The capability for differentiating particles according to sizeis provided in an improved acoustical detection apparatus andmethod for detecting particulate matter in air or other gases. Thisis accomplished by controlling the flow of the gas through thecapillary section of an acoustic sensor such that the flow conformsto a predetermined Reynolds number selected according to theparticle size of interest. It has been found that acousticalsensors exhibit a threshold for particle size detection whichvaries with the Reynolds number of the flow of a gas through it.Thus, the detection of particles above a given size is achieved bycontrolling the flow parameters to yield a Reynolds numberappropriate for detecting particles of such size.
Acoustical particle detector and method
Coover, SR., & Reist, PC. (1980). IPC No. U.S. Acoustical particle detector and method. (U.S. Patent No. 4212190).