双波长抗干扰光电感烟探测机理

基于T矩阵法, 选取双波长入射光, 对火灾烟颗粒与非火灾烟雾颗粒的光散射矩阵进行了详细的数值计算和比较分析. 结果表明, 入射光波长改变时, 烟颗粒光散射矩阵元素的变化明显不同于非火灾烟雾颗粒. 选用双波长脉冲激光入射, 通过检测合适的光散射矩阵元, 结合异或逻辑运算, 可区分火灾烟雾颗粒和非火灾烟雾颗粒, 降低非火灾烟雾颗粒引起的误报.     

Discrimination of Smoke Particles Using Infrared Photoelectrical Detection

A method of discrimination of smoke particles using infrared photoelectrical detection is proposed in this paper. Principle of the method is that smoke particles of different materials have different scattering light intensities at same scattering angle according to Mie Theory. Facility used to realize the method includes an infrared laser as light source and an array of avalanche photodiodes distributed at assigned angles as sensing devices. Scattered light signal at these angles are collected and processed. Categories of smoke particle are discriminated by signal processing results. Experiments show that by using this method cigarette smoke, kerosene smoke and water vapor can be discriminated with rate of discrimination of greater than 95%. Application of this technology in the field of fire detection will eliminate some effects of human activities such as cigarette smoking and steam on smoke detection, and improve sensitivity as well as reliability of smoke detection.     

基于光散射的火灾烟雾粒子激光图像探测技术研究

本文结合火灾探测领域的特点,分析了火灾烟雾粒子的光散射特性。通过与其他类型的光电感烟火灾烟雾探测技术的比较,阐述了基于光散射的火灾烟雾粒子激光图像探测技术的原理、特点和技术优势。     

火灾烟颗粒分形模型和球形模型光散射的比较研究

对烟颗粒的光散射进行模拟计算是研究火灾烟颗粒光散射特性的重要手段,目前对于火灾烟颗粒光散射的数值计算多采用球形或椭球模型.实际上,火灾烟颗粒的形貌与球形和椭球均存在着显著差异.扫描电子显微镜图像表明,烟颗粒具有近似分形的结构.本文利用离散偶极近似方法计算了随机取向的火灾烟颗粒分形凝团以及同体积的球形颗粒的光散射Muller矩阵,并对两者的归一化Muller矩阵元素随散射角的分布进行了比较.研究表明:火灾烟颗粒分形模型和球形模型的归一化矩阵元素F₁₁(θ)/     

火灾烟颗粒的分形结构形状模拟与光散射计算

针对火灾烟颗粒的形状特点，提出并建立火灾烟颗粒分形结构凝团的形状模型，并对烟颗粒扫描电镜(SEM)图像进行分析，获取分形结构模型中的单个凝团中基本颗粒个数、凝团分形维数、基本颗粒半径等参数.利用该模型对火灾烟颗粒的形状进行模拟的结果表明，该模型能够较好反映出烟颗粒的形貌特征.利用形状模型对火灾烟颗粒散射进行初步计算表明，在其他参数相同的情况下，相对于同体积的球形颗粒，分形凝团具有前向散射较弱，后向散射较强的特征.     

降雨粒子的无线紫外光散射特性

紫外光与降雨粒子相互作用发生散射,散射光特性改变能够反映降雨粒子的相关物理特性（如粒子尺寸参数、浓度、形态）,因此研究粒子的物理参数对散射光特性的影响对有效提高光谱法定量探测降水的精度有很大意义。由于雨滴在非球形降水粒子中具有代表性,以群雨滴粒子为例,采用T矩阵理论,利用紫外光直视和非直视单次散射模型,分析了入射光波长、群雨滴粒子形态、降雨强度、粒径大小与散射光强之间的关系。并用蒙特卡洛方法仿真分析了非球形群雨滴粒子在不同降雨强度和粒径下散射角与散射光强之间的关系,以及降雨环境中的风切变对紫外光散射特性的影响。通过理论及仿真分析,得到了不同群雨滴粒子形态下的路径损耗,不同降雨强度、风切变率和粒径下的散射光强分布。仿真结果表明：在紫外光直视与非直视通信方式下,降雨环境中的通信质量比晴天条件下的通信质量差,即路径损耗增大。当粒径分布已知时,随着降雨强度的增大,衰减系数增大,路径损耗增加,且直视通信方式的路径损耗比非直视降低7 dB左右。随着降雨强度、风切变率和粒子粒径的增大,散射光强曲线整体呈下降趋势,其中,降雨强度的变化对散射光强分布影响程度最大。相同通信距离时,不同降雨强度下的紫外光散射光强分布均随着散射角的增大而减小,当散射角继续增大到90°时,有效散射体体积逐渐减小,接收到的光子能量减小,暴雨中的散射光强衰减程度最大。相同降雨强度下考虑风切变时,相比较无风时的路径损耗增大5 dB左右。除此之外,还研究了椭球形和切比雪夫形粒子对紫外光散射光强的影响,结果表明当粒子粒径分布相同时,椭球形粒子的散射光强衰减较广义切比雪夫形粒子大。根据散射粒子的散射光强分布以及路径损耗能够区分雨滴粒子是否由相同粒径及形态组成,为粒子测量提供理论基础。分析降水中群雨滴粒子的光散射特性,为提高光谱法评估降水衰减的数值模拟方面提供理论依据,为光学技术在探测识别降水现象等气象领域的广泛应用提供了设计参考。     

Fractal Character of Dynamic Light Scattering of Particles

Dynamic light scattering signals from particles, exhibit fractal characteristics. This feature can be used to determine the particle size. The use of the fractal dimension, as a quantitative method to analyze the properties of dynamic light scattering signals from submicron particles, is presented. The analysis is performed directly on the time‐resolved scattered intensity, and the Box Dimensions of light scattering signals of particles with diameters 100, 200, 500 and 1000 nm. The experimental results show that the fractal dimensions of light scattering signals correlate well with particle size. In the submicron size range, the smaller the particles, the larger their fractal dimensions. Compared with the PCS technique, only several hundreds of samples are required in the fractal method. Therefore, the data processing is easily accomplished. However, this method only provides the mean particle size, but not the particle size distribution.     

光散射聚集速率测定中T矩阵方法的应用

聚集速率是评估胶体体系特性及稳定性的关键参数, 静态光散射和动态光散射则是测量聚集速率的两个重要方法. 然而, 用静态光散射和动态光散射测量聚集速率时, 需要知道有关单粒子和双粒子聚集体光散射特性的数据. 为此, 通常需要把动、静两种方法结合, 才能消去这个数据. 以前各种近似理论曾用来解决这个问题, 但因粒子尺寸和形状的限制, 结果并不理想. 而T矩阵方法可以不受粒子大小和形状的限制计算其光散射特性. 本工作用T矩阵方法直接计算静态光散射和动态光散射所必须的粒子散射特性, 并将该法得到的聚集速率与动静态光散射结合法得到的聚集速率进行了比较, 两者结果很接近. 本工作为简化静态光散射和动态光散射测量聚集速率, 扩展其应用范围开辟了新途径. 关键词： T矩阵')" href="#">T矩阵 光散射法 聚集速率     

气溶胶凝聚粒子散射特性的数值计算

利用Cluster-cluster aggregation (CCA)模型,模拟了由相同数目球形原始微粒凝聚而成的四种随机取向气溶胶凝聚粒子．根据物质的电结构,将气溶胶凝聚粒子离散为一系列偶极子,结合离散偶极子近似方法,在获得每一个偶极子的电偶极矩之后,数值计算了气溶胶凝聚粒子散射强度的角分布,并分析了散射强度随入射光入射角度和气溶胶凝聚粒子尺寸参数变化的规律．结果显示：当散射角较小时,气溶胶凝聚粒子取向和入射光的入射角度对散射强度影响不大,当散射角增大时,散射强度则明显依赖于气溶胶凝聚粒子取向和入射光的入射角度;对于不同尺寸参数的气溶胶凝聚粒子,在同一角度入射情况下,随尺寸参数的增加,气溶胶凝聚粒子的散射主要集中于前向散射．     

A review of the light scattering properties of cirrus

In this review paper the light scattering properties of naturally occurring ice crystals that are found in cirrus are discussed. Cirrus, also referred to as ice crystal clouds, due to their cold temperatures, consist of a variety of non-spherical ice particles which may take on a variety of geometrical forms. These geometrical forms can range from symmetric pristine hexagonal ice columns and plates, single bullets and bullet-rosettes to non-symmetric aggregates of these shapes. These aggregates may also consist of highly complex three-dimensional structures, which may themselves consist of symmetric components. Not only does cirrus consist of a wide variety of shapes but also sizes too, and these sizes can range between <10 μm to over 1 cm. With such a variety of shapes and sizes predicting the light scattering properties from such an ensemble of ice crystals is the current challenge. This challenge is important to overcome since with cirrus being so high in the Earth's atmosphere it has an important influence on the Earth-atmosphere radiation balance and consequently adds to the uncertainty of predicting climate change. This is why it is important to represent as accurately as possible the single-scattering properties of cirrus ice crystals within general circulation models so that uncertainties in climate change predictions can be reduced.In this review paper the current measurements and observations of ice crystal size and shape are discussed and how these observations relate to current ice crystal models is reviewed. The light scattering properties of the current ice crystal models are also discussed and it is shown how space-based instruments may be used to test these models. The need for particular microphysical and space-based measurements is stressed in order to further constrain ice crystal light scattering models.     

非球形生物气溶胶对偏振光的多次散射特性研究

基于回转椭球模型和有限长圆柱模型,采用T矩阵方法研究了非球形生物气溶胶的单次散射特性,计算了鼠疫耶尔森氏杆菌、土拉热杆菌二种生物气溶胶对氦氖激光的单次相矩阵、单次散射反照率以及不对称因子。根据矢量辐射传输理论,研究了激光在生物气溶胶中传输的偏振散射特性,基于累加-倍加法(adding-doubling method)求解矢量辐射传输方程,并计算了非球形生物气溶胶对激光多次散射的斯托克斯参量。计算结果表明,生物气溶胶的尺寸和形状对光的极化更为敏感,因此在利用激光进行生物气溶胶微观特性探测和反演时,利用激光的偏振散射特性为非常有效的方法。     

Visible light scattering study at 470, 550, and 660 nm of components of mineral dust aerosol: Hematite and goethite

Iron oxides, usually in the form of hematite or goethite, comprise an important component of atmospheric mineral dust aerosol. Because these minerals are strong visible absorbers they play a critical role in determining the overall impact of dust aerosol on climate forcing. In this work, results from light scattering measurements from hematite and goethite dust aerosol are presented for three visible wavelengths, λ=470, 550, and 660 nm. We observe important systematic differences in the scattering between these different iron oxide samples, as well as significant wavelength dependence across the visible region of the spectrum. Aerosol size distributions are measured simultaneously with the light scattering, enabling a rigorous comparison between theoretical light scattering models and experimental data. Theoretical simulations of the scattering are carried out using both Mie and T-Matrix theories. Simulations are in reasonably good agreement with experimental data for hematite; thus, our data offer a useful check on tabulated optical constants for hematite. However, simulations show very poor agreement for goethite. The poor agreement in the goethite case is likely the result of particle shape effects related to the rod-like morphology of the goethite particles. This study demonstrates how particle mineralogy and morphology play an important role in dictating the optical properties of mineral dust aerosol, a major component of tropospheric dust.     

炸药爆炸作用下液体破碎后颗粒尺寸分布的研究

 对液体抛撒的液滴尺寸进行研究在军事和民用上是很重要的,国内刚开始使用激光散射仪开展此项研究工作。利用R. A. Dobbins等人的液体颗粒测量技术,研制了一套既简单又实用的测量液体抛撒过程中液滴尺寸的实验装置——激光散射仪。对于激光与液体微粒的相互作用,当微粒的反射与折射和吸收效应可被忽略时,可导出液体微粒对激光散射的光强公式。只要测量激光被微粒散射的光强,就可推算出微粒的Sauter平均直径。在使用激光散射仪测量液体抛撒液滴尺寸的实验中,用水代替爆炸抛撒液体,测量结果表明：液体抛撒二次破碎中,在固定位置测量到的云雾区液滴Sauter平均直径随测量时间的增加呈现出减小的趋势;而云雾区的宽度则随着与抛撒中心距离的增大而呈现出增加的趋势;云雾区前沿的液滴Sauter平均直径随着与抛撒中心距离的增加而呈现出先逐渐增大然后迅速减小的趋势。为便于比较,对燃料抛撒二次破碎进行了回收法测量和数值模拟计算,其测量与计算结果与用激光散射仪测量的结果有较好的一致性。     

Comparative Test of Methods to Determine Particle Size and Particle Size Distribution in the Submicron Range

Among the most important characteristic properties of disperse systems such as latices, pigments, ceramic materials or drug formulations are the particle size and the particle size distribution. To measure these quantities, several methods and measuring instruments based on different physical principles are available. These include turbidimetry, dynamic and static light scattering, electron microscopy with image analysis, ultra- and disc centrifugation, light diffraction and the electrical sensing zone method. All these measuring techniques are doubtless necessary because of the large product variety and the broad particle size range. However, some problems arise if different techniques are used and the results are compared uncritically without considering to the application range and the resolution of the methods. An extensive comparative test was therefore carried out using seven latices in the submicron range with defined monomodal, bimodal and hexamodal particle size distributions. The most important methods of determining average particle size values and particle size distributions were tested and compared. Of the methods to determine only average particle sizes, turbidimetry is the most efficient, followed by dynamic light scattering with cumulants evaluation. Static light scattering only yields accurate results for small particles with narrow particle size distributions. Of the methods to determine particle size distributions, ultracentrifugation and, somewhat less, disc centrifugation and electron microscopy with image analysis are the most efficient. Dynamic light scattering only yields reliable results in the case of small particles with narrow distribution curves. Light diffraction and the electrical sensing zone method are less suitable for the submicron range.     

Optical modeling of mineral dust particles: A review

Dust particles are uniquely and irregularly shaped, they can be inhomogeneous, form agglomerates, be composed of anisotropic materials, and have a preferred orientation. As such, modeling their light scattering is very challenging. This review takes a look at the advances in dust optical modeling over the last decade. It is obvious that our ability to model the single-scattering properties of dust particles accurately depends on the size parameter. Unfortunately, our ability to account realistically for all the relevant physical properties in light-scattering modeling is the best for small particles; whereas, the realistic treatment of the particles would be most important for large size parameters. When particles are not much larger than the wavelength, even simple model shapes such as homogeneous spheroids appear to perform well; practically any reasonable shape distribution of non-spherical model particles seems superior compared to the Mie theory. Our ability to model scattering by dust particles much larger than the wavelength is very limited: no method presently exists to predict reliably and accurately the single-scattering properties of such particles, although there are models that can be tuned to agree well with the laboratory-measured reference scattering matrices. The intermediate size parameters between the resonance domain and the geometric-optics domain appear to be almost uncharted territory and, consequently, very little can be said about the impact of different physical properties on scattering in this region. Despite the challenges, the use of Mie theory should be avoided: contrary to the popular belief, the use of Mie spheres is a major source of error even in radiation-budget considerations.     

Theoretical studies on particle shape classification based on simultaneous small forward angle light scattering and aerodynamic sizing

Particle shape contributes to understanding the physical and chemical processes of the atmosphere and better ascertaining the origins and chemical compositions of the particles. The particle shape can be classified by the aspect ratio,which can be estimated through the asymmetry factor measured with angularly resolved light scattering. An experimental method of obtaining the asymmetry factor based on simultaneous small forward angle light scattering and aerodynamic size measurements is described briefly. The near forward scattering intensity signals of three detectors in the azimuthal angles at 120?offset are calculated using the methods of T-matrix and discrete dipole approximation. Prolate spheroid particles with different aspect ratios are used as the shape models with the assumption that the symmetry axis is parallel to the flow axis and perpendicular to the incident light. The relations between the asymmetry factor and the optical size and aerodynamic size at various equivalent sizes, refractive indices, and mass densities are discussed in this paper. The numerically calculated results indicate that an elongated particle may be classified at diameter larger than 1.0 μm, and may not be distinguished from a sphere at diameter less than 0.5 μm. It is estimated that the lowest detected aspect ratio is around 1.5:1 in consideration of the experimental errors.     

微纳粒子光学散射分析

为实现利用光学方式对微纳尺度粒子性质的研究,探讨了亚微米线及亚微米球对光电磁波的散射效应.微纳米尺度粒子的光学散射,散射粒子尺寸与入射光波长尺寸可满足米氏(Mie)散射条件.利用Matlab数值模拟的方式,将分析结果以模拟图的形式清晰地展现出来.满足尺寸条件的层状粒子以及任意多个散射粒子存在时对电磁波的散射都可采用Mie散射分析方法,并且针对多粒子散射,分析了散射体位于不同位置时对散射造成的影响.通过分析光学散射光场相关的微分散射截面及近场散射电磁场分布,可得出散射光场随散射角度的变化趋势,以及散射光场受各类因素的影响,包括入射光偏振态、散射粒子尺寸、散射粒子结构及粒子构成层数、散射粒子数量等的影响,也包括一些隐含因素对散射光场的影响,如散射粒子与周围介质的相对折射率.本文的科学意义体现在:与入射光波长尺寸可比的亚微米尺度的粒子,可用作传感器,对于其位移的探测可通过光学方式来实现,而由于粒子本身特性对散射光的影响具有一定的参考价值,从而使通过光学方式对机械位移的读出具有更高准确度.研究结果对于光学方式探测亚微米线机械振动具有指导意义.     

Particle Size Characterization of an Extra Fine Milled Product

The present research aims to characterize the particle size distribution of sub micron particles suspended in a liquid. The particles milled are an organic poorly water soluble crystalline product. To characterize the size of these particles, different techniques have been tested: imaging techniques (SEM, CryoTEM), static light scattering techniques, dynamic light scattering techniques, centrifugation and flow field flow fractionation. The results indicate that the studied milled particles have a primary particle size close to 180nm and there is strong evidence of larger particles which are very likely aggregates. This is clearly seen from the Cryo TEM results. All the above mentioned techniques should in principle be able to measure samples of dispersion containing particles of ca 180 nm but several are disturbed by the presence of large aggregates. It is difficult to estimate the amount of aggregate present, but most of the time one is interested in what the primary particle size distribution is. It is clear that no single piece of equipment is capable of exactly determining the particle size distribution of our samples, but the static light scattering with low shear on mixing does give a good representation of what is seen with the image analysis by cryo TEM.     

Particle Manipulation by Ultrasonic Standing Wave Fields to complement dynamic light scattering experiments

Dynamic light scattering is a widely used technique for the sizing of colloidal suspensions. It is capable of measuring particles across the size range from approximately 1 nm to several microns. However the larger particle sizes tend to pose problems for the interpretation of the scattered light signal either by virtue of their light scattering efficiency relative to the smaller species present or the departure of the scattered light signal from Gaussian statistics. Rapid removal of such particles in-situ could extend the use of dynamic light scattering particularly in on-line analysis or laboratory automated measurement. In this paper a method is demonstrated for the in-situ removal of larger particles in suspension by means of ultrasonic standing waves and concurrent dynamic light scattering measurement. The theory behind ultrasonic particle manipulation and its effect on the motion of the particles is discussed. Data from a scattering cell designed to incorporate the ultrasonic technology is presented showing that dynamic light scattering measurements may be carried out under such conditions. Varying the energy density of the ultrasonic field allows particles greater than a defined cut-off diameter to be removed from the measurement region. Theory shows that the minimum cut-off size may be as small as 100 nm. Results presented here demonstrate complete removal at a lower diameter threshold of approximately 2000 nm.     

椭圆截面非球形颗粒群的多重光散射

尽管非球形下一些特殊形状颗粒的单散射已被得到,球形多颗粒系（颗粒群）的多重散射也被研究,但至今仍未得到非球形颗粒群的多重散射.文中建立了一类椭圆截面非球形颗粒模型,求得其散射相位函数,借助于辐射传播方程,考虑形状及大小分布,得到了该类颗粒群的多重光散射.在两种特例情况下的结果能与已有的结果符合较好,说明了方法的可靠性.计算分析表明：非球形颗粒群的多重散射光强角分布要比球形颗粒平坦.椭圆截面颗粒的粒度或形状参数越大,多重散射光越集中于小的散射角;粒度分布或形状分布越宽,多重散射光强的角分布越平坦.随着光学厚 关键词： 多重光散射 颗粒 非球形 椭圆截面