Recent developments of a novel technique using an acoustic transducer for aerosol particle detection are reviewed. Theoretical backgrounds are first described so that the experimental results may be reviewed in a systematic manner. The acoustic signal arises from vortex shedding by aerosol particles undergoing fast flow acceleration in a capillary section with area contraction. The pressure fluctuation associated with the vortex is then amplified using a transducer (a round tube), which resembles an organ pipe, with an open-ended round cylindrical tube connected to the capillary. Acceleration of the aerosol flow is drawn by a vacuum pump downstream of the measurement region. The organ-pipe nature of the transducer is examined, with various harmonic components. Its ability of detecting particle concentration is revealed. The possibility to detect the shape of the aerosol particle is discussed based on the relative strength of the harmonics. The signal strength as a function of particle size and flow rate through the acoustic transducer is examined. The real-time capability of detecting particles is presented. Discussion also points to the potential of constructing a miniature particle detection device, which may find application in clean rooms and in space exploration should particle monitoring be desired on board of vehicles or in extraterrestrial environments.
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