Ultrasound and SONAR

Definition

Ultrasound is sound of frequency above the human hearing range (over 20,000 hertz); SONAR (Sound Navigation and Ranging) is a technique that uses such sound waves to detect and locate objects under water.

Key points

• The human ear hears roughly 20 hertz to 20,000 hertz; below 20 hertz is infrasound and above 20,000 hertz is ultrasound.
• SONAR sends out sound pulses and measures the time for the echo to return; since sound travels faster in water than in air, distance and depth can be calculated.
• SONAR is used to map the sea floor, measure ocean depth, detect submarines and shoals of fish, and navigate, which is central to naval and maritime security.
• Medical ultrasound (sonography) uses high-frequency sound to image internal organs and the foetus during pregnancy, without ionising radiation; Doppler ultrasound measures blood flow.
• Other ultrasound uses include cleaning delicate instruments, non-destructive testing of metals for cracks, and ultrasonic distance sensors.

Why it matters for CAPF

The audible-range limits, ultrasound and infrasound, and SONAR for submarine detection and sea-floor mapping are recurring physics facts with a strong naval and coastal-security connection.

Common confusion

Ultrasound is sound above human hearing, not a form of light or electromagnetic radiation; SONAR uses sound, whereas RADAR uses radio (electromagnetic) waves. Medical ultrasound is safe because it uses sound, not ionising radiation like X-rays.

Related concepts

concept doppler effect, concept electromagnetic spectrum

Parent note

physics everyday