ABSTRACT
Ultrasound is a sound wave characterized by such parameters as pressure, particle (or medium) velocity, particle displacement, density, and temperature. It differs from a sound wave in that its frequency is higher than 20
×
cycles per second or 20 kHz (kilohertz). The audible range of human ear is from 20 Hz to 20 kHz. Because ultrasound is a wave, it transmits energy just like an electromagnetic wave or radiation. Unlike an electromagnetic wave, however, sound requires a medium in which to travel and thus cannot propagate in a vacuum.
