New Receiving Mode of Extinction for Determining Particle Size and Density without Convex Lens

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｉｆａｌｉｇｈｔｂｅａｍ ｐａｓｓｅｓｔｈｒｏｕｇｈｔｈｅｐａｒｔｉｃｕｌａｔｅｔｒａｎｓｐａｒｅｎｔｍｅｄｉｕｍ ,ｉｔｓｉｎｔｅｎｓｉｔｙｗｉｌｌｂｅｗｅａｋｅｎｅｄｂｅｃａｕｓｅｏｆｔｈｅｅｘｔｉｎｃｔｉｏｎｏｆｐａｒｔｉｃｌｅｓ[1] .Ｔｈｉｓｐｈｅｎｏｍｅｎｏｎｉｓｃａｕｓｅｄｂｙｔｈｅｓｃａｔｔｅｒｉｎｇａｎｄａｂｓｏｒｐｔｉｏｎｏｆ ｐａｒｔｉｃｌｅｓ.Ｔｈｅｓｃａｔｔｅｒｉｎｇｅｌｅｃｔｒｏｍａｇｎｅｔｉｃｗａｖｅｓａｒｅｄｉｆｆｕｓｅｄｉｎｓｐａｃｅａｌ…     

颗粒溶液颗粒尺寸及浓度的差分偏振弹性散射光谱在线分析方法

偏振弹性散射光谱技术的基本原理为在偏振光入射条件下,根据出射光的偏振特性不同可以筛选出浅表层组织的单次散射光信息和深层组织的漫散射光信息。该研究的创新点在于将这种方法应用于颗粒溶液检测,目的是在颗粒溶液原始状态下实现对颗粒尺寸及浓度的同时检测。设计了一个共轴笼式光学系统,测量了聚苯乙烯微球颗粒溶液某一角度的背向散射信号,通过控制入射端和收集端偏振片的偏振方向获得了颗粒溶液的偏振平行光谱与偏振垂直光谱,两者之差即偏振差分光谱对应颗粒的单次散射信息,将该单次散射信息与Mie散射数据库进行比对获得颗粒的尺寸,然后在颗粒尺寸作为已知的条件下进一步分析偏振垂直光谱,将该垂直光谱对应的颗粒溶液的漫散射信息代入光漫散射下的近似表达式拟合得到颗粒的浓度信息。将实验结果与样品提供值进行了比对,并进一步分析了在获取颗粒数浓度时,颗粒直径的方差分布对结果的影响,最终验证了该实验方法的可行性。该方法的潜在应用包括对标准颗粒制造厂商的产品在线检测以及对牛奶制品中脂肪和蛋白质的浓度检测研究。     

近场接收时颗粒的消光特性

讨论了在近场接收条件下颗粒的消光特性。计算表明：在近场接收时，颗粒的实际消光将性与远场接收相比，存在很大的区别－－实际消光纱数不但同颗粒的性质和大小有关，而且与颗烊在光束中的位置相联系。对于大颗粒，近场间的消光系数在数值上也有很大差异，如果采用近场接收来测量颗粒的大小，必须考虑这些因素的影响，否则将极大增加测量误差。还论述了近场接收时消光法测量颗粒时测量区定义中的问题，论证了如何能恰当定义测量区，     

光全散射法颗粒测量中的一种自适应非独立模式算法

光全散射颗粒测量法中需求解第一类Ｆｒｅｄｈｏｌｍ积分方程。在不知道被测颗粒的尺寸范围的情况下如何确定积分方程的上下限、即测量范围，迄今仍是个问题。本文针对此问题提出了一种自适应非独立模式算法。该算法可根据双参数颗粒分布函数的分布参数Ｋ自动确定积分的上下限．数值模拟和实验都证实了此算法。     

颗粒系的可见消光光谱分析及最佳波长的选择

在光全散射法颗粒粒径测量中,被测颗粒系的消光光谱包含有颗粒粒径、折射率等信息。对常用的单峰及双峰R-R分布的可见消光光谱进行模拟,分析了可见消光光谱随粒径和相对折射率变化的规律。选取二阶微分可见消光光谱不连续点对应的波长作为测量波长,并将可见光边界波长同时作为测量波长,在非独立模式下,采用遗传优化算法反演粒径分布。仿真计算与实验验证结果表明,通过消光光谱分析,可以预先确定被测颗粒系的分布状况,缩小优化算法中反演参数的搜索范围。结合最佳波长选择方法,使测量的精度和可靠性明显提高。对测量光谱加入1%随机噪声时,单峰及多峰分布粒径反演均能得到满意的结果。     

Experimental Study on Particle Size Distribution and Concentration Using Transmission Fluctuation Spectrometry with the Autocorrelation Technique

Based on the statistical characteristics of the transmission fluctuations in the particle suspension, transmission fluctuation spectrometry with autocorrelation (TFS‐AC) is described theoretically, with the assumptions of geometric ray propagation and completely absorbent particles in the suspension. The experiments presented here are realized in a focused Gaussian beam with the TFS‐AC technique. The acquisition of transmission fluctuation signals is achieved by using a high‐resolution digital oscilloscope. The transition function of TFS‐AC is obtained by varying the autocorrelation time. With a modified iterative Chahine inversion algorithm, solving a linear equation retrieves information on the particle size distribution and particle concentration. Some experimental results on spherical and non‐spherical particles are presented and discussed. The experiments cover a particle size range from 1μm to 1000 μm and a particle concentration of up to 12 %.     

Resolving Concentrated Particle Size Mixtures Using Dynamic Light Scattering

Dynamic light scattering (DLS) is a technique used for measuring the size of molecules and particles undergoing Brownian motion by observing time‐dependent fluctuations in the intensity of scattered light. The measurement of samples using conventional DLS instrumentation is limited to low concentrations due to the onset of a phenomenon called multiple scattering. The problems of multiple scattering have been addressed in a light scattering instrument incorporating non‐ invasive backscatter optics (NIBS). This novel optic arrangement maximizes the detection of scattered light while maintaining signal quality and allows for measurements of turbid samples. This paper discusses the ability of backscatter detection to accurately determine particle sizes at 1 %w/v sample concentrations and demonstrates the correct resolution of different size populations using a series of latex standard mixtures with known volume ratios. The concentration of 1 %w/v is much higher than can be measured on conventional dynamic light scattering instruments.     

可见-红外波段光全散射法颗粒粒径测量范围的研究

在光全散射法颗粒粒径测量中,采用独立模式算法在可见-红外波段对粒径测量范围进行了深入的研究。通过对多种R-R分布函数反演结果进行分析,比较,以确定光全散射法颗粒粒径测量范围。同时在消光系数计算中,采用修正的消光系数代替原始的消光系数,以便得到更准确的粒径测量范围。仿真计算结果表明,在可见-红外光谱区,相对折射率m=1.235时的粒径测量范围为0.05～18 μm。在此区域内测量粒径分布,反演结果与真值基本吻合。随着颗粒相对折射率、波长范围的变化,粒径测量范围也随之发生改变。采用限制最小二乘算法能够最大限度地克服随机噪声对测量结果的影响,使测量的精度和可靠性明显提高。对测量的消光值加入±1%随机噪声时,颗粒粒径分布的反演均能得到满意的结果。     

非独立模式算法下粒径分布反演及分类的研究

在光全散射法颗粒粒径测量中,提出一种非独立模式算法下粒径分布反演及分类的方法。对被测颗粒系分别按照不同的粒径分布函数同时进行反演,并依据反演误差大小判断被测颗粒系符合哪种分布函数。仿真实验结果表明,在非独立模式下,完全可以利用已知的不同分布函数的反演误差作为分类依据,从而更准确地确定被测颗粒系的粒径分布。采用的遗传反演算法能够在3个可见光波长下得到较准确的粒径分布,反演结果稳定可靠,最大限度地减少了多个波长的使用,从而对光源有更大的选择余地。对透射消光测量结果加入5%随机噪声时,单峰分布颗粒系的反演误差小于5%,多峰分布颗粒系的反演误差小于10%。整个算法运行时间小于2 s。该方法具有原理简单,计算速度快等优点,能够满足颗粒粒径在线测量的要求。     

Particle Size Distribution Retrieval from Elastic Light Scattering Measurements by a Modified Regularization Method

Retrieval of polymeric emulsions Particle Size Distribution (PSD) from Elastic Light Scattering (ELS) measurements requires the solution of an ill conditioned inverse problem. In this paper we compare the performance of classical regularization methods such as Truncated Singular Value Decomposition and Tikhonov's, to a regularization technique due to Pike that includes positivity constraints on the PSD. We also propose a new method that combines Tikhonov's approach with Pike's method. Simulated ELS measurements for two polymeric materials were generated under different experimental noise assumptions. Uncertainties on the polymer refractive index value were also considered. The PSD estimations obtained show that the implementation of the proposed more sophisticated algorithm is convenient for this very ill‐conditioned problem.     

Investigations on the Capability of the Statistical Extinction Method for the Determination of Mean Particle Sizes in Concentrated Particle Systems

Due to the fast growing number of processes involving particulate systems, simple and robust measurement techniques which enable an inline monitoring of the particle size and their concentration are urgently required, since this ensures control but also process optimization. In this work, an inline measurement technique based on the statistical extinction method is developed that provides a process monitoring for a wide range of particulate processes, such as dispersion processes and spray processes. The method allows the determination of the mean size and concentration for particle systems with the size larger than 1 µm. For this purpose, a light beam illuminates the particle system, whereby the fluctuating light intensity due to the particle movement through the light beam is detected. The statistical fluctuation of the signal can be related to a mean particle size and a particle concentration. Since concentrated particle systems cause effects that additionally influence the signal, such as multiple scattering, approaches are needed to reduce or eliminate these effects. In this work, an approach using a spatial frequency filter is applied. The experimental investigations reveal that the effects can be significantly reduced with the spatial frequency filter.     

光复散射对消光法粒径测量的影响:复散射模型与数值模拟

复散射效应在光散射颗粒测量中不仅重要．且尚未得到很好解决。采用蒙特卡罗方法,对不同的光波长,颗粒浓度以及收接器条件下的光复散射进行了数值模拟．数值算法程序经与四通量模型进行对比验证,数值结果与单散射条件的郎伯-比尔模型进行比较．进而讨论了复散射效应对消光法颗粒粒径测量影响。表明复散射对消光法颗粒测量的影响不仅取决于颗粒系自身的浓度．而且接收器的几何尺寸和接收位置起着非常重要的作用,减小颗粒介质层厚度和减小光接收器接收面积．增大接收距离以及减小接收角都能减小复散射效应对消光法粒径测量的影响。     

动态光散射测量粒径分布的格雷码编码遗传算法反演运算

采用格雷码编码的遗传算法对动态光散射测量的粒径分布进行反演运算,数字测试结果表明,对于无噪声的分布,算法能精确的反演出各种粒子分布图像;对于加了一定噪声的分布,算法显示出较好的稳定性,能反演出主峰的分布图像.聚苯乙烯乳球的实验结果表明,该算法能反演双分布的粒径分布图像.与标准遗传算法和反演蒙特卡罗算法相比,该算法具有较高的搜索效率,能够用较少的计算时间快速搜索到最优解.格雷码编码遗传算法是一种更有效的随机反演算法.     

基于PCA-BP神经网络的光谱消光法颗粒粒径反演算法研究

光谱消光法广泛应用于颗粒粒径测量领域,在利用光谱消光法对颗粒粒径进行反演的过程中,由于颗粒的消光系数存在理论复杂、计算繁琐、收敛速度慢以及求解不稳定等问题,很大程度上影响了整个反演过程的快速性和准确性。且在众多波长的消光数据中,存在较多重复冗余的信息,也很大程度上增加了反演算法的时间。针对光谱消光法粒径反演算法计算繁琐、反演效率低的问题,提出了基于主成分分析（PCA）和BP神经网络的光谱消光颗粒粒径分析方法。基于Mie散射理论对不同粒径、不同波长下的光谱消光值进行了仿真计算,通过对光谱消光数据集的主成分分析及各个波长综合载荷系数的计算,实现了最优特征波长的选取,利用降维后的光谱消光数据训练了PCA-BP神经网络模型,并利用该网络模型计算了粒径颗粒分布。通过仿真计算,比较了PCA-BP神经网络模型与传统的BP神经网络模型的预测精度,并分析了波长数目对两种神经网络模型预测结果的影响。针对训练得到的PCA-BP神经网络模型开展光谱消光法粒径参数反演算法的验证实验,搭建了光谱消光法颗粒粒径参数测量实验系统,测量了粒径范围在0.5～9.7 μm内的6种不同粒径参数的聚苯乙烯标准颗粒。仿真和实验结果表明：基于主成分分析方法可确定各个波长向量之间的相关性,利用综合载荷系数选取最优特征波长对应的消光值对整体的光谱数据具有较好的代表性,可实现光谱数据的降维。相比传统的BP神经网络模型,基于PCA-BP神经网络模型的颗粒粒径分布的分析方法预测精度更高,对于较分散颗粒系的分布参数的预测有更加明显的优势。而且,被选取的波长数较少时,PCA-BP神经网络模型依然有较高的预测精度。利用训练好的PCA-BP神经网络模型对颗粒粒径参数进行实验验证,预测结果可瞬时输出,颗粒粒径分布误差在5%以内,验证了该算法的可行性。     

Particle Size Distributions from Static Light Scattering with Regularized Non‐Negative Least Squares Constraints

Simulated data from static light scattering produced by several particle size distributions (PSD) of spherical particles in dilute solution is analyzed with a regularized non‐negative least squares method (r‐NNLS). Strong fluctuations in broad PSD's obtained from direct application of NNLS are supressed through an averaging procedure, as introduced long ago in the inversion problem in dynamic light scattering. A positive correlation between the best PSD obtained from several averaging schemes and the condition number of the respective data transfer matrices was obtained. The performance of the method is found to be similar to that of constrained regularization (CONTIN), which uses also NNLS as a starting solution, but incorporates another regularizing strategy.     

基于模式搜索的光谱消光粒径分布反演算法的研究

发展快速有效的反演算法用于粒径分布的重建是颗粒测量领域重要的研究课题之一。在光谱消光法粒径测量中,提出将模式搜索算法用于独立模式下粒径分布的重建,同时引入Tikhonov平滑泛函构建算法的目标函数,为保证搜索过程的快速性和准确性,设计了关于初始点的优选策略。利用该算法测量国家标准颗粒体积平均直径的相对误差为3.14%,不超过国家标准物质局给出的±8%的范围,且粒径分布宽度合理,没有明显展宽和伪峰现象。与Phillips-Twomey方法和遗传算法的对比结果表明,在综合考虑反演精度和反演时间条件下,该算法具有明显优势,更适合于快速准确的现场测量,具有较好的应用前景。     

The Fundamentals of Particle Size Analysis by Transmission Fluctuation Spectrometry.

A transmission signal measured on a flowing suspension of particles with a high spatial and temporal resolution shows significant fluctuations, which contain the complete information on particle size distribution and particle concentration. In Parts 1 and 2, the basic properties of signal fluctuations were studied for temporal averaging by a gliding time window and for spatial averaging by a circular beam of uniform intensity. However, the experimental implementation of such conditions is difficult. Now, the theory is extended for Gaussian beams of variable diameter and averaging by signal filtering in the frequency domain. This provides the basis for an experimental implementation by transmission of a laser beam and analog signal processing by an array of low pass filters.     

基于光阻法的小光束截面粒径信息提取方法

为了实现同时兼顾大、小颗粒测量的液体颗粒计数,在分析细小光束照射下球形颗粒脉冲信号波形特征的基础上,提出了一种颗粒粒径信息提取方法,该方法通过对脉冲信号积分将颗粒脉冲信号的幅度与持续时间结合,可更加准确地提取颗粒的等效粒径信息.对理想脉冲信号进行数值模拟,并采用乳胶微粒标准物质进行实验测试,结果表明,该方法能够有效地提取大颗粒和小颗粒的粒径信息,从而拓宽了仪器检测范围.同时,分析了流速和噪声对该方法提取粒径准确性的影响,结果表明当流速波动小于10%时,测量误差小于5.41%;当噪声小于1%时,测量误差小于0.50%.     

Determination of Soot Particle Size in a Premixed Flame: a Static and Dynamic Light Scattering Study

In this contribution we report upon our static and dynamic light scattering experiments to characterize soot particles in flames. We studied sooting laminar premixed flame with acetylene as fuel mixed with air as oxidizer. The air equivalence ratio of the combustion was larger than one. We used a Kaskan type burner with circular geometry and a stabilizing flow of nitrogen around the flame. We focused on the determination of the size of the soot particles in the center of the flame as a function of height above burner. In addition we investigated the influence of the mixing ratio of the gases on the size of the particles. Our results show that static light scattering is better suited than dynamic light scattering for a fast and reliable characterization of soot particles in flames. The latter needs detailed a priori information about the flame to allow the unique determination of sizes from the diffusion measurements. The soot particles grow monotonously with height above burner and with decreasing air equivalence ratio. The aggregates have a fractal dimension lower than two.     

Particle Size Analysis by Transmission Fluctuation Spectrometry: Experimental Results Obtained with a Gaussian Beam and Analog Signal Processing

Transmission fluctuation spectrometry (TFS) is a method for the analysis of particle size distributions based on the statistical fluctuations of a transmission signal. Complete information on the PSD and particle concentration can be retrieved by a special transformation of the transmission signal, whereby the expectancy of the transmission square (ETS) is determined after the signal has been subjected to a procedure of spatial and temporal averaging. By varying the averaging parameters over a wide range, a spectrum of ETSs is obtained and introduced into a linear equation system, which yields the PSD. In the experimental realization presented here, variable temporal averaging is realized in the frequency domain with a series of low pass filters at different cutoff frequencies while spatial averaging inevitably occurs as the particles pass through a focused Gaussian beam of finite cross section. Experimental results on spherical particles (glass beads) and non‐spherical particles (SiC) are presented. The PSDs are resolved in 30 intervals within a particle size range from 1–1000 μm, employing a modified Chahine inversion algorithm. So far, the measurements are limited to moderate particle concentrations. Some influences affecting the measurements, especially for higher particle concentrations, are discussed in detail.