SH Acoustic Waves in a Lithium Niobate Plate and the Effect of Electrical Boundary Conditions on Their Properties

It is theoretically and experimentally confirmed that the electromechanical coupling coefficient of SH waves propagating in a Y-cut lithium niobate plate along the X direction can exceed 30% when the plate thickness satisfies the condition h/λ= 0.02–0.15. This value of the coupling coefficient is approximately six to seven times greater than the maximal value obtained for SAW in the same material. Such a high value of K2 offers a possibility to control the wave velocity by varying the electrical boundary conditions, e.g., by moving a conducting screen toward the plate surface. The effect of such a screen on the properties of the SH waves is studied both theoretically and experimentally. On the whole, the results of the study show that the use of SH waves offers considerable improvements in the parameters of the known SAW devices and also opens up the possibilities for the development of new devices and sensors that have to operate in contact with a liquid medium.