Introduction to Sonar Transducer Design

3Waves in Solid Media

This chapter introduces the basic principles of waves in solid media. One can visualize a transducer as a device that generates acoustic waves within its structure (i.e. a spring‐mass system) and then guides or transmits these waves into a fluid media. In a sense, a transducer is an acoustic wave generator and wave guide that subsequently interfaces with fluid media. Therefore, it is essential that we understand how waves are generated in and propagate through the solid structures that make up the transducer. We will first discuss waves in homogeneous media such as aluminum and steel. Many components of transducers are made of these materials. We will develop the equivalent circuits that can be used to model this wave propagation. Further, this discussion forms a solid foundation for the introduction of piezo‐electric materials. Piezo‐electric materials are solid materials that act as wave guides but have the additional feature of being able to generate or induce wave motion within their very structure. The application of a voltage to these solid materials induces a propagating wave. Similarly, if the piezo‐electric material interfaces with an acoustic wave, a voltage can be generated of sufficient magnitude to be of use as a sensor. The concepts of this chapter and the previous two chapters will then be combined in Chapters 4 and 5 when we put all this together and develop sonar projectors and receivers.

3.1 Waves in Homogeneous, Isotropic, Elastic, ...