Direct finite-element analysis of the frequency responseof a Y-Z lithium niobate SAW filter

Abstract

A direct finite-element model is developed for the full-scaleanalysis of the electromechanical phenomena involved in surface acoustic wave (SAW) devices. The equationsof wave propagation in piezoelectric materials are discretized using theGalerkin method, in which an implicit algorithm of the Newmark family withunconditional stability is implemented. The Rayleigh damping coefficients areincluded in the elements near the boundary to reduce the influence of thereflection of waves. The performance of the model is demonstrated by theanalysis of the frequency response of a Y-Z lithium niobate filter withtwo uniform ports, with emphasis on the influence of the number of electrodes.The frequency response of the filter is obtained through the Fourier transformof the impulse response, which is solved directly from the finite-elementsimulation. It shows that the finite-element results are in good agreementwith the characteristic frequency response of the filter predicted by thesimple phase-matching argument. The ability of the method to evaluate theinfluence of the bulk waves at the high-frequency end of the filter passbandand the influence of the number of electrodes on insertion loss is noteworthy.We conclude that the direct finite-element analysis of SAW devices can be usedas an effective tool for the design of high-performance SAW devices. Somepractical computational challenges of finite-element modeling of SAW devicesare discussed.