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.
Parasitic BAW excitation in LSAW transducers
The parasitic excitation of bulk acoustic waves at high frequencies in synchronous leaky surface-acoustic wave resonators is studied experimentally in 36/spl deg/ and 42/spl deg/ YX-cut lithium tantalate. To characterize the strength of the bulk-wave excitation, the admittance curves measured from test structures with varying apertures, metallization ratios, and the number and the thickness of the aluminum electrodes are fitted numerically to a modified coupling-of-modes model. A theoretical formula for the dependence of the level of the bulk-wave excitation on the coupling-of-modes parameters is proposed.
Secoiridoids from Olea europaea
Abstract Three new secoiridoids have been isolated from the leaves of Olea europaea along with the previously reported. The compounds were identified by spectral means.