Ultrasound is anoscillating sound pressure wave with a frequency greater than the upper limitof the human hearing range. Ultrasound is thus not separated from 'normal'(audible) sound based on differences in physical properties, only the fact thathumans cannot hear it. Although this limit varies from person to person, it isapproximately 20 kilohertz (20,000 hertz) in healthy, young adults. Ultrasounddevices operate with frequencies from 20 kHz up to several gigahertz.
Ultrasound is usedin many different fields. Ultrasonic devices are used to detect objects andmeasure distances. Ultrasonic imaging (sonography) is used in both veterinarymedicine and human medicine. In the nondestructive testing of products andstructures, ultrasound is used to detect invisible flaws. Industrially,ultrasound is used for cleaning and for mixing, and to accelerate chemicalprocesses. Organisms such as bats and porpoises use ultrasound for locatingprey and obstacles.
Ultrasonics is theapplication of ultrasound. Ultrasound can be used for medical imaging,detection, measurement and cleaning. At higher power levels, ultrasonics isuseful for changing the chemical properties of substances.