Speckle Velocimeter Research Articles

Noncontact 2-D In-Plane Speckle Velocimeter

In this paper, the authors present a noncontact 2-D speckle velocimeter, which is realized by means of a compact setup and based on an improved binary correlation algorithm for image processing. Starting from the results obtained in our previous work, where we demonstrated the feasibility of the method for the assessment of the surface velocity for one direction, we have extended the study to a 2-D velocity and displacement sensor by overcoming the previously encountered limits. In addition, the configuration is further simplified by introducing a low-coherence source and a simpler electronic circuit. Sensor performance is compared with that measured using a triangulation laser sensor. The main advantages of the proposed sensor, as compared with those of the traditional velocimeters, are the simplicity of the optical setup, the easily controlled device, and the small dimension of the sensor. The velocity of frame acquisition (15.6 frames/s) is the principal limiting factor of the sensor bandwidth (BW = 3.5 Hz). Such a noncontact optical sensor is suitable for small 2-D in-plane vibration measurements and allows one to overcome the limits of the classical Doppler velocimeters affected by speckle noise in this range of displacement.

Some issues concerning the development of a speckle velocimeter

The application of integrated statistics in the space-time plane to laser speckle velocimetry is considered. A new approach to determining the contrast function is proposed. This approach makes it possible to considerably improve the stability of the solution to the problem under nonideal conditions. The results of experimental investigations are presented.

Speckle velocimeter for a self-powered vehicle

Laboratory tests of a laser speckle velocimetry technique are reported. The use of integral statistics in the space-time plane is discussed. Preliminary experimental results are compared with data obtained by other speckle velocimeter methods.

Speckle velocimetry by means of holographic time-integrative correlation

We develop the theory of the speckle velocimeter that is based on use of a photorefractive real-time hologram in four-wave mixing as a time-integrative correlator. The theory of the speckle velocimeter has been developed for the time correlation between the far-field spectrum of light scattered from the diffuser and the reference wave that is Doppler shifted. Our theoretical derivation shows that it is possible to extract the velocity with minor processing of the output correlation.

A speckle velocimeter using a semiconductor laser with external opticalfeedback from a moving surface: effects of system parameters on thereproducibility and accuracy of measurements

A speckle velocimeter exploiting the effects of external opticalfeedback in a semiconductor laser is analysed. The laser diode is used both asthe light source and as the detector making the system self-detecting andself-aligning with a single optical axis. The velocimeter employs anautocorrelation method to analyse the detected self-mixing speckle signal. Thelinear relation between the velocity and the reciprocal of the autocorrelationtime of fluctuations in the amplitude of the speckle signal allows thedetermination of the velocity. Effects of various parameters of themeasurement system are analysed and the dependences of the reproducibility andaccuracy of the measurements on these parameters are discussed in order toachieve optimization of the system. The optimized system has a measurementerror of less than 1.4% within the range of calibration velocities and lessthan 2.7% outside this range.

Noninvasive blood flow measurement using speckle signals from a self-mixing laser diode: <italic>in vitro</italic> and <italic>in vivo</italic> experiments

A semiconductor laser speckle velocimeter that uses the self- mixing effect is studied for noninvasive relative blood flow measure- ments. The random modulation of intensity and spectra of the laser di- ode caused by the backcoupling of the scattered light from the red blood cells into the laser cavity is detected as a speckle signal with a photodi- ode inside the laser package. The autocorrelation of this self-mixing speckle signal gives information on the flow velocity of the blood. The proposed method is elucidated with in vitro and in vivo experiments. The results of these measurements are given together with a discussion of dependence of speckle signal of a self-mixing laser diode (SMLD) on various parameters such as velocity, hematocrit level of blood, and back- ground reflectance of blood suspension. © 2000 Society of Photo-Optical Instru- mentation Engineers. (S0091-3286(00)01009-6)

Self-mixing laser speckle velocimeter for blood flow measurement

A velocimeter using speckle phenomena in self-mixing laser diodes (SM-LDs) is used to evaluate the blood flow noninvasively. The mean frequency of the speckle signal obtained from the self-mixing laser diode reflects the activity of the blood flow in a certain probing area. The experimental results show that this new type of speckle velocimeter can be useful for the relative evaluation of blood flow in human tissues.

Correlation-based speckle velocimeter with self-mixing interference in a semiconductor laser diode

We propose a novel self-mixing laser diode speckle velocimeter based on autocorrelation. The self-mixing laser diode launches and receives reflected light from a moving surface that has a random reflection profile. Some portion of the scattered light backcouples into the laser cavity and causes random intensity variations in the form of speckle signals. These speckle signals obtained from a self-mixing laser diode are processed by use of autocorrelation. The linear relation between the velocity and the reciprocal of the correlation time of the speckle intensity fluctuations allows us to determine the velocity easily if proper calibration is performed. The range of the investigated velocity is 20-450 mm/s. For an aluminum target that moves at a velocity of 350 mm/s, the measurement error is less than 2%.

Simultaneous measurement of velocity and length of moving surfaces by a speckle velocimeter with two self-mixing laser diodes

A novel laser speckle velocimeter with two self-mixing laser diodes (SM-LD's) for velocity and length measurements of moving surfaces is reported. The mean frequency of the speckle signal obtained in the measurement system depends on the surface path illuminated by the SM-LD. This behavior of the speckle signal in the SM-LD's is exploited to detect the front and the end edges of a target surface by sampling continuously the number of intensity changes in a speckle signal waveform. Once the edges are determined, the velocity and the length of the surface are calculated easily. The error for length and velocity measurements of a target with a homogeneous rough plane surface of 60-mm length, moving at a velocity of 200 mm/s, can be as low as 2.1% and 1.75%, respectively.

Automatic measurement of velocity and length of moving plate using self-mixing laser diode

We propose and demonstrate to automatically measure both a velocity and a length of a moving plate, employing a novel laser speckle velocimeter using a self-mixing laser diode (SM-LD). We derive two empirical equations including velocity of length of a moving plate made of white paper or plastic. After determining a pair of constants fs(0) and /spl beta/ in advance calibration, we can automatically obtain velocity or length from the measured mean speckle signal frequency and/or the number of speckle pulses counted during the measuring time. The investigated range of velocity and length is 100 mm/s to 950 mm/s, and 10 mm to 100 mm, respectively. The measurement accuracy of the velocity and the length is approximately 1% and a few percent, respectively.

Laser speckle velocimeter using self-mixing laser diode

We have built a novel laser speckle velocimeter using a self-mixing laser diode (SM-LD). The speckle signal obtained by the measurement system has a waveform independent of the target velocity when the same path on the target surface is iteratively measured. The mean frequency of the speckle signal is directly proportional to the target velocity when the laser beam spot diameter is kept constant, and greater than 0.36 mm. The mean speckle signal frequency is automatically measured by using a computer. Its measurement error is inversely proportional to the scanned length, and is 2% for 100 mm. It is possible to detect velocity of the target transversely moving across the laser light beam using this compact measuring system.

Novel Speckle Velocimeter Using the Double Clipping Cross-Correlation Method

A new speckle velocimeter using the cross-correlation method was developed. Its optical system achieved wide working distance range of ±5mm and small measuring errors for various materials. Furthermore the realtime correlation processor for the clipped signals makes the cross-correlation method applicable to in-line measurement in factories.

Pulsed laser velocimetry measurements of the vortex shedding from structural elements

Previous work by the Authors demonstrated the existence of two shedding states for T-beams and L-beams. The Strouhal number was shown to change from 0.14 to 0.20 when the angle of approach of the wind altered by approximately 5° at certain angles. No complete explanation of this effect was available at the time. The present paper explores this bistability by intaanteneous flow field mapping using the pulsed laser velocimeter speckle velocimeter). The formation of the eddies is both visualised and measured using a 10 joule ruby laser.

Space-time correlation function of spatially and temporally integrated laser speckle intensity in a two-lens imaging optical system

An analytical form of the cross correlation function in a two-lens imaging optical system has been obtained by calculating the integrated speckle intensity with a gaussian profile approximation for the transmittance of the detection area and the weight function of the sampling time. Adapting the results to a speckle velocimeter, the experimental conditions of the sampling time and the optimal relation between the speckle size and the detection area have been discussed.

Laser speckle velocimeter utilizing optical fibers

A laser speckle velocimeter with a newly developed optical fiber probe is reported. An optical fiber with a graded-index rod lens at the end face is used for a laser beam guide and speckle velocity is detected by an optical fiber array spatial filter constructed with linearly arrayed end faces of optical fibers. By using optical fibers, a noncontact flexible and object distance independent velocimeter can be simply constructed.

Velocity sensitivity of laser-speckle velocimeters

The method of increasing sensitivity in laser speckle velocimetry is studied theoretically and experimentally. The sensitivity of the velocimeters is shown to have a fairly strong dependence on the optical configurations, such as the diameter of the incident laser beam-waist, or its position relative to the moving diffuse object to be measured. It is pointed out that the minimal sensitivity appears in the configuration where the converging incident light beam produces its beam waist at the position of a detecting pinhole. In some cases when using image speckles to obtain finite spatial resolution in the object plane, an optimum condition exists which gives the maximal sensitivity. The sensitivity of a laser speckle velocimeter using a spatial filter and two point cross-correlation technique is also discussed.

Laser Speckle Velocimeter Using A Zero-Crossing Technique For Spatially Integrated Intensity Fluctuation

The laser speckle velocimeter based on the zero-crossing rate of the spatially integrated speckle intensity variations is studied under various optical configurations of illumination and detection. The eliminating method of the additional noise is also experimentally investigated by using Schmitt trigger circuits for the counting of zero-crossings.