Forward scatter in particulate matter sensor

Abstract

Embodiments relate generally to systems and methods for detecting particulate matter in the air. A particulate matter sensor may comprise an airflow channel; a light source configured to pass light through the airflow channel; an airflow generator configured to generate airflow into the airflow channel; a waveguide configured to direct light from the light source after it passes through the airflow channel and scatters off of particulate matter within the airflow channel; a photodiode configured to receive light scattered by the waveguide; and a computing device coupled to the photodiode having a processor and a memory storing instructions which, when executed by the processor, determines a mass concentration of particles in the airflow channel based on an output of the photodiode.

1 . A particulate matter sensor comprising:
 an airflow channel;   a light source configured to pass light through the airflow channel;   an airflow generator configured to generate airflow into the airflow channel;   a waveguide configured to direct light from the light source after it passes through the airflow channel and scatters off particulate matter within the airflow channel, wherein the waveguide includes a first condensing lens and a second condensing lens, wherein the first condensing lens is configured to receive scattered light that is scattered off the particulate matter within the airflow channel, and is configured to direct the received scattered light to the second condensing lens, and the second condensing lens is configured to direct the scattered light to a photodiode;   the photodiode is configured to receive the scattered light from the second condensing lens; and   a computing device coupled to the photodiode having a processor and a memory storing instructions which, when executed by the processor, determines a mass concentration of particles in the airflow channel based on an output of the photodiode.   
     
     
         2 . The particulate matter sensor of  claim 1 , wherein the first condensing lens of the waveguide directs light that scatters between approximately 10 and 40 degrees from a beam produced by the light source. 
     
     
         3 . The particulate matter sensor of  claim 1 , wherein the first condensing lens of the waveguide directs light that scatters at least 5 degrees from the beam produced by the light source. 
     
     
         4 . The particulate matter sensor of  claim 1 , wherein the first condensing lens of the waveguide directs light that scatters less than 90 degrees from the beam produced by the light source. 
     
     
         5 . The particulate matter sensor of  claim 1 , wherein light scattered by the particulate matter is forward scattered by the waveguide toward the photodiode. 
     
     
         6 . The particulate matter sensor of  claim 1 , further comprising a light trap configured to prevent the beam produced by the light source from reaching the photodiode. 
     
     
         7 . The particulate matter sensor of  claim 6 , wherein the light trap is further configured to prevent the beam from reflecting back into the airflow channel. 
     
     
         8 . The particulate matter sensor of  claim 1 , wherein the first condensing lens includes a curved output surface and the second condensing lens includes a curved input surface, wherein the curved output surface of the first condensing lens faces the curved input surface of the second condensing lens. 
     
     
         9 . The particulate matter sensor of  claim 1 , wherein the light source is a laser diode. 
     
     
         10 . A method for determining the concentration of particulate matter within an environment, the method comprising:
 allowing ambient air to enter a particulate matter sensor;   generating an updraft into an airflow channel within the particulate matter sensor;   powering a light source within the particulate matter sensor to produce a light beam;   directing the light beam through the airflow channel;   receiving, by a first condensing lens of a waveguide, scattered light that is scattered by particulate matter within the airflow channel;   directing, by the first condensing lens of the waveguide, the scattered light to a second condensing lens of the waveguide;   directing, by the second condensing lens of the waveguide, the scattered light toward a photodiode; and   determining a mass concentration of particles in the airflow channel based on an output of the photodiode.   
     
     
         11 . The method of  claim 10 , wherein the light source comprises a laser diode. 
     
     
         12 . The method of  claim 10 , further comprising directing scattered light within a range of angles from the light source toward the photodiode. 
     
     
         13 . The method of  claim 10 , further comprising preventing the light beam produced by the light source from directly reaching the photodiode. 
     
     
         14 . The method of  claim 10 , further comprising preventing the light beam from directly reaching the photodiode by a light trap located within the waveguide. 
     
     
         15 . The method of  claim 10 , wherein determining the mass concentration of particles in the airflow channel is completed by a computing device operatively coupled to the photodiode. 
     
     
         16 . A particulate matter sensor comprising:
 an airflow channel;   a laser diode;   a housing configured to contain the elements of the sensor;   an airflow generator configured to generate airflow into the airflow channel;   a photodiode configured to receive light produced by the laser diode;   a waveguide positioned between the laser diode and the photodiode, configured to direct light scattered by particulate matter within the airflow channel toward the photodiode;   wherein the waveguide includes an ellipse mirror, the ellipse mirror having an inlet that is configured to receive light scattered by the particulate matter within the airflow channel, and the ellipse mirror is configured to direct at least some of the received scattered light toward the photodiode; and   a computing device coupled to the photodiode having a processor and a memory storing instructions which, when executed by the processor, determines a mass concentration of particles in the airflow channel based on an output of the photodiode.   
     
     
         17 . The particulate matter sensor of  claim 16 , wherein the ellipse mirror of the waveguide directs light that scatters less than 90 degrees from the beam produced by the light source. 
     
     
         18 . The particulate matter sensor of  claim 16 , further comprising a light trap configured to prevent the beam produced by the light source from directly reaching the photodiode. 
     
     
         19 . The particulate matter sensor of  claim 18 , wherein the light trap is further configured to prevent the beam from reflecting back into the airflow channel. 
     
     
         20 . The particulate matter sensor of  claim 18 , wherein the light trap comprises one or more angled surfaces.