Project “Backward acoustic waves in multilayered structures based on piezoelectrics and piezosemiconductors”

Project 19-07-00070 “Backward acoustic waves in multilayered structures based on piezoelectrics
and piezosemiconductors

Backward acoustic waves are characterized by oppositely directed phase and group velocities. In
recent years, these waves have attracted the attention of researchers in connection with the
implementation of a new type of acoustic sensors or signal processing devices on their basis. The
aim of this project was a theoretical and experimental study of the features of the excitation and
propagation of backward acoustic waves in piezoelectric and piezosemiconductor materials and
structures under various boundary conditions and in contact with a liquid. To achieve this goal,
the following tasks were solved: i) a theoretical analysis of the features of propagation of
backward waves in piezoelectric semiconductor plates under various boundary conditions was
carried out and ii) an experimental study of the effect of liquid and conducting layers on the
properties of backward waves in piezoelectric plates was carried out. As a result of the project,
the frequency ranges were discovered for the first time in which there is a reverse antisymmetric
wave of the 1st order (A1) and a symmetric wave of the 2nd order (S2), propagating in the [001]
direction in the (110) plane of GaAs. Analysis of the effect of a layer with arbitrary conductivity,
placed on the surface of the GaAs plate, on the characteristics of the detected backward acoustic
waves A1 and S2 showed that their attenuation decreased with increasing surface conductivity.
While their phase velocity remained practically unchanged. In addition to backward waves in
piezoelectric semiconductor plates, the influence of various boundary conditions on the
properties of the previously detected backward wave A1 in the YX plate of lithium niobate was
studied. It was shown that in the case of contact of the plate under consideration with a residual
and non-conducting liquid, the amplitude of forward waves with transverse-horizontal
polarization increases, and in the case of antisymmetric waves, both forward and backward, their
amplitude decreases significantly. The main conclusions of the theory were confirmed
experimentally. We also studied the A1 backward wave in the structure “lithium niobate YX
plate – vacuum gap – metal plane”. It was shown that approaching the metal plane to the
piezoelectric plate leads to an increase in the phase velocity of the wave under consideration. At
the same time, the phase velocity of the forward A1 wave – decreased. In addition, it was found
that the approximation of the metal plane leads to a change in the distribution of the amplitudes
of mechanical displacement over the thickness of the plate, and the electric potential of the wave
in the plate decreases relative to the potential on the surface. In general, the results obtained
allowed a deeper understanding of the features of propagation of backward acoustic waves in
piezoelectric semiconductor plates and structures with a gap.