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Transmission of light by dispersion is, among other factors, a function of the number concentration of particles in dispersion. Given that the number, N, of particles in a volume of dispersion is a Poisson-distributed random variable (for example, http://mathworld.wolfram.com/PoissonDistribution.html), the number of particles in different volumes of dispersion varies. The relative magnitude of these variations (fluctuations) equals 1/sqrt(N), i.e. increases with decreasing N. Thus, the transmission of light by a volume of dispersion, sufficiently small so that the relative magnitude of the particle number fluctuations is significant, does fluctuate as well.
Such fluctuations can be readily measured, for example, by measuring transmission of dispersion flowing past a stationary light beam. Gregory J 1985 shown that by measuring transmission fluctuations, one can determine the concentration of monodisperse particles without having to know or calculate optical properties of the particles such as the attenuation cross section. By measuring the average transmission itself, one can also determine the particle size.
In the Gregory’s technique, the Poisson distribution of the particle number within a volume of a dispersion implies that the measuring volume should be much larger than the volume of a single particle, so that several particles could be found in the measuring zone. However, the increase of the measuring volume diminishes the spatial resolution of the measurement and leads to the decrease of the signal fluctuations. Recently, Shen J et al 2008c indicated that, by using a new model which was originally proposed by Kräuter U 1995, it is possible to measure the particle size and concentration of the monodisperse particle system even if the beam size is much less than the particle size.
Transmission fluctuations have been more recently shown to enable the measurement of PSD. In this capacity, the measurement of transmission fluctuations is referred to as the transmission fluctuations spectrometry (TFS).
| CITATION: Shen J., Jonasz M. 2006. Transmission fluctuations: Introduction (www.tpdsci.com/Tpc/TF.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 17-Jan-2006 Modified: 14-Dec-2011 Peer-reviewed: 03-May-2006 |
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