Particle sensor

A particle sensor, comprising:

• a light projector that projects light to a detection area;
• a light receiver that receives scattered light, the scattered light being light from the light projector that has been scattered by particles in the detection area;
• a first reflector that reflects the scattered light to the light receiver;
• and
• a light attenuator that attenuates stray light that exits the first reflector,
• wherein the first reflector includes a first aperture that introduces the light from the light projector into an interior of the first reflector and a second aperture that exits the stray light from the first reflector,
• the light attenuator includes a third aperture through which the stray light that exits the first reflector passes,
• an aperture area of the third aperture is smaller than an aperture area of the second aperture, wherein the first reflector includes an elliptical mirror, the elliptical mirror including an inner surface that forms a segment of a spheroid, and
• wherein the inner surface of the elliptical mirror includes a cross-sectional shape of a segment of an ellipse, and
• among two focal points that define the ellipse, a first focal point is located in the detection area and a second focal point is located in a center of the light receiver.

A particle sensor, comprising:

• a light receiver configured to receive scattered light, the scattered light being light from a light projector that has been scattered by particles in a detection area;
• a first reflector configured to reflect the scattered light to the light receiver;
• a light attenuator configured to attenuate stray light that exits the first reflector,
• wherein the first reflector includes a first aperture configured to introduce the light from the light projector into an interior of the first reflector and a second aperture configured to exit the stray light from the first reflector,
• the light attenuator includes a third aperture configured to receive the stray light that exits the first reflector, and
• a cross-sectional area of the third aperture is smaller than a cross-sectional area of the second aperture;
• and
• a second reflector that reflects, to the third aperture, the stray light that exits the first reflector.