Study On The Model Of Light Scattering By Smoke Particles

Smoke particles are important characteristic parameters for early fire detection. Currently photoelectric smoke detectors based on light scattering principle arc gradually taking the place of ionization ones. The development of photoelectric smoke detection technology asks urgently for a light scattering model for smoke particles.In this work, two kinds of shape models are developed for the smoke particles based on their microcosmic morphologies. The Stokes scattering matrices of smoke particles are analyzed by solving the Maxwell equations through the T-matrix method. Firstly, a detailed model of light scattering by smoke aggregates is developed. The spherical primary particles in each aggregate are seen as the basic monomers of light scattering, while taking into account the multiple scattering among them. Basing on this model, and using the Smoke Aggregates Generation software programmed in this work, the influences of several parameters of smoke aggregates on the light scattering are studied, namely, the fractal dimension, the fractal prefactor, the refractive index and the number of monomers in the smoke aggregate. Secondly, a spheroid model is developed taking the whole smoke aggregate as a unit. Based on a prolate and an oblate spheroid model, the influences of the refractive index and si(?)c parameter of smoke aggregates on the light scattering are analyzed, not only for a single smoke particle, but also for a collection of smoke particles.Aiming at the measurements of the Stokes scattering matrix for smoke particles, an experimental setup is built with an electro-optic modulator, a quarter-wave plate and polarizers. The constant (dc) part, fundamental harmonic and secondary harmonic of the scattered light are measured. With a smoke generator, the Stokes scattering matrices are measured for the smoke particles generated by a smoldering cotton, n-haptane flaming fire and a smoldering sandal.The experimental results suggest that the nonspherical effect of the smoke particles on the light scattering is clearly shown, especially for the two kinds of gray smoke. Besides, some distinguished differences exist between the light scattering by...