Airborne Particle Detection UsingAcoustic Transducers

Abstract

Aerosol particle detection finds important applications in the commercial, military, and aerospace sectors and is of special importance in clean room monitoring. To date, most laboratory-based particle detection devices rely on laser scattering measurements which drive up the cost of these instruments. This experimental study demonstrates a novel and inexpensive particle detection technique which is based on the acoustic signature of airborne particles as they are accelerated through a converging-diverging tube consisting of a capillary (i.e. the acoustic transducer). As a particle-laden flow accelerates through the transducer, the suspended particles cannot follow the rapidly changing flow velocity and vortices are generated which excite the air column inside the transducer tube producing audible noise. Results show how the frequency content of the acoustic signatures relates to the fundamental frequency of the transducer’s air column. The acoustic transducer is able to detect micron-sized particles and the sound intensity is a function of flowrate but, unexpectedly, not of particle size. The ability of the transducer to determine particle concentration (as low as a few ppl) is also shown and compared to data obtained from a commercially available aerodynamic particle sizer.