Piezoelectric generation of surface waves by interdigital array

The paper shows how the variational principle can be used to analyse the generation of ultrasonic surface waves by an infinite interdigital array of electrodes on the surface of a piezoelectric material. The method is used to analyse the behaviour of such an array deposited on a piezoelectric ceramic. Representation of surface-wave generation by an approximate electrical equivalent circuit is discussed, and the variation of piezoelectric coupling factor with the electrode width/gap ratio is computed for the fundamental resonant frequency, and the third and fifth harmonics. Bulk-wave generation is also treated in some detail.