Ultrasonic sound waves are waves of sound beyond the range of perception. These sound waves are used by bats and dolphins for navigation and by medical imaging and in non-destructive testing.
The range of ultrasonic sound, or ultrasound, between 20 and 100 kilohertz is used by bats, dolphins and other species to navigate and communicate with others of their kind. Medical ultrasounds use a much higher frequency in the range of 1 to 20 megahertz. Medical testing utilizes the echo time and the Doppler shift of sounds reflected back for medical imaging. With this, they can use ultrasonic sound waves to determine the distance between organs or the speed at which those organs are moving such as with an echocardiogram.
Non-destructive testing uses both high- and low-frequency ultrasonic sound waves to test for fractures and flaws in building materials and to measure the thickness of those materials. Less-dense materials utilize lower sound frequencies in the range of 50 to 500 kilohertz. Non-destructive testing has used ultrasound technology to test the welding on joints as an alternative to radiology since the 1960s.
Sonar also uses ultrasonic sound waves similar to the way a bat uses them for navigation. A pulse of sound is sent in a particular direction, and when it bounces back as an echo, the time between the pulse and echo is measured to determine distance.