  Plate acoustic waves (PAW) propagating along X-axis in the Z-cut wafer of a
single crystal of lithium niobate are considered theoretically and
experimentally. For eight lowest PAW modes, the dispersion curves for
wavenumber k(f) are calculated by the equations of motion and electrodynamics,
by the Finite Element Method, and then measured experimentally. The spectra
k(f) obtained by the numerical solution and FEM-simulation are in good
agreement, and experimental measurements agree with theoretical predictions.
The PAW modes are identified by the components of their total acoustic
displacements and cutoff frequencies. Analysis of the longitudinal and normal
acoustical displacements permits to find PAW mode capable for usage in
ultrasonic actuators. The results obtained may be useful for ultrasonic
transducers, acousto-electronic and acousto-optic applications, and ultrasonic
motors/actuators fabricated in the Z-cut ferroelectric lithium niobate wafers
including periodically poled wave-guides.
