1)human ear: Different sounds produced in our surroundings are collected by pinna that sends these sounds to the ear drum via ear canal.The ear drum starts vibrating back and forth rapidly when the sound waves fall on it.The vibrating eardrum sets the small bone hammer into vibration. The vibrations are passed from the hammer to 2nd bone anvil and finally the 3rd bone stirrup.The vibrating stirrup strikes on the membrane of the oval window and passes it's vibration to the liquid in the cochlea. This produces electrical impulses in the nerve cell. The auditory nerve carries the electrical impulses to the brain. These electrical impulses are interpreted by the brain as sound and we get a sensation of hearing.

2)SONAR: SONAR is an acronym for SOund Navigation And Ranging. It is an acoustic device used to measure the depth, direction and speed of under water object such as submarines and ship wrecks with the help of ultrasound. A beam of ultrasound is produced and transmitted by the transducer of the SONAR, which travels through the water. The echo produced by the reflection of this sound is detected and recorded by the detector, which is converted into electric signals.