Instrument for measuring particle parameters
View Patent ↗Values for one or more particle properties, such as an aerosol asymmetry parameter g, can be measured directly using a detector that measures scattered light. The detector can comprise two or more diffusers coupled to optical sensors responsive to scattered light that is incident on the surfaces of the diffusers. One or more weighing functions can be obtained based on diffuser geometry. In an example, the diffusers correspond to quadrants of a circular toroid.
1. A method of measuring the aerosol asymmetry parameter, comprising:
with a plurality of sensors and diffusers appropriately positioned relative to an optical axis, measuring light forward-scattered and backward-scattered by an aerosol sample; and
comparing the amounts of forward-scattered and backward-scattered light to determine the aerosol asymmetry parameter.
2. The method of claim 1 , wherein measuring light forward-scattered and backward-scattered by the sample comprises detecting light received by a plurality of diffusers, each of the plurality of diffusers having an outer surface with a cross section at least generally corresponding to a quadrant of a circle, wherein the outer surface of each diffuser admits light to a respective sensor.
3. The method of claim 2 , wherein the outer surfaces of the diffusers are contiguous.
4. The method of claim 2 , wherein two of the diffusers have outer surfaces directed towards the optical axis and two of the diffusers have outer surfaces directed away from the optical axis.
5. The method of claim 4 , wherein the two diffusers having an outer surface directed towards the optical axis measure forward-scattering and backward-scattering, one of the diffusers having an outer surface directed away from the optical axis measures forward-scattering, and one of the diffusers having an outer surface directed away from the optical axis measures backward-scattering.
6. The method of claim 4 , wherein the two diffusers having an outer surface directed towards the optical axis measure forward-scattering and backward-scattering and generate signals designated s 1 and s 2 , respectively, one of the diffusers having an outer surface directed away from the optical axis measures forward-scattering and generates a signal designated s 3 , and one of the diffusers having an outer surface directed away from the optical axis measures backward-scattering and generates a signal designated s 4 and wherein comparing the amounts of forward-scattered and backward-scattered light to determine the aerosol asymmetry parameter, g retr , comprises determining:
g
retr
=
k
(
s
1
-
s
2
+
s
3
-
s
4
)
(
s
1
+
s
2
-
s
3
-
s
4
)
where k is a proportionality constant.
7. The method of claim 6 , wherein the proportionality constant is
1.165
4
π
.
8. The method of claim 4 , wherein the two diffusers having an outer surface directed towards the optical axis measure forward-scattering and backward-scattering and generate signals designated s 1 and s 2 , respectively, one of the diffusers having an outer surface directed away from the optical axis measures forward-scattering and generates a signal designated s 3 , and one of the diffusers having an outer surface directed away from the optical axis measures backward-scattering and generates a signal designated s 4 and wherein comparing the amounts of forward-scattered and backward-scattered light comprises determining a raw detector signal s raw , as:
s
raw
=
(
s
1
-
s
2
+
s
3
-
s
4
)
2
π
(
s
1
+
s
2
-
s
3
-
s
4
)
.
9. An apparatus useable to measure the aerosol asymmetry parameter comprising a plurality of diffusers and light sensors, the diffusers having outer surfaces with an at least generally circular cross section that admit light to a respective light sensor, the light sensors allowing forward and backward scattering of light to be measured, at least two of the plurality of diffusers positioned such that their outer surfaces are directed towards an optical axis and at least two of the plurality of diffusers positioned such that their outer surfaces are directed away from the optical axis.
10. The apparatus of claim 9 , further comprising a housing, the diffusers being disposed inside the housing.
11. The apparatus of claim 10 , wherein the housing defines an optical inlet and the optical inlet defines the optical axis.
12. The apparatus of claim 11 , wherein the housing defines an optical outlet and the optical axis is defined between the optical inlet and the optical outlet.
13. The apparatus of claim 9 , wherein the diffuser outer surfaces are contiguous.
14. The apparatus of claim 9 , wherein the plurality of diffusers are arranged in a toroid about the optical axis.
15. The apparatus of claim 9 , further comprising at least one optical barrier coupled to each of the plurality of diffusers so that the diffusers are at least substantially optically isolated from each other.
16. The apparatus of claim 9 , further comprising a light source.
17. The apparatus of claim 13 , wherein the light source comprises a laser.
18. An apparatus useable to measure the aerosol asymmetry parameter, comprising a plurality of diffusers and light sensors positioned relative to an optical axis such that forward scattering and backward scattering of light by an aerosol are measurable, each diffuser admitting light to a respective light sensor.
19. The apparatus of claim 18 , further comprising a housing, the plurality of diffusers and light sensors positioned in the housing, and wherein the housing defines an optical inlet that defines the optical axis.
20. The apparatus of claim 19 , wherein the housing defines an optical outlet and the optical axis is defined between the optical inlet and the optical outlet.
21. The method of claim 1 , wherein forward-scattered and backward-scattered light are simultaneously measured.
22. The apparatus of claim 9 , wherein the diffusers and light sensors are configured to allow forward and backward scattering of light to be measured simultaneously.
23. The apparatus of claim 18 , wherein the plurality of diffusers and lights sensors are positioned relative to an optical axis such that forward scattering and backward scattering of light by an aerosol are simultaneously measureable.