What are ultrasonic waves?

Ultrasonic waves are those sound waves that are inaudible to our ears because they have a very high frequency. These high frequency. These energy-rich waves are used in many ways such as cleaning dental braces or spectacle glasses. Ultrasonic waves excite the liquid to vibrate so fast that it removes the dirt. Ultrasonic waves are also reflected from the inner organs of our body; thus, an echo is  produced. This echo can be recorded and displayed by medical devices.  In this way, doctors can safely monitor the development of a foetus inside the mother's womb.

How do bats orient themselves with ultrasound?

Bats cannot see very well. To orient themselves during their night flights, they emit ultrasounds. We cannot hear these sounds. The ultrasonic waves falling on obstacles or preys get 'reflected' back and reach the sensitive ears of bats. Thus, they come to know what all is present around them and where their prey is. This concept is also used in shipping to determine the depth of the seal using a device called sonar. It comprises a sound transmitter,  a receiver, and a clock. The time difference e between sending and receiving sound waves is measured, which is used to calculate the depth of the sea.

What is an echo?

If you call out your name in the direction of a vertical bare rocky wall, you will hear it again after some time. An echo comes because the sound waves are reflected back from the wall. When sound is produced in enclosed space, such as churches any gymnasiums, multiple reflections build up and blen together.

This phenomenon is known as reverberation.