High sensitivity particle detection

Details High sensitivity particle detection High sensitivity particle detection

2000-01-27

2002-04-23

Font, Frank G. (Department: 2877)

Optics: measuring and testing

For size of particles

By particle light scattering

C356S337000, C356S341000, C356S340000, C250S574000

Reexamination Certificate

active

06377345

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a particle detector for detecting particles of sizes of less than one micron, comprising radiation emitting means for emitting radiation at two different wavelengths along a predetermined path through a scattering volume, the radiation at one of the wavelengths lying between about 400 nm and about 500 nm, and radiation detection means for receiving and detecting the radiation scattered from the scattering volume by the presence of particles at a predetermined forward scattering angle of less than 45° to the predetermined path of radiation.
2. Description of the Related Art including Information Disclosed under 37C.F.R. 1.97 and 1.98.
The invention also relates to a particle detecting method for detecting particles of sizes of less than one micron, comprising the steps of emitting radiation at two different wavelengths along a predetermined path through a scattering volume, one wavelength lying between about 400 nm and 500 nm, and receiving and detecting the radiation scattered from the scattering volume by the presence of particles at a predetermined forward scattering angle of less than 45° to the predetermined path of radiation.
Such a detector and such a method are shown, for example, in GOODMAN D. S.: “METHOD FOR LOCALISING LIGHT-SCATTERED PARTICLES”; IBM TECHNICAL DISCLOSURE BULLETING vol. 27, no. 5, October 1984, page 3164 XP 002066860, and in WO-A-89 09392. Reference is also made to U.S. Pat. No. 6,011,478 (Suzuki et al).
BRIEF SUMMARY OF THE INVENTION
The invention aims to improve the sensitivity of such a detector and such a method so that the detector and the method are better able to discriminate against particles of a type which are not intended to be detected.
According to the invention, therefore, the detector as first set forth above is characterised in that the radiation of the other wavelength is infra-red radiation, and by output means for comparing outputs from the detecting means respectively corresponding to the received and detected radiation between about 400 nm and 500 nm and the received and detected infra-red radiation whereby to produce a warning signal when the comparison indicates that the particles are of a predetermined type but not when the comparison indicates otherwise. Similarly, according to the invention the method as first set forth above is characterised in that the other wavelength is a wavelength of infra-red radiation, and by the step of comparing two outputs respectively corresponding to the received and detected radiation between about 400 nm and about 500 nm and the received and detected infra-red radiation whereby to produce a warning signal when the comparison indicates that the particles are of a predetermined type but not when the comparison indicates otherwise.


REFERENCES:
patent: 4221485 (1980-09-01), Schulze
patent: 4547675 (1985-10-01), Muggli et al.
patent: 5416580 (1995-05-01), Trainer
patent: 6011478 (2000-01-01), Suzuki et al.
patent: 0 877 345 (1998-11-01), None
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patent: 1 533 192 (1977-04-01), None
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patent: 2 032 617 (1980-05-01), None
patent: 2 319 605 (1998-05-01), None
patent: WO 89/09392 (1989-10-01), None
Goodman, “Method for Localizing Light-Scattered Particles, ”IBM Technical Disclosure Bulletin, vol. 27, No. 5, p. 3164 (19894).

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