spatial derivatives, to first order, of the optical flow field obtained from a third part of the field of view, and thereby obtain two further linear constraints on the direction of the translational velocity. Only two linear constraints are required to identify the direction of the translational velocity. Therefore, with three linear constraints, there are three ways of estimating the direction of the translational velocity. Although all three estimates are derived from the same set of information, we show that the three estimates are not, in general, equally stable. We assume that each cluster of flow vectors arises from a plane in the environment and show that a linear constraint is most stable when it emanates from a pair of parallel planes, with the camera between them. We also identify the relative orientations of the clusters of flow vectors that maximize and minimize the stability of the linear constraint that they give rise to. © 1996 John Wiley & Sons, Inc.     

Proposal and testing for a fiber-optic-based measurement of flow vorticity

A fiber-optic arrangement is devised to measure the velocity difference, deltav(l), down to small separation l. With two sets of optical fibers and couplers the new technique becomes capable of measuring one component of the time- and space-resolved vorticity vector omega(r, t). The technique is tested in a steady laminar flow, in which the velocity gradient (or flow vorticity) is known. The experiment verifies the working principle of the technique and demonstrates its applications. It is found that the new technique measures the velocity difference (and hence the velocity gradient when l is known) with the same high accuracy and high sampling rate as laser Doppler velocimetry does for the local velocity measurement. It is nonintrusive and capable of measuring the velocity gradient with a spatial resolution as low as ~50 mum. The successful test of the fiber-optic technique in the laminar flow with one optical channel is an important first step for the development of a two-channel fiber-optic vorticity probe, which has wide use in the general area of fluid dynamics, especially in the study of turbulent flows.     

Measurement of the properties of fluids inside pipes using guided longitudinal waves

A new technique for measuring the longitudinal bulk velocity and shear viscosity of a fluid contained inside a pipe without a need for extracting a sample from inside of the pipe is presented. It is based on the measurement of the change of the dispersion properties and attenuation of longitudinal guided modes propagating in the pipe due to the presence of the fluid. The technique to extract longitudinal bulk velocity and shear viscosity is discussed and experimentally demonstrated by measuring both low-viscosity (distilled water and glycerol) and highly viscous fluids. The measured properties of glycerol agreed well with conventional methods and literature data for both the longitudinal bulk velocity (within 0.8%) and the viscosity (within 4%). For highly viscous fluid, the accuracy of the velocity measurement was found to be reduced slightly (within 1%), and the viscosity measurement became more accurate (within 1%).     

Application of the Electrochemical Method for Measuring the Fluid Velocity in a Two‐Phase Bubble Flow

A technique for measuring the fluid velocity in a twophase flow using a combination of the electrochemical method and the conduction method is described. The point of this technique is numerical analysis of complete realizations of signals from the electrodiffusion velocity transducer. The dependence of the results of measurements of local hydrodynamic characteristics of the bubble flow on the level of gasphase cutting out has been investigated. The measurement data for the local gas content, the fluid velocity, and the velocity pulsations during bubble mixture motion in a tilted channel are presented.     

Planar measurement of three-component velocity by streaked-particle-imaging velocimetry

A streaked-particle-imaging-velocimetry (SPIV) technique for the instantaneous planar measurement of three-component velocity has been developed and demonstrated. In this system a camera images the scattered light from two laser sheets onto the same recording medium. One of the laser sheets, double pulsed with short pulse duration, freezes the tracer particle motion and records a pair of images from each tracer. The other laser sheet, cw, provides tracer trajectories whose length is controlled by the sheet thickness. The recorded image from each tracer is then its streak trajectory superimposed on its frozen paired particle image. The planar two components of velocity are deduced from the distance between image pairs and the time separation of the double light pulses. This information, combined with the tracer trajectory streak length, determines the trace particle staying time within the laser sheet. The tracer velocity normal to the laser sheet is then calculated from this staying time and the laser sheet thickness that can be calibrated from the measurements. The resultant SPIV technique was demonstrated with a free jet seeded with small particles, and the derived velocity was reported.     

The motion of micron-sized particles in He II counterflow as observed by the PIV technique

No Heading The motion of micro-spheres in He II thermal counterflow has been measured using the Particle Image Velocimetry (PIV) technique. Although the tracer particles are able to track the motion of the normal fluid component, a significant discrepancy between the measured particle velocity and theoretical normal fluid velocity is observed. Further analysis of this velocity discrepancy suggests that it may be caused by the interaction between particles and vortex lines in the superfluid component. A semi-empirical correlation for the interaction force is developed and compared to the experimental results, from which new dynamic behavior of particles in He II is presented in the form of an effective kinematic viscosity of the superfluid.PACS numbers: 67.40.Pm, 67.40.Vs, 47.80.+v     

多点激励下绝对位移直接求解算法的误差频域分析

多点激励地震响应分析时,相对运动法将结构内部节点绝对位移分解成拟静位移和动态位移两部分分别进行求解,而绝对位移直接求解法直接对内部节点绝对位移进行求解,在两种求解算法中,阻尼分别假定与内部结点相对速度、绝对速度成比例。两种算法的阻尼假定不同可能会引起计算结果误差,在瑞利阻尼、单元阻尼模型下,采用随机振动方法对两种算法计算结果误差在频域内进行了理论分析,指出了瑞利阻尼模型下两种算法求得的结构动态内力功率谱密度误差主要受结构阻尼比、激励频率与结构基频率比值影响,但单元阻尼模型下两种算法得出的动态内力功率谱密度不存在误差。最后从概率意义上指出：瑞利阻尼模型下,两种算法得出的结构内力响应方差的误差随结构阻尼比的增大而增大,当结构阻尼比不大于5%时,两种算法计算结果误差很小。     

The stiffening of arteries by the tissue-mimicking gelatin

Pulse wave velocity (PWV) is widely used for estimating the stiffness of an artery. PWV is measured by the time of travel of the "foot" of the pressure wave over a known distance. This technique has a low time resolution and is an average measurement of artery stiffness between the two measuring sites. The elastic modulus of the artery can be estimated with PWV, but the surrounding tissue effects are not considered. In this paper an external short pulse wave is generated noninvasively in the arterial wall by the radiation force of ultrasound. The pulse wave velocity in the artery is measured by a scanning technique with high-time resolution. The effect of tissue-mimicking gelatin on the artery is analyzed by measuring the wave velocity of the artery without and embedded in gelatin. It is found that the tissue-mimicking gelatin significantly stiffens the rubber tube and the artery if they are embedded in gelatin.     

Three-dimensional vector flow estimation using two transducers andspectral width

Current ultrasonic blood flow measurement systems estimate only that component of flow which is parallel to the incident ultrasound beam. This is done by relating the mean backscattered frequency shift to the axial velocity component through the classical Doppler equation. A number of ultrasonic techniques for estimating the two-dimensional (2D) blood velocity vector have been published, both Doppler and non-Doppler. Several three-dimensional (3D) blood velocity vector techniques have also been proposed, all of which require a multiplicity of transducers or lines of sight. Here a technique is described for estimating the total velocity vector, using only two transducers. This is achieved by measuring not only the frequency shifts but also the bandwidths of the backscattered spectra, making use of the fact that the bandwidth of a Doppler spectrum has been shown to be proportional to the velocity component normal to the sound beam. Partial experimental verification of the proposed vector flow estimation scheme is demonstrated by using a constant velocity thread phantom     

Experimental measurements of orientation and rotation of dense 3D packings of spheres

Many recent advances in the study of granular media have stemmed from the improved capability to image and track individual grains in two and three dimensions. While two-dimensional systems readily yield both translational and rotational motion, a challenge in three-dimensional experiments is the tracking of rotational motion of isotropic particles. We propose an extension of the refractive index matched scanning technique as a method of measuring individual particle rotation. Initial measurements indicate that shear-driven rotational motion may stem from gear-like motion within the shear zone.     

Recent developments in velocity and stress measurements applied to the dynamic characterization of brittle materials

The synthesis of novel brittle materials with tailored microstructures requires the understanding of new physical phenomena related to the failure of these materials. Observation capabilities with spatial resolution of atomic dimensions, e.g., scanning tunneling microscopy (STM) and high resolution electron microscopy (HREM), have opened new frontiers in the mechanical characterization of these advanced materials. The challenge is to design experiments capable of loading the material in a controlled fashion such that defects, resulting in well defined macroscopic stress and velocity features, are produced. In this article, techniques for the measurement of surface and in-material particle velocities and in-material axial and transverse stress measurements are reviewed. Examples on the usefulness of these techniques in the study of brittle failure are provided. A variable sensitivity displacement interferometer is used in the measurement of normal and in-plane motion in pressure–shear recovery experiments conducted on fiber composite materials. In-material stress measurements with piezoresistance gauges are used in the identification of so-called failure waves in glasses.     

Relative measurements of the velocity and attenuation of ultrasound in highly absorbing liquids

It is shown that it is possible to use a continuous sinusoidal signal to make relative measurements of the velocity and absorption coefficient of ultrasound in highly absorbing liquids such as liquid crystals. Compared with the traditional variable-frequency pulse-phase method, the technique described has the advantage of giving a direct reading of the results under dynamic measurement conditions. A block diagram and the characteristics of the equipment for measuring the anisotropy of acoustic parameters by both pulse and continuous methods are presented.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 66–67, January, 1995.     

Monochromatic heterodyne fiber-optic profile sensor for spatially resolved velocity measurements with frequency division multiplexing

Investigating shear flows is important in technical applications as well as in fundamental research. Velocity measurements with high spatial resolution are necessary. Laser Doppler anemometry allows nonintrusive precise measurements, but the spatial resolution is limited by the size of the measurement volume to approximately 50 microm. A new laser Doppler profile sensor is proposed, enabling determination of the velocity profile inside the measurement volume. Two fringe systems with contrary fringe spacing gradients are generated to determine the position as well as the velocity of passing tracer particles. Physically discriminating between the two measuring channels is done by a frequency-division-multiplexing technique with acousto-optic modulators. A frequency-doubled Nd:YAG laser and a fiber-optic measuring head were employed, resulting in a portable and flexible sensor. In the center of the measurement volume of approximately 1-mm length, a spatial resolution of approximately 5 microm was obtained. Spatially resolved measurements of the Blasius velocity profile are presented. Small velocities as low as 3 cm/s are measured. The sensor is applied in a wind tunnel to determine the wall shear stress of a boundary layer flow. All measurement results show good agreement with the theoretical prediction.