Performances of short reflectors on 128° LiNbO3

We study numerically the phase of SAWs reflected from, or transmitted through, short reflectors comprising only 1-3 aluminium electrodes on 128° YX-cut LiNbO₃. We also try to find the optimum geometry for the reflectors to achieve the minimum of ratio of energy lost due to the scattering into the bulk to that of the reflected SAW. The electrodes have a finite thickness and they are either open-circuited or grounded. We use FEM/BEM software for numerical experiments with a tailored 3-IDT test structure, simulating experimental conditions with an incident wave and reflected and transmitted SAWs. Employing a procedure for enhancement of time resolution in conjunction with the fast Fourier transform (FFT) and time-gating, calculation of the Y-parameters in a reasonably wide frequency range allows us to determine the phase of the reflection and transmission coefficients. Our quantitative results suggest that the phase change attributed to the reflection depends on both the relative electrode thickness (h/λ₀ = 2-8%) and the metallisation ratio (a/p = 0.2-0.8).