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.