Theory for shear horizontal surface acoustic waves in finite synchronous resonators
An analytic approach is developed for simulating synchronous resonators employing shear horizontally polarized surface acoustic waves, such as surface transverse waves, and leaky surface acoustic waves on LiTaO/sub 3/ and LiNbO/sub 3/ substrates. The approach, based on a simplified parametrized Green's function theory, allows the description of the localization of the wave and the interaction with bulk acoustic waves. An analytic expression is found for the harmonic admittance of an infinite periodic electrode array, and approximate corrections for finite structures are presented. The model enables fast computation of the admittance of synchronous resonators, and it compares favorably with experiments and numerical simulations.
An analysis of shear horizontal surface acoustic wave propagation under mechanical losses
In piezoelectric materials, two kinds of losses can be distinguished: mechanical and dielectric. The loss effects are introduced in the Christofell formalism via complex elastic and dielectric coefficients, to evaluate the piezoelectric properties of shear horizontal surface acoustic waves. The surface permittivity concept is used to express the influences of losses on phase velocity, and the electromechanical coupling coefficient of the piezoelectric materials. The feasibility of this method is demonstrated with ZnO and AlN piezoelectric substrates.
Global attractivity in time-delayed predator-prey systems
Abstract For a predator-prey model with time-delay due to gestation, criteria are obtained for persistence and global attractivity. The global attractivity criteria apply only to models with a decreasing prey isocline.