Sivakumar Manickavasagam

Scattering matrix elements of fractal-like soot agglomerates

The possibility of measuring scattering-matrix (Mueller matrix) elements of soot agglomerates with laser diagnostic techniques is explored. To show this, we calculated the scattering-matrix elements of arbitrary-shaped soot agglomerates. The sensitivity of scattering-matrix elements to optical and morphological characteristics of fractal-like soot agglomerates is discussed. Finally, possible measurement techniques are suggested to identify soot structures from scattering-matrix elements.

Characterization of size and structure of agglomerates and inhomogeneous particles via polarized light

Characterization of size and structure of small particles is required in many fields, including environmental and process control and monitoring, biological and pharmaceutical research, atmospheric remote sensing, as well as combustion systems. In this paper, the use of polarized light and the concept of Mueller matrix elements for possible particle characterization studies is discussed. A summary of the research carried out in our laboratory for application to agglomerates and inhomogeneous spherical and cylindrical particles is presented. Sensitivity of the technique on a number of diAerent physical parameters is outlined. Finally, an inverse solution methodology is discussed to identify particle/ agglomerate characteristics. # 1998 Elsevier Science Ltd. All rights reserved.

Scattering-matrix elements of coated infinite-length cylinders

The angular variations of scattering-matrix elements of coated cylindrical particles are presented. The sensitivity of different elements for a number of physical parameters are discussed, including size parameter, real and imaginary parts of the refractive index of the outer coat, and the inner core. The numerical predictions are presented for typical index-of-refraction values of cotton fibers. These results show that the physical structure of coated cylinders can be determined from carefully conducted light-scattering experiments.

Chaotic map models of soot fluctuations in turbulent diffusion flames

Abstract In this paper, we introduce a methodology to characterize time-dependent soot volume fraction fluctuations in turbulent diffusion flames via chaotic maps. The approach is based on the hypothesis that fluctuations of properties in turbulent flames are deterministic in nature, rather than statistical. Our objective is to develop models of these fluctuations to be used in comprehensive algorithms to study the nature of turbulent flames and the interaction of turbulence with radiation. To this end we measured the time series of soot scattering coefficient in an ethylene diffusion flame from light scattering experiments and fit these data to linear combinations of chaotic maps of the unit interval. Both time series and power spectra can be modeled with reasonable accuracy in this way.

IDENTIFICATION OF NON-HOMOGENEOUS SPHERICAL PARTICLES FROM THEIR SCATTERING MATRIX ELEMENTS

In this paper, a procedure is described to identify the structure of inhomogeneous spherical particles using polarized light. The scattering (Mueller) matrix elements are shown to provide valuable information about the spatial variation of the optical properties of a scattering particle. Two non-homogeneous systems are considered, i.e., a water droplet with soot accumulating at its surface and a coal particle surrounded by a soot cloud. For both systems, the results show that the Mueller matrix elements are sensitive to the thickness of soot layer and soot volume fraction on the surface layer. If the angular variation of the scattering matrix elements can be accurately measured, it would provide an important diagnostic tool in detecting the presence of inhomogeneity in the scattering particle. Since the elements vary considerably with changing soot volume fraction, an accurate measurement would also provide important quantitative information about the soot present in the shell layer. Copyright 0 1966 Elsevier Science Ltd

Effect of Particle Shape Irregularities on the Angular Profiles of Scattering Matrix Elements

We discuss a methodology to determine the scattering characteristics of irregular-shaped particles. We concentrate on particles with sharp edges and broken corners in order to simulate actual ceramic and metallic particles. A volume-integral formulation (encoded in AGGLOME) is used to determine the angular profiles of their scattering matrix elements. A compendium of results is given in a series of figures. These numerical results show that if the scattering matrix elements of such irregular shaped particles are measured in carefully conducted experiments at specified angular regions, their shapes and sizes can be inferred. INTRODUCTION Characterization of size and structure of small particles is required in many fields, including process control and monitoring, biological and pharmaceutical research, atmospheric remote sensing, environmental pollution detection, as well as combustion systems. During the last decade, using the elliptically polarized light scattering concept, we have investigated spherical and cylindrical particles, as well as agglomerates. This approach is based on the measurement of the scattering matrix elements of single scatterers and is known to be the most comprehensive particle characterization methodology. There are several accounts available in the literature that focus on calculation of the irregular shaped particle properties. A detailed review of past models was given in a book compiled by Mischenko et al. and was recently the focus of a conference dedicated to light scattering techniques. Unfortunately, the data available for the scattering matrix elements of irregular shaped particles are quite limited. In this paper, we extend the available data base to irregularly shaped particles. Below, we discuss the ________________________ †Ph. D. Candidate, Radiative Transfer Laboratory ‡Professor, Radiative Transfer Laboratory, menguc@engr.uky.edu effects of shape, size, degree of irregularity, the complex index of refraction, and wavelength on the scattering matrix elements of cubical, rectangularpiped, and pyramidal particles. These structures are quite common in practice, as the lattice structure of metallic compounds favor formation of these shapes. In addition, imperfections in a given process, as well as natural grinding and collision between the particles, yield broken structures. It is imperative to understand the effect of shape and imperfections on the scattering signals from these particles in order to characterize these particles via light scattering techniques. ANALYSIS AND FORMULATION The analysis we present here is based on the measurement of the polarization of the scattered light by a cloud of particles. If we know how a given particle changes the polarization of incident light, then we can use that information as its “fingerprints” and estimate the shape variations. To do this, we need to understand the relationship between the change in polarization of the incident and scattered waves. The polarization state of a beam can be described as a column vector of the four Stokes parameters. Here, for clarity, we omit the multiplicative factor k/2ωμ, and use the brackets to indicate the time-averages: These four parameters can be obtained by using a set of four filters in front of the incident beam. If the first filter is isotropic, it allows all the energy to go through. The other three are polarizing filters: the second one is a linear polarizer oriented horizontally, the third is a linear polarizer oriented at 45 degrees from horizontal in the clockwise direction, and the fourth is a circular polarizer. By measuring the irradiance that passes * // * // * // * // * * // // * * // // E E E E i V E E E E U E E E E Q E E E E I

Scattering matrix elements of fractal-like soot agglomerates: erratum

The possibility of measuring scattering-matrix (Mueller matrix) elements of soot agglomerates with laser diagnostic techniques is explored. To show this, we calculated the scattering-matrix elements of arbitrary-shaped soot agglomerates. The sensitivity of scattering-matrix elements to optical and morphological characteristics of fractal-like soot agglomerates is discussed. Finally, possible measurement techniques are suggested to identify soot structures from scattering-matrix elements.