Diffraction divergence of SH0 wave in thin piezoelectric plate of lithium niobate

By present time the profiles of aperture of Rayleigh surface acoustic wave (SAW) launching by interdigital transducers (IDTs) set on the surface of the wave-guide have been investigated in details. It has been shown that the SAW profile strongly depends on geometry of IDT and when moving off transducer the beam profile changes its shape. Recently the great interest of researchers was caused by acoustic waves in piezoelectric plates due to some advantages compared to surface acoustic waves. It has been also found that these waves are characterized by more values of angle between phase and group velocities (PFA). Plate waves may be effectively launched and received by IDTs. But the profiles of these waves along aperture were not investigated. This paper is devoted to experimental study of profiles of acoustic SH₀ waves with shear-horizontal polarization, which propagates in piezoelectric plate of Y-X+220 lithium niobate. The profiles were studied by electrical probe set on the special precision mechanism, which allowed moving the probe in two directions. Because the wave was piezoactive it accompanied by alternating in time electrical field, which was detected by measuring probe. As a result the distribution of amplitude of electric field at different distances from launching IDT was measured. The measurement has shown that the profiles of SH₀ wave significantly differ from ones of SAW. These profiles practically keep their shape at different distances from transducer but their amplitude and width change. The comparison with theoretical results showed their satisfactory compliance.