Study on the bulk wave radiation of finite-length SAW devices using FEM/BEM

Based on the distributions of stress and free charge on the interface of the surface acoustic wave (SAW) device calculated with the combination of boundary element method and finite element method(FEM/BEM), the power of each of the three possible bulk waves radiated by the SAW device is calculated, and their contributions to the overall input conductance are separated respectively. Moreover, the formula of angular distributions of their power radiation into the substrate is derived. Consider the effect of mass loading, the resistance density, defined as a scalar, is extended to generalized resistance densities which can be written as three 4 x 4 tensors and for which the formulas are derived. The bulk wave radiations for a synchronous one-port resonator on 42 degrees Y-rotated LiTaO3 are simulated. It is found that the radiated energy by slow shear wave contributes a very high proportion to input electrical energy in some frequency range.