Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
  • G01F1/661—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters using light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M3/00—Investigating fluid-tightness of structures
  • G01M3/38—Investigating fluid-tightness of structures by using light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N2021/1765—Method using an image detector and processing of image signal
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
  • G01N2021/416—Visualising flow by index measurement

Definitions

• Typical systems used in the prior for the visualization of index of refraction have included shadowgraphs, Schlieren effect systems and others.
• the image I from lens L of the light source S is removed using a knife edge 8 near the focus of the field mirror M2 such that only the optical perturbations (for example, due to the pressure and temperature change in compressible fluids in object 0) can be observed.
• mirrors Ml and M2 are normally used to compensate for the prohibitive cost of large
• TE SHEET- lenses These mirrors are usually c-anted, which contributes to optical parallax. Models must be used since the cost of large lenses or mirrors makes real object sized test fields expensive. Variations in fluid density due to changes in pressure, temperature or type of fluid mixing with the host, result in variations of refractive index. This in turn causes the light to image at variable locations and a visual two-dimensional record of the effects results. Typical references are included for flow visualization.
• the object or system generating the optical disturbance(s) must be placed close to the retroreflecting screen in order that the optically encoded signal is decoded by passing back along essentially the .same light path. This filters out the offending optical noise.
• the technique particularly utilizes a retroreflector material such as -Scotchlite 7615 manufactured by 3M making possible the application to large fields of view.
• a retroreflector material such as -Scotchlite 7615 manufactured by 3M making possible the application to large fields of view.
• Such material is typically comprised of large numbers of small retroreflective elements such as reflective glass beads.
• the disclosed invention is much more energy efficient and further is capable of irradiating much larger areas since there is no requirement for large lenses, mirrors or the like. In addition, it requires very little alignment and is capable of much easier set up and use.
• FIGS 1A and IB illustrate the prior art in the form of shadowgraphs (Fig.1A) and Schlieren effect (Fig. IB) used for examination of fluid flow.
• Figures 3A and 3B illustrate alternative off-axis and on-axis optical arrangements of the invention.
• Figure 4 illustrates an application of the invention to monitoring turbulence of airflow near airfields.
• Figure 6 illustrates an application of the invention to the determination of leaks in car bodies.
• Figure 7 illustrates the detection of water waves.
• Figures 2A and 2B illustrate a substantially point light source 10 located near the eye 11 of the observer, or a camera 30, used to obtain the data.
• the medium 15 in this case is air near a human arm 16 whose deviation in index of refraction is to be determined.
• the medium 15 is arranged to be between the camera 30 and the retroreflective screen 20, which are preferably distant from each other so that maximum optical leverage occurs.
• the camera system 30 (or eye 11) is focused to make the effect visible. It is generally preferable to have the image of the screen 20 substantially in focus.
• the medium 15 be remote from the screen 20 so that the deviations become manifest. While effects can be noticed -as close as one (1) foot (1/3 m) , best results occur at distances over 1 meter. For example, in the experiment depicted in Figs. 2A and 2B, the distance LI from the screen 20 to the human arm 16 was 10 meters (30 ft.) , while the distance L2 from the camera 30 to the person's arm 16 was 6 meters (20 ft.) . It is also generally preferable that the light source 10 be substantially a "point" source, for best resolution of minute index change related fluctuations.
• a camera such as 30 can be utilized with a telephoto lens whose field of view substantially encompasses the screen 20 and/or medium 15 whose distortion is to be examined. This allows for clear discernment of index gradient effects including the heat waves which occur when a thermally variant object radiates into its surroundings.
• images are produced with the light source 10 directly along the axis of the
• SUBSTITUTE SHEET camera 30 This can be accomplished by either a beam splitter 22 and light source 19 or by placing a small point light source, such as a fiber optic, in the middle of the lens.
• a substantially off-axis arrangement 40 can also be used as shown in Fig. 3A.
• the object is, for example, a butane fuel lighter, the fuel coming out of the lighter can be seen as an index change but the flame •. can be seen only in the direct image.
• SUBSTI e.g, from a bad door seal
• Another application is in determining over large expanses the presence of potential fires or overheating components in areas, electrical devices, etc. Another is studying air flow in air conditioner or heating ducts, pipes or other heat transfer situations. The sole requirement is to create a refractive index change which can be detected with the invention.
• the on-axis version of the invention appears to produce light and dark shadows on the screen, such shadows corresponding to positive or negative gradients of index.
• When one moves the light off-axis there is an apparent change in the type of phenomenon being examined in respect of the positive gradients, such change being different but related.
• the positive and negative going slopes of the refraction surface are being resolved differently.
• the viewing angle slope is either positive or negative going.
• FIG. 5 An analogous case, for example, is depicted in Figure 5 wherein waves 60 in the surface of and within a piece of glass 61 are visualized using a light source 64, a screen 66, and a TV camera 68. Such waves 60 are typically within 2 in. (5 cm) in wavelength and are visible in reflection as well. (See window glass "ripple" in the DiffractoSight photograph in the above-mentioned patent) .
• Figure 6 illustrates such an embodiment of the invention, used for leak tests on vehicles 70.
• a very important task in the production of vehicles 70 is to ascertain the structural integrity of numerous door, window and body seals. Le-aks occurring in transmission cases, engines, cylinder blocks/oil pans and the like are similarly important. However, the major leak tests of interest relate to the passenger area.
• gaseous helium, Freon or the like gas 74 such that a difference in refractive index between the introduced gas 74 and the ambient air is thereby created.
• Human vision or TV camer.as 72 can examine the vehicle 70 as it passes by or rests in a fixed position adjacent a screen 78 to check for a leak 82.
• gas 74 may be pressurized or
• a remote monitor 80 could be. used to display an image of the section of vehicle 70 of interest. It is felt at this writing (and this applies also to the copending applications) that the return cone angle of the individual retroreflective elements, be they beads or corner cubes, etc., in the large array of such elements used on Scotchlite, Reflexite or similar screens, contributes to the sensitivity of the system. This is particularly thought to be true in the off-axis viewing mode; in other words the present roughly 2 degree return cone angle of the glass beads used in Scotchlite 7610 or 7615 produces good results.
• SUBSTITUTE SHEET applications this allows grids to be easily changed rotated, dithered, etc.
• data may also be processed by determining grid line deviations (as a result of index change) , by comparing the returning grid images to standard images (e.g. by optical filtering) or the like.
• the returning image can be filtered to show changes only when deviation occurs.
• the effect is seen by looking through the distorted index medium of the screen.
• both a "primary” (first pass that hits the screen) and a “secondary” (on the return pass through the medium) effect occurs.
• UTE SHEET of creating a screen which directs the light to an imaging camera positioned such that the light never passes back through the medium in reaching the camera.
• the glass inspection system of Figure 5 has been shown to be capable of detecting forming irregularities in windshields and waves both caused by the tin in the float glass process.
• Figure 7 illustrates both reflective and transmissive (refractive) e_r_ood__ments of the invention wherein waves 120 on water in a tank are viewed.
• the reflective e ⁇ ixxJiment light from a light source 122 is reflected off of waves 120 to a screen 124 and back to an observer 126.
• the transmissive (refractive) embodiment light from a light source 128 is passed through the water and a glass bottom 130 to a screen 132 and then back to an observer
• wave data can be studied for its own sake, or the system used to view waves carrying ultrasonic image data produced by coherent beating of waves passing through an object with a reference wave (ultrasonic holography), for example.
• any suitable wavelength of light from ultraviolet to to infrared can be used, commensurate with the function of the retroreflective screen.
• the latter is typically composed of glass beads, but can be a myriad of minute corner cube reflectors for example.
• t pical retroreflector size is 20-200 microns in width (diameter) , spaced closely adjacent to each other for maximum efficiency.
• the best light source for producing these effects is a substantially point light source.
• a 1/2" (1.2 cm) wide source works much better than a source 4" (10 cm) wide when viewing thermal gradients.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Fluid Mechanics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Electromagnetism (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Optical Elements Other Than Lenses (AREA)

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• 1987
  • 1987-05-29 WO PCT/US1987/001279 patent/WO1987007383A1/en not_active Application Discontinuation
  • 1987-05-29 EP EP19870903960 patent/EP0267956A4/de not_active Withdrawn

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