What is a SONAR? Briefly explain its working principle.

SONAR- The acronym SONAR stands for Sound Navigation and Ranging.

Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

Principle: It uses the phenomenon of echoes in determining the sea-depth and locating the presence of under-water objects.

Working:

i) A strong beam of ultrasonic waves is sent from a transmitter mounted on the ship.

ii) The beam is reflected from the seabed and is received by an under-water detector which is also mounted on the ship.

iii) The time interval between transmission and reception of the ultrasonic signal is noted. 

Industrial applications of ultrasound in industry and medicine are: 

Industrial application: 

1. Ultrasonic detection of defects in metals: The construction of big structures like buildings, bridges, machines, scientific equipments, etc use metallic components. The cracks or holes inside the block reduce the strength of the structure. Such defects are not visible from outside. Ultrasonic waves can be used to detect such defects. Ultrasonic waves are allowed to pass through the metal block and detectors are used to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back and does not reach the detector. This is how the presence of a flaw or defect is detected. 

Medical application:

1. Echocardiography: In this technique, ultrasonic waves are made to reflect from various parts of the heart to form the image of the heart.

2. Ultrasonography: Ultrasonic waves can be used to develop three dimensional photographs of different parts of the human body. This technique is called ultrasonography.

This technique is also used to monitor the growth of a foetus inside its mother’s womb. In this technique the ultrasonic waves travel through the tissues of the body and get reflected from a region where there is a change of tissue density. These waves are then converted into electrical signals that are used to generate images of the organ. These images are then displayed on a monitor or printed on a film.

3. In surgery: Ultrasonic waves are commonly used in cataract removal. Ultrasonic waves are used to grind small stones formed in the kidneys. These grinded grains are flushed with urine. 

SONAR. The acronym SONAR stands for Sound Navigation and Ranging.

Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

Principle. It uses the phenomenon of echoes in determining the sea-depth and locating the presence of under-water objects.

Working. A strong beam of ultrasonic waves is sent from a transmitter mounted on the ship. The beam is reflected from the seabed and is received by an under-water detector which is also mounted on the ship. The time interval between transmission and reception of the ultrasonic signal is noted.

Fig. 12.26. Ultrasound sent by a transmitter and received by a detector.

If ultrasonic waves travel with speed v in sea-water and time t is elapsed between the transmission and reception of the ultrasound signal, then the sea depth will be

The SONAR method is also called echo ranging. This technique is used to determine the depth of the sea and to locate underwater hills, valleys, submarine, icebergs, sunken ship etc.

The disturbance arising due to repeated vibrations of the particles of the medium, moving from one particle to another is known as a wave. 

Waves can be classified as follows, on the basis of the medium in which they travel. 

1. Mechanical/elastic waves: The waves which require a material medium for their propagation are known as mechanical waves.

e.g., sound waves.

2. Electromagnetic waves: Waves which do not require any material medium for their propagation.

e.g., light waves. 

Ultrasound or ultrasonic wave is a wave in which the compressions and rarefactions in a material medium propagates with a frequency above 20 kHz.

Ultrasonic wave travels freely in solids and liquids but its intensity decreases rapidly in gases. 

Ultrasonic waves have the following two important properties, because of their high frequencies:

1. They have high power.

2. They are able to travel along well-defined straight paths, even in the presence of obstacles. 

The above two properties make the ultrasonic waves highly useful for industrial and medical purposes.