DIFFERENT APPLICATIONS OF ULTRASOUND

DIFFERENT APPLICATIONS OF ULTRASOUND

Ultrasounds are high-frequency waves. Ultrasounds are able to travel along well-defined paths even in the presence of obstacles. Ultrasounds are used extensively in industries and for medical purposes.

*   Ultrasound is generally used to clean parts located in hard-to-reach places, for example, spiral tube, odd-shaped parts, electronic components, etc. Objects to be cleaned are placed in a cleaning solution and ultrasonic waves are sent into the solution. Due to the high frequency, the particles of dust, grease, and dirt get detached and drop out. The objects thus get thoroughly cleaned.

*   Ultrasounds can be used to detect cracks-flaws in metal blocks. Metallic components are generally used in the construction of big structures like buildings, bridges, machines, and also scientific equipment. The cracks or holes inside the metal blocks, which are invisible from outside reduces the strength of the structure. 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 indicating the presence of the flaw or defect, as shown in Fig. 12.16.

Figure 12.16: Ultrasound is reflected back from the defective locations inside a metal block

Ordinary sound of longer wavelengths cannot be used for such purpose as it will bend around the corners of the defective location and enter the detector.

*   Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘ echocardiography ’.

*   Ultrasound scanner is an instrument which uses ultrasonic waves for getting images of internal organs of the human body. A doctor may image the patient’s organs such as the liver, gall bladder, uterus, kidney, etc. It helps the doctor to detect abnormalities, such as stones in the gall bladder and kidney or tumours in different organs. 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. This technique is called ‘ ultrasonography ’. Ultrasonography is also used for examination of the foetus during pregnancy to detect congenial defects and growth abnormalities.

*   Ultrasound may be employed to break stones formed in kidneys into fine grains. These grains later get flushed out with urine.

Source: This topic is taken from NCERT TEXTBOOK

SONAR

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. How does the sonar work? Sonar consists of a transmitter and a detector and is installed in a boat or a ship, as shown in Fig. 12.17

Figure 12.17: Ultrasound sent by the transmitter and received by the detector

The transmitter produces and transmits ultrasonic waves. These waves travel through water and after striking the object on the seabed, get reflected back and are sensed by the detector. The detector converts the ultrasonic waves into electrical signals which are appropriately interpreted. The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound. Let the time interval between transmission and reception of ultrasound signal be t and the speed of sound through seawater be v. The total distance, 2d travelled by the ultrasound is then, 2d = v \(\times\) t.

The above method is called echo-ranging.

The sonar technique is used to determine the depth of the sea and to locate underwater hills, valleys, submarines, icebergs, sunken ship, etc.

As mentioned earlier, bats search out prey and fly in dark night by emitting and detecting reflections of ultrasonic waves. The high-pitched ultrasonic squeaks of the bat are reflected from the obstacles or prey and returned to the bat’s ear, as shown in Fig. 12.18. The nature of reflections tells the bat where the obstacle or prey is and what it is like. Porpoises also use ultrasound for navigation and the location of food in the dark.

Figure 12.18: Ultrasound is emitted by a bat and it is reflected back by the prey or an obstacle

Illustration 12.3:

A ship sends out ultrasound that returns from the seabed and is detected after 3.42 s. If the speed of ultrasound through seawater is 1531 m/s, what is the distance of the seabed from the ship?

Sol:

Given,

Time between transmission and detection, t = 3.42 s.

Speed of ultrasound in seawater,

v = 1531 m/s

Distance travelled by the ultrasound

= 2 \(\times\)depth of the sea = 2d

where d is the depth of the sea.

2d = speed of sound \(\times\)time

     = 1531 m/s\(\times\) 3.42 s = 5236 m

d = 5236 m/2 = 2618 m.

Thus, the distance of the seabed from the ship is 2618 m or 2.62 km.

Questions

A submarine emits a sonar pulse, which returns from an underwater cliff in 1.02 s. If the speed of sound in saltwater is 1531 m/s, how far away is the cliff?

Source: This topic is taken from NCERT TEXTBOOK