On September 27, 2022
Water bubbles have a very sharp acoustic resonance frequency, as evidenced by the sound of bubbling produced in a glass when blowing through a straw. But does this resonance depend on the shape of the bubbles? Although bubbles are most often spherical, they can also be toroidal, like those produced by dolphins in their water games, which are the equivalent of our smoke rings.
To study toroidal bubbles at our leisure, we trapped them within 3D-printed cages (using DLP) with openings small enough to prevent water from entering. We have shown that their resonant frequency is higher when the tori are thin, i.e. when their small radius becomes much smaller than their large radius. These bubbles can be assembled to produce original acoustic fields: for example in a long tunnel of rings
At the ocean level, we hypothesize that dolphins should already be aware of the acoustic properties of rings since they often emit pulsed sounds when making rings. In particular, they should be able to detect a “glissando” toward higher resonance frequencies when a ring enlarges and narrows during its ascent.
Physical Review Letters
Acoustic Resonance Frequencies of Underwater Toroidal Bubbles (PDF, 587 Ko)