Particulate matter sensor

A method of manufacturing a particulate matter sensor module, the method comprising:

• forming a first section of a housing, the first section of the housing comprising an aperture, a first part of a light trap chamber, a first part of a light reflection chamber, a first part of a fluid flow conduit, and a first part of a particle-light interaction chamber;
• forming a second section of a housing, the second section of the housing comprising a second part of the light trap chamber, a second part of the light reflection chamber, a second part of the fluid flow conduit, and a second part of the particle-light interaction chamber;
• attaching the first section of a housing to a substrate, wherein the substrate has a light source and a light detector mounted thereon, and arranging the first section such that light emitted by the light source can pass through the aperture;
• attaching the second section of the housing to the first section, such that the first section is disposed between the substrate and the second section, and such that the first and second sections, in combination, define the light reflection chamber, the fluid flow conduit, the particle-light interaction chamber, and the light trap chamber;
• and
• disposing a reflective surface in the light reflection chamber,
• wherein the particle-light interaction chamber has an input end and an output end, the particle-light interaction chamber having a tapered cross-section that widens along an axis parallel to a light beam path between the reflective surface and the light trap chamber, and
• wherein the tapered cross-section widens continuously from the input end to the output end, in a direction toward the light trap chamber.