Self‐Consistent Theory of Interdigital Transducers

The generation and absorption of surface waves by an interdigital transducer with uniform finger spacing are calculated with the aid of a surface dielectric constant related to the TM‐wave impedance. It is found that the response of an infinite transducer can be calculated with complete consistency, i.e., the field due to the distortion of the piezoelectric medium is correctly included in the determination of the distortion. For a finite transducer, the solutions given are in error only at lines on the surface at either end of the transducer, and are therefore accurate when the transducer is long. It is found that the parallel equivalent circuit derived in the weak coupling approximation is a reasonably accurate representation of the transducer when the coupling is strong and the transducer long, but that the central resonance is then distorted.