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Abstract: A novel approach, based on spectral analysis, for determination of the upper frequency bound for the homogenization domain is developed. The method is based on displacement field analysis, which is calculated using the recursive transfer matrix. It makes up a description of the equivalent homogenous material associated to the multilayer in the low frequency area. Inside the homogenization domain the displacements field perpendicular to layers, in term of deepness, are plotted. A fast-Fourier transform (FFT) processing is used to compute the wave numbers propagating in the multilayer. The plot of the dispersion curves show that, for a limiting frequency, we may consider the multilayer as an effective homogeneous anisotropic medium supporting at the most three plane waves. Above this frequency the medium becomes dispersive and has a nonhomogeneous character. Multilayered systems resulting from the stratification of carbon–epoxy cells of the type [0/90] and [0/45/90/−45], are used for the illustrations. [Copyright &y& Elsevier]

Theoretical analysis of surface acoustic wave (SAW) propagation in a pre-stressed layered piezoelectric structure basing on the modified ordinary differential equation (ODE) is described. Numerical calculations involve a thin piezoelectric layer of ZnO bonded perfectly to an elastic substrate of Al 2 O 3 . ZnO thin films are deposited on Al 2 O 3 substrates using plasma assisted molecular beam epitaxial (MBE). The crystallographic orientation of ZnO thin films and the surface morphology are analyzed by X-ray diffraction (XRD) and atomic force microscopy (AFM) respectively. The density and the thickness of the ZnO films are determined by X-ray reflectivity. The initial stress and strain of ZnO films are measured by X-ray diffraction method. The effect of initial stress on the propagation behavior of Rayleigh and Love waves and on the coupled electromechanical factor is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Piezoelectric thin films on high acoustic velocity non piezoelectric substrates, such as ZnO and AlN, deposited on diamond or sapphire substrates, are attractive for high frequency and low-loss surface acoustic wave devices. In this work, ZnO films were epitaxialy grown on R-Al2O3 and C-Al2O3 substrates using plasma-assisted molecular beam epitaxy (MBE). The surface roughness of the ZnO layers is about 0.2nm for a 2μm×2μm AFM scan area. The absolute epitaxial relationships between ZnO films and α-plane sapphire are investigated by X-ray diffraction techniques. The resulting relationships for ZnO films on R-Al2O3 and C-Al2O3 substrates are found to be and , respectively. An analytical technique to determine residual strain in epitaxial ZnO films by X-ray diffraction (XRD) was studied. Based on piezoelectric constitutive equations and Bragg law, we applied an extended model, in which the elastic, piezoelectric and dielectric constants are introduced, to evaluate the residual stress in these films. [Copyright &y& Elsevier]