Optics: measuring and testing – For size of particles – By particle light scattering
Patent
1999-01-28
2000-12-26
Font, Frank G.
Optics: measuring and testing
For size of particles
By particle light scattering
385119, G01N 1502
Patent
active
061668060
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved fibre optic probe, or sensor, for remote flow measurements. In particular, this sensor is designed for accurate flow measurements of fluids flowing in remote vessels, such as blood flow within arteries or veins or flows within pipes.
2. Background Information
Fibre-optic anemometry is employed in velocimetry to measure flow rates, velocity gradients, and turbulence at remote points which are otherwise inaccessible. For example, by measuring the velocity of blood flow in an artery before, during, and after an angioplasty procedure, the success of the procedure can be ascertained. Laser light is transmitted, via optic fibres, into the flow where it is scattered. A portion of the scattered light is collected and transmitted, also via optic fibres, to an anemometer for analysis. By analyzing the Doppler shift between the transmitted light and the collected scattered light, the velocity of fluid flow can be ascertained.
Optical fibres were first used in laser Doppler anemometers for the measurement of localized blood flow velocities by T. Tanaka and G. B. Benedek and described in an article entitled Measurement of the Velocity of Blood Flow (In Vivo) Using Fibre Optic Catheter and Optical Mixing Spectroscopy, 14 Applied Optics 189-196 (1975). In their system they used a 500 .mu.m core diameter monofibre to deliver the laser beam into the femoral vein of a rabbit. The immersed distal end of the fibre was cut and polished at 30.degree. relative to the fibre axis in an attempt to minimize flow disturbance caused by the mere presence of the fibre in the blood stream. A laser beam was projected out through the fibre wall, opposite the cut end surface, into the flow by total internal reflection at the angled polished distal end of the fibre. Light scattered by the erythrocytes at the fibre tip was collected by the same fibre and mixed with the reference beam on the surface of a photomultiplier tube. Analysis of the resultant signal was done on an 18-channel digital autocorrelator.
The sensor of the Tanaka-Benedek system suffers from a number of disadvantages. Projection of light out of the side of the fibre necessitates that the fibre be stripped to its core, thus leaving the brittle and fragile fibre core exposed and unprotected. Cutting and polishing the distal end of the fibre is a difficult operation to perform, thus causing manufacturing complications. Finally, due to the small radius of curvature of the exposed fibre, the curved outer surface of the fibre could cause most of the light scattered back to the fibre to be lost at the fibre-fluid interface, especially if there are irregularities on the surface.
R. B. Dyott, in an article entitled The Fibre-Optic Doppler Anemometer, 2 Microwaves, Optics and Acoustics 13-18 (1978), discusses making flow measurements using a single optic fibre laser Doppler anemometer with the fibre normally terminated. He reported that the region in which light is back-scattered into the fibre extends only to a few tens of the core diameter in front of the fibre tip. As demonstrated in FIG. 10, the flow in this region, indicated at 70, is perturbed by the presence of the distal end of the fibre which could seriously affect the accuracy of any measurements of flow velocity. The Dyott system is well suited, however, to measurements in situations where the medium is stationary and the particles are moving.
For flow measurements, G. A. Holloway, Jr. and D. W. Watkins modified the Tanaka-Benedek system by using separate fibres for delivering the laser beam and receiving the scattered light as described in Laser Doppler Measurement of Cutaneous Blood Flow, 69 J. Investigative Dermatology 306-309 (1977). They applied such a modified system for non-invasive measurement of cutaneous microcirculation. The disadvantages described above regarding the single fibre Tanaka-Benedek system are exacerbated by the inclusion of a second fibre.
For invasive flow measurements, D. Kilpatrick adapted Dyott's s
REFERENCES:
patent: 4281929 (1981-08-01), Lord et al.
patent: 4529267 (1985-07-01), Nishioka et al.
patent: 5512034 (1996-04-01), Finn et al.
Font Frank G.
Nguyen Tu T.
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