Apple Inc.
Compact particulate material sensor

Abstract:

A particulate matter sensing device includes a light source to generate a pulsed light at a first wavelength in response to a drive pulse. The device further includes one or more photodetectors. A thin-film filter is formed over the photodetectors and is tuned to be transparent to scattered light having a second wavelength substantially equal to the first wavelength. The scattered light is produced as a result of scattering of the pulsed light by the particulate matter. A charge collection circuit of the plurality of photodetectors electronically rejects background light.