Physics
In physics, the word “ultrasound” refers to sound with a frequency the human ear cannot perceive.
Application
Ultrasound is used among other things as a sonic depth finder in navigation, for cleansing of sensitive objects (e.g. contact lenses) and in testing non-disruptive materials in order to detect faults and fractures.
In medical diagnostics, ultrasound can be used for visualisation of anatomical structures and for assessment of physiological processes.
The ultrasound used for medical diagnostics is usually between 2 and 18 MHz.