Applications of ultrasonic and infrasonic sound waves

Ultrasonic or Ultrasound

The sound waves greater than 20,000 Hz is called ultrasonic sound. Humans cannot hear ultrasound and some animals can hear. Ex: Dogs, Deer etc. Ultrasonic whistles are used in vehicles such as cars to alert Deers that cross the roads.

Ultrasonics has an important application in the medical field. It is used as an alternative to X-Rays used to image internal organs, tissues, bones etc. The ultrasonics hit the internal organs and the reflection is captured by the computer and processed to give an X-Ray Image called an Echogram.

Ultrasound Range Diagram
Ultrasound Range Diagram By Ultrasound_range_diagram.png: The original uploader was LightYear at English Wikipedia.Ultrasound_range_diagram_png_(sk).svg: The original uploader was LightYear at English Wikipedia.derivative work: Coolth (talk) – Ultrasound_range_diagram.pngUltrasound_range_diagram_png_(sk).svg, CC BY-SA 3.0,

Ultrasonics is also used in Marine Surveying. Animals such as dolphins, oil birds, rats, and bats navigate using ultrasonic waves. Bats, some toothed whales, and dolphins use echolocation, an ultrasonic technique that is used to locate and identify objects.

Echolocation is used to navigate and catch their prey. Many Nocturnal insets such as Grasshoppers, praying mantis, beetles, moths, lacewings etc have ultrasonic hearing which helps them to escape.

Oilbirds use ultrasonic waves to fly at night, they lower echolocation frequencies compared to bats and other nocturnal insects.

Application of Ultrasonic waves

  • Used for cleaning purposes, small foreign particles can be removed from objects in a liquid bath via which the ultrasonic is passed.
  • Used to detect cracks and defects in metal blocks.
  • They are used in medicine for electrocardiography.
  • Used to break kidney stones, and flushed them out with urine.
A medical ultrasound
A medical ultrasound on small paper By Julan Shirwod Nueva – Own work, CC BY-SA 4.0,


Used to calculate the distance, speed of underwater objects, and direction. It has a transmitter and a detector ( receiver) installed at the bottom of boats and ships. The transmitter transmits ultrasonic waves, it hits the objects such as rocks on the water surface, or seabed and gets reflected.

Sonar Image under the sea
Sonar Image under the sea By Tuukritööde OÜ – Muinsuskaitseamet, CC BY-SA 4.0,

The detector detects the reflected signals and calculates the target’s distance by measuring the difference between the transmission time and reception of reflected waves. The time interval between the transmission and reception of ultrasound is ‘t’ and the speed of sound through seawater is 2d = v x t.  This method is called echo ranging.

Sonar is widely used in sea navigation to detect underways valleys, hills, icebergs, submarines etc.

ECG (Electrocardiogram)

In ECG the sound variations produced by the heart are converted into electrical signals.ECG is simply a representation of electric changes in the heart concerning time. Usually, the output is printed on paper for easy analysis.

* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.