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Schlieren
Schlieren ( ; , ) are optical inhomogeneities in transparent media that are not necessarily visible to the human eye. Schlieren physics developed out of the need to produce high-quality lenses devoid of such inhomogeneities. These inhomogeneities are localized differences in optical path length that cause deviations of light rays, especially by refraction. This light deviation can produce localized brightening, darkening, or even color changes in an image, depending on the directions the rays deviate. History Schlieren were first observed by Robert HookeHooke, R. (1665), "Of a New Property in the Air," ''Micrographia'', Observation LVIII, pp. 217–219, London. in 1665 using a large concave lens and two candles. One candle served as a light source. The warm air rising from the second candle provided the schliere. The conventional schlieren system is credited mostly to German physicist August Toepler, though Jean Bernard Léon Foucault invented the method in 1859 that Toeple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schlieren Photography
Schlieren photography is a process for photographing fluid flow. Invented by the German physicist August Toepler in 1864 to study supersonic motion, it is widely used in aeronautical engineering to photograph the flow of air around objects. Classical optical system The classical implementation of an optical schlieren system uses light from a single collimated source shining on, or from behind, a target object. Variations in refractive index caused by density gradients in the fluid distort the collimated light beam. This distortion creates a spatial variation in the intensity of the light, which can be visualised directly with a shadowgraph system. Classical schlieren imaging systems appear in two configurations, using either one or two mirrors. In each case, a transparent object is illuminated with collimated or nearly-collimated light. Rays that are not deflected by the object proceed to their focal point, where they are blocked by a knife edge. Rays that are deflected by t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Background-oriented Schlieren Technique
Schlieren photography is a process for photographing fluid flow. Invented by the German physicist August Toepler in 1864 to study supersonic motion, it is widely used in aeronautical engineering to photograph the flow of air around objects. Classical optical system The classical implementation of an optical schlieren system uses light from a single collimated source shining on, or from behind, a target object. Variations in refractive index caused by density gradients in the fluid distort the collimated light beam. This distortion creates a spatial variation in the intensity of the light, which can be visualised directly with a shadowgraph system. Classical schlieren imaging systems appear in two configurations, using either one or two mirrors. In each case, a transparent object is illuminated with collimated or nearly-collimated light. Rays that are not deflected by the object proceed to their focal point, where they are blocked by a knife edge. Rays that are deflected by t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schlieren Video Of A Handgun
Schlieren ( ; , ) are optical inhomogeneities in Transparency and translucency, transparent optical medium, media that are not necessarily visible to the human eye. Schlieren physics developed out of the need to produce high-quality lenses devoid of such inhomogeneities. These inhomogeneities are localized differences in optical path length that cause deviations of light ray (optics), rays, especially by refraction. This light deviation can produce localized brightening, darkening, or even dispersion (optics), color changes in an image, depending on the directions the rays deviate. History Schlieren were first observed by Robert HookeHooke, R. (1665), "Of a New Property in the Air," ''Micrographia'', Observation LVIII, pp. 217–219, London. in 1665 using a large Lens (optics)#Types of simple lenses, concave lens and two candles. One candle served as a light source. The warm air rising from the second candle provided the schliere. The conventional schlieren system is credite ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schlieren Imaging
Schlieren imaging is a method to visualize density variations in transparent media. The term "schlieren imaging" is commonly used as a synonym for schlieren photography, though this article particularly treats visualization of the pressure field produced by ultrasonic transducers, generally in water or tissue-mimicking media. The method provides a two-dimensional (2D) projection image of the acoustic beam in real-time ("live video"). The unique properties of the method enable the investigation of specific features of the acoustic field (e.g. focal point in HIFU transducers), detection of acoustic beam-profile irregularities (e.g. due to defects in transducer) and on-line identification of time-dependent phenomena (e.g. in phased array transducers). Some researchers say that schlieren imaging is equivalent to an X-ray radiograph of the acoustic field. Setup The optical setup of a schlieren imaging system may comprise the following main sections: Parallel beam, focusing eleme ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synthetic Schlieren
Synthetic schlieren is a process that is used to visualize the flow of a fluid of variable refractive index. Named after the schlieren method of visualization, it consists of a digital camera or video camera pointing at the flow in question, with an illuminated target pattern behind. The method was first proposed in 1999.{{citation , doi=10.1017/S0022112099005017 , first1=B. R. , last1=Sutherland , first2=S. B. , last2=Dalziel , first3=G. O. , last3=Hughes , first4=P. F. , last4=Linden , title=Visualization and measurement of internal waves by "synthetic schlieren". Part 1: Vertically oscillating cylinder , journal=Journal of Fluid Mechanics , volume=390 , issue=1 , pages=93–126 , year=1999 , bibcode=1999JFM...390...93S Variations in refractive index cause the light from the target to refract as it passes through the fluid, which causes a distortion of the pattern in the image seen by the camera. Pattern matching algorithms can measure this distortion and calcu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laser Schlieren Deflectometry
Laser schlieren deflectometry (LSD) is a method for a high-speed measurement of the gas temperature in microscopic dimensions, in particular for temperature peaks under dynamic conditions at atmospheric pressure. The principle of LSD is derived from schlieren photography: a narrow laser beam is used to scan an area in a gas where changes in properties are associated with characteristic changes of refractive index. Laser schlieren deflectometry is claimed to overcome limitations of other methods regarding temporal and spatial resolution. The theory of the method is analogous to the scattering experiment of Ernest Rutherford from 1911. However, instead of alpha particles scattered by gold atoms, here an optical ray is deflected by hot spots with unknown temperature. A general equation of LSD describes the dependence of the measured maximum deflection of the ray ''δ''1 on the local maximum of the neutral gas temperature in the hot spot ''T''1: : \frac + \frac = 1, where ''T'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shadowgraph
Shadowgraph is an optical method that reveals non-uniformities in transparent media like air, water, or glass. It is related to, but simpler than, the schlieren and schlieren photography methods that perform a similar function. Shadowgraph is a type of flow visualisation. In principle, a difference in temperature, a different gas, or a shock wave in the transparent air cannot be seen by the human eye or cameras. However, all these disturbances refract light rays, so they can cast shadows. The plume of hot air rising from a fire, for example, can be seen by way of its shadow cast upon a nearby surface by the uniform sunlight. Sunlight shadowgraph Some aquatic predators detect their transparent prey by way of their shadows cast upon the ocean floor. It was Robert Hooke who first scientifically demonstrated the sunlight shadowgraph and Jean-Paul Marat who first used it to study fire. A modern account of shadowgraphy is given by Gary S. Settles. Applications Applications ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
August Toepler
August Joseph Ignaz Toepler (7 September 1836 – 6 March 1912) was a German chemist and physicist known for his experiments in electrostatics. Biography August Toepler was born on 7 September 1836. He studied chemistry at the Gewerbe-Institut Berlin (1855–1858) and graduated from the University of Jena in 1860. Later Toepler turned to experimental physics. August Toepler was a lecturer of chemistry and physics at the Academy Poppelsdorf (1859-1864). He received a chair of chemistry and chemical technology at the Polytechnic Institute of Riga and he hold this position between 1864 and 1868. In 1864, he applied Foucault's knife-edge test for telescope mirrors to the analysis of fluid flow and the shock wave. He named this new method schlieren photography, for which he is justifiably famous. He also developed the Toepler machine, an electrostatic influence machine (high voltage generator) in 1865, which would one day find use in early medical x-ray machines. Improved v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lens
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), usually arranged along a common axis. Lenses are made from materials such as glass or plastic, and are ground and polished or molded to a desired shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called lenses, such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. Lenses are used in various imaging devices like telescopes, binoculars and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia. History The word ''lens'' comes from '' lēns'', the Latin name of the lentil (a seed of a lentil plant), b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Video Projector
A video projector is an image projector that receives a video signalling (telecommunication), signal and projects the corresponding image on a projection screen using a lens (optics), lens system. Video projectors use a very bright ultra-high-performance lamp (a special mercury arc lamp), Xenon arc lamp, LED or solid state blue, RB, RGB or remote fiber optic RGB lasers to provide the illumination required to project the image, and most modern ones can correct any curves, blurriness, and other inconsistencies through manual settings. If a blue laser is used, a phosphor wheel is used to turn blue light into white light, which is also the case with white LEDs. (White LEDs do not use lasers.) A wheel is used in order to prolong the lifespan of the phosphor, as it is degraded by the heat generated by the laser diode. Remote fiber optic RGB laser racks can be placed far away from the projector, and several racks can be housed in a single, central room. Each projector can use up to two ra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transparency And Translucency
In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without appreciable scattering of light. On a macroscopic scale (one in which the dimensions are much larger than the wavelengths of the photons in question), the photons can be said to follow Snell's law. Translucency (also called translucence or translucidity) allows light to pass through, but does not necessarily (again, on the macroscopic scale) follow Snell's law; the photons can be scattered at either of the two interfaces, or internally, where there is a change in index of refraction. In other words, a translucent material is made up of components with different indices of refraction. A transparent material is made up of components with a uniform index of refraction. Transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color. The opposit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Medium
An optical medium is material through which light and other electromagnetic waves propagate. It is a form of transmission medium. The permittivity and permeability of the medium define how electromagnetic waves propagate in it. Properties The optical medium has an '' intrinsic impedance'', given by ::\eta = where E_x and H_y are the electric field and magnetic field, respectively. In a region with no electrical conductivity, the expression simplifies to: ::\eta = \sqrt\ . For example, in free space the intrinsic impedance is called the characteristic impedance of vacuum, denoted ''Z''0, and ::Z_0 = \sqrt\ . Waves propagate through a medium with velocity c_w = \nu \lambda , where \nu is the frequency and \lambda is the wavelength of the electromagnetic waves. This equation also may be put in the form : c_w = \ , where \omega is the angular frequency of the wave and k is the wavenumber of the wave. In electrical engineering, the symbol \beta, called the ''phase constant'', ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
