Coefficients of Coupled-Mode Equations for a Natural-Single-Phase-Unidirectional Transducer and an Electrode-Width-Difference-Reversal-of-Directivity Transducer on a 50° Y-24° X La₃Ga₅SiO₁₄ Substrate

Abstract

Computed results of all the coefficients of coupled-mode equations are presented for a natural-single-phase-unidirectional transducer (NSPUDT) and an electrode-width-difference-reversal-of-directivity transducer on a 50 • Y -24 • X La 3 Ga 5 SiO 14 substrate. In order to determine all the coefficients, edge frequencies of a stop-band, standing-wave distributions at these frequencies on a substrate surface, and static capacitances of a transducer are calculated using the hybrid finite-element method. Therefore, all the effects of piezoelectric perturbation, mechanical perturbation, and energy storage due to nonradiated bulk waves are taken into account. The aluminum electrode width dependences of the coefficients are investigated in detail. Numerical results reveal that we can choose pairs of width and height of the active electrodes for a distance of λ/8 with λ being the surface acoustic wave wavelength at the center frequency between the reflection center and the transduction center. Our results of the transducer loss for NSPUDT agree well with previous experimental ones.