(Received August 18, 1973)
The influence of poling on the frequency of surface acoustic waves was experimentally studied using PZT and several interdigital transducers with the same period but different finger width and spacing. The poling was done by applying a dc electric voltage across the transducer electrodes near the Curie temperature, Tc.
With weak poling, transducer fingers wider than or equal to the spacing generated second- and fourth-harmonic signals (referred to the fundamental frequency normally expected of the transducer). The generated second-harmonic increased to a saturation value while the fourth, first increased, and then decreased as poling was carried to completion. For transducers with fingers narrower than the spacing, the generation of the fourth harmonic was too weak to observe.
The largest conversion efficiency, -8.5 dB, was obtained for second harmonic generation using transducer fingers slightly wider than the spacing. This efficiency was comparable with that of the same transducer on a uniformly poled PZT generating the fundamental frequency. These results indicate that second- and fourth-harmonic generation for appropriate poling conditions and transducer geometry is possible and extension of the transducer-frequency capability without size reduction can be achieved.