The influence of mode shape on the acceleration sensitivity of SAW resonators

The acceleration-induced frequency shifts for distinct transverse modes of surface acoustic wave (SAW) resonators have been calculated and experimentally validated using a 98.5 MHz SAW resonator. The calculations were made using a recently developed finite element approach to develop numerical solutions for the static biasing state. The SAW mode shapes were determined by applying the variational formulation of Sinha and Tiersten. The calculated mode shapes were compared to actual resonator transverse mode shapes imaged using acousto-optic diffraction with a beam-expanded helium-neon (HeNe) laser to visualize the acoustic power flow. The static biasing state solutions were combined with the calculated mode shapes to compute theoretical acceleration-induced frequency shifts using the perturbation integral formulation derived by Tiersten. For the experimental confirmation, the 98.5 MHz SAW resonator was mounted in a voltage controlled oscillator (VCO) and submitted to acceleration sensitivity tests at frequencies corresponding to those resonator transverse modes previously imaged. The theoretical and experimental frequency shifts both indicate that the acceleration sensitivity of SAW resonators does not strongly depend on the transverse mode shape.