Question

what is basic principal from which SONAR works

Answer 1

Radar uses radio waves, which are a type of electromagnetic energy. Sonar uses the echo principle by sending out sound waves underwater or through the human body to locate objects. 

Answer 2

Your returning voice is called an echo. ... Both radar and sonar locate objects from the echo of a signal that is bounced off the object. Radar uses radio waves, which are a type of electromagnetic energy. Sonar uses the echo principle by sending out sound waves underwater or through the human body to locate objects.