Neat thing about ultrasonic cleaners is the principle uses is induced cavitation; that is, the transducer vibrations cause vacuum pockets in the fluid to form and collapse very evenly and rapidly all throughout the fluid. Creating the vacuum bubble is nothing special, but the collapsing creates considerable force and heat at that exact spot in the fluid of the implosion.

Some studies indicate that the exact temperature at the center of the implosion approaches the temperature of the surface of the sun. Temperature and pressure generated is excellent for cleaning rigid solids... bad for flammable liquids. Cavitation is alluded to fluid-sand-blasting. It is that powerful, just ask the Navy.