TABLE OF CONTENTS In this chapter we concern ourselves with the calculation of acoustic characteristics of transducers, such as directivity function, directivity factor, directivity index, and self radiation impedance. Convenient formulae and numerical information for frequently used cases will also be given. The classical analytical methods are limited in their ability to calculate the acoustical characteristics of realistic transducers, and it is usually necessary to simplify the details of a transducer and its surrounding structure in order to apply those methods. However, finite element numerical modeling of the acoustic field can provide more realistic information to augment the analytical results in many cases. The well-known acoustics books by Kinsler and Frey et al. [1], Morse and Ingard [17], Pierce [2] and Blackstock [3] provide excellent background for this chapter.
The acoustic medium is an essential part of electroacoustic transduction. It is usually a fluid, in most cases either water or air, characterized by only two properties, static density, ?, and bulk modulus, B. But in transducer analysis and design, ? and sound speed, c = (B/ ?) 1/2, are the more convenient properties. The product of these two quantities, ?c, the specific acoustic impedance, is much higher for water than for air (~ 1.5 10 6 vs. 420kg/m 2s) causing water to have a much more significant effect on the operation of a transducer than air. We will consider that the medium surrounding an individual transducer is homogeneous, isotropic, non-viscous...
