Parameters in the Coupling-of-Modes Equations for a Natural Single-Phase Unidirectional Transducer and a Transduction Center Shift Reversal of Directivity Transducer on a La₃Ga₅SiO₁₄ Substrate

Abstract

Parameters included in coupling-of-modes equations such as coupling coefficient, transduction coefficient and electrode capacitance are theoretically determined using the finite-element method (FEM) for a natural single-phase unidirectional transducer (NSPUDT) and a transduction center shift reversal of directivity transducer (TCS-RDT) on La3Ga5SiO14 piezoelectric single crystal which has a higher electromechanical coupling coefficient compared to quartz. The electrode thickness dependence of the parameters and the excitation characteristics of NSPUDT and TCS-RDT are investigated in detail. For NSPUDT, the parameters obtained by the present method are compared with those obtained by the perturbation method. Furthermore, numerical results for the frequency characteristics of NSPUDT are compared to the experimental data, and the validity and usefulness of the present method are demonstrated.

All-Optical Logic Functions in a Bent Nonlinear Y-Junction Waveguide

“…9,10,12,[16][17][18][19] Considering the two cases, namely, electrically shorted and open infinite arrays, the relations 10,12,[17][18][19] are derived between the edge frequencies of a stop-band and the three parameters of copled-mode equations; the self-coupling coefficient κ 11 , the absolute value of the mutual-coupling coefficient |κ 12 |, and the normalized absolute value of transduction coefficient |ζ | p/ √ π f 0 C s with f 0 and C s being the center frequency and static capacitance per one pair of IDT, respectively. Using these relations, we can calculate the amplitudes of all the coefficients.…”

“…The phases of the two coefficients, Arg(κ 12 ) and Arg(ζ ), are determined from the standing-wave distribution of electric potential on the substrate surface, which is predicted by the coupled-mode theory, at the edge frequencies of the stopband for infinite shorted and open gratings. 10,12,17,19) These standing-wave distributions may be obtained from computed standing-wave distributions of infinite gratings as follows:…”

“…If we take an assumption that the field distribution on all the planes z ≤ −2λ with λ being the SAW wavelength can be approximated with that of the unperturbed substrate surface, employing unperturbed mode functions, we may determine the required standing-wave distribution. 10,19) By this method, NSPUDTs on ST-25 • X quartz and 15 • Y -11.5 • X La 3 Ga 5 SiO 14 substrates were analyzed. When this assumption is invalid, for example, for a 50 • Y -24 • X La 3 Ga 5 SiO 14 substrate case, the standing-wave distributions on the substrate surface can be derived from the projection of the standing-wave distributions onto the set of those predicted by the coupledmode theory.…”

“…Few reports 9,10) have been published on SAW grating characteristics on an LGS substrate. Recently, employing coupled-mode and perturbation theories, Takeuchi et al theoretically investigated doubly rotated Y -cut plates and demonstrated that a (0 • , 140 • , 24 • ) plate has a naturalsingle-phase-unidirectional transducer (NSPUDT) orientation.…”