Theoretical and experimental investigation of spurious modes in a SAW delay line based on langasite

The measured characteristics of a test SAW device built on YX cut of LGS were analyzed in the time-frequency domain, using spectrogram representation. Especially, spurious modes were detected and investigated. A combination of numerical techniques was applied to the analysis of the observed spurious modes, including simulation of the admittance of a Pt grating on an LGS plate of finite thickness and visualization of the wave structure at different frequencies. The influence of the anisotropy on the frequency-time ratio was taken into account for each of three obliquely propagating bulk waves via detailed numerical investigation of the BAW slowness surface. The main spurious BAW modes propagating parallel to the surface or at certain tilt angles and reflected from the bottom were identified. The frequency-time dependences predicted via analysis of BAW anisotropy showed good agreement with experimental results.