Scattering from a finite ribbed plate with attached oscillators.

Double layer structures consisting of stainless steel and polymer rods are designed to blur and attenuate Bragg and Bloch-Floquet scattering from a periodically ribbed plate in a given frequency bandwidth. These structures can be considered as ribbed plate-spring-mass systems, the resonance frequencies of which are obtained from random and circular permutations of five basic oscillators. Analytical and finite element methods are used to find their parameters and tank tests have been carried out to ensure the accuracy of the numerical results and validate the relevance of such a model. It has been found that the typical features associated with the periodicity of the ribs are replaced by a "Christmas tree" appearance when the far field pressure backscattered from the model is displayed in the (frequency, aspect angle) plane. An analysis of backscattering patterns is presented and comparisons with Naval Research Laboratory results are made.

3-D electrostatic hybrid element model for SAW interdigital transducers.

In this work, the singular behavior of charges at corners and edges on the metallized areas in SAW transducers are investigated. In particular, it is demonstrated that a tensor product of the commonly used Tchebychev bases overestimates the singularities at corners, and, hence, it cannot be used in a proper boundary element method formulation. On the other hand, it is shown that a simple finite element method-like approach is impractical due to the enormous number of unknowns required to model the electrode's large length-to-width ratio. These considerations are then used for defining a hybrid element model, which combines Tchebychev and linear polynomials over differently meshed domains. Such an approach is shown to suitably account for charge singularities while greatly reducing the number of unknowns. Results are obtained for isotropic and anisotropic substrates for non-periodic configurations.

High-frequency surface acoustic waves excited on thin-oriented LiNbO3 single-crystal layers transferred onto silicon.

The need for high-frequency, wide-band filters has instigated many developments based on combining thin piezoelectric films and high acoustic velocity materials (sapphire, diamond-like carbon, silicon, etc.) to ease the manufacture of devices operating above 2 GHz. In the present work, a technological process has been developed to achieve thin-oriented, single-crystal lithium niobate (LiNbO3) layers deposited on (100) silicon wafers for the fabrication of radio-frequency (RF) surface acoustic wave (SAW) devices. The use of such oriented thin films is expected to favor large coupling coefficients together with a good control of the layer properties, enabling one to chose the best combination of layer orientation to optimize the device. A theoretical analysis of the elastic wave assumed to propagate on such a combination of material is first exposed. Technological aspects then are described briefly. Experimental results are presented and compared to the state of art.

Prediction of the thermal sensitivity of surface acoustic waves excited under a periodic grating of electrodes.

The prediction of the temperature sensitivity of surface acoustic wave (SAW) devices still requires improvement because the nature of the implemented surface modes and the devices' complexity strongly change from the early basic Rayleigh-wave-based devices. To address this problem, a theoretical analysis and a numerical tool have been developed to predict the thermal dispersion of general electro-acoustic devices. The proposed model accounts for the electrode contribution to the frequency-temperature law. The computed thermal sensitivities are compared to experimental results for different kinds of substrates and waves.