Vibrational or stress waves in elastic media that have a frequency above 20 kilohertz, the highest frequency of sound waves that can be detected by the human ear.
The waves may be longitudinal (as in air or solids) or transverse (as in liquids). They can be generated or detected by piezoelectric transducers (see piezoelectricity ). High-power ultrasonics produce distortion in the medium; applications include ultrasonic welding, drilling, irradiation of fluid suspensions (as in wine clarification), cleaning of surfaces (such as jewelry), and disruption of biological structures. Low-power ultrasonic waves do not cause distortions; the uses include sonar , structure testing, and medical imaging and diagnosis. Some animals, including echolocation for navigation.