An improved propagation model for chirped slanted SAW devices

An accurate and numerically efficient model that takes into account the two-dimensional nature of the propagation effects in chirped slanted SAW (surface acoustic wave) devices is described. It is shown that the spatial SAW profiles can be accurately represented by a small number of Gaussian modes. A Gaussian-beam-based diffraction theory is then applied that leads to a simple closed-form description of the mode diffraction behavior. A separate parabolic approximation to the SAW substrate is made for each mode, based on its propagation direction and the exact slowness characteristics. The parabolic approximations are justified, as the angular spectrum of each mode is sufficiently narrow. The modal decomposition of the spatial profile also allows evaluation of wave refraction on an individual-mode basis. The amplitude and phase front distortions caused by internal reflections in a solid electrode transducer are shown to require only one additional Gaussian mode. This model yields a realistic propagation transfer function for devices using chirped slanted transducers. Comparison with laser probe measurements is also presented