Sound Navigation Ranging (Sonar) Sonar is an underwater detection system based on horizontally directed sound waves and their echo reception. Sonar operates on a principle similar to that of radar, but instead of electromagnetic waves, it uses sound waves. There are two main types of sonar, passive and active. Passive sonar listens for sound given off by possible targets and can determine the direction in which an object is located, but not its distance. Submarines generally use passive sonar systems because they do not give off any sound that another sonar might detect. Active sonar sends sound waves through the water and receives echoes from any object struck by the outgoing waves. Most surface ships must use active sonar because noise from the ship itself interferes with passive sonar. Recall the familiar ping of the sonar in movies featuring submarines. This ping is an electrically produced sound wave transmitted by a sonar transducer. The transducer uses a crystal and pulses of high-frequency voltage to produce the vibration that is transmitted through the water. When the crystal is subjected to pulses of high frequency voltage, the crystal will distort at the same rate as the frequency. It is the crystal’s distortion that produces the vibration. Goodheart-Willcox Publisher Sound waves Electrodes Sonar transducer Wiring connections Crystal Acoustic lens The transducer is lowered through the bottom of the ship’s hull and sound waves are sent out through the water at regular intervals in bursts. If the outgoing waves strike a target, an echo is returned to the sonar receiver. The transducer rotates in complete circles, allowing the sonar operator to determine the direction from which an echo comes by noting the transducer’s position when the echo is received. Since the speed of sound through water is known, the range or distance from the sonar-equipped vessel to the target can be determined by measuring the time interval between the ping, or outgoing sound wave, and the return of its echo. Advances in underwater sound transmission and increased understanding of natural sea noises have helped to make the use of sonar more effective in everything from submarine warfare to mapping the ocean fl oors. New transducers and electronic scanning and searchlight techniques have made possible an extensive underwater communication system to assist in fl eet operations and in the guidance of submarines. Sonar has proved to be more effective than radar in warning against the presence of icebergs and smaller fragments of ice dangerous to navigation. Fishermen are able to detect schools of fi sh and observe the shape and pattern of the nets and the movements of fi sh entering or avoiding the net. Sonar can also be used to fi nd sunken vessels and aircraft. In the medical fi eld, sonar technology is used for various ultrasonic tests. The images produced by transmitting and receiving sound echoes in the human body are sonograms. A sonogram does not provide the high-quality picture of the body as some other imaging techniques, but it is very safe for the patient. Ultrasonic imaging is cost-effective, and the images produced can be enhanced through the use of a computer. A p p l i e d E & E Voltage oscillation Transmitter’s oscillation Transmitter Receiverr Echo wave Sound wave transmitter Object Time Time Monitor Radar beam reflected from ocean’s surface Sea level Typical depth 5,000 m Fishing boat finding sonar Signal Sonar Diagram Transducer Transducer Studio BKK/Shutterstock.com 121 Copyright Goodheart-Willcox Co., Inc.