Application of sound wave
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Destructive interference, if applied correctly, can be very useful. It is very important that an airplane pilot hears what's going on around him, but engine noise presents a problem. So, pilots can use special headphones mounted with a microphone that picks up the engine noise. A component in the headphones then creates a wave that is the inverse of the wave that represents the engine noise. This wave is then played back through the headphones allowing destructive interference to produce a quieter background. Other applications for destructive interference are "quieting" rides in automobiles and passenger sections in airplanes.
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Sonar stands for SOund NAvigation Ranging. Sonar is used in navigation, forecasting weather, and for tracking aircraft, ships, submarines, and missiles. Sonar devices work by bouncing sound waves off objects to determine their location. A sonar unit consists of an ultrasonic transmitter and a receiver. On boats, the receiver is mounted on the bottom of the ship. To measure water depth, for instance, the transmitter sends out a short pulse of sound, and later, the receiver picks up the reflected sound. The water depth is determined from the time elapsed between the emission of the ultrasonic sound and the reception of its reflection off the sea-floor. In the diagram below, a ship sends out ultrasonic waves (green) in order to detect schools of fish swimming beneath. The waves reflect off the fish (white), and return to the ship where they are detected and the depth of the fish is determined.
