Study On Polarized Light Scattering Characteristics Of Fire Smoke Particles

Fire detection is an essential way to preventing the occurrence of a fire, and photoelectric smoke detectors are playing an increasing important role in fire detections. Normally, photoelectric smoke detectors use scattering of non-polarized by smoke particles to sensing the exists of smoke in the detector chamber, and false alarms are commonly met for in the using photoelectric smoke detectors, because they can not distinguish between smoke and other nuisance aerosols, like dust. It is possible to obtain more detail information of the characteristics of the particles with the polarized light scattering method, so it can be an effect way and valuable practically and theoretically to draw the false alarm rate by studying the polarized light scattering properties by different particles, analyzing the cause factors of different light scattering patterns which is equivalents to analyzing the particle characteristics using the light scattering pattern.The work begin with the introductions of the basic equations and the form of the solutions of light scattering, and then the factors that can influence the polarized light scattering patterns which can be presented by the light scattering Muller matrices were analyzed, that is the particles' size, morphologies, and complex refract indices. The study on the morphologies and size of smoke and dust particles were carried out using the particles' SEM(Scanning Electron Microscopy) images, and the shape models for smoke and dust particles were established, the difference between smoke and dust's complex refract indices were investigated based on the existing research results. The calculation of particles with different size, morphologies, and complex refract index were implemented using the DDA(Discrete Dipole Approximation) method, with the resulting Muller matrices, the different scattering pattern between particles with different size, morphologies, and complex refract index were analyzed using the statistics methods, and the possible methods to estimate the size, morphologies and complex refract index with the scattering pattern were discussed.The platform which measure the light scattering Muller matrices of smoke particles based on light polarization state transformation devices such as the electronic optical modulator, polarizer, quad wave plates and polarization analyzer were improved, including the improvement of the optical system and the signal equitation methods. The methods to calibrate the alignments and orientations of the quad wave plates and the polarization analyzer using the polarization modulated light were established with which the system were carefully calibrated, and the system were tested with estimating the precisions of the measurements, and the light scattering Muller matrices of several typical smoke and dust particles were measured using the platform.The research results showed that, the different Muller matrices distribution patterns on the scattering angles of particles with different size, morphologies and complex refract indices can be predicted using the calculations and measurements with the experiment platform, and the the properties of particle size, morphologies, complex refract indices can be inferred from the Muller matrices as the functions of scattering angles. It can be concluded that using polarized light scattering, the smoke detectors could be used to distinguish between different particles, and the false alarm rate could be reduced, and could induce breakthrough achievements for photoelectric smoke detection.