Optics: measuring and testing – Refraction testing
Reexamination Certificate
2001-07-09
2003-04-15
Stafira, Michael P. (Department: 2877)
Optics: measuring and testing
Refraction testing
C356S134000
Reexamination Certificate
active
06549276
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to measurement of optical properties of materials, and, more particularly, to precision optical measurement of refractive index, concentration and temperature of materials.
BACKGROUND OF THE INVENTION
The precise measurement of concentration in liquids is important in fields such as chemical analysis and processing, diagnostics, semiconductor manufacturing, waste inspection, and measurement of liquid diffusion coefficients. Measurement of liquid temperature is also important, as is determination of the refractive index for both liquids and non-liquid materials. As such, a variety of techniques have been developed to measure concentration, temperature and/or refractive index. Bergman et al. developed a fiber-optic probe to measure salinity distribution in liquids, as described in T. L. Bergman, F. P. Incropera and W. H. Stevenson, “Miniature Fiber-Optic Refractometer for Measurement of Salinity in Double-Diffusive Thermohaline Systems,” 56
Rev. Sci. Instrum
. 291-96 (1985) and T. L. Bergman, D. R. Munoz, F. P. Incropera and R. Viskanta, “Measurement of Salinity Distributions in Salt-Stratified, Double-Diffusive Systems by Optical Deflectometry,” 57
Rev. Sci. Instrum
. 2538-41 (1986). Other techniques include a planar laser-induced fluorescence technique, as described in A Lozano, S. H. Smith, M. G. Mungal, and R. K. Hanson, “Concentration Measurements in a Transverse Jet by Planar Laser-Induced Fluorescence of Acetone,” 32
AIAA Journal
218-21 (1993), and an invasive heat-marker method as described in V. A. Vink, G. A. Sokolov, and Yu. S. Fomochev, “Measurement of the Concentration of Flowing Liquid Solutions,” 58
Journal of Applied Chemistry of the USSR
357-59 (1985). Interferometric techniques are described in T. Konishi, S. Naka, A. Ito and K. Saito, “Transient Two-Dimensional Fuel-Concentration Measurement Technique,” 36
Applied Optics
8815-19 (1997), T. A. Wilson and W. F. Reed, “Low Cost, Interferometric Differential Refractometer,” 61
Am. J. Phys
. 1046-48 (1993) and R. J. Harris, G. T. Johnston, G. A. Kepple, P. C. Krok and H. Mukai, “Infrared Thermooptic Coefficient Measurement of Polycrystalline ZnSe, ZnS, CdTe, CaF
2
, and BaF
2
, Single Crystal KCI, and TI-20 Glas,” 16
Applied Optics
436-38 (1977), and a phase-locked-loop ultrasonic method is described in K. Ikeda, “Ultrasonic Measurement of Concentration in Solutions by a Phase-Locked Loop Method,” 36
Jpn. J. Appl. Phys
. 3180-83 (1997).
Refractometers are routinely used to evaluate the refractive index to determine the concentration of a liquid mixture, as described in J. E. Geake, “Linear Refractometers For Liquid Concentration Measurement,”
Chemical Engineer
305-08 (1975). Still other techniques reported in the literature for accurately measuring the refractive index of solids and gases include the minimum deviation method as set forth in I. H. Malitson, “Refractive Properties of Barium Fluoride,”
Journal of the Optical Society of America
628-32 (1964) and B. C. Platt, H. W. Icenogle, J. E. Harvey, R. Korniski and W. L. Wolfe, “Technique for Measuring the Refractive Index and Its Change with Temperature in the Infrared,” 65
Journal of the Optical Society of America
1264-66 (1975), the use of a Littrow prism as described in E. D. McAlister, J. J. Villa and C. D. Salzberg, “Rapid and Accurate Measurements of Refractive Index in the Infrared,” 46
Journal oft he Optical Society of America
485-87 (1956) and A. R. Hilton and C. E. Jones, “The Thermal Change in The Nondispersive Infrared Refractive Index of Optical Materials,” 6
Applied Optics
1513-17 (1967), Brewster angle techniques as described in I. K. Smirnov, Y. G. Polyakov and G. N. Orlov, “Arrangement for Measurement of Index of Refraction and Thickness of Transparent Dielectric Films by an Optical Method,”
Journal of the Optical Society of America
546-47 (1980), and others.
Examples of other techniques are set forth in S. M. Chernov, K. K. Zhilik and P. G. Rabzonov, “Determination of the Index Refraction of Liquids and Gases in Capillaries,” 37
Journal of Applied Spectroscopy
(English Translation of Zhurnal Prikladnoi Spektroskopii) 1069-72 (1982), L. A. Danisch, “Removing Index of Refraction Constraints in the Optical Measurement of Liquid level,”
Fiber Optics and Laser Sensors X
268-79 (1992) and D. R. Lide, Ed.,
CRC Handbook of Chemistry and Physics
(CRC Press, Boca Raton, 1998). All of these techniques, however, suffer from one or more of the following shortcomings: direct contact is required with the material being measured, poor resolution is noted, complicated and expensive components are required, systems are physically large and difficult to operate, or a visual, subjective analysis of the data is relied upon.
In view of the foregoing deficiencies of currently known techniques for measurement of concentration and temperature in materials, including liquids, a need clearly exists for an apparatus and method for precision, non-contact measurement of concentration and temperature of a material, such as a liquid, where the apparatus and method does not require complicated and expensive components, is compact, easy to operate, and does not rely on visual, subjective readings of measurement data.
SUMMARY OF THE INVENTION
The present invention, which substantially overcomes the shortcomings of the currently known techniques, provides a method for determining the concentration and temperature of a transparent liquid. The method includes the steps of causing the liquid to be contained in a vessel having a transparent entrance side and a transparent exit side; causing a beam of light to impinge on the entrance side; and then calculating the refractive index of the liquid using Snell's law. In the step of causing the liquid to be contained in the vessel, the vessel can have an entrance side and an exit side with a known angular relationship therebetween, and can be immersed in known surroundings. In the step of causing the beam of light to impinge on the entrance side of the vessel, the impingement can be at an angle &thgr;
i
with the normal to an outer surface of the entrance side. The beam can then pass through the material, and then through the exit side, from which it exits at an angle &thgr;
e
with respect to the normal to an outer surface of the exit side impinged by the light beam.
The calculation of the refractive index of the material using Snell's law can be based on the angles &thgr;
i
and &thgr;
e
, and can be done by applying Snell's law at the interface between the surroundings and the entrance side, the interface between the entrance side and the material, the interface between the material and the exit side, and the interface between the exit side and the surroundings.
The present invention also provides a method for determining the concentration of a given component (e.g., a solute) in a sample of a multi-component liquid mixture (e.g., a solution). The method includes the step of determining the refractive index of the sample of the multi-component liquid mixture as described above and then comparing the determined refractive index of the sample of the multi-component liquid mixture to predetermined data relating different concentrations of the given component of the multi-component liquid mixture to corresponding values of the refractive index of the multi-component liquid mixture. In this manner, the concentration of the given component of the sample of the multi-component liquid mixture can be determined from the refractive index of the sample of the multi-component liquid mixture determined as described above.
The present invention yet further provides a method for determining a change in concentration of a given component of a sample of a multi-component liquid mixture from an initial concentration of the given component which corresponds to an initial refractive index of the sample of the multi-component liquid mixture, at an initial sample temperature. The method includes determining an initial and a subsequent refractive index of the sam
Baker & Botts L.L.P.
Research Foundation of State University of New York
Stafira Michael P.
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