It's a combination of both heat and vibration, but mostly the vibration. Typically, an ultrasonic cleaner vibrates, causing the water in the tank to create waves. Those waves are what break apart dirt, grease, etc. When it comes to juice, the vibrations agitate the bubbles and juice in your bottle. As far as I know, that's all there is to it.
What he said.
The sound waves produce cavitation (micro) bubbles that store energy inside them as they grow. They reach a point where the bubbles implode from this energy. The imploding cavitation bubble is what does the cleaning.
I have decided to limit any heat in my steeping to around 120F or so, a couple hours inside the hot car. IF that. Most all Pro mixer steep instructions call for Dark and Cool. Heat is already known to degrade Nic, I also suspect it even more easily degrades flavor.
I would change the Sonicator water at the point it starts to stray from Warm into Hot.
For grins, put a drop of food coloring into the Sonicator water and turn it on.
For fountain pen parts, I often make a dual Sonicator bath. Cleaning solution goes into a thin plastic Wendy's Frosty Cup (Discontinued), the parts in the cup too and the whole cup into the Sonicator. This greatly reduces the amount of cleaner used (just clean water in the Sonicator tank) and the sound waves go right through the Wendy's cup. I may toss a few quarters into the cup if it needs weighting down.)
Bruce in Ocala, Fl