A fiber-optic sensor for measuring mass concentration of small particles

This paper is a theoretical investigation into an non-invasive instrument that would measure the mass concentration of a distribution of small (0.05 microns to 100 microns), homogeneous, absorptive particles of known density suspended in air, via back-scattered light. This instrument would utilize fiber optics for a design that is more rugged than existing instruments, and would utilize a small computer or microcontroller for signal processing to increase overall accuracy over a wide range of particle sizes. This paper assumes that the instrument is used in an area with little or no ambient light sources (an enclosed duct), and that either the gas/particle flow is laminar and homogenous across the duct, or that the instrument's sampling region is representative of particles flowing through the duct. The response of the instrument was calculated mathematically and using computer simulation. Findings indicate that an instrument could be constructed that would maintain an accuracy of at least 1% over the abovementioned range of particle sizes, with a minimum detection limit of twenty micrograms per cubic meter (20 μg/m³).