FEM/BEM analysis of a generalized periodic array.
ABSTRACT Recent developments in wide bandwidth SAW filter design led to the use of complex electroacoustic cells, such as the Hanma-Hunsinger cell. For this kind of structure, it is not sufficient to use only a single electrode periodic FEM/BEM model to derive the P-matrix parameters. The present paper proposes a mixed FEM/BEM numerical model for the simulation of a periodic array of metallic electrodes, the elementary cell of which can be as complex as necessary: it can contain several electrodes, connected to active ports, or short-circuited, or floating.
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ABSTRACT: Because of more and more stringent requirements on SAW filter performances, it is important to compute, with very good accuracy, the SAW propagation characteristics, which include the calculation of reflection and scattering parameters. For that reason, the analysis of periodic structures on a semi-infinite piezoelectric substrate is one of the most important problems being investigated by SAW researchers. For infinite periodic grating modeling, we developed numerical mixed FEM/BEM (finite element method-boundary element method) models using an efficient interpolation basis function that takes into account the singularity at both edges of each electrode. In this paper, a review of the numerical program that has been developed during the past few years will be presented. For an infinite periodic grating, it is convenient to solve the propagation problem in the Fourier domain (wave number space and harmonic excitation), and important efforts have been spent to properly integrate the so-called periodic harmonic Green function. Using this numerical model together with the general P-matrix formalism, it is possible to compute all of the basic parameters with a very good accuracy. These consist of the single strip reflectivity, acoustic wave-phase velocity, and position offset between reflection and transduction centers. Simulations and comparisons with experiments are shown for each model.IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 10/2001; · 1.82 Impact Factor
Conference Proceeding: Fast analysis of SAW propagation under multi-electrode-type gratings with finite thickness[show abstract] [hide abstract]
ABSTRACT: The paper proposes the method for the fast and accurate analysis of SAW propagation under metallic gratings consisting of multiple electrodes having unequal width, pitch and/or thickness: the grating structure is promising for developing single-phase unidirectional transducers (SPUDTs) with controlled passband shapes. The finite element method (FEM) is applied to the electroded region to take account of the effect of electrode thickness (mass-loading effect), and spectral domain analysis (SDA) to the substrate region for rapid computation. Electrical properties of the grating are determined by applying Aoki's theory to the results of FEM and SDA at the boundary. Two kinds of typical metallic gratings were analysed, and the unidirectionality was discussed for SPUDTs employing these grating structuresUltrasonics Symposium, 1997. Proceedings., 1997 IEEE; 11/1997
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ABSTRACT: A method of periodic Green's functions with a propagation factor exp(i/spl beta/x), unknown in advance, is used to calculate dispersion curves and attenuation coefficients for Rayleigh- and leaky- waves propagating in a periodic system of thin electrodes on a piezoelectric surface. To describe the charge distribution on the electrodes both a step approximation and Chebyshev polynomials are used, the last being more adequate in most cases. Numerically determined values of the Green's function are used and interpolated either linearly or using a modified variant of Ingebrigtsen's formula. Such basic parameters as stopband width, stopband center frequency, wave velocity and attenuation in the stopband are found. These parameters can be used in the coupling-of-modes (COM) analysis and design of SAW devices. The analysis includes bulk wave radiation and scattering. The dependence of the corresponding attenuation coefficient on frequency is determined. Results obtained allow the determination directly and properly of the COM parameters and the design of SAW devices having large number of electrodes most precisely and rapidly. Numerical results for Rayleigh waves on YZ-LiNbO/sub 3/ and leaky waves on 36/spl deg/YX-LiTaO/sub 3/ substrates are presented.< >IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 04/1995; · 1.82 Impact Factor