Study of Miniature Laser Airborne Particle Counter

基于尘埃粒子在光束中产生的散射现象为原理的光学尘埃粒子计数器，因其可以实时测量空气中尘埃粒子的尺寸和颗粒数浓度，所以在洁净环境洁净度检测、空气悬浮颗粒物监测、气溶胶研究等方面得到广泛的应用。随着工业技术的发展，工业生产对生产环境洁净度的要求越来越高，特别是微电子行业，空气中尘埃粒子直接影响芯片的成品率；同时，医疗、食品、化妆品、生物制品等部门越来越多地采用这一专业环境检测仪器，以提高产品质量。为了满足用户实时实地测量的要求，国内自主研制微型化激光尘埃粒子计数器变得十分迫切。 本文基于Mie光散射理论系统地讨论了单个颗粒在平面光照射下的光散射特性；分析了光学尘埃粒子计数器的散射光收集系统结构、建立了不同结构的数学模型，分别对不同结构下单颗粒散射光通量和粒径之间的对应关系进行了数值计算和分析，为光学尘埃粒子计数器光学传感器的设计提供了理论依据。 研制成功便携式激光尘埃粒子计数器的核心部件-微型光学传感器。该传感器采用直角散射光收集形式，以高功率半导体激光器作为光源，同时采用高性能的阿N型光电二极管作为光电探测器。散射光收集系统是单一大数值孔径的球面反射镜，其对粒子散射光的收集角范围从20°到160°。粒子散射光信号是脉冲信号，其频谱成份主要在高频段，所以在PIN型光电二极管后用一个带通式前置放大器来消除外界的低频噪声。 根据Mi。散射理论计算了该光学传感器的光散射响应特性，并用聚苯乙烯标准粒子实测了该光学传感器的性能。结果表明，该系统具有高的信噪比、计数效率，适用于洁净度检测和环境空气中尘埃粒子的粒径分布测量。 以此微型光学传感器为核心部件的BCJ－型激光尘埃粒子计数器具有体积小巧和重量轻等优点，其使用不受时间和地点的限制。Optical Particle Counters (OPCs) which are operated on the principle of light scattering by individual particles have found widespread use in clean-room monitoring, air pollution control and laboratory aerosol studies, because of their ability to make in situ measurement of the concentration and size distribution of particles suspended in the air. With the rapid development of various industries, clean environment is becoming more and more important, such as semiconductor, pharmaceutics, food, cosmetics, biologic fields, and so on. For example, in semiconductor industry, airborne particles directly degrade production yield of the chip. It becomes very demanding to manufacture the miniaturized laser particle counter by domestic manufacturers independently to satisfy the customers' real-time measurement requirement. Based on the Mie scattering theory, light scattering characteristic are synthetically discussed under the condition of single particle irradiated by plane monochromatic light. Collection system for scattered light of the optical particle counters is analyzed, and mathematical models for different configurations are set up. The relationships between luminous flux and particle diameter are calculated for single particle scattering under different configurations, and the affecting factors are analyzed in detail. The above results are the theoretical foundation for designing optical sensor for OPCs. A miniature optical sensor, the core of a miniature laser aerosol particle counter, has been developed. The optical system of the sensor is a right-angle scattering optics, which consists of an illumination system and a collection system for scattered light. A high-powered laser diode module is used as the light source, and a PIN photodiode with high performance is used as the photo-detector. By using a reflective spherical mirror with large numerical aperture, the light scattered by individual particles is collected over a large angular range of 20° to 160°. The scattered light signal from the particle is short pulse, which consists mainly of high frequency components. A band-pass preamplifier is used to eliminate lower-frequency electromagnetic interference from external environment. The light scattering response characteristics of the sensor are calculated based on Mie-scattering theory. The sensor performance has been tested with standard particles of polystyrene latex, the results show that the sensor has high signal-to-noise ratio, counting efficiency, and size resolution. The Model BCJ-1 Laser Airborne Particle Counter with this miniaturized laser-diode based optical sensor as its core component has been constructed. Extremely compact dimension and light weight make the particle counter easy to carry anywhere