In an elastically isotropic semiinfinite medium having a free surface with a weak harmonic corrugation, the interaction between the Rayleigh wave guided along the free surface and the shear vertical and pressure bulk elastic waves propagating in the substrate is investigated for the propagation directions lying in a plane perpendicular to the average free surface and containing the grating vector. The governing equations of this interaction are deduced and are shown to be consistent with the requirements of reciprocity and power conservation. The theory is applied to determine the characteristics of the output coupler in which the Rayleigh wave guided along the free surface radiates the bulk elastic waves in the substrate as well as those of an input coupler in which the shear and the pressure bulk elastic waves in the substrate incident on the corrugated region of the free surface launches the Rayleigh wave. Techniques for optimizing the performance of the input coupler to achieve maximum excitation efficiency of the Rayleigh wave are examined. The characteristics of these transducers are presented with the help of some illustrative numerical results.