SAW Excitation and Detection

The discovery by R. M. White of the University of California at Berkeley that surface acoustic waves could be excited and detected by lithographically patterned interdigital electrodes on the surface of piezoelectric crystals [42] has led to widespread use of SAW devices in a number of signal-processing applications. These include frequency filters, resonators, delay lines, convolvers, and correlators [43,44]. 

The transducer operates most efficiently when the SAW wavelength, A, matches the transducer periodicity, d. This occurs when the transducer is excited at the synchronous frequency, defined by/ , = vjd, where v is the SAW propagation velocity. 

As discussed in Section 2.2.1, propagation of a mechanical wave in a piezoelectric medium is accompanied by an associated wave potential, tj . When the wave is incident on a receiving transducer, diis potential induces a current flow in each transducer electrode these currents combine to produce a current flow in the external detection circuit. The addition of current contributions in the receiving transducer is also optimized when the transducer periodicity matches the acoustic wavelength. Thus, a reciprocity relation holds, as it must for a passive linear device, between the wave and external signals. 

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