Giant frequency down-conversion of the dancing acoustic bubble

Abstract

We have demonstrated experimentally the existence of a giant frequency down-conversion of the translational oscillatory motion of individual submillimeter acoustic bubbles in water in the presence of a high frequency (500 kHz) ultrasonic standing wave. The frequency of the translational oscillations (~170 Hz) is more than three orders of magnitude smaller than that of the driving acoustic wave. We elucidate the mechanism of this very slow oscillation with an analytical model leading to an equation of translational motion of a bubble taking the form of Mathieu’s equation. This equation illuminates the origin of the giant down conversion in frequency as arising from an unstable equilibrium. We also show that bubbles that form chains along the direction of the acoustic standing wave due to radiation interaction forces exhibit also translation oscillations that form a spectral band. This band extends approximately from 130 Hz up to nearly 370 Hz, a frequency range that is still at least three orders of magnitude lower than the frequency of the driving acoustic wave.

Acoustic frequency combs using gas bubble cluster oscillations in liquids: a proof of concept

“…However, a theoretical insight can be gained from the analysis of a system consisting of just two moving gas bubbles 52 , where it has been shown that stronger ultrasound forcing prevents bubble collision and coalescence thereby increasing the stability of their oscillations. On the other hand, similar to a single oscillating bubble [54][55][56][57][58] , the translational motion in bubble clusters should depend www.nature.com/scientificreports/ on the frequency and pressure of the driving wave. Thus, it is plausible to assume that driving the bubble cluster at a higher frequency but lower pressure, which is the case in Fig.…”