What is Ultrasonic?
Ultrasonic is sound generated above human audible level. In real life, high pitch sound is created by high frequency, and alternatively, the low and base tone is created by low frequency. Frequencies above 16 kHz in general are being considered as ultrasonic. Typical ultrasonic frequencies used for cleaning purpose are from 20 kHz to 80 kHz.
How a sound can clean?
A physical effect called "cavitations" ultrasonic generates in liquid is responsible for the cleaning process. Cavitations are form when ultrasonic travels through liquid. When a sound wave travels through water, it stretches and compresses the water medium to transmit sound. When the amplitude of such sound wave increases to a level when water cannot hold the stretch, the sound literally tears the water apart, and millions of vacuumed "bubbles" are formed under such negative pressure.
The sizes of vacuumed "bubbles" increase until their equilibrium are reached; the "bubbles" then rapidly compress by water and create millions of tiny liquid jets.
The jet actions release tremendous amount of energy stored within vacuumed bubbles; each "bubble" is estimated to have a temperature of more then 5000 degree Celsius and a pressure of more then 10,000 PSI at molecular level when such implosion takes place. The huge amount of pressure releases at each "bubble" provides an ideal physical phenomenon responsible for the effective cleaning action ultrasonic cleaner offers.