On the threshold of 1/2 order subharmonic emissions in the oscillations of ultrasonically excited bubbles

A J Sojahrood; H Haghi; N R Shirazi; R Karshafian; M C Kolios

doi:10.1016/j.ultras.2021.106363

On the threshold of 1/2 order subharmonic emissions in the oscillations of ultrasonically excited bubbles

Ultrasonics. 2021 Apr:112:106363. doi: 10.1016/j.ultras.2021.106363. Epub 2021 Jan 20.

Authors

A J Sojahrood¹, H Haghi², N R Shirazi², R Karshafian², M C Kolios²

Affiliations

¹ Department of Physics, Ryerson University, Toronto, Canada; Institute for Biomedical Engineering, Science and Technology (IBEST) a partnership between Ryerson University and St. Michael's Hospital, Toronto, Ontario, Canada. Electronic address: amin.jafarisojahrood@ryerson.ca.
² Department of Physics, Ryerson University, Toronto, Canada; Institute for Biomedical Engineering, Science and Technology (IBEST) a partnership between Ryerson University and St. Michael's Hospital, Toronto, Ontario, Canada.

PMID: 33508558
DOI: 10.1016/j.ultras.2021.106363

Abstract

The pressure threshold for 1/2 order subharmonic (SH) emissions and period doubling during the oscillations of ultrasonically excited bubbles is thought to be minimum when the bubble is sonicated with twice its resonance frequency (f_r). This estimate is based on studies that simplified or neglected the effects of thermal damping. In this work, the nonlinear dynamics of ultrasonically excited bubbles is investigated accounting for the thermal dissipation. Results are visualized using bifurcation diagrams as a function of pressure. Here we show that, and depending on the gas, the pressure threshold for 1/2 order SHs can be minimum at a frequency between 0.5f_r≤f≤0.6f_r. In this frequency range, the generation of 1/2 order SHs are due to the occurrence of 5/2 order ultra-harmonic resonance. The stability of such oscillations is size dependent. For an air bubble immersed in water, only bubbles bigger than 1 μm in diameter are able to emit non-destructive SHs in these frequency ranges.

Keywords: Bubbles; Cavitation; Nonlinear dynamics and chaos; Subharmonics; Ultraharmonics; Ultrasound.