Study of bubble fragmentation using optical and acoustic techniques

From Seas to Surgeries, From Babbling Brooks to Baby Scans: The Acoustics of Gas Bubbles in Liquids

“…The first measurements 30 of the size distribution of bubble population in the natural world using the passive acoustic emission were made in 1985. The technique of inferring bubble radii in the natural world from the natural frequencies they emit (Figure 4), has since given rise to hundreds of studies 5,6,31 , from rainfall sensing 32 , 33 to industrial sparging 1, 34 , to extra-terrestrial studies ( Figure 5). Development of this technique included innovative use of the Gabor Transform 33,35 and spectral methods for when entrainment rates are high 31 .…”

“…The technique of inferring bubble radii in the natural world from the natural frequencies they emit (Figure 4), has since given rise to hundreds of studies 5,6,31 , from rainfall sensing 32 , 33 to industrial sparging 1, 34 , to extra-terrestrial studies ( Figure 5). Development of this technique included innovative use of the Gabor Transform 33,35 and spectral methods for when entrainment rates are high 31 . Whilst the bubble wall can undergo a variety of modes of oscillation 36 , with some exceptions [37][38][39][40] it is the pulsation which is the most acoustically active, generating a strong monopole emission.…”

“…These processes convert the population initially produced by the breaking wave (the one measured by the passive acoustic technique) into the background population (as measured by the active acoustic technique). One process not included in this is bubble fragmentation, although the same research programme did see the only testing to date of the relevant theory for this process 33,35 .…”

The detection of tethered and rising bubbles using multiple acoustic techniques

“…However, a TFR of the Gabor coefficients, rather than the acoustic power invested in each frequency band, will readily identify the bubble signatures. [29][30][31] A routine uses thresholds on the value and gradient of the Gabor coefficients, then automatically counts and sizes the bubbles, giving their rate of production before they rise into the active detection zones. A second count is made by placing a greased Petri dish in the rising bubble stream above the detection zones.…”

High-resolution bubble sizing through detection of the subharmonic response with a two-frequency excitation technique

“…By controlling the amount of the plunger that was inside the needle, different flow rates and bubble sizes could be obtained. The bubbles produced by this method were sized using a passive technique, 17 which measured their characteristic resonant ring upon formation, and this measurement of their acoustic resonance was used to verify the results from the active tests. The bubbles were found to be reproducible in size and formed at a constant flow rate, due to the large pressure drop at the needle tip.…”