Laser Doppler Vibrometer

picture info	Laser Doppler Vibrometer A laser Doppler vibrometer (LDV) is a scientific instrument that is used to make non-contact vibration measurements of a surface. The laser beam from the LDV is directed at the surface of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the reflected laser beam frequency due to the motion of the surface. The output of an LDV is generally a continuous analog voltage that is directly proportional to the target velocity component along the direction of the laser beam. Some advantages of an LDV over similar measurement devices such as an accelerometer are that the LDV can be directed at targets that are difficult to access, or that may be too small or too hot to attach a physical transducer. Also, the LDV makes the vibration measurement without mass-loading the target, which is especially important for MEMS devices. Principles of operation A vibrometer is generally a two beam laser interferometer that measures the frequency (or phase) differe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	LDV Schematic LDV may refer to: LDV Group, formerly Leyland DAF Vans, UK * The Football League Trophy was called LDV Vans Trophy 2000-2007 * LDV USA Manufacturer of the iconic Snap-on vans & Custom Specialty Vehicles in USA Local Defence Volunteers, renamed Home Guard (United Kingdom) Lansing Derby Vixens, a roller derby league, Michigan, US Laser Doppler vibrometer, for measuring vibration Lactate dehydrogenase elevating virus Lactate dehydrogenase elevating virus (LDV) constitutes the species ''Gamamaarterivirus lacdeh'' which is part of the family ''Arteriviridae'' and order '' Nidovirales''. The order ''Nidovirales'' also includes the family of coronaviruses. Arteri ... Lisa De Vanna, an Australian soccer player Leonardo da Vinci In transport: Light truck, Light Duty Vehicle, a light commercial vehicle * “Light delivery vehicle” in South Africa: motor vehicle designed or adapted for the conveyance of persons and freight with no heavy axle. {{disambig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Beat (music) In music and music theory, the beat is the basic unit of time, the pulse (regularly repeating event), of the ''mensural level'' (or ''beat level''). The beat is often defined as the rhythm listeners would tap their toes to when listening to a piece of music, or the numbers a musician counts while performing, though in practice this may be technically incorrect (often the first multiple level). In popular use, ''beat'' can refer to a variety of related concepts, including pulse, tempo, meter, specific rhythms, and groove. Rhythm in music is characterized by a repeating sequence of stressed and unstressed beats (often called "strong" and "weak") and divided into bars organized by time signature and tempo indications. Beats are related to and distinguished from pulse, rhythm (grouping), and meter: Metric levels faster than the beat level are division levels, and slower levels are multiple levels. Beat has always been an important part of music. Some music genres such as fu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Laser Doppler Velocimetry 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. Technology origin 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. 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. At the Research Laboratories of Brown Engineering Company (later Teledyne Brown Engineering), this phenomenon was used to develop the first laser ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Laser Doppler Imaging Laser Doppler imaging (LDI) is an imaging method that uses a laser beam to scan live tissue. When the laser light reaches the tissue, the moving blood cells generate doppler components in the reflected ( backscattered) light. The light that comes back is detected using a photodiode that converts it into an electrical signal. Then the signal is processed to calculate a signal that is proportional to the tissue perfusion in the scanned area. When the process is completed, the signal is processed to generate an image that shows the perfusion on a screen. The laser doppler effect was first used to measure microcirculation by Stern M.D. in 1975. And it is used widely in medicine, some representative research work about it are these: Use in Ophthalmology The eye offers a unique opportunity for the non-invasive exploration of cardiovascular diseases. LDI by digital holography can measure blood flow in the retina and choroid. In particular, the choroid is a highly vascularized tissue s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Continuous Scan Laser Doppler Vibrometry Continuous-scan laser Doppler vibrometry (CSLDV) is a method of using a laser Doppler vibrometer (LDV) in which the laser beam is swept across the surface of a test subject to capture the motion of a surface at many points simultaneously. This is different from scanning laser vibrometry (SLDV) in which the laser beam is kept at a fixed point during each measurement and quickly moved to a new position before acquiring the next measurement. Advantages and disadvantages CSLDV can allow one to capture the mode shapes of a structure with high resolution much more quickly than would be possible with SLDV. Allen & Sracic show results where measurements were acquired with CSLDV in a hundredth of the time that would be required for LDV. Allen & Aguilar postulated that the additional detail available from CSLDV might provide important information when validating structural dynamic models. CSLDV also makes testing with an instrumented hammer practical with LDV, and some have speculated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Self-mixing Interferometry Self-mixing or back-injection laser interferometry is an interferometric technique in which a part of the light reflected by a vibrating target is reflected into the laser cavity, causing a modulation both in ''amplitude'' and in ''frequency'' of the emitted optical beam. In this way, the laser becomes sensitive to the distance traveled by the reflected beam thus becoming a distance, speed or vibration sensor. The advantage compared to a traditional measurement system is a lower cost thanks to the absence of collimation optics and external photodiodes. Background After the development of the classic external interferometric configurations ( Michelson and Mach-Zehnder interferometers) which consisted of lenses, beam splitter, mirrors, and corner cube, the possibility of creating a much simpler and more compact system was investigated. Starting in the 1980s, this new configuration known as retro-injection or self-mixing was explored and applications based on the retro-injection ef ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Digital Holography Digital holography refers to the acquisition and processing of holograms with a digital sensor array, typically a CCD camera or a similar device. Image rendering, or reconstruction of object ''data'' is performed numerically from digitized interferograms. Digital holography offers a means of measuring optical phase data and typically delivers three-dimensional surface or optical thickness images. Several recording and processing schemes have been developed to assess optical wave characteristics such as amplitude, phase, and polarization state, which make digital holography a very powerful method for metrology applications . Digital recording and processing of holograms Off-axis configuration In the off-axis configuration, a small angle between the reference and the object beams is used to prevent overlapping of the cross-beating contributions between the object and reference optical fields with the self-beating contributions of these fields. These discoveries were made by Emmett Le ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Holographic Laser Doppler Vibrometry Holography is a technique that enables a wavefront to be recorded and later re-constructed. Holography is best known as a method of generating real three-dimensional images, but it also has a wide range of other applications. In principle, it is possible to make a hologram for any type of wave. A hologram is made by superimposing a second wavefront (normally called the reference beam) on the wavefront of interest, thereby generating an interference pattern which is recorded on a physical medium. When only the second wavefront illuminates the interference pattern, it is diffracted to recreate the original wavefront. Holograms can also be computer-generated by modelling the two wavefronts and adding them together digitally. The resulting digital image is then printed onto a suitable mask or film and illuminated by a suitable source to reconstruct the wavefront of interest. Overview and history The Hungarian-British physicist Dennis Gabor (in Hungarian: ''Gábor Dénes'') ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	Laser Scanning Vibrometry The scanning laser vibrometer or scanning laser Doppler vibrometer, was first developed by the British loudspeaker company, Celestion, around 1979, further developed in the 1980s,Stoffregen, B., Felske, A., “Scanning Laser Doppler Analysis System,” SAE Paper No. 850327, 1985. and commercially introduced by Ometron, Ltd around 1986. It is an instrument for rapid non-contact measurement and imaging of vibration. Fields where they are applied include automotive, medical, aerospace, micro system and information technology as well as for quality and production control. The optimization of vibration and acoustic behavior are important goals of product development in all of these fields because they are often among the key characteristics that determine a product's success in the market. They are also in widespread use throughout many universities conducting basic and applied research in areas that include structural dynamics, modal analysis, acoustic optimization and non-destruc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
	Ground Vibrations Ground vibrations is a technical term that is being used to describe mostly man-made vibrations of the ground, in contrast to natural vibrations of the Earth studied by seismology. For example, vibrations caused by explosions, construction works, railway and road transport, etc. - all belong to ground vibrations. General information Ground vibrations are associated with different types of elastic waves propagating through the ground. These are surface waves, mostly Rayleigh waves, and bulk longitudinal waves and transverse waves (or shear waves) propagating into the ground depth. Typical frequency range for environmental ground vibrations is 1 – 200 Hz. Waves of lower frequencies (below 1 Hz) are usually called microseisms, and they are normally associated with natural phenomenae, e.g. water waves in the oceans. Environmental ground vibrations generated by rail and road traffic may cause annoyance to residents of nearby buildings both directly and via generated str ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]
picture info	CRC Press The CRC Press, LLC is an American publishing group that specializes in producing technical books. Many of their books relate to engineering, science and mathematics. Their scope also includes books on business, forensics and information technology. CRC Press is now a division of Taylor & Francis, itself a subsidiary of Informa. History The CRC Press was founded as the Chemical Rubber Company (CRC) in 1903 by brothers Arthur, Leo and Emanuel Friedman in Cleveland, Ohio, based on an earlier enterprise by Arthur, who had begun selling rubber laboratory aprons in 1900. The company gradually expanded to include sales of laboratory equipment to chemists. In 1913 the CRC offered a short (116-page) manual called the ''Rubber Handbook'' as an incentive for any purchase of a dozen aprons. Since then the ''Rubber Handbook'' has evolved into the CRC's flagship book, the '' CRC Handbook of Chemistry and Physics''. In 1964, Chemical Rubber decided to focus on its publishing ventures ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu]