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What is Ultrasound or Ultrasonic Sound and it's uses?
Ultrasonic Sound or Ultrasound
The range of sound that can be heard clearly by a human being extends from about 20 Hz to 20000 Hz (one Hz = one cycle/s). Animals such as dogs and children under the age of five can hear up to 25 kHz (1 kHz = 1000 Hz). Ears of people will get less sensitive to higher frequencies as they grow old.
Infrasonic sound or infrasound
Frequencies of below 20 Hz sounds are called infrasonic sound or infrasound. Animals can listen low-frequency infrasounds and can be get distrubed by it. Before the main shock of an earthquake, the earth produces low frequency infrasounds which is a disturbance to many animals. That is why many animals react and run for safe places before an earthquake. It is interesting to know that Rhinoceroses communicate using infrasound of frequency of 5Hz.
Ultrasonic Sound or Ultrasound
Sounds of frequencies higher than 20kHz are called Ultrasound or ultrasonic sound. Dolphins, bats, porpoises and rats can produce ultrasonic sounds.
Applications of Ultrasound
Ultrasounds are used extensively in industries and for medical purposes. As mentioned above, Ultrasounds are high frequency waves (higher than 20kHz). Even in the presence of obstacles, they are able to travel along well defined paths.
- To clean parts located in hard to reach places, Ultrasound can be used. Ultrasonic waves are sent into the cleaning solution where the objects to be cleaned are placed. The particles of dust, dirt and grease get detached and drop out due to the high frequency. This help to clean the objects thoroughly. Spiral tube, electronic components and odd shaped parts are examples of such hard-to-reach objects.
- To detect cracks and flaws in metal blocks ultrasounds can be used. To ensure safety and quality of metal used in manufacturing of machines, scientific equipments, bridges and buildings etc., it is important to test the metal used before manufacturing the same. Detectors are used to detect the strength/quality of the metal blocks while ultrasonic waves are allowed to pass through it. Even a small defect can be identified by using ultrasound test of metal objects.
- Doctors use the technique called Echocardiography in which ultrasonic waves are made to reflect from various parts of the heart and form image of the heart.
- Doctors also use an instrument called ultrasound scanner for getting images of internal organs such as kidney, gall bladder, uterus, liver etc, of the human body. These images of internal organs helps the doctor to detect the abnormalities such as tumors in different organs, stones in kidney and gall bladder etc. In this technique, ultrasonic waves travel through the tissues of the body and get reflected from a region where there is a change of tissue density. This technique is called 'ultrasonography'. Images of internal organs are printed in a film or displayed on a monitor. During the pregnancy, to detect congenial defects and growth abnormalities, doctors use ultrasonography to examine the fetus.
- Another use of ultrasound is to break small stones formed in the kidneys into fine grains. These grains later get flushed out with urine.
- Another use of ultrasound is in the Sound Navigation and Ranging (SONAR) It is a device that uses ultrasonic waves to measure the speed, direction and distance of an underwater object. Sonar consists of a detector and transmitter which is installed in a ship or a boat. Transmitter emits ultrasonic waves and these waves travel through water. These ultrasonic waves get reflected back after striking the object on the seabed. The detector detects these waves and converts into electrical signals which are appropriately interpreted. The sonar technique is used to determine the depth of the sea and to locate icebergs, sunken ships, underwater hills, valleys, submarine etc.
- Bats search for its prey and fly in dark night by emitting and detecting reflections of ultrasonic waves. The nature of reflections of high-pitched ultrasonic squeaks of the bat tells where the obstacle or prey is and what it is like.
- For navigation and location of food in the dark, Porpoises also use ultrasound.