Miniature particulate matter counter and analyzer based on lens-free imaging of light scattering signatures with a holed image sensor

Abstract

We report our latest developments on a novel miniature particulate matter (PM) sensor for personal air quality monitoring. This optical sensor combines a visible fibered light source and a vertical air channel drilled out of a holed retina. The fabrication of such retina features an unconventional design of a CMOS image sensor and a specific drilling post process at wafer level. The scattering of light by a single particle generates a distinctive pattern. By using a compact optical set-up, we measure a lens-free projection of the scattering signature on the image sensor. We present the design and fabrication of such sensor as well as experimental signatures that are consistent with our in-house analytical model. We demonstrate counting and differentiation between calibrated particles of different sizes. Our current setup allows for the detection of single 320 nm polystyrene particles. Finally, we describe our image analysis procedure that fits a measured signature with a modelled one in order to retrieve particle's size and refractive index.

Keywords

• Air quality
• Particulate matter sensor
• Light-scattering
• CMOS image sensor
• Lens-free imaging
• Image processing