Effective nonlinear constants for SAW devices from FEM calculations

Recently we demonstrated that a single frequency-independent constant in a P-matrix approach is sufficient to describe the IMD3 of a variety of devices on LiTaO3-42YX including test devices and duplexers. In this work we investigate this effective nonlinear constant in more detail. Starting from a FEM simulation we calculate the linear fields at the frequencies of the input tones and combine them with the help of nonlinear tensors to get sources for nonlinear fields at mixing frequencies. The determination and analysis of the nonlinear shift of the resonance frequency yields an effective nonlinear coupling constant. This approach has been applied to LiNbO3-rot128YX. The value of the effective nonlinear constant calculated for this system is compared to the corresponding value extracted from nonlinear P-matrix simulations of IMD3 measurements.