SAW propagation in the two domain states of ferroelectric LiNbO/sub 3/ crystal

We propose a new geometry of ferroelectric LiNbO/sub 3/ domain systems, which may be useful for SAW applications. Since two domain states of this material differ in elastic coefficients and in signs of piezoelectric constants, different domain geometry influencing the propagation of SAW can be considered. Here we wish to point out that even a simple system of two domains D1 and D2 can offer properties, which may be useful for SAW applications. The SAW propagates from the interdigital transducer IDT1 to IDT2. Each domain is provided with pair of electrodes A/sub 1//A/sub 1/', A/sub 2//A/sub 2/', so that electric fields perpendicular to the propagation direction of SAW can be applied. As shown before (Nosek (1977)), it is possible to influence the group velocity of SAW in either of the domains by static or slowly changing electric field, and this can be achieved in each domain in a different way. The effect can be described simply by the change of elastic and piezoelectric coefficients: c*=c+aE, e*=e+bE, but more detailed tensor equations are derived in this paper. As a result, two time delay lines are produced on the substrate. On the domain wall considered here to be perpendicular to the signal propagation, significant reflection of the surface acoustic wave can occur. Interference of the original and reflected SAW can be influenced by the electric field in domain D1. The whole system can be used for signal processing.