Ultrasound is a cyclic sound pressure wave with a frequency greater than the upper limit of the human hearing range. Ultrasound is thus not separated from audible sound based on differences in physical properties only the fact that humans cannot hear it.
Ultrasound is used in many different fields. Ultrasonic devices are used to detect objects and measure distances. Ultrasonic imaging is used in human and veterinary medicine. In non-destructive testing of products and structures, ultrasound is used to detect invisible flaws. For Industries, ultrasound is used for cleaning and for mixing, and to accelerate chemical processes.
Ultrasonics is the application of ultrasound. Ultrasound can be used for imaging, detection, measurement, and cleaning. At higher power levels ultrasonics are useful for changing the chemical properties of substances.
Figure. Ranges of Ultra sound
A common use of ultrasound is in range finding; this use is also called SONAR, (sound navigation and ranging). An ultrasonic pulse is generated in a particular direction. If there is an object in the path of this pulse, part or all of the pulse will be reflected back to the transmitter as an echo and can be detected through the receiver path. By measuring the difference in time between the pulse being transmitted and the echo being received, it is possible to determine the distance.
Principle of Active SONAR
Here is the animation for the Ultrasound....
Animation of ultra sound