Researches On Micro-particle Measurement Techniques Based On Multi-angular Light Scattering

Fine particles with aerodynamic diameters of 2.5 ?m or less(PM2.5)have received considerable attention because of their adverse impacts on human health.Scientific and effective management of these particles depends on the timely and accurate high resolution monitoring.Fast and accurate detection of PM2.5 mass concentration is a not only realistic but also really challenging task.Light scattering technique for the measurement of particle mass concentration has received extensive attention from the industry and academia since its birth.Affected by multiple factors such as particle size,refractive index and composition,the precision of light scattering technique for the measurement of particle mass concentration has been unable to guarantee and the relevant study has once come to a halt.In general,there are three drawbacks in the study of this field:in the design of the measurement system,particle information is not comprehensively acquired,scattered light at a single angle can't effectively identify the variations of particles'various parameters;in measurement theory,there is no complete theory analysis to provide concise and applicable signal optimization schemes for different precision demand;in countermeasures to the effect from meteorological parameters,there is no calibration scheme by using scattered light itself and then make the instrument complicated and inefficient.Based on the above three problems,this paper designed and developed a new type of particle sensor based on multi-angle light scattering,a variety of signal optimization schemes are put forward on the basis of comprehensive information acquisition,and through the variations of particle scattering light,the impact of meteorological parameters on particle mass concentration is corrected.The research content and innovations are summarized as follows:(1)Through analyzing the basic theory of light scattering techniques,the relationship between particle size and light flux with different scattering angles and solid angles is created by making use of Mie theory.The new particle sensor creatively select 40°,55°,140° as the light scattering angles.Light detectors at the three angles can collect particles' refractive index and shape information.Based on computer-aided design technology,3D printing technology and weak signal detection technology,a prototype of multi-angle light scattering particle sensor is produced.A particle mass concentration detection system is then built based on the new particle sensor.(2)This thesis puts forward three kinds of signal optimization and fusion schemes after analyzing the relationship among particle's diameter,refractive index and scattered light flux.The particle detection scheme based on true RMS detection has reduced the influence of large particles on sensor precision and has the characteristics of simple structure,good performance and low price.By combining Fraunhofer diffraction and Rayleigh scattering,a simplified measurement model is proposed and optimized.The measurement model can greatly improve the detection performance.According to the different particle information collected from the three angles,a data fusion model is proposed.By fusing the information from different light detectors,the particle sensor has better performance than particle sensor of single angle.The data fusion model is simple and efficient.The above three kinds of signal optimization schemes can meet the needs of different detection accuracies.(3)Instead of adding meteorological sensors or dehumidification devices used widely in commercial PM2.5 measurement instruments,weather index is introduced as the ratio of scattered light fluxes collected at two forward angles to eliminate the effect of meteorological factors.Simulations based on Lorenz-Mie theory and field experiments establish the feasibility of this scheme.This scheme has the characteristics of high reliability,easy to implement and can effectively deal with the influence of meteorological parameters especially relative humidity on the measurement results of particle concentration sensor.(4)Through the analysis of the research work at home and abroad,indoor particulate matter composition varies and the calibration of measurement results are difficult,a new scheme is put forward to obtain mass median diameter through the particle light flux ratio.Baesd on the mass median diameter of particle,particle classification and mass concentration correction can be made.The feasibility of the scheme is verified by scanning electron microscope analysis and measurement results of different types of indoor particles.This scheme expands the using range of the multi-angle light scattering particle sensor.