Ultrasonic cleaning is like taking a bath for things that can't get wet. Have you ever seen a machine with small bubbles all over it? That's what ultrasonic cleaning machines do.
When things are dirty, they have tiny bits of gunk that stick to them like glue. Ultrasonic cleaning machines make very very very small bubbles that are so tiny you can't even see them. When these bubbles form, they pop and create little waves that move really fast.
When these tiny bubbles pop, the waves they make are really strong and can clean things like nobody's business! This is because the waves are so strong that they can loosen up those tiny bits of gunk and make them jump off the thing being cleaned.
And just like taking a bath, we add some soap or cleaning fluid to the water to make it even better at cleaning things. The ultrasonic machine helps the cleaning fluid get all over and into the tiny nooks and crannies of the thing being cleaned.
So just like you're squeaky clean after a bath, things that go through an ultrasonic cleaning machine come out sparkling clean!