ABSTRACT
There are almost an infinite number of ways that ultrasonic transducers can be used in widely diverse applications. For purposes of this chapter, in specifying the medium that the transducer is coupled to, we group the use of BAW transducers into four main application areas:
1. Excitation for delay lines 2. General coupling into solids for NDE 3. Emission into aqueous media 4. Resonators in air for sensors and timing applications
The section starts with a summary of the representation of a BAW transducer by an equivalent circuit, followed by a discussion of transducer behavior in the neighborhood of the resonance frequency. Various cases of impedance matching and backing of the transducer are discussed and it is shown how these parameters influence the transducer operation in the time and frequency domain. Piezoelectric tranducers are discussed in most books on ultrasonics. One of the most comprehensive and useful contributions is given by Kino [20] and much of this section summarizes his treatment.
