Method for particle size and concentration measurement
View Patent ↗The present invention provides a system and method of particle size and concentration measurement based on providing a focused, synthesized, non-Gaussian laser beam, causing the beam to interact with the particles, measuring the interaction signal and the number of interactions per unit time of the beam with the particles, and using algorithms to map the interaction signals to the particle size and the number of interactions per unit time to the concentration. The particles are fluid borne, airborne, or on a surface and have a size ranging from sub-micron to thousands of microns. In an embodiment of the invention, the focused, synthesized, non-Gaussian laser beam is a dark beam. The measurements can be made using the duration of interaction with a scanning beam, including dark field.
1. A method of particle size and concentration measurement comprising the following steps:
using one or more lasers to produce a Gaussian laser beam;
using means for converting said Gaussian laser beam into a focused, synthesized, non-Gaussian dark beam;
causing said particles to flow relative to a stationary dark beam or using a scanning mechanism to cause said beam to interact with said particles;
using a detection system to measure the interaction signal and number of interactions per unit time of said dark beam with said particles; and
feeding an output of said detection system into a computer comprising algorithms adapted to map said interaction signals to said particle size and said number of interactions per unit time to said concentration.
2. A method according to claim 1 , wherein the particles are one of fluid borne, airborne, and on a surface.
3. A method according to claim 1 , wherein the size of the particles ranges from sub-micron to thousands of microns.
4. A method according to claim 1 , wherein the measurements are made in the intensity domain.
5. A method according to claim 1 , wherein the measurements are made using the mapping of the interaction pulse width to particle size.
6. A method according to claim 1 , wherein the focal properties of the laser beam are changed depending on the size and concentration range of the particles.
7. A method according to claim 1 , wherein the non-Gaussian beam is generated by employing a mask over a Gaussian laser beam.
8. A method according to claim 1 , wherein the Gaussian beam is spatially modulated.
9. A method according to claim 8 , wherein the Gaussian beam is one of spatially modulated by use of spatial-filter, a set of spatial filters, an electronic spatial light modulator, and a liquid crystal device.
10. A method according to claim 8 , wherein the spatial modulation of the Gaussian beam is chosen from the group comprising:
(i) intensity modulation;
(ii) phase modulation;
(iii) wavelength modulation;
(iv) polarization modulation; and
(v) combinations of these.
11. A method according to claim 8 , wherein the spatial modulation is implemented statically.
12. A method according to claim 8 , wherein the spatial modulation is implemented dynamically.
13. A method according to claim 1 , wherein the non-Gaussian beam is generated by one of directly modifying the laser cavity and combining the beams from several lasers.
14. A method according to claim 1 , wherein the interaction of the focused beam with the particles is accomplished by providing the scanning mechanism that provides a linear scanning path for said focused beam.
15. A method according to claim 1 , wherein the interaction of the focused beam with the particles is accomplished by providing the scanning mechanism that provides a rotary scanning path for said focused beam.
16. A method according to claim 1 , further comprising the use of a second detection system to measure radiation scattered at 90 degrees to the beam direction one of (i) to verify single particle interaction in the focal area and (ii) as an additional dark field information.
17. A method according to claim 16 , wherein the second detection system used to measure radiation scattered at 90 degrees to the beam direction comprises a CCD camera.
18. A method according to claim 16 , wherein the second detection system used to measure radiation scattered at 90 degrees to the beam direction comprises several detectors.
19. A method according to claim 18 , wherein the several detectors are connected in a way selected from the group: addition, differential, and coincidence.
20. A method according to claim 1 , wherein the detection system is used to measure radiation back-scattered from the particles.
21. A method according to claim 1 , further comprising the use of a detector to measure radiation scattered at 90 degrees to the beam direction to detect smaller particles using dark field TOT measurement.
22. A method according to claim 1 , wherein high concentrations of particles are measured by using a reflection, back scatter, mode, collecting the back-scattered interaction energy from the particle.
23. A method according to claim 18 , wherein counting interaction signals, of the scanning laser beam, per unit time is used to measure high concentrations of particles.
24. A method according to claim 1 , wherein the algorithms adapted to map the interaction signals to the particle size and the number of interactions per unit time to the concentration are explicitly based on said interaction signals.
25. A method according to claim 1 , wherein the algorithms adapted to map the interaction signals to the particle size and the number of interactions per unit time to the concentration are based on an advanced artificial intelligence method.
26. A method according to claim 25 , wherein the advanced artificial intelligence method is a Neural Network or support vector method (SVM).
27. A system for particle size and concentration measurement comprising:
one or more lasers to provide a Gaussian laser beam;
a scanning mechanism;
means for converting said Gaussian laser beam into a focused, synthesized, non-Gaussian laser beam; and
detection means;
wherein said focused, synthesized, non-Gaussian laser beam is a dark beam and said means for converting said Gaussian laser beam into said focused, synthesized, non-Gaussian laser beam are chosen from the following group:
a combination of a spatial filter and a lens; and
a liquid crystal device.
28. A system according to claim 27 additionally comprising a second detection system to measure the radiation scattered at 90 degrees to the beam direction.
29. A system according to claim 27 , additionally comprising a beam splitter to divert back-scattered interaction energy from the particle to the detection means.
30. A method according to claim 1 , wherein the synthesized, non-Gaussian laser beam is circular.
31. A method according to claim 1 , wherein the synthesized, non-Gaussian laser beam is linear.
32. A method according to claim 1 , wherein the particle size is determined by differential interference of the light scattered from said particle with the two lobes of a linear synthesized, non-Gaussian laser beam.
33. A method according to claim 1 , wherein the particle size is determined by analyzing the polarization of the light scattered from said particle.
34. A method according to claim 1 , wherein two or more confocal beams are simultaneously generated, each of said beams having a different wavelength.