Advanced numerical methods for the simulation of SAW devices

The continuing improvement of the computer models for parasitics and second-order effects and their straight-forward implementation often leads to a dramatic increase in the complexity of the simulation code and a corresponding increase in the run-time of the programs, which may easily surpass the speed-up provided by the ongoing technical advance in computer hardware. When the refined computer models are to be used on a daily basis in the iterative design processes of SAW devices, special attention has to be paid to the selection of the numerical algorithms and their proper implementation in order to find a good compromise between acceptable program run time and the necessary accuracy. Several areas symptomatic for the impact of numerical methods on the simulation of SAW devices are addressed in this paper. We look at improving the numerical accuracy in the calculation of the electrostatic Green's function, and we investigate how the underlying tapped-delay-line structure of all SAW devices can be used to speed up the cascading of P-matrix unit cells and help to efficiently provide IDT parameters during diffraction simulation. We also address the efficient solution of large systems of linear equations that typically arise when equations have to be solved numerically. The high rank and/or the complicated structure may prevent a direct solution of these equations. We show how an iterative technique may be successfully used under such circumstances.