SAW strain sensitivity of selected rayleigh wave crystal cuts

ST-quartz is commonly used for pressure sensor applications. Drawbacks are its frequency limitations and poor coupling coefficient. In particular for medical applications, where the temperature range is limited and the antenna size is critical, good signal coupling and higher frequencies may trump the temperature effects. This work compares experimental data on the sensitivity to mechanical loads of langasite 138.5°, lithiumtantalate 112.2° and ST-quartz. The measurements were performed on a dedicated test stand, using differential delay lines. The impulse responses versus varying mechanical loads were measured. The strain and stress distributions in the SAW elements were calculated from the measured mechanical loads using advanced FEM methods considering anisotropic elasticity. Sensitivity values to stress and strain have been deduced for the investigated substrates.