Short reflectors operating at the fundamental and second harmonics on 128° LiNbO3

In this work, we study numerically surface acoustic wave (SAW) reflectors comprising a small number of electrodes operating at the fundamental and second harmonic frequencies on 128° YX-cut LiNbO₃. The electrodes have a finite thickness and they are either open-circuited or grounded. We use software based on the finite-element and boundary-element methods (FEM/BEM) for numerical experiments with a tailored 3-IDT test structure, simulating experimental conditions with an incident wave and reflected and transmitted SAWs. Employing the fast Fourier transform (FFT) and time-gating techniques, calculation of the Y-parameters allows us to determine the reflection coefficients and to estimate the energy loss due to bulk-wave scattering. The detailed dependencies of the attenuation and reflectivity on the metallization ratio and the electrode thickness are given for 128° LiNbO₃.