Non-intrusive Particle Size Measurement Method Based on Scattered Light Intensities of Polarized Lights

Abstract

Non-intrusive particle size measurement method based on scattered light intensities of polarized lights is introduced. A linearly polarized laser passes through the test particles having a certain size distribution. Scattered light intensities observed in the perpendicular and parallel directions to the polarization plane are different. The ratio of the scattered light intensities is called the polarization ratio and is given as a function of the size distribution, the refractive index, the scattering angle and the incident beam wavelength. The two of four parameters, the scattering angle and the wavelength are known values. By comparing the polarization ratio calculated by Mie's scattering theory and that observed experimentally, the size distribution and refractive index are determined. But in this case, the number of equations is insufficient to determine the rest unknown parameters even if a simple log-normal distribution is assumed. By introducing another wavelength, this problem is solved. The multi-wavelength polarization ratio method extends the measurement range of the original single wavelength method, and is applied to soot particle measurement in flames and microplastics suspended in water.