Millimeter-wave tomography of dense particle clouds

A novel millimeter-wave interferometric tomographic instrument is presented that provides quantitative measurements of particle concentration in dense multiphase flows opaque to conventional optical diagnostics. A 77-GHz automotive radar is combined with an array of passive reflectors to achieve path-integrated concentration measurements, which are then reconstructed into local concentration distributions using an inverse Abel transform. This work evaluates the different contributions to the measurement uncertainty and the total measurement error and demonstrates the instrument capabilities in a dispersed multiphase flow experiment relevant to plume-surface interaction in Lunar and Martian landings. Measured particle concentrations exceeded 10 particles/mm3 with 10 kHz temporal resolution. Cumulative concentration errors were shown to amount to -9 dB. Millimeter-wave radar tomography enables spatially resolved measurements of particle concentration in dense particle-laden flows relevant to aerospace, chemical processing, and other industrial applications. Its high temporal resolution makes it ideally suited for quantitative measurements of rapid transient phenomena in dense particle-fluid mixtures.