TABLE OF CONTENTS This chapter will describe the six major electroacoustic transduction mechanisms in a unified way using one-dimensional models to derive pairs of linear equations specific to each mechanism as discussed in general in Section 1.3. Important characteristics of the transducer types will be summarized and compared to show why piezoelectric and magnetostrictive transducers are best suited for most applications in water.
In piezoelectric, electrostrictive, and magnetostrictive materials applied electric or magnetic fields exert forces on charges or magnetic moments contained within their crystalline structure. In these body force transducers the electric or magnetic energy is distributed, with the elastic energy and some of the kinetic energy, throughout the active material. Thus the stiffness, mass, and drive components are not completely separated as implied by Fig. 1.22; instead the stiffness, drive, and some of the mass are included in the active material as suggested by Fig. 2.5. Figure 1.22, where the symbol M is only mass and the symbol K m is only stiffness, represents the lumped parameter approximation. This very frequently used approximation holds for body force transducers only when the dimensions of the active material are small compared to the wavelength of stress waves in the material and the mass and stiffness are independent of frequency. Lumped parameter models will be used in this chapter because, although relatively simple, they still include the basic characteristics of each transduction mechanism.
The transducer models in this chapter do not include important dynamic effects that will be discussed in Chapters 7...
