Reflection Properties of Shear-Horizontal Surface Acoustic Wave in Periodic Gold Grating on Langasite

Abstract

The reflection properties of a pure shear-horizontal (SH) surface acoustic wave (SAW) in a periodic gold (Au) grating on rotated Y-cut 90° X propagation langasite (LGS) with Euler angles of (0°,θ,90°) are investigated experimentally. The reflection coefficient was directly measured using an electrode consisting of two probe interdigital transducers and a shorted grating with 60 metal strips. When the Au film thickness was 0.015λ and the metallization ratio η was 0.43, the reflection coefficient was measured to be 0.73, which was larger than similarly measured values for Rayleigh waves on Al/ST-X quartz of 0.62 and Al/LGS(0°,140°,25°) of 0.41. By taking the measured propagation loss for SH SAW on Au/LGS(0°,0°,90°) into consideration, a reflection coefficient close to 1.0 was obtained. Furthermore, the equivalent-circuit parameters for SH SAW on Au/LGS(0°,0°,90°) were determined from the measured resonance characteristics of a normal IDT with 60 finger pairs; then the reflection coefficient was calculated using those parameters. The reflection coefficient predicted was 0.98 for the shorted grating with 60 metal strips on Au/LGS(0°,0°,90°), and agreed with the result obtained by direct measurement. The number of strips on Au/LGS(0°,0°,90°) required to obtain a reflection coefficient of 0.9 was predicted to be 20, which was one-fourth that in the case of Al/ST-X quartz.