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. >

Periodic Green's functions analysis of SAW and leaky SAW propagation in a periodic system of electrodes on a piezoelectric crystal

The paper describes how the propagation loss /spl alpha/ of leaky surface acoustic wave (LSAW) is dependent upon the Al thickness h of grating electrodes and rotation angle /spl theta/ for rotated Y-X LiTaO/sub 3/. Since the energy leak of LSAW originates from the coupling of the slow-shear field component with other components through the surface boundary conditions, zero /spl alpha/ can be realised when the slow-shear component is decoupled. This means that the optimal /spl theta/ giving zero /spl alpha/ should change with h as well as the surface electrical boundary conditions. Since relatively large h of 0.07-0.1 wavelengths is needed for present LSAW devices, the optimal /spl theta/ shifts to 40-42/spl deg/ from the conventional value of 36/spl deg/. Thanks to the minimised propagation loss, experimental results showed that device performances are markedly improved only by increasing /spl theta/ to circa 42/spl deg/ from 36/spl deg/. We also describe the state-of-the-art of the performances obtainable in commercially available LSAW devices based on 42/spl deg/YX-LiTaO/sub 3/.

Optimum leaky-SAW cut of LiTaO/sub 3/ for minimised insertion loss devices

A new high-performance surface-acoustic-wave (SAW) filter for use in mobile telephones is presented in this paper. The design for the actual realization of the new filter is examined, from the new filter configuration to the final device operation, A low-loss weighting technique in an interdigital transducer (IDT), a new resonant structure, computer simulation procedures, and material properties are treated. Experimental results with this SAW filter included an 830-MHz center frequency, 3-percent bandwidth, insertion loss of as low as 3.5 ~ 4.0 dB, and 50-dB sidelobe suppression filter.

R.F. Milsom

Papers

Surface Acoustic Waves on Rotated Y-Cut LiTaO 3