A miniaturized optical sensor for particulate matter detection

Abstract

We present an innovative optical particulate matter sensor. This optical sensor 'on-a-chip' combines a visible fibered light source and a custom-made CMOS image sensor chip. By illuminating a single particle in an air channel, we can record the light scattering signature on the photodiode matrix. A piece realized in 3D printing achieves fiber alignment and an efficient stray light protection. A specific scattering pattern occurs from the interaction of light with a single particle. Unlike traditional optical PM sensors based on a single photodiode detection, we measure a lens-free projection of the scattering signature on the nearby image sensor (1.5mm projection distance). This allows us to count particles and determine their size and refractive index. These parameters are retrieved through image processing and by comparison with a radiometric model that calculates the projection of a Lorenz-Mie's scattering pattern. We describe the sensing technique, the architecture and fabrication of this sensor as well as the characterization results, which are in good agreement with our theory-based predictions. In particular, we show that it is possible to differentiate calibrated particulates of different sizes (monodisperse polystyrene-latex spheres). The sensor is sensitive enough to detect single particle and smallest than 1µm.

Miniature Optical Particle Counter and Analyzer Involving a Fluidic-Optronic CMOS Chip Coupled with a Millimeter-Sized Glass Optical System

“…In order to properly record particle scattering signatures, a CMOS (or ’Complementary metal oxide semi-conductor’, which refers to the manufacturing technology) imager chip (referred to as the ‘holed retina’) has been developed and customized for our specific requirements [ 50 ] on the basis of the CreaPYX standard platform (by Pyxalis) [ 51 ]. The specificity of our design is to allow the formation of a fluidic channel through the chip.…”

Millimeter-sized particle sensor using a wide field of view monolithic lens assembly for light scattering analysis in Fourier domain

“…The former is able to count and record a particle's scattering signature projected onto a holed CMOS image sensor (that is both a detector and a fluidic channel). More details are presented in reference [16] (same conference). Similar designs are also found in conference papers [17] [18] and in patent [19].…”