基于Mie散射理论的微球体颗粒数值模拟计算和实验研究

应用Mie散射理论,在散射角0～π范围内,模拟微球体颗粒的散射光强度与粒径大小的变化关系,分析了相对折射率的大小对散射光强度的影响;在实验装置条件下,分别模拟了散射光强度与粒径大小的变化关系及2um、5um、10um三种粒子的散射光强度与波长的变化关系。实验验证了数值模拟与实验结果基本一致,也证明实验中粒子散射遵从Mie散射理论模型。     

球形粒子对平面偏振光散射的数值计算与分析

论文在Mie理论基础上,给出了球形粒子对平面偏振光的散射强度和散射系数公式,利用连分式递推算法进行了编程计算,重点对1.06μm激光的模拟结果进行了分析.从得到的散射图像可以看出,散射强度角分布与散射粒子尺度有密切关系,随着粒子尺度的逐渐增大,散射光强主要集中到前、后向散射方向,集中的角度越来越窄,模拟结果明显出现了散射强度最弱的极值角,且该极值角随粒径的增大而增大,最后逼近90°方向.散射强度角分布与波长有关,当它们在同一数量级时达到最大值,与散射粒子折射率无关.该递推算法因为每一步计算都是独立的,与前后项的准确性没有关系,不存在不稳定、发散等情况,能够计算粒径参数范围从10-4开始,对上限不受任何限制.     

焦区附近球形粒子对高斯光束的弹性散射

本文应用复源球面波理论,将高斯光束场按矢量球波函数展开,对高斯光束入射到单个球形粒子上时的弹性散射问题进行了理论分折。并对球形粒子在波束传播轴上时的远场散射光强角分布进行了数值计算,同时还与平面波散射的结果进行了比较。     

超细颗粒物近场散射光场分布特性研究

为研究超细颗粒物近场散射光强分布的特性,应用了时域有限差分方法系统对不同尺寸微小颗粒的近场散射光强进行分析。对于单颗粒的散射光场,颗粒越小,散射光主要表现为各向同性,随着颗粒增大,前向散射光将占主要部分,这与传统的Mie散射理论相一致。对于紧靠的两个颗粒,由于多重散射的作用,散射光场表现出更多的复杂性,两个颗粒的排列方式不同也会对结果有较大影响。这些结果为进一步分析复杂颗粒系统的光散射特性提供了基础。     

Mie理论在静态光散射粒度测量的应用下限研究

测量下限是光散射颗粒测试技术的关键问题。本文通过理论分析、比较归一化散射光强的分布图和构造方差函数F(d)对颗粒散射光的光强分布进行了定性和定量的讨论,对Mie散射向Rayleigh散射趋近的情况进行了分析,讨论了散射光光强大小的分布,分析了测量不同粒径的颗粒的可行性,最终得到在入射光源是波长为0.6328μm的He-Ne激光器的情况下,当粒径d取200nm以上时,不同粒径颗粒的M ie散射光强分布有较大差别,适合用静态光散射的方法来判断颗粒粒径。     

粗糙表面镜向散射光强统计

粗糙表面散射可分为镜向散射和非镜向散射,镜向散射光强的分析不仅具有理论上的简洁性,而且能够给出粗糙表面散射的一些重要特性.论文根据相干散射和傅里叶光学理论,对粗糙表面的镜向散射光场进行了理论分析和推导,结果表明:镜向散射光场的主要特征由粗糙表面高度分布的傅里叶变换和入射光场的傅里叶变换共同决定.对于均匀平行光照射高斯表...     

生物组织微弱散射光的检测装置

首先讨论了生物组织中光传播的高散射特点以有散射光测量方法,建立了组织散射光检测装置,分析了光电池的光电特性及其用于生物散射光检测的可行性。并通过实测给出了使用光电池对人体皮肤、腺瘤等组织的散射光信号的检测结果。     

基于拉曼散射分布式光纤测温系统的理论分析

对分布式光纤测温系统涉及的光时域散射技术与自发拉曼散射进行理论分析,给出拉曼散射的定量描述,论述了斯托克斯拉曼散射光与温度的关系,纠正了斯托克斯光与温度无关的错误认识,统一了理论与实际应用中关于斯托克斯光与温度关系的认识,最后确定了利用反斯托克斯拉曼散射光功率曲线解调瑞利散射光功率曲线的表达式,为分布式光纤测温系统进行温度解调提供参考.     

X射线散射光子对剂量当量电离室影响

为了测量X射线辐射散射光子对剂量当量电离室的影响,根据ISO-4037建立X射线防护水平参考辐射场.采用PTW-32002 1L和PTW-32003 10L两个不同体积的球形空腔电离室在不同辐射质条件下通过影锥屏蔽法测量散射光子对不同电离室的影响程度.实验结果表明:散射光子对不同体积电离室影响程度不同,对于10 L球形电离室散射份额在2％左右,而对于1L球形电离室散射份额在4％左右.能量越高,散射光子的散射份额也会相对增大.     

激光损伤的光散射法判别研究

在激光损伤测量系统中,利用光散射法判别激光薄膜损伤,需要寻求光源和探测器之间的最佳位置。为此,在不同损伤激光脉冲能量、不同测量入射角度(0°,30°,45°,60°)和不同探测器距离(200,250 mm)条件下,研究了损伤点散射光能量的角分布。获得结果如下:在相同的探测角度上,散射光能量随着损伤面积和测试光入射角度增加而增加。在探测角度小于反射角度时,随着探测角度增加散射光能量逐渐变强;当探测角度大于反射角度后,随着散射角度增加散射光能量逐渐变弱。散射光相对能量在反射光方向附近出现极大值;在60°入射时,散射光相对能量具有最大值;探测距离在200 mm时,最大散射光相对能量大于探测距离在250 mm时。根据以上结论,可以确定在利用光散射判别损伤的测量系统中,探测器应放置在反射光方向的两侧,并且尽量增加测试光入射角度和缩小探测器与样片间距离。     

Photon correlation spectroscopy on flowing polydisperse fluid-particle systems: theory

We develop an analytical expression for the homodyne autocorrelation function of laser light scattered by a laminar flow of a polydisperse particle-fluid system. In contrast to the already existing literature on the development of autocorrelation functions, we explicitly begin with the effects of the finite linewidth of the light source, the spatial and temporal intensity averaging that is due to the detection process, the Brownian particle movement on the amplitudes of the scattered light waves as well as on the degree of resolution that we introduce in this paper, and a general system velocity v = (v(x), v(y), v(z)). One main result is a new physical interpretation of the well-known, generally empirically introduced coherence factor. Quantities that are comparable to the well-known degree of coherence, coherence area, and number of coherence areas have also been obtained. Finally the investigations are simplified to an autocorrelation function that can be used for the analysis of fluid-particle systems in the low Knudsen number regime. It is shown that in this case particle size or size distribution, system velocity, and particle concentration can be obtained simultaneously. The developed autocorrelation function is related to frequently analyzed special cases and compared with expressions from the literature.     

Probing creep motion in granular materials with light scattering

We describe a dynamic light scattering experiment designed in order to study creep motion in granular materials. This method is based on the recording of the speckle pattern with a charge coupled device (CCD) camera. The autocorrelation function of the scattered electric field is calculated and related to the displacement field of the beads. As an application, the measurement of the thermal expansion of a granular material subjected to temperature variations is presented.     

Particle image velocimetry analysis using an optically addressed spatial light modulator: effects of nonlinear transfer function

Optical processors for generating a two-dimensional squared autocorrelation function have been presented for postprocessing particle image velocimetry photographs of fluid flows. The incoherent-tocoherent conversion can be performed by an optically addressed spatial light modulator. The transfer function of these devices is far from linear and will influence the performance of the optical processor.

Two different transfer functions, characterizing the two main types of commercial optically addressed spatial light modulators as an analog and a binary transfer function, have been simulated digitally.

Results of numerical simulations on the influence of introducing these nonlinear transfer functions to the correlation function for particle image velocimetry analysis are presented.

     

Electro-orientation in particle light valves

Electro-orientation of rod-like particles in liquids, under the application of an external AC field, is analysed. A rod shape is suitable for particle light valve (PLV) applications. When they are aligned with their long axes parallel to the electric field (and the direction of light is assumed to be parallel to the applied electric field), then it can lead to good transmission of light. Various criteria to arrive at appropriate parameters for PLV applications are proposed. It is found that good electric conductors are excellent rod materials for PLV applications. They lead to an appropriate orientation of the rods and at the same time result in maximum orientational torque. Water-like liquids with higher values of permittivity are appropriate choices as suspending liquids since the Brownian dispersion in the presence of the electric field is minimized. The time it takes the rods to fully diffuse in the orientational space, once the electric field is turned off, decreases with decreasing liquid viscosity.     

Magnetophoretic velocity modulation mass analysis of a single microparticle in an atmosphere

A new principle of the magnetophoretic velocity modulation mass analysis of microparticles, which can determine simultaneously the mass and magnetic susceptibility of a single microparticle, has been proposed, and the measurement system was constructed by applying a magnetophoretic force on a falling microparticle through a magnetic field gradient in an atmosphere. A polystyrene microparticle as a test particle adsorbed on a glass plate was selectively knocked off by a pulsed Nd:YAG laser impact into a narrow gap of pole pieces of permanent magnets having a magnetic field gradient with a maximum intensity of 850 T2 m(-1). The falling particle was irradiated by a He-Ne laser, and the scattered light was detected through a slit array mask as a function of time. A bundle of spiked signals of scattered light intensity was analyzed to obtain velocities, which gave acceleration and deceleration of the falling particle. On the basis of the equation of motion under the magnetic field gradient, the mass and magnetic susceptibility of the test particle were reasonably determined.     

Low-coherence light-scattering calculations for polydisperse size distributions

The calculation of angular light-scattering distributions is considered for low-coherence light incident on a polydisperse particle size distribution of scatterers. As low-coherence light is now commonly used in interferometry schemes when applied to biomedical imaging, the difference between detecting scattered intensity and interferometrically detecting the scattered field is examined. An expression is derived that allows the presence of multiple wavelengths lambda and particle sizes d to be described by a single distribution in the size parameter x = pi d/lambda, which simplifies numerical calculations. The applicability of this expression is examined numerically.     

Material dependent dielectric breakdown model

Dielectric breakdown in ceramics and composites has previously been determined by the dielectric breakdown model, dependent only on the electric field strength at a certain point and intermolecular distance in a lattice. This does not take into account quantum aspects of the lattice structure into account. The present model takes into account quantum variations of particles in conjunction with different particle characteristics. Dielectric breakdown patterns are characterised by their quantum breakdown probabilities and studies are carried out as a function of the applied electric field, temperature and specific material constants responsible for breakdown, such as the mean free path and the potential barrier present.     

基于FPGA高速信号采集的多角度动态光散射法纳米粒径测量

根据动态光散射装置测量纳米粒径原理,开发了一套基于现场可编程门阵列(FPGA)的纳米粒径测量系统。该系统通过光电倍增管(PMT)输出光子脉冲信号,利用FPGA实现高速脉冲采集及自相关运算,采用双脉冲计数器实现高精度可控的连续计数,并实现DDR3异步存储以及USB通信交互等接口功能。自研板卡既可实现自相关函数实时采集运算,又可无丢失地保存海量原始数据信号。采用该系统对200nm聚苯乙烯颗粒进行了测量,分析了不同采样时间及延迟时间等参数对粒径测量结果的影响。实验结果表明:自研FPGA采集板卡测量重复性为1.2%,具有很好的稳定性和重复性。     

Pulsed laser technique application to liquid and gaseous flows and the scattering power of seed materials

Mie scattering computations have been performed for light scattered by small particles from a pulsed sheet of laser illumination and collected and imaged by a camera lens. From these computations the smallest particles that can be photographed in various fluid measurement situations, including air and water, have been determined in terms of system parameters such as laser power, light sheet geometry, f/No., and photographic film properties. The particle scattering requirements of the individual particle image mode and the speckle mode are compared.     

Detection of process upsets—sample autocorrelation control chart and group autocorrelation control chart applications

This paper presents an application of the sample autocorrelation function to statistical process control where the process data are serially correlated. Two innovative control charts are illustrated: the sample autocorrelation control chart and the group autocorrelation control chart. The important feature is that these control charts will detect shifts in the autocorrelative structure as well as shifts in the mean of the process. The sample autocorrelation function is typically used to identify an appropriate ARIMA model for a time series. The sample autocorrelation function may also be used as the basis of control charts to detect process upsets. Two unique features distingush this application of the sample autocorrelation function to statistical process control. First, the sample autocorrelations are exponentially smoothed estimates. This allows the user to control the sensitivity of the sample autocorrelation control chart. Secondly, the sample autocorrelation control chart is applied to a continuous stream of data—rather than to a static set of data that has been used to fit an ARIMA model.