Analysis of bulk waves in surface-acoustic wave devices

A spurious response due to bulk waves has often been observed in surface-acoustic filters. This paper shows how bulk waves are radiated by the charge source on the surface of a semi-infinite piezoelectric solid. The expression for each component of bulk waves is evaluated asymptotically, in the form of the Fourier integral, by assuming that the observation point is located far from the source in comparison with a wavelength. In doing this, the method of steepest descents is used in order to integrate analytically. The numerical results are obtained for rotated Y-cut X-propagating LiNbO3 and Y-Z LiNbO3. These results are in good agreement with the experiment reported by Togami and Chiba.