Acoustic radiation by interdigitated grids on LiNbO3

Measurements are presented which show the acoustic power radiated as a function of frequency by an interdigitated transducer on the surface of a lithium-niobate boule. Several peaks are seen which are identified as either surface waves or bulk longitudinal waves travelling close to the boule surface. The transducer is seen to cause radiation at all frequencies above that for fundamental surface-wave generation. Additionally, the signal radiated to a nearby transducer is measured. This signal comprises just surface waves and a weaker bulk longitudinal wave. These are associated with the peaks in the launched power spectrum if reflections are suppressed. In finite regular-shaped samples reflections cannot be entirely suppressed and cause many anomalous signals. Over-all the results show that the average strength of bulk-wave generation is at least an order of magnitude more than that of surface-wave generation.