The fundamentals of particle size analysis by transmission fluctuation spectrometry part 1: A theory of temporal transmission fluctuations in dilute suspensions

The extinction of radiation in suspensions is traditionally described by th e Bouger-Lambert-Beer law (BLBL). Based on a quasicontinuum approach, the B LBL does not account for the discrete nature of particles or their spatial extension and arrangement. If an extinction measurement is made with a high spatial and temporal resolution, the transmitted intensity signal shows si gnificant fluctuations. The strength of fluctuation is related to the physi cal properties of the suspension and the process of spatial and temporal av eraging. Exploiting this connection, it is possible to calculate the partic le size distribution and the particle concentration from transmission measu rements. This part of the series of papers provides a method for the temporal decomp osition of the transmission's power spectrum, which permits the information on the particle size and concentration to be extracted from the seemingly irregular fluctuation of the transmission signal.