Multiple methods for obtaining particle size distribution with a particle sizing interferometer

Use of Particle Sizing Interferometers (PSI) for sizing particles smaller than 3µm is investigated analytically and experimentally. The individual particle sizing concept involves simultaneous measurement of four PSI signal characteristics: peak amplitude of the pedestal signal, averaged amplitude of the pedestal signal, number of Doppler signal cycles, and signal visibility. A multiple beam Mie scattering solution was used to find collection optics configureations which show monotonic relationships between particle size and scattering intensity, and between particle size and visibility. A 50° off-axis forward scatter optical arrangement with and effective f-number 1.0 colleter was found to provide monotonic relationships for particle diameters up to 10µm (the upper size limit calculated for this work) with a particle size increment of 0.15µm.

The experimental investigation was conducted using this 50° off-axis arrangement. Three uniform sizes of latex spheres were aerosolized in monodisperse and polydisperse distributions in the experimental investigation. Particle size distribution measurements were obtained independently from the four measurement methods and from measurement volume cross-sectional area matrices of each measurement. These were determined from analytical evaluations of PSI responses and through the use of a non-negative least square method. The resulting size distributions were found to be consistent with each other and to accurately reproduce the input of particle sizes.