Rapid Recognition of Solid and Liquid Microparticles through Lateral Mie Scattering

Recognition of solid and liquid airborne particles is important in many areas such as biomedicine, industrial production, environmental science, etc. The capability of single particle detection is essential to realize accurate distinctions between solid and liquid particles. Light scattering is a powerful technique to resolve the physical features of single particles. According to Mie theory of particle scattering, intensities and fringes collected from distinct angles of scattered light allow extraction of particle diameter, refractive index and shape. In this contribution, a real-time technique for identifying the solid and liquid microparticles is presented. Lateral Mie scattering patterns (i.e., 90-degree scattering) from spherical and non-spherical microparticles are collected by a CCD camera at a distance a few hundred micrometers away from the particle. Hough Transform is firstly used to determine the region in which scattering patterns are mainly located. Different orders of statistical moments of the intensity distribution in the considered region is then calculated to identify the particle morphologies, given the fact that liquid particles tend to form spherical shapes due to surface tension while solid particles are expected to maintain their irregular shapes. The technique has been verified by performing around 2000 times of tests with water droplets and polyethylene glycol terephthalate (PET) particles. The measured accuracy rate is over 80% for the tested sets of particles. The proposed technique provides a fast, accurate and cost-effective approach to identify the type of particles at the single particle level, and may be exploited in the rapid identification of types of air pollutant in the open atmosphere.