Wavefront Distortion of Acoustic Surface Waves from Apodized Interdigital Transducers

The acoustic surface wave launched by an interdigital transducer is experimentally shown to have a distorted wavefront when the transducer has a varying finger overlap (apodization) and is on a high-coupling piezoelectric substrate, LiNbO3. Results are shown for different transducer geometries, when an acoustic wave passes under the comb and when the apodized comb itself is driven. One geometry having extra metal fingers significantly reduces the wavefront distortion. The origin of the distortion is a retardation of the wave passing under metal fingers.