THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

424 15. Underwater AcousticsFigure 15.7. A computer-produced ray diagram for sound transmission from a 50-ft(15.24-m) source in a 200-ft (61-m) mixed layer.15.10 Deep Sound ChannelIn Section 15.4 reference was made to a region constituting the deep sound channelwhere the sound propagation speed reaches a minimum in the ocean depths. All raysoriginating near the axis of this channel and making small angles with the horizontalwill return to the axis without reaching the ocean surface or bottom, thus remainingentrapped within that channel. Absorption of low frequencies in seawater tends tobe quite small, so the low-frequency components of explosive charges detonatedin this channel can travel tremendous distances, and they have been detected morethan 3000 km away. The reception of these explosive signals by two or morewell-separated hydrophone arrays can permit an accurate determination of theexplosion’s location by triangulation. Passive sonar is currently being used in deepsound channels to monitor activities in deep ocean.15.11 Sonar Transducers and Their PropertiesUnderwater sound equipment are designed to detect and analyze underwater sound.They generally consist of a hydrophone array that consists of transducers thatconvert acoustic energy into electrical energy, and vice versa, and a signal processingsystem to analyze and display the signals aurally or visually. A transducerthat accepts sound and converts it into electricity is called a receiver orhydrophone. A transducer that converts electrical energy into sound is called a projector.Some sonar systems use the same transducer to generate and receive sound.There are two principal types of transducers according to the special propertiesof their activation materials. One type of transducer depends on piezoelectricity