Anomalous diffraction approximation method for retrieval of spherical and spheroidal particle size distributions in total light scattering

Using total light scattering technique to measure the particle size distribution has advantages of simplicity in measurement principle and convenience in the optical arrangement. However, the calculation of extinction efficiency based on Mie theory for a spherical particle is expensive in both time and resources. Thus, a simple but accurate approximation formula for the exact extinction efficiency may be very desirable. The accuracy and limitations of using the anomalous diffraction approximation (ADA) method for calculating the extinction efficiency of a spherical particle are investigated. Meanwhile, the monomodal and bimodal particle size distributions of spherical particles are retrieved using the genetic algorithm in the dependent model. Furthermore, the spheroidal model in the retrieval of non-spherical particle size distribution is also discussed, which verifies the non-sphericity has a significant effect on the retrieval of particle size distribution compared with the assumed homogeneous isotropic sphere. Both numerical computer simulations and experimental results illustrate that the ADA can be successfully applied to retrieve the particle size distributions for spherical and spheroidal particles with high stability even in the presence of random noise. The method has advantages of simplicity, rapidity, and suitability for in-line particle size measurement.     

Testing a new photocentrifuge for submicron particles with silica spheres

A theory has been developed for spectral photosedimentation in a centrifuge. The use of several wavelengths allows particle size analyses in the submicron range without a knowledge of the optical material properties and is not restricted to spherical particles. As a result of this theory the extinction efficiency and the particle size distribution of the analysed particles can be calculated even for non-spherical particles from an experiment. A photocentrifuge has been built according to the developed theory. The theory has been verified by the measurement of spherical particles for which Mie theory is applicable. The experimentally obtained extinction efficiency agrees well with computations according to Mie theory. The accuracy of measured particle size distributions is comparable to those measured with other sedimentometers.     

On the Sizing Accuracy of Laser Optical Particle Counters

The performance of a narrow-angle and a wide-angle, forward scattering laser aerosol spectrometer has been studied as a function of particle size and refractive index. The results have been compared with theoretical calculations based on light scattering theory. The results indicate that for the narrow-angle instrument, the scattered-light intensity is not a monotonic function of particle size for transparent particles (a monotonic relationship is required for unambiguous particle size measurement) above 0.7 μm. The instrument is therefore limited in its useful range to size distribution measurement between 0.2 μm – its lower particle size limit – and 0.7 μm for transparent particles. In the case of the wide-angle instrument, the instrument output is a monotonic function of particle size for transparent particles, but the output is severely attenuated for light absorbing particles above 0.3 μm. The instrument, therefore, cannot be used for accurate size measurements above 0.3 μm for light absorbing particles.     

Size Measurement of Small Magnetic Particles

Many different methods for size measurement are known and since they differ in their physical principles, different results are also obtained. In the recent past, there were rapid developments in new measurement techniques and one can now quickly and routinely determine particle sizes in the very fine range. Smaller particle sizes, on the other hand, tend to increase the probability of agglomeration. The measurement of the particle sizes for magnetic materials is not well understood and this paper reports results regarding the size determination of very fine magnetic materials. Because of their dipole moment, these particles tend to agglomerate even more, which in turn causes certain difficulties during the measurements. Wet and dry laser measurement systems were compared and also magnetic materials with different permeabilities in order to establish the influence of individual factors on the measurement process and on the accuracy of the results obtained.     

光散射法测量颗粒尺寸、浓度的实验研究

为了能够准确快速地求解出微米量级颗粒系的尺寸和浓度,设计了一套基于Fraunhofer衍射,以线阵CCD为接收器件的实验颗粒测量装置.采用Shifrin积分变换方法,分析了给定样品颗粒的粒径分布、峰值、平均值和体积浓度.实验结果表明,与传统的Swithenbank方法采用环形光电管阵列为探测器接收衍射光强来反演颗粒分布方法相比,该方法不需要知道颗粒粒径上下限,各粒径区间间隔等预知信息,而且对粒径、浓度的实验测量值与理论值相差较小,样品峰值粒径为9.849 8 μm,与给定峰值的相对误差为3.432%,具有较高的测试准确度和较好的测试效果.     

随机取向椭球粒子的吸收特性

用Ｔ矩阵方法计算了折射率虚部的范围在０．００１至０．１的几种椭球粒子随机取向时在几种等效尺度参数下的光散射与吸收特性，并与等效的球形粒子的光散射结果进行了比较。分析结果表明：椭球粒子的吸收特性与等效的球形粒子的吸收特性存在着差别，这种差别随粒子的形状、尺度和折射率而改变，考虑到目前气溶胶粒子复折射率虚部的测量精度，以等效的球体粒子处理非球形粒子的吸收不会带来显著的误差。     

Simultaneous measurement of particle size, velocity, andtemperature in thermal plasmas

The in-flight measurement of particle parameters (size, velocity, temperature, and local number density) can prove insight into the plasma processing of solid materials. A measurement technique for simultaneously obtaining the size, velocity, and temperature of particles entrained in high-temperature flow fields is described. Particle size and velocity are obtained from a combination laser-particle-sizing system and laser Doppler velocimeter. The particle temperature is determined by a two-color pyrometry technique and the data rate is a measure of relative particle number density. Typical measured temperatures and velocities for the 5-100 μm particles used in plasma spraying are 1600-3500 K and 100-300 m/s, respectively. Since particle size, velocity, and temperature are measured simultaneously, cold particles (<1600 K) are identified and their relative number density can be quantified. Data from two plasma spray systems, a metal one (Ni-Al) and a metal oxide one (Al₂O₃), are presented and their application to understanding the plasma spray-coating process is illustrated     

Monte Carlo Simulations of Reflected Spectra Derived from Tissue Phantom with Double-Peak Particle Size Distribution

We made a tissue phantom with double-peak particle size distribution, which has polystyrene particles of cell nuclear size and mitochondrial size, and measured the spectrum from the tissue phantom using a single optical fiber. In this paper we investigate the characterization method for the tissue phantom with double-peak particle size distribution by comparing the measured spectra with the calculated ones using the Monte Carlo (MC) method. It is first shown that the Mie phase function characterizes better than the Henyey-Greenstein (H-G) phase function in MC calculation. Next, we compare the measurement spectra with those obtained by modeling as single-peak, conventional modeling for particle size distribution, and for double-peak particle size distribution. The single-peak modeling is found to cause considerable error for the tissue phantom with double-peak particle size distribution, which seems to simulate a biological tissue. We suggest that if one simulates the particle size distribution of a biological tissue by conventional modeling, the accuracy of estimation will be lower.     

双峰分布颗粒体系的多角度动态光散射数据反演

采用多角度动态光散射和加权正则化反演方法,对4组模拟的双峰分布颗粒体系(100/600 nm,200/600 nm,300/600 nm和350/600 nm)分别选取1、3、6和10个散射角进行测量.粒度反演结果表明,采用加权正则化方法反演双峰颗粒体系的多角度动态光散射测量数据,可获得峰值位置比小于2∶1且含有大粒径(＞350 nm)颗粒的双峰颗粒粒度分布.采用标准聚苯乙烯乳胶颗粒进行实测的结果验证了这一结论.得到含大粒径颗粒的双峰粒度分布反演结果的原因在于,多角度动态光散射能提供更多的大粒径颗粒的粒度信息,加权正则化反演方法能减少测量数据中的噪声,因而多角度动态光散射测量数据的加权反演能实现峰值位置比小于2∶1且含有大粒径颗粒的双峰颗粒体系的测量.     

表征超声衰减谱粒度的改进和声搜索算法

针对超声衰减谱法颗粒粒径测量,提出一种改进和声搜索算法,在和声搜索算法迭代达到200次时,加入拟牛顿算法,调节和声搜索算法全局和局部搜索能力,提高算法的收敛精度.对服从3种典型粒径分布函数颗粒系进行数值模拟,改进算法反演得出罗辛-拉姆勒(Rosin-Rammler)分布参数值相对误差小于8％,正态分布参数值相对误差小于...     

The Measurement of Particles Suspended in a stirred vessel using microphotography and digital image analysis

A novel technique to determine the size of particles suspended in a stirred vessel is investigated. The method uses microphotography to obtain a still image of the particles in situ. The equivalent circular diameter of the particles is obtained from the photographs using digital image analysis. The particles used for the test were certified particle size standards of a very small tolerance in diameter deviation. The size comparison was determined as a percent error between the measured particle diameter (equivalent circular diameter) and the diameter established by the particle manufacturer. To determine the limiting ranges of particle size and concentrations, spherical particles in a size range of approximately 1 to 10.0 μm (microns) in diameter were employed in the test. Concentrations varied from 0.00005% to 0.1% (mass basis). For each particle size, an aqueous solution of the particles was prepared at the desired concentration and placed in a stirred vessel. Photographs of the solutions were made at 25.5x, 40x, 60x and 80x magnification. For all sizes of particles, the entire range of concentration was examined. The results indicate a minimum size resolution of approximately 3μm, in a corresponding concentration range of 0.0001% to 0.05%. Similar limits on concentration were found for the larger diameter particles, although a true upper limit for the largest particle sizes was not established. The functional concentration range appears to shift towards higher mass concentrations with increasing particle size. For 2.92 μm diameter particles, the error in size measurement was found to be below 10% for a concentration range of 0.0005% to 0.05%. Additionally, a relationship between turbidity and the error was seen at low particle concentration levels where decreasing levels of turbidity generated increasing levels of error.     

PM2.5气溶胶光学特性研究

利用FA-3型Anderson撞击式气溶胶粒度分布采样器采集大气中的可吸入颗粒物。在实验室使用光学测量系统对粒径低于PM2.5的气溶胶颗粒物进行透过率测量。结果表明,透过率随气溶胶粒子粒径的增大具有逐渐增加的趋势。粒径低于PM2.5的气溶胶颗粒与PM10粒径范围内的透过率相比,具有明显的波长选择性。     

Diffusion of Anisotropic Colloidal Microparticles Fabricated Using Two-Photon Lithography

Polymeric particles with complex shapes are required for biomedical therapies, colloidal self-assembly, and micro-robotics. It has been challenging to synthesize particles beyond simple shapes (e.g., spheres, cubes) with high structural accuracy using existing methods. Here, a method for fabricating polymeric microparticles of complex 3D shapes is reported using two-photon lithography, and dispersing the particles in an aqueous solution on a glass substrate. The fabrication of polyhedrons (e.g., tetrahedron, pyramid), polypods (e.g., tetrapod, hexapod), and other shapes of 5–10 µm in size is demonstrated. Confocal microscopy is used to track the motion of the sphere, tetrahedron, tetrapod, and screw-shaped particles near the substrate, and determine their translational diffusion coefficients. HYDRO++ is used to simulate the motion of the particles far from the substrate. The influence of particle size and substrate effects on diffusion in the spherical particles is determined and finds that the non-spherical particles have increased hindrance at the substrate compared to the spherical particles.     

渤海近岸水体悬浮颗粒物对后向散射特性的影响研究

进行海洋水体悬浮颗粒物的空间分布及粒径构成对后向散射特性变化影响,研究对于加深水体散射性质的认识、提高水色遥感反演参数的精度及海洋环境监测等具有重要意义。结合渤海海域2017年6月、9月的现场数据,获得了夏季、秋季各站位总悬浮颗粒物浓度(SPM)、颗粒粒径以及后向散射系数等参数并进行研究。结果表明,后向散射系数b_bp在可见光波段随波长的增加而减小;同时,夏季和秋季,大多数站位b_bp(550)的变化趋势与SPM的变化趋势基本一致;在进行两者之间的相关性研究时发现,相关系数R2并不高,仅为0.24。该研究还建立了平均粒径(D_A)、中值粒径(D₅₀)与b_bp的关系,得出D_A与b_bp呈线性关系,受季节及水体颗粒构成的影响,夏季,水体颗粒物以小颗粒为主,两者之间的相关性高于秋季,两个季节的R2分别为0.7和0.3;同时得出当水体以小颗粒为主时,b_bp随D_A增大而增大,以大颗粒为主的时,b_bp随D_A增大而减小。D₅₀与b_bp的关系则不同,两者之间呈现非常好的幂指数关系,在同一季节里,b_bp均随着D₅₀的增大而减小,即水体中颗粒物粒径越小,其后向散射系数越大,夏季和秋季两者之间的相关系数分别为0.66和0.5;并且发现如果不分季节差异,现场水体颗粒物的粒径构成对b_bp的影响很难确定。     

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%.     

Choice of geometrical parameters of schemes for recording and reconstructing holograms of small-size particles

The effect of inequality of hologram recording and reconstruction wavelengths on the dimensions of images of microscopic particles reconstructed by using this hologram is considered within the framework of the third-order aberration theory. Recommendations on the choice of geometrical parameters of schemes for hologram recording and reconstruction providing the realization of a given accuracy of particle size measurement are given and substantiated. Limits of admissible variations of these parameters are determined.     

基于MIE散射理论的粒度分布测量系统研究

粒度测量广泛应用于粉体工程,测量结果直接影响粉体产品优劣。在深入研究MIE散射理论的基础上,提出一种基于改进反演算法的粒度测量系统设计方案,利用激光器、傅里叶透镜、光电传感器采集含有待测微粒信息的电信号,通过调理电路进行处理,应用改进反演算法分析得出粒度值及分布。通过实验验证,效的本文提出的设计方案能实现准确高粒度测量。     

Modeling Focused Beam Reflectance Measurement and its Application to Sizing of Particles of Variable Shape

A model for particle detection in focused beam reflectance measurement is presented in the general case of particles of any convex shape. Shape dependent convolution relationships between measured chord length distribution (CLD), particle size distribution (PSD) and particle mass distribution (PMD) are derived and an explicit formula for the weighting characteristic length is given in terms of particle shape. Based on the derived convolution relationships, equations relating moments of the CLD, PSD and PMD are obtained. Issues related to the definition of particle size of non spherical objects and its connection to the particle sizing technique are discussed. Based on the moment relationships, particle size is defined for focused beam reflectance measurement measurements in terms of a CLD equivalent sphere. CLD and characteristic length for a thin cylinder are obtained analytically and used as simple model in order to illustrate issues in sizing particles of variable shape. General conclusions regarding the role of the weighting characteristic length on the behavior of the measured CLD are drawn.     

Electro-optical granulometer for measurements of flowing particles

An electro-optical technique is described for the measurement of the size distribution of particles from 2.5 μm upwards, in a flow. The apparatus utilizes a white light source, a photodiode array and particle-sizing electronics. The data acquisition system is a multichannel analyser or a microcomputer. This device is an extension to the flow case of a previous device designed for static size analysis, and a critical comparison with size acquisition systems commercially available is given. Shape of particles and outline of waveform during particle detection are discussed.