181:. The sensor also splits the laser beam into two parts; one (the measurement beam) is focused into the flow and the second (the reference beam) passes outside the flow. A receiving optics provides a path that intersects the measurement beam, forming a small volume. Particles passing through this volume will scatter light from the measurement beam with a Doppler shift; a portion of this light is collected by the receiving optics and transferred to the photodetector. The reference beam is also sent to the photodetector where
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the fringes are perpendicular to the flow direction, the electrical signal from the photodetector will then be proportional to the full particle velocity. By combining three devices (e.g., He-Ne, Argon ion, and laser diode) with different wavelengths, all three flow velocity components can be simultaneously measured.
173:
The scattered light fluctuates in intensity, the frequency of which is equivalent to the
Doppler shift between the incident and scattered light, and is thus proportional to the component of particle velocity which lies in the plane of two laser beams. If the sensor is aligned to the flow such that
111:
At the
Research Laboratories of Brown Engineering Company (later Teledyne Brown Engineering), this phenomenon was used to develop the first laser Doppler flowmeter using heterodyne signal processing. This instrument became known as the laser Doppler velocimeter and the technique was called laser
241:
One disadvantage has been that laser
Doppler velocimetry sensors are range-dependent; they have to be calibrated minutely and the distances where they measure has to be precisely defined. This distance restriction has recently been at least partially overcome with a new sensor that is range
357:
device has allowed greater accuracy in the measurement of small forces than previously possible, through directly measuring the ratio of this velocity to the speed of light. This is a fundamental, traceable measurement that now allows traceability of small forces to the S.I. System.
352:
devices, often to compare the performance of devices such as accelerometers-on-a-chip with their theoretical (calculated) modes of vibration. As a specific example in which the unique features of Laser
Doppler velocimetry are important, the measurement of velocity of a MEMS
148:
laser light in the flow of the fluid being measured. The two beams are usually obtained by splitting a single beam, thus ensuring coherence between the two. Lasers with wavelengths in the visible spectrum (390–750 nm) are commonly used; these are typically He-Ne,
119:
with speeds up to 1000 m/s, as well as determining flow in a near-surface blood artery. Similar instruments were also developed for solid surface monitoring, with applications ranging from measuring product speeds in production lines of
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and generate a set of straight fringes. As particles (either naturally occurring or induced) entrained in the fluid pass through the fringes, they scatter light that is then collected by a receiving optics and focused on a
589:
Portoles, Jose F.; Cumpson, Peter J.; Allen, Stephanie; Williams, Phillip M.; Tendler, Saul J. B. (2006). "Accurate velocity measurements of AFM-cantilever vibrations by
Doppler interferometry".
286:
and return to be concentrated on a detector. These measurements are useful to monitor the effect of exercise, drug treatments, environmental, or physical manipulations on targeted micro-sized
274:
in human tissues such as skin or the eye fundus. Within the clinical environment, the technology is often referred to as laser
Doppler flowmetry; when images are made, it is referred to as
53:
flows or the linear or vibratory motion of opaque, reflecting surfaces. The measurement with laser
Doppler anemometry is absolute and linear with velocity and requires no pre-calibration.
800:
Cumpson, Peter J.; Hedley, John (2003). "Accurate analytical measurements in the atomic force microscope: a microfabricated spring constant standard potentially traceable to the SI".
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The signal detection scheme of the instrument is using the principle of optical heterodyne detection. This principle is similar to other laser
Doppler-based instruments such as
645:
Moir, Christopher I (2009). "<title>Miniature laser doppler velocimetry systems</title>". In
Baldini, Francesco; Homola, Jiri; Lieberman, Robert A (eds.).
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produces an electrical signal proportional to the
Doppler shift, by which the particle velocity component perpendicular to the plane of the beams can be determined.
157:, allowing the beam path to be observed. A transmitting optics system focuses the beams to intersect at their waists (the focal point of a laser beam), where they
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Laser Doppler velocimetry can be useful in automation, which includes the flow examples above. It can also be used to measure the speed of solid objects, like
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because the equipment can be outside of the flow being measured and therefore has no effect on the flow. Some typical applications include the following:
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In the decades since the laser Doppler velocimetry was first introduced, there has been a wide variety of laser Doppler sensors developed and applied.
333:
lunar lander to automatically find a safe landing place contains a lidar Doppler velocimeter that measures the vehicle's altitude and velocity. The
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Velocity measurements in water flows (research in general hydrodynamics, ship hull design, rotating machinery, pipe flows, channel flow, etc.)
200:, and therefore in one sense Laser Doppler velocimetry is a particularly fundamental measurement traceable to the S.I. system of measurement.
516:
Watson, R. C. Jr., Lewis, R. D. and Watson, H. J. (1969). "Instruments for Motion Measurement Using Laser Doppler Heterodyning Techniques".
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Another form of laser Doppler velocimetry, particularly used in early device developments, has a completely different approach akin to an
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Wind tunnel velocity experiments for testing aerodynamics of aircraft, missiles, cars, trucks, trains, and buildings and other structures
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Foreman, J. W.; George, E. W.; Lewis, R. D. (1965). "Measurement of Localized Flow Velocities in Gases with a Laser Doppler Flowmeter".
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Goode, RL; Ball, G; Nishihara, S; Nakamura, K (1996). "Laser Doppler vibrometer (LDV)--a new clinical tool for the otologist".
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196:. It is possible to apply digital techniques to the signal to obtain the velocity as a measured fraction of the
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Fuel injection and spray research where there is a need to measure velocities inside engines or through nozzles
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258:(or a different mechanical speed measurement device) to the conveyor belt is impossible or impractical.
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Stern, Michael D. (1985). "Laser Doppler velocimetry in blood and multiply scattering fluids: Theory".
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Yeh, Y.; Cummins, H. Z. (1964). "Localized Fluid Flow Measurements with an He-Ne Laser Spectrometer".
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In its simplest and most presently used form, laser Doppler velocimetry crosses two beams of
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Early laser Doppler velocimetry applications included measuring and mapping the exhaust from
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White, A. D., and J. D. Rigden, "Continuous Gas Maser Operation in the Visible".
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Laser Doppler anemometry facility operating at Laboratory of Gas Technology (
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Doppler velocimetry. It is also referred to as laser Doppler anemometry.
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Laser Doppler velocimetry is used in the analysis of vibration of
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head displacement in response to sound inputs of 80- to 100-dB
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uses laser doppler velocimeter for precise terminal guidance.
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Laser Doppler velocimetry is often chosen over other forms of
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Environmental research (combustion research, wave dynamics,
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The laser Doppler vibrometer is being used in clinical
254:. This can be useful in situations where attaching a
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Principles and Practice of Laser Doppler Anemometry
568:Durst, F; Melling, A. and Whitelaw, J. H. (1976)
408:Velocity interferometer system for any reflector
776:"AGM-129 Advanced Cruise Missile [ACM]"
747:"ALHAT Detects Landing Hazards on the Surface"
327:Autonomous Landing Hazard Avoidance Technology
270:research as a technique to partially quantify
278:. The beam from a low-power laser (usually a
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534:: CS1 maint: multiple names: authors list (
237:, tidal modeling, river hydrology, etc.).
88:source that was highly concentrated at a
430:, vol. 50, p. 1697: July 1962, p. 1697.
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751:Research News, Langley Research Center
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27:Optical method of measuring fluid flow
266:Laser Doppler velocimetry is used in
81:provided the optics community with a
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649:. Vol. 7356. pp. 73560I.
591:Journal of Experimental Nanoscience
104:on a He-Ne beam scattered by small
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37:, is the technique of using the
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96:(nm) in the red portion of the
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398:Particle tracking velocimetry
388:Molecular tagging velocimetry
183:optical heterodyne detection
822:10.1088/0957-4484/14/12/009
550:The Laser Doppler Technique
344:Calibration and measurement
79:Bell Telephone Laboratories
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633:”Laser Doppler Anemometry”
572:, Academic Press, London,
403:Photon Doppler velocimetry
393:Particle image velocimetry
611:10.1080/17458080500411999
552:, John Wiley & Sons,
383:Laser surface velocimeter
194:laser surface velocimeter
86:electromagnetic radiation
31:Laser Doppler velocimetry
378:Laser Doppler vibrometer
317:(stirrup) displacement.
190:laser Doppler vibrometer
35:laser Doppler anemometry
18:Laser Doppler anemometry
483:Applied Physics Letters
448:Applied Physics Letters
297:for the measurement of
77:(He-Ne) in 1962 at the
73:The development of the
108:spheres in the fluid.
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433:U.S. patent 3,242,439
373:Laser Doppler imaging
276:laser Doppler imaging
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698:10.1364/AO.24.001968
647:Optical Sensors 2009
548:Drain, L. E. (1980)
311:sound-pressure level
262:Medical applications
168:avalanche photodiode
132:Operating principles
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877:Transport phenomena
814:2003Nanot..14.1279C
690:1985ApOpt..24.1968S
603:2006JENan...1...51P
495:1965ApPhL...7...77F
460:1964ApPhL...4..176Y
368:Hot-wire anemometry
235:coastal engineering
862:Laser applications
780:GlobalSecurity.org
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786:2015-01-30
415:References
321:Navigation
307:prosthesis
272:blood flow
246:Automation
138:collimated
94:nanometers
90:wavelength
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518:ISA Trans
489:(4): 77.
159:interfere
151:Argon ion
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428:Proc IRE
362:See also
288:vascular
146:coherent
47:velocity
838:2500055
810:Bibcode
733:8915406
686:Bibcode
599:Bibcode
491:Bibcode
456:Bibcode
410:(VISAR)
303:malleus
295:otology
290:areas.
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153:, or
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122:paper
51:fluid
43:laser
41:in a
826:PMID
762:2013
755:NASA
729:PMID
702:PMID
574:ISBN
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536:link
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