Performance and Robustness Improvements in Ultrasonic Transportation Against Large-Scale Streaming

Acoustic streaming generated from the traveling-wave component of a synthesized sound field often has considerable influence on ultrasonic manipulations, in which the behavior of microparticles may be disturbed. In this work, the large-scale streaming pattern in a chamber with three incident plane waves is simulated, illustrating a directional traveling stream pattern and several vortical structures. Based on the numerical results, the trapping capability of an acoustic potential well is quantitatively characterized according to several evaluation criteria: the boundary and elastic constant of the acoustic potential well, the acoustic radiation force offset ratio, and the elastic constant offset ratio. By optimizing these parameters, the constraint of the acoustic potential well can be strengthened to promote the performance and robustness of the ultrasonic transportation. An ultrasonic manipulation device employing three 1.67-MHz lead zirconate titanate (PZT) transducers with rectangular radiation surface is prototyped and performance tested. The experimental results show that the average fluctuations of a microparticle during transportation have been suppressed into a region less than 0.01 times the wavelength. Particle displacement from equilibrium is no longer observed.