Propagation characteristics of surface acoustic waves on langasite

The propagation characteristics of surface acoustic waves (SAW) on La₃Ga₅SiO₁₄ were investigated by both experimental and numerical methods. The experimental results of the SAW velocity and the coupling coefficient (k²) on X-cut and K-cut substrates were in good agreement with the numerical results using the material constants reported previously. However, the experimental results of the temperature coefficient of delay (TCD) differed from that of the numerical calculations. So, a modification of the temperature coefficients of the material constants was performed numerically by the measured data using the direct search of optimization method. The numerical results obtained using the new constants were in good agreement with the experiment result on the X-cut and Y-cut substrates. Other cuts were also studied using the new constants. Then it was confirmed theoretically and experimentally that the temperature stable cut was located at (0°, 140°, 22.5°) cut with k² of 0.32% and TCD (second-order coefficient) of 5.2 × 10^-8/°C².