Short reflectors operating at the fundamental and second harmonics on 128/spl deg/ LiNbO/sub 3/

Abstract

In this work, we study numerically the operation of surface acoustic wave (SAW) reflectors comprising a small number of electrodes on the 128/spl deg/ YX-cut lithium niobate (LiNbO/sub 3/) substrate. The electrodes have a finite thickness, and they are either open circuited or grounded. The center-to-center distance between adjacent electrodes d corresponds roughly either to half of the characteristic wavelength d /spl prop/ /spl lambda//sub 0//2 or to d /spl prop/ /spl lambda//sub 0/, for the reflectors operating at the fundamental and second harmonic modes, respectively. We use software based on the finite-element and boundary-element methods (FEM/BEM) for numerical experiments with a tailored test structure having 3 interdigital transducers (IDTs), simulating experimental conditions with an incident wave and reflected and transmitted SAWs. Using the fast Fourier transform (FFT) and time-gating techniques, calculation of the Y-parameters in a wide frequency range with rather a small step allows us to determine the reflection coefficients, and to estimate the energy loss due to bulk-wave scattering. The detailed dependences of the attenuation and reflectivity on the metallization ratio and the electrode thickness are given for the classic 128/spl deg/-cut of LiNbO/sub 3/.