Impact of Backward Waves to FEM Simulations of SAW Resonators

This paper discusses the impact of backward waves in finite-element method (FEM) simulations of radio frequency surface acoustic wave/bulk acoustic wave devices. Owing to anisotropy of the material, backward waves not only appear at the vertical direction, but also exist in lateral directions, which will invalidate the commonly used perfectly matched layer (PML) in two directions. The ineffectiveness of PMLs may further result in inaccuracy in the numerical analysis. It is demonstrated that the infinite long damping boundary based on hierarchical cascading technique can give proper attenuation to backward waves, thus provide a possible solution to the problem.