Transducers as Projectors

Abstract

Active sonar and acoustic communication systems rely on electroacoustic transducers which "project" sound that is subsequently detected by hydrophones through a direct path or reflection from a target. Our focus in this chapter is on the projector which is significantly larger and more complex than the hydrophone because of the need to generate high acoustic intensity. Because of the reciprocal nature of transducers, the underlying concepts presented in this chapter will also apply to hydrophones, which are discussed in Chapter 4, although the details may differ considerably. The fundamentals of Chapters 1 and 2 form the basis for our discussion of both projectors and hydrophones. The basis, and the details, for analyzing transducers using equivalent circuits, matrix representations, and finite element models will be presented in Chapter 7, while acoustic radiation from transducers will be discussed in Chapter 10. Naval applications present the principal needs for underwater sound transducers and the main motivation for new transducer developments. Surface ships use hull-mounted arrays containing hundreds of projectors for medium frequency active search sonar and high frequency mine-hunting sonar. Similar arrays are also mounted in towed bodies. Other projectors are used on surface ships for acoustic communications and depth sounding. Submarines, which depend on underwater sound more than other ships do, use all the above types of sonar, but also need sonar for obstacle avoidance and navigation under ice. Submarine transducers must also be capable of operating over a wide range of hydrostatic pressure. Long range active sonar surveillance presents the greatest challenge to transducer development because of the need for high power at low frequency. Underwater communication systems require ship mounted transducers, but also involve networks of fixed transducers with special requirements. In addition there are many non-military applications for underwater sound transducers such as depth sounding , bottom mapping, fish finding, investigation of ship and aircraft wrecks, oil exploration, and various research projects. Depending on source level, bandwidth, and system requirements, projectors can take various geometrical and mechanical forms such as spheres, cylinders, rings, piston radiators (see Figs.