Abstract
An ordinary surface acoustic wave (SAW) interdigital transducer has a uniform launching aperture in the x direction (parallel to the wavefronts), and periodic finger pairs in the z direction (normal to the wavefronts). Hence, it has one-dimensional periodicity only in the z direction. In this paper we present a new type of a SAW transducer with two-dimensionally periodic electrodes, whose configuration has periodicity not only in the z direction but also in the x direction, (Fig. 1 (b)). It is possible to predict the beam profiles emitted from the two dimensionally periodic transducer (2-PT) using the method of the angular spectrum of plane waves (ASPW). It has been shown from this analysis that the 2-PT causes deflection of the SAW beam, and that the deflecting angle is determined by θ^*=tan^-1λ_z/λ_x, where λ_z and λ_x are the periodic lengths in the z and x directions, respectively. There are two advantages for this 2-PT ; (1) the SAW beam can be scanned by the deflection when the exciting frequency is swept, and (2) it is possible to decrease the sidelobe levels in a SAW filter substantially by controlling the angles of the SAW wavefronts. In order to verify the theoretical results, samples of 2-PT have been designed and fabricated on a Y-cut LiNbO_3 wafer and a sputtered ZnO film on glass. Experimental configurations of these are shown in Figs. 7 and 8, respectively. the observed propagation patterns by the FTH techniqueare shown in Figs. 9 and 10. Figs. 11 and 12 illustrate the experimental and theoretical frequency characteristics for the 2-PT's on a LiNbO_3 wafer and a ZnO film, respectively. Comparing the experimental results with the theoretical predictions, reasonable agreements have been obtained. In conclusion, it is found that the 2-Pt has promising characteristics for acousto-optic deflectors and SAW bandpass filters.
