Project “Backward acoustic waves in strong anisotropic materials and structures based on such materials”

Project 20-07-00139 “Backward acoustic waves in strong anisotropic materials and structures based
on such materials”
One of the types of acoustic waves propagating in the plates are backward acoustic waves with
different polarizations. The phase and group velocities of these waves are directed in different
directions. The aim of this project is a theoretical and experimental study of the features of the
excitation and propagation of backward acoustic waves in highly anisotropic materials and
structures based on them and containing, inter alia, piezoelectric and piezosemiconductor layers
under various boundary conditions. In 2021, within the framework of the project, the features of
the propagation of backward acoustic waves in structures containing a highly anisotropic
material TeO2 and piezoelectric semiconductor layers made of gallium arsenide were
investigated. Earlier, crystallographic orientations of TeO2 were found, at which the existence of
backward acoustic Lamb waves of various types is possible. The backward acoustic
antisymmetric wave of the first order (A1), which exists in TeO2 at Euler angles φ = θ = ψ = 0,
is studied in detail. At this stage, the influence of a layer made of a piezoelectric semiconductor
material (gallium arsenide) on the characteristics of this wave was investigated. It was found
that, as in the case of a layer with a strong piezoelectric, with an increase in the thickness of the
piezoelectric semiconductor layer, the velocity of the backward wave increases, and the point
with zero group velocity shifts to the region of lower frequencies. It should be noted that, in the
case of a piezoelectric semiconductor, this displacement is greater than in the case of a strong
piezoelectric, despite the weak piezoelectric effect. This is due to the conductivity of the layer
material. In this case, the type of wave did not change. The influence of an infinitely thin layer
with arbitrary conductivity on the characteristics of the backward wave A1 in the structure
“TeO2 plate – GaAs plate” was also investigated. It is found that the bulk conductivity of the
GaAs plate almost completely screens the TeO2 piezoelectric effect, which leads to almost
complete absence of the influence of the layer with arbitrary conductivity, which is in contact
with the piezoelectric plate from the back side, on the velocity of backward acoustic waves.