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1 . g. the shape of 39 906 V. Plessky & J, Koskela Fig. 10. Test structure for COM parameter extraction. the fingers) are not known. The problem of exact measurement of SAW parameters in periodic electrode structures is not new - it has existed as long as SAW devices have been designed. The pioneering work was done by C. S. Hartmann 8 4 who proposed a multi-transducer test structure and original methods to determine SAW propagation parameters from the electrical measurements of scattering parameters.

37 904 V. Plessky & J. Koskela The physical interpretation of the parameters is very illustrative from the point of understanding the dispersion characteristics. As discussed above, A B marks the threshold frequency for STW scattering into bulk waves. The parameter v2 *v = - \ (111) describes the position of the center of the stopband at the limit of vanishing interaction between the counterpropagating waves, e -> 0. The interaction consists of the coupling between surface waves, described through the parameter « =±H^±Me«-, (112) and the influence of the bulk wave, present through t h e parameter and the function v(A).

In some cases, such as in 45°XZ-cut lithium tetraborate, 5 2 the first term is positive while the second term in negative, resulting first in an increase and then in a decrease in the velocity with growing metal thickness. 2. 6859 dB). 6859 • 7 P / [dB/fjs], (76) where 7 P is attenuation in Neper/wavelength, v is the velocity in m / s and / is frequency in MHz. Note, however, that the parameter includes all acoustic energy loss mechanisms in the device and that it itself also depends on frequency.