The typical audible sound wave of the human ear is restricted to the bandwidth of frequencies ranged from 300 Hz to 3,400 Hz. The frequencies over 20,000 Hz fall beyond the scope of human hearing. The sound waves with a frequency greater than 20,000 Hz are called "ultrasound" and applied to a range of medical treatments and diagnosis practices. Ultrasonic waves are mainly applied to different beauty devices such as skin peeling machines depending on the purpose. The vibrations with a frequency of 1 MHz are mostly applied to body slimming beauty equipment because, above all, it can decompose cellulose and subcutaneous fat. Facial massage machines use the frequency band of 3 MHz for safety. The massage has a stimulating effect on the skin increasing its elasticity.
In addition, as it is matched well with water waves, it is very effective to remove the dead skin cells when applied to skin peeling devices using liquid.