PERIODIC GREENS-FUNCTIONS ANALYSIS OF SAW AND LEAKY SAW PROPAGATION IN A PERIODIC SYSTEM OF ELECTRODES ON A PIEZOELECTRIC CRYSTAL

A method of periodic Green's functions with a propagation factor esp(i Bx), unknown in advance, is used to calculate dispersion curves and at tenuation coefficients for Rayleigh- and leaky- waves propagating in a periodic system of thin electrodes on a piezoelectric surface, To des cribe the charge distribution on the electrodes both a step approximat ion and Chebyshev polynomials are used, the last being more adequate i n most cases. Numerically determined values of the Green's function ar e used and interpolated either linearly or using a modified variant of Ingebrigtsen's formula. Such basic parameters as stopband width, stop band center frequency, wave velocity and attenuation in the stopband a re found. These parameters can be used in the coupling-of-modes (COM) analysis and design of SAW devices. The analysis includes bulk wave ra diation acid scattering. The dependence of the corresponding attenuati on coefficient on frequency is determined. Results obtained allow the determination directly and properly of the COM parameters and the desi gn of SAW devices having large number of electrodes most precisely and rapidly. Numerical results for Rayleigh waves on YZ-LiNbO3 and leaky waves on 36 degrees YX-LiTaO3 substrates are presented.