Transmission fluctuation spectrometry in concentrated suspensions part two: Particle overlapping

Transmission fluctuations measured on a flowing suspension of particles with a high spatial and temporal resolution can be used to measure the particle size distribution and particle concentration. The theory of transmission fluctuation spectrometry (TFS) was recently developed, whereby the statistical behavior of the entire suspension is described on the basis of a single monolayer, in combination with a layer model describing the suspension as a series of independent monolayers. As the monolayers are assumed to be statistically independent from each other, the transmission through the 3-dimensional suspension is modeled as the product of transmissions through the monolayers. Effects from steric interactions within the same monolayer, i.e., effects from the suspension, were reported in the first part of this publication. The second part investigates the particle-particle interactions between different monolayers. The mechanism of particle-particle interactions between different monolayers is one of shielding or particle overlapping. By numerical simulations it is found that particle overlapping affects the transmission fluctuation spectrum in both the frequency response and the step height, with the strength related to the particle concentration, the number of layers and the beam-to-particle diameter ratio.