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This paper presents theoretical and experimental study of QSH waves propagating in thin plates of lithium niobate. The electromechanical coupling coefficient K/sup 2/ has been calculated as a function of plate thickness and propagation direction for all main crystallographic cuts. Y-cut and X-propagation for which K/sup 2/ may be more than 30% were chosen for our experiments. We have measured K/sup 2/ as a function of plate thickness and have obtained a good agreement with theory. The extremely large value of K/sup 2/ opens possibility of realizing devices whose parameters can be controlled by electrical boundary conditions. We have studied SH waves propagating in the presence of a conducting electrode. It is found that by varying the gap between plate and electrode, the phase shift for a 3.2 MHz delay line can be varied by as much as 240/spl deg/. We have also studied the influence of a thin layer of arbitrary conductivity on the velocity and attenuation of the QSH wave. Analysis show that the variations in these parameters can be as high as 18% and 4 dB//spl lambda/ for a change of surface conductivity from 10/sup -7/ to 10/sup -5/ S.

This paper presents the first report on the reflection of ultrasonic Lamb waves produced by a periodic array of thin conducting strips deposited on a piezoelectric plate. A repetitively mismatched transmission line model was used to analyze the performance of the reflector. The reflection coefficient of a single strip is given by r/spl ap//spl Delta/v/v, where /spl Delta/v/v is the fractional change in velocity produced by electrical shorting of the surface. An attractive property of Lamb waves is that they can provide a much higher value of /spl Delta/v/v than is possible with surface acoustic waves. Efficient Lamb wave reflectors can therefore be realized with relatively few strips in the reflector. Experimental results obtained with a number of Lamb wave reflectors confirm this hypothesis. For example, reflection coefficient very close to unity, R/spl ap/0.98, has been obtained in a SH wave reflector consisting of just 12 strips. To obtain comparable reflection with SAWs, one would need to use more than 70 strips. Details of the theoretical analysis used and experimental results obtained will be presented.