Interdigital Transducer Frequency Response

Each transducer finger may be considered to be a discrete source for the generation of surface waves in a piezoelectric medium because the piezoelectrically generated stress varies with position near each transducer finger. A simple trans- 

When an array of fingers is excited, as occurs with an interdigital transducer (IDT), the wave potential for a rightward propagating wave evaluated at position z is a vector sum of the contributions from each linger  

If Nf identical fingers are spaced periodically with period d and excited with alternating voltages = ( -1) V , Equation 3.40 becomes 

Moving away from the synchronous frequency, the addition of components from individual fingers becomes incoherent, giving rise to the frequency response 

the transducer bandwidth B is inversely proportional to the number of IDT fingers. As will be described in Chapter 4, a narrow bandwidth is desirable for oscillator applications in order to avoid spurious oscillations and to improve stability. 

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Figure 3.21 The frequency response measured between a pair of interdigital transducers. (Reprinted with pemission.

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