Acoustic Surface Wave Coupling Across an AIr Gap

Transfer of acoustic surface waves between two noncontacting surfaces by means of passive, co-directional piezoelectric coupling is achieved in LiNbO3. Minimum coupling loss is less than 3 dB. When the surfaces are maintained parallel, periodic variation of insertion loss with coupling length is observed. Measurements are in close agreement with predictions using coupled mode theory. A 100-MHz delay line with a mechanically variable, nondispersive differential delay of 6.1 μsec and a total insertion loss less than 17 dB which utilizes this coupling mechanism is reported.