Introduction

Abstract

The development of underwater electroacoustic transducers expanded rapidly during the twentieth century, and continues to be a growing field of knowledge that combines mechanics, electricity, magnetism, solid state physics, and acoustics with many significant applications. In the most general sense a transducer is a process or a device that converts energy from one form to another. Thus, an electroacoustic transducer converts electrical energy to acoustical energy or vice versa. Such processes and devices are very common. For example, a thunderstorm is a naturally occurring process in which electrical energy, made visible by the lightning flash, is partially converted to the sound of thunder. On the other hand, a familiar man-made transducer is the moving coil loudspeaker used in radio, television, and other sound systems. Loudspeakers are so common that they probably outnumber people in developed parts of the world. The familiar designations loudspeaker and microphone for transducers used as sources and receivers of sound in air become projector and hydrophone for sources and receivers in water. The term SONAR (SOund Navigation And Ranging) is used for the process of detecting and locating objects by receiving the sounds they emit (passive sonar), or by receiving the echoes reflected from them when they are “insonified” in echo ranging (active sonar). Every use of sound in the water requires transducers for its generation and reception, and most are based on electroacoustics. Several non-electroacoustic transducers also find applications in water, e.g., projectors based on explosions, sparks, and hydroacoustics as well as optical hydrophones, but they are not included in this book.