METHODS AND APPARATUS FOR DETERMINING CHARACTERISTICS OF PARTICLES

• US 20100225913A1
• Filed: 05/21/2010
• Published: 09/09/2010
• Est. Priority Date: 03/06/2004
• Status: Active Grant

• Current Assignee: Michael Trainer
• Original Assignee: Michael Trainer
• Inventors: Trainer, Michael
• Granted Patent: US 8,634,072 B2
• Time in Patent Office: Days
• US Class Current: 356/338
• CPC Class Codes: G01N 15/0205 by optical means
• CPC Class Codes: G01N 15/0211 Investigating a scatter or diffraction pattern

Abstract

An instrument for measuring characteristics of a particle sample by counting and classifying particles into selected ranges of particle characteristics. The particle concentration is reduced to the level where the probability of measuring scattering from multiple particles of interest at one time is reduced to an acceptable level. A light beam is projected through a sample space, through which the particles flow. As each particle passes through the beam, it scatters, absorbs, and transmits different amounts of the light, depending upon the particle characteristics. So both the decrease in the beam intensity, due to light removal by the particle, and light scattered by the particle, may be used to determine the particle characteristics, to classify the particle and count it in a certain range of particle characteristics.

Claims

1. A method for analyzing particles, comprising:

a) passing a plurality of particles through a sample space, the sample space having a volume,

b) illuminating at least one of the particles,

c) detecting light scattered only from particles located within a region of the sample space, said region having a volume which is smaller than the volume of the sample space,

i) wherein the detecting step includes passing said light through an aperture which allows light scattered from particles located within said region to reach at least one detecting means and which blocks light scattered from particles and objects located outside said region,

ii) wherein the aperture is located in a plane which is generally conjugate to said region of the sample space,

iii) wherein the probability of multiple particles of interest, occupying said region simultaneously, is sufficiently low to avoid a significant number of coincidence counts of particles of interest, and

d) analyzing the scattered light detected in step (c) to derive information about the particles.

2. The method of claim 1, wherein said region consists of a portion, of a nonuniformly illuminated volume, over which the illuminating light intensity is sufficiently uniform.

3. The method of claim 1, wherein step (c) is performed a plurality of times simultaneously, wherein each performance of step (c) detects light scattered at a different range of scattering angles and/or a different range of scattering planes and/or with different weighting as a function of scattering angle, and wherein the probability of multiple particles of interest, occupying said region simultaneously, is sufficiently low to avoid a significant number of coincidence counts of particles of interest.

4. The method of claim 1, wherein step (c) is performed a plurality of times for multiple particles, all such performances being with regard to a same range of scattering angles and same range of scattering planes, and wherein the probability of multiple particles of interest, occupying said region simultaneously, is sufficiently low to avoid a significant number of coincidence counts of particles of interest,

wherein the multiple performances of step (c) measure scattered light from multiple regions, simultaneously, and

wherein the detecting step comprises using a two-dimensional array of generally contiguous detectors.

5. The method of claim 1, further comprising the steps of:

mixing light which illuminates the particles in step (b) with some of the scattered light detected in step (c), so as to create an interference signal, and

accepting only a portion, of said interference signal, with a certain range of frequency or phase, for input to the analysis of step (d),

wherein the probability of multiple particles of interest, occupying said region simultaneously, is sufficiently low to avoid a significant number of coincidence counts of particles of interest.

6. The method of claim 1, wherein the detecting step comprises using a lens to detect light scattered at relatively low scattering angles, and using a mirror to detect light scattered at relatively high scattering angles.

7. The method of claim 1, further comprising:

e) measuring light flux of light scattered from a particle, the measuring being performed for at least two different ranges of scattering angles and/or different weightings as a function of scattering angle, and

f) computing a ratio of light flux measurements of scattered light taken for different ranges of scattering angles and/or different weightings as a function of scattering angle, and using said ratio to determine particle characteristics.

8. The method of claim 1, further comprising:

e) detecting scattered light from a particle, in a plane which is generally conjugate to said particle,

f) determining a position of the center of the distribution of said detected scattered light, in said generally conjugate plane, along a direction which is generally perpendicular to the flow direction of the particles, and

g) rejecting particles with said positions indicative of particles which have passed through a portion, of said region, where the light intensity is outside of a certain range, insuring that all accepted particles have passed through a portion of said region with sufficient intensity uniformity.

9. The method of claim 8, wherein step (e) is performed by a plurality of detectors and step (f) comprises using at least one ratio between signals from different detectors to determine said position.

10. The method of claim 1, wherein step (c) is performed a plurality of times, wherein each performance of step (c) detects scattered light from a region of different size and wherein the probability of multiple particles of interest, occupying each said region simultaneously, is sufficiently low to avoid a significant number of coincidence counts of particles of interest for that particular region.

11. Apparatus for analyzing particles, comprising:

a) means for passing a plurality of particles through a sample space, the sample space having a volume,

b) means for illuminating at least one of the particles,

c) means for detecting light scattered only from particles located within a region of the sample space, said region having a volume which is smaller than the volume of the sample space,

i) wherein the detecting means includes means for passing said light through an aperture which allows light scattered from particles located within said region to reach at least one detecting means and which blocks light scattered from particles and objects located outside said region,

ii) wherein the aperture is located in a plane which is generally conjugate to said region of the sample space,

iii) wherein the probability of multiple particles of interest, occupying said region simultaneously, is sufficiently low to avoid a significant number of coincidence counts of particles of interest, and

d) means for analyzing the scattered light detected by the detecting means, to derive information about the particles.

12. The apparatus of claim 11, wherein said region consists of a portion, of a nonuniformly illuminated volume, over which the illuminating light intensity is sufficiently uniform.

13. The apparatus of claim 11, wherein there are multiple detecting means, each detecting means adapted to receive scattered light having a different range of scattering angles and/or a different range of scattering planes and/or with different weighting as a function of scattering angle corresponding to a same particle, and wherein the probability of multiple particles of interest, occupying said region simultaneously, is sufficiently low to avoid a significant number of coincidence counts of particles of interest.

14. The apparatus of claim 11, wherein there are multiple detecting means, and wherein each detecting means measures scattered light having a same range of scattering angles and a same range of scattering planes, and wherein the probability of multiple particles of interest, occupying said region simultaneously, is sufficiently low to avoid a significant number of coincidence counts of particles of interest,

wherein each detecting means detects light scattered from a different region of the sample space, and

wherein said multiple detecting means comprise a two-dimensional array of generally contiguous detectors.

15. The apparatus of claim 11, wherein the detecting means includes a mirror having an opening, and a lens disposed generally within said opening, wherein the lens is positioned to detect light scattered at relatively low scattering angles, and the mirror is positioned to detect light scattered at relatively high scattering angles.

16. The apparatus of claim 11, further comprising:

e) means for detecting scattered light from a particle, in a plane which is generally conjugate to said particle,

f) means for determining the position of the center of the distribution of said detected scattered light, in said generally conjugate plane, along a direction which is generally perpendicular to the flow direction of the particles, and

g) means for rejecting particles with said positions indicative of particles which have passed through a portion, of said region, where the light intensity is outside of a certain range, insuring that all accepted particles have passed through a portion of said region with sufficient intensity uniformity.

17. The apparatus of claim 16, wherein the means for detecting scattered light in a generally conjugate plane comprises a plurality of detectors, and wherein the rejecting means comprises means for calculating a ratio between signals from different detectors to determine said position.

18. The apparatus of claim 11, the apparatus including a sample cell into which particles to be analyzed are directed, the sample cell being bounded by a pair of walls, the walls including windows for allowing light to enter the sample cell and to leave the sample cell after interacting with particles, the sample cell also defining a path for particles to pass through the sample cell, the sample cell and detecting means defining an interaction volume within which particles, passing through the sample cell, produce scattered light which is received by said detecting means,

wherein the sample cell includes at least one transparent shaped object, attached to one of said walls, the shaped object being positioned outside of a desired portion of the interaction volume so as to prevent particles from passing through a volume occupied by said object and wherein said occupied volume comprises the portion of illuminated volume in the particle dispersion outside of the desired portion of the interaction volume, and wherein the occupied volume is shaped such that particles, which are too large to pass through the desired portion of the interaction volume, pass around said object in the particle flow.

19. The apparatus of claim 11, the apparatus including a sample cell into which particles to be analyzed are directed, the sample cell being bounded by a pair of walls, the walls including windows for allowing light to enter the sample cell and to leave the sample cell after interacting with particles,

wherein the windows include at least one curved surface, the curved surface having a center of curvature, the curved surface being shaped such that its center of curvature is located generally at a position where a particle is to be observed.

20. Apparatus comprising an optical element for use in directing light scattered from particles to a plurality of detectors, the optical element comprising:

a) a plurality of segments,

b) each segment comprising means for capturing light from a different area of a scattering distribution, each area comprising a different range of scattering angles and/or a different range of scattering planes and/or different weighting as a function of scattering angle, and

c) each segment comprising means for redirecting, or redirecting and focusing, light captured by said segment onto a different light detector.

21. The apparatus of claim 20, further comprising:

d) wherein each segment includes a plurality of diffractive structures, wherein the diffractive structures in different segments differ in at least one of orientation, shape, and spatial frequency.