Thesis-2000-Barnett.pdf (26.09 MB)
On multiple optical scattering in a scanning nephelometer
thesis
posted on 2010-11-18, 11:46 authored by David M. BarnettOptical nephelometry is the measurement of the angular distribution of light scattered from a
particle suspension. Experimental nephelometers confirm the predictions of optical models
and their readings are inverted to determine properties of unknown suspensions.
Single scattering models, which assume a single particle interaction prior to detection, are
used to model tenuous suspensions in the nephelometer. Multiple scattering models can be
used to obtain higher-order solutions, but lack generality. Any given method addresses some
subset of possible problems, e.g. tenuous or dense suspensions, small or large particles. This
thesis explores the feasibility of using empirical models to extrapolate the single scattering
approach in a non-linear manner, improving the generality of a multiple-scattering
description.
Initially, single scattering (Mie) theory for spherical particles is presented and extended to
polydispersions of particles and to spectral scattering. The principle of integrating the single
scattering result over a finite scattering volume is examined as a precursor to modelling the
actual nephelometer.
A low-cost, PC controlled scanning nephelometer is developed with a 0.9° resolution and
±150° range and a small (-25ml) volume sample cell. The photodiode detector has a
numerical aperture of 0.079, providing, for most angles, a scattering volume with length
10mm and cross-section determined by the HeNe laser source ('-1mrn 2). The optics of the
air/glass/water interfaces and of single and first-order multiple scattering over the scattering
volume are modelled. These models are found to predict the scattering footprints observed
in tenuous suspensions of spherical latex particles.
Experimental data are obtained from tenuous to relatively dense (5% by volume)
suspensions of latex spheres over a size range of 54nm to 14tm. These data are compared
with single and first-order multiple scattering and their form and dependencies are
considered.
They are used to train an empirical neural (multi-layer perceptron) model of the multiple
scattering based on particle characteristics and on the scattering footprint of the individual
particles. This non-linear extrapolation of the single scattering model is applied to the
nephelometer, improving the generality over a purely theoretical multiple scattering
approach. The trained neural model is used, initially, to investigate some of the empirical
characteristics of the multiple scattering process.
History
School
- Mechanical, Electrical and Manufacturing Engineering
Publisher
© David M. BarnettPublication date
2000Notes
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.EThOS Persistent ID
uk.bl.ethos.323870Language
- en