Acoustic grating couplers for mode conversion between bulk and surface waves are promising for intense surface acoustic wave (SAW) generation in the frequency rarge from VHF to UHF. In this paper, the performance of the grating couplers is theoretically analyzed on the basis of the leaky wave concept and the coupled mode theory, and the following points are clarified : 1) the mode conversion efficiency to be expected, 2) the dependence of the efficiency on the coupling length, 3) the difference between P-wave coupling and S-wave coupling to SAW, 4) the frequency characteristics of conversion efficiency. Also, the attenuation constant and the distribution factor, wihch determine the optimum coupling length and the conversion efficiency, are numerically calculated for several grating configurations.
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