Dynamic measurement of the acoustic streaming time constant utilizing an optical tweezer

Abstract

The combination of a bulk acoustic wave device and an optical trap allows for studying the buildup time of the respective acoustic forces. In particular, we are interested in the time it takes to build up the acoustic radiation force and acoustic streaming. For that, we measure the trajectory of a spherical particle in an acoustic field over time. The shape of the trajectory is determined by the acoustic radiation force and by acoustic streaming, both acting on different time scales. For that, we utilize the high temporal resolution ( t = 0.8 μs) of an optical trapping setup. With our experimental parameters the acoustic radiation force on the particle and the acoustic streaming field theoretically have characteristic buildup times of 1.4 μs and 1.44 ms, respectively. By choosing a resonance mode and a measurement position where the acoustic radiation force and acoustic streaming induced viscous drag force act in orthogonal directions, we can measure the evolution of these effects separately. Our results show that the particle is accelerated nearly instantaneously by the acoustic radiation force to a constant velocity, whereas the acceleration phase to a constant velocity by the acoustic streaming field takes significantly longer. We find that the acceleration to a constant velocity induced by streaming takes in average about 17 500 excitation periods (≈4.4 ms) longer to develop than the one induced by the acoustic radiation force. This duration is about four times larger than the so-called momentum diffusion time which is used to estimate the streaming buildup. In addition, this rather large difference in time can explain why a pulsed acoustic excitation can indeed prevent acoustic streaming as it has been shown in some previous experiments.

Enhanced Performance of an Acoustofluidic Device by Integrating Temperature Control

“…Although combining the mentioned temperature control system significantly improves the performance of the acoustofluidic setup, it still has limitations. Figures 4b and 5a both show that the expected increasing trend fails after around 200-240 V applied potential [43]. This shows that although the temperature control system is active after some level of heat production, it cannot cool down the system properly.…”

Dynamic light scattering for particle characterization subjected to ultrasound: a study on compact particles and acousto-responsive microgels

“…These slower processes may lead to more pronounced oscillations in the autocorrelation function, especially if particles are undergoing more complex and correlated motions. One example in our case might be acoustic streaming which has a time scale of milliseconds to seconds 27 . Thus, the growing NACF due to the aforementioned reasons at larger lag times may be superimposed by the NACF from Eq.…”

“…On the other hand, the small particle, dominated by drag force from acoustic streaming rolls, moves in circular paths 30 . All of the aforementioned scenarios are related to large time scales ( ) 27 . So far, it has not been possible to resolve the µs-ranged particle motion experimentally.…”