Abstract:
Acoustic streaming is generated even by tone-burst waves, because the driving force is given by a time-averaged value of the acoustic properties. It was pointed out theoretically that the driving force of the streaming is enhanced at a higher level of sound pressure. If the applied electric power is kept the same, a tone-burst wave with a shorter active period has a larger source amplitude, which brings a stronger driving force. The present paper describes experimental results of acoustic streaming driven by tone-burst waves of various parameters using a laser Doppler velocimeter and shows that the enhancement of streaming is due to nonlinear attenuation of ultrasound. The generation of streaming is often observed in noncontact manipulation using acoustic radiation pressure, which is undesirable for the stable operation. Noting the difference in the time scales of the phenomena, incorporation of a tone-burst wave of the same amplitude makes it possible to suppress the generation of acoustic streaming (slow mode), keeping the sufficient strength of acoustic radiation pressure (fast mode). Experiments of acoustic manipulation of suspended particles showed that this medium-mode operation worked well.