Abstract
Using simple models of granular or powdered materials in motion, the possibility of utilizing the Doppler Effect in air-borne ultrasonic waves scattered by the materials, for the purpose of measurement of their average motion, was investigated. Main peak of the frequency spectrum of beat, due to the superposition of waves with modulated frequency scattered by the moving materials and those with unmodulated frequency reflected by the fixed wall of the apparatus, is found to correspond to that produced by a single body under average motion of the granular or powdered matrials. A simple explanation to this effiect is also given.
