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laser doppler velocimetry wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 technology origin 2 operating principles 3 applications toggle applications subsection 3 1 flow research 3 2 automation 3 3 medical applications 3 4 navigation 3 5 calibration and measurement 4 see also 5 references 6 external links toggle the table of contents laser doppler velocimetry 7 languages deutsch français italiano 日本語 português српски srpski தமிழ் edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikimedia commons wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia optical method of measuring fluid flow laser doppler velocimetry also known as laser doppler anemometry is the technique of using the doppler shift in a laser beam to measure the velocity in transparent or semi transparent fluid 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 laser doppler anemometry facility operating at laboratory of gas technology poznań university of technology technology origin edit the development of the helium neon laser he ne in 1962 at the bell telephone laboratories provided the optics community with a continuous wave electromagnetic radiation source that was highly concentrated at a wavelength of 632 8 nanometers nm in the red portion of the visible spectrum 1 it was discovered that fluid flow measurements could be made using the doppler effect on a he ne beam scattered by small polystyrene spheres in the fluid 2 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 3 this instrument became known as the laser doppler velocimeter and the technique was called laser doppler velocimetry it is also referred to as laser doppler anemometry early laser doppler velocimetry applications included measuring and mapping the exhaust from rocket engines 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 paper and steel mills to measuring vibration frequency and amplitude of surfaces 4 operating principles edit in its simplest and most presently used form laser doppler velocimetry crosses two beams of collimated monochromatic and coherent 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 argon ion or laser diode 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 interfere 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 photodetector typically an avalanche photodiode 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 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 5 another form of laser doppler velocimetry particularly used in early device developments has a completely different approach akin to an interferometer 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 optical heterodyne detection 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 6 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 laser doppler vibrometer or laser surface velocimeter it is possible to apply digital techniques to the signal to obtain the velocity as a measured fraction of the speed of light and therefore in one sense laser doppler velocimetry is a particularly fundamental measurement traceable to the s i system of measurement 7 applications edit in the decades since the laser doppler velocimetry was first introduced there has been a wide variety of laser doppler sensors developed and applied flow research edit laser doppler velocimetry is often chosen over other forms of flow measurement 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 wind tunnel velocity experiments for testing aerodynamics of aircraft missiles cars trucks trains and buildings and other structures velocity measurements in water flows research in general hydrodynamics ship hull design rotating machinery pipe flows channel flow etc fuel injection and spray research where there is a need to measure velocities inside engines or through nozzles environmental research combustion research wave dynamics coastal engineering tidal modeling river hydrology etc 8 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 independent 9 automation edit 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 conveyor belts this can be useful in situations where attaching a rotary encoder or a different mechanical speed measurement device to the conveyor belt is impossible or impractical medical applications edit laser doppler velocimetry is used in hemodynamics research as a technique to partially quantify blood flow 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 laser doppler imaging the beam from a low power laser usually a laser diode penetrates the skin sufficiently to be scattered with a doppler shift by the red blood cells 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 vascular areas 10 the laser doppler vibrometer is being used in clinical otology for the measurement of tympanic membrane eardrum malleus hammer and prosthesis head displacement in response to sound inputs of 80 to 100 db sound pressure level it also has potential use in the operating room to perform measurements of prosthesis and stapes stirrup displacement 11 navigation edit the autonomous landing hazard avoidance technology used in nasa s project morpheus lunar lander to automatically find a safe landing place contains a lidar doppler velocimeter that measures the vehicle s altitude and velocity 12 the agm 129 acm cruise missile uses laser doppler velocimeter for precise terminal guidance 13 calibration and measurement edit laser doppler velocimetry is used in the analysis of vibration of mems 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 watt balance device 14 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 see also edit hot wire anemometry laser doppler imaging laser doppler vibrometer laser surface velocimeter molecular tagging velocimetry particle image velocimetry particle tracking velocimetry photon doppler velocimetry velocity interferometer system for any reflector visar references edit white a d and j d rigden continuous gas maser operation in the visible proc ire vol 50 p 1697 july 1962 p 1697 u s patent 3 242 439 yeh y cummins h z 1964 localized fluid flow measurements with an he ne laser spectrometer applied physics letters 4 10 176 bibcode 1964apphl 4 176y doi 10 1063 1 1753925 foreman j w george e w lewis r d 1965 measurement of localized flow velocities in gases with a laser doppler flowmeter applied physics letters 7 4 77 bibcode 1965apphl 7 77f doi 10 1063 1 1754319 watson r c jr lewis r d and watson h j 1969 instruments for motion measurement using laser doppler heterodyning techniques isa trans 8 1 20 28 cite journal cs1 maint multiple names authors list link drain l e 1980 the laser doppler technique john wiley sons isbn 0 471 27627 8 durst f melling a and whitelaw j h 1976 principles and practice of laser doppler anemometry academic press london isbn 0 12 225250 0 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 journal of experimental nanoscience 1 1 51 62 bibcode 2006jenan 1 51p doi 10 1080 17458080500411999 s2cid 136618366 dantec dynamics laser doppler anemometry moir christopher i 2009 title miniature laser doppler velocimetry systems title in baldini francesco homola jiri lieberman robert a eds optical sensors 2009 vol 7356 pp 73560i doi 10 1117 12 819324 s2cid 123294042 stern michael d 1985 laser doppler velocimetry in blood and multiply scattering fluids theory applied optics 24 13 1968 bibcode 1985apopt 24 1968s doi 10 1364 ao 24 001968 pmid 18223825 goode rl ball g nishihara s nakamura k 1996 laser doppler vibrometer ldv a new clinical tool for the otologist the american journal of otology 17 6 813 22 pmid 8915406 alhat detects landing hazards on the surface research news langley research center nasa retrieved february 8 2013 agm 129 advanced cruise missile acm globalsecurity org 2011 07 24 retrieved 2015 01 30 cumpson peter j hedley john 2003 accurate analytical measurements in the atomic force microscope a microfabricated spring constant standard potentially traceable to the si nanotechnology 14 12 1279 1288 bibcode 2003nanot 14 1279c doi 10 1088 0957 4484 14 12 009 pmid 21444981 s2cid 2500055 external links edit wikimedia commons has media related to laser doppler velocimetry authority control databases national czech republic retrieved from https en wikipedia org w index php title laser_doppler_velocimetry oldid 1261379914 categories laser applications doppler effects measurement transport phenomena hidden categories articles with short description short description matches wikidata cs1 maint multiple names authors list commons category link from wikidata this page was last edited on 5 december 2024 at 20 16 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of conduct developers statistics cookie 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