Ultrasound is a sound just like other sounds. It is a wave consisting of [?] and rarefactions. The only difference is in the [?], 20 000 Hz and above, which is the range of human hearing.

Many animals can hear ultrasound and use it for communication. Animals like bats and dolphins use ultrasound to and detect their prey.

In medicine ultrasound scans are carried out on women to see how the unborn is developing. Ultrasound is also used to diagnose other conditions, and for non-surgical treatment.

In industry, ultrasound is used to detect in castings, and for delicate components.