Megasonic

Megasonic cleaning works at much higher frequencies than conventional ultrasonics, and it exists to solve a specific problem: removing sub-micron particles from surfaces that low-frequency cavitation would damage.
The physics is different in a way that matters. Conventional ultrasonic cavitation implodes bubbles with enough energy to dislodge heavy soils — and enough energy to pit soft metals, erode coatings and damage fine features. Megasonic energy produces a much gentler action that sweeps fine particulate off a surface without that impact, which is why it is used on wafers, optical surfaces and other work where the particle specification is tight and the surface is delicate.
It is not a replacement for ultrasonic cleaning — it will not shift machining oil or heavy grease. In practice it belongs at the end of a process, after conventional cleaning has removed the bulk soil.