Acoustic Radiation Force on Small Spheres Due to Transient Acoustic Fields

Acoustic radiation force is a net force experienced by an object under the action of an acoustic wave. Most theoretical models require the acoustic wave to be periodic, if not purely monofrequency, and are therefore irrelevant for the study of acoustic radiation force due to acoustic pulses. Here, we introduce the concept of finite-duration pulses, which is the most general condition to derive the acoustic radiation force. In the case of small spheres, we extend the Gor?kov formula to unsteady acoustic fields such as traveling pulses and interfering wave packets. In the latter case, our study suggests that the concept of acoustic contrast is also relevant to express the acoustic radiation force. For negative acoustic contrast particles, the acoustic trapping region narrows with shorter pulses, whereas positive contrast particles (such as biological cells) can fall in secondary traps when the pulse width deviates from an optimal value. This theoretical insight may help to improve the selectivity of pulsed acoustic tweezers.

Automated summary

This study introduces the concept of finite-duration pulses as the most general condition for deriving the acoustic radiation force. For small spheres, the Gor?kov formula is extended to unsteady acoustic fields, and the concept of acoustic contrast is suggested to express the acoustic radiation force. Experimental results show that the acoustic contrast can influence the action of the acoustic radiation force.