The article reveals and describes the existing regularity in the form of algebraic polynomial transformations between the time changes of the signal of the control object of varying degrees of complexity and the change of its spectral characteristics-decomposition coefficients obtained using an adaptive orthonormal basis. It is shown that if the signal can be represented in the form of a trigonometric polynomial, then the change in spectral characteristics can be described by algebraic polynomials of various degrees depending on the order of the model which describes the control object. The change of the signals in time is understood their compression or stretching. This regularity is manifested when using the spectral characteristics of the signal calculated according to the adaptive orthonormal basis proposed by the author. It is shown that this regularity is universal and it is valid for any time-finite signals. This property has a general theoretical value, it can be interpreted as the dependence of the spectral characteristics of a signal from its change of time: acceleration or deceleration. This property can be practically used when identifying control objects, modeling and recognizing spatio-temporal changes of aggregate signals in control systems, in monitoring, in diagnostics, in non-destructive testing and other digital signal processing systems. © 2020 IEEE.

The problem of harmonic oscillations in electro-electromagnetic composites is studied. Oscillations can be initiated by the extended load vector, including the horizontal and vertical components of mechanical displacements, and electrical induction distributed on top of the surface. Boundary conditions assume full mechanical coupling for all layers of the structure. Electrical conditions on the surface top can be both electrically open, and electrically shorted. Magnetic conditions are similar to electric ones and describe the continuity of fields in between two mediums, or indicate the isolation of the magnetic field between them. The Green's function of electro– magneto–elastic medium is constructed. Phase velocities are obtained for various geometric proportions and materials. © 2020 Trans Tech Publications Ltd, Switzerland.

The problem of a posteriori experimental and theoretical estimation of the correctness of the choice of the signal sampling frequency from the point of view of taking into account all the main frequency components of its spectrum is considered. An approach is proposed that implements this estimate from the point of view of the Kotelnikov's sampling theorem for the current operational measurement of signal samples. Compared to traditional, the proposed approach provides higher speed, reliability, accuracy of assessment and requires a small number of additional measurements. It has an absolute (not relative) character because it does not require comparison of the spectrum of the estimated signal sample group with the spectrum of the reference group with a large number of samples, for which the condition of the Kotelnikov's theorem must be proved. The relative character of the traditional approaches sharply narrows the range of their applicability. © 2019 IEEE.

From the point of view of the fulfillment of the condition of the sampling theorem a new criterion for the operative estimation of the adequacy of the choice of the sampling frequency of the measured signal is considered. Its feature is the comparison of two sequences of samples of the signal, measured with the desired sampling frequency and with a lower one. The second frequency is chosen the less one than the sampling theorem requires in order to cause the effect of spectrum aliasing. On the basis of the arising effect of spectrum aliasing of the measured signal the proposed formula of the criterion allows to conclude about the correctness of the choice of the sampling frequency in the first samples sequence with a higher sampling frequency. The criterion allows to draw a conclusion about the adequacy of the selected sampling interval of the signal to its frequency spectrum more accurately, quickly, directly in the measurement process, with a small number of additional samples and without uncertainties. This is more important at the recording of wave and resonant changes of mechanical and physical fields in automation, energy, transport and other fields. © 2019 IEEE.

In the framework of the linearized theory of the propagation of thermoelastic waves, a dynamic mixed coupled problem on the oscillations of an inhomogeneous medium under the action of a thermal load oscillating on its surface is considered. The medium is a thermoelastic prestressed layer rigidly coupled with a thermoelastic prestressed half-space. At the boundary of the medium, two types of thermal conditions are considered: ideal thermal contact and heat insulation. Using operational calculus methods, the boundary value problem with mixed thermal boundary conditions is reduced to an integral equation of the first kind with respect to the unknown distribution function of the heat flux in the contact zone. We studied the distribution of the poles of the Green's function of a medium, taking into account the effect of initial strains and preheating. It is shown that thermal conditions at the interface between the medium have little effect on the distribution of the vertical displacement of the layer surface in the natural state. At the same time, the condition of thermal insulation between the layer and half-space allows to compensate for the effect of body pre-heating on the formation of the surface wave field. © Published under licence by IOP Publishing Ltd.

The dynamic problem of the surface acoustic wave propagation in a thin-film structure is investigated. The propagation of plane waves in the film-substrate structure is considered. Thin film is made of barium titanate oxide, and solid substrate is made of magnesium oxide. Ferroelectric film is subjected to misfit strain because of the deposition. Assumed that the solid substrate retains its properties due to the large difference in the hardness of the materials. Built Green function, obtained phase velocities and electromechanical coupling coefficients in the C-phase of BaTiO3. The present investigation is of practical interest for developing high-frequencies smart ferroelectric devices for engineering applications. © 2019 Published under licence by IOP Publishing Ltd.

The dynamic problem of the surface acoustic wave propagation in a thin-film structure is investigated. The propagation of plane waves in the film-substrate structure is considered. Thin film is made of barium titanate oxide, and solid substrate is made of magnesium oxide. Ferroelectric film is subjected to misfit strain because of the deposition. Assumed that the solid substrate retains its properties due to the large difference in the hardness of the materials. Built Green function, obtained phase velocities and electromechanical coupling coefficients in the C-phase of BaTiO3. The present investigation is of practical interest for developing high-frequencies smart ferroelectric devices for engineering applications. © 2019 Published under licence by IOP Publishing Ltd.

A problem on surface sh-waves' propagation in a piezoelectric structure with a coating from a functionally graded material is considered. As a base material, a piezoelectric of 6mm class hexagonal syngony is used. The problem solution is based on the approach, which combines analytical methods of constructing the solution for homogeneous components and numerical methods of constructing the solution for inhomogeneous components of a heterogeneous structure. For problems with an electrically open or closed free surface, the transformation of the surface wave field, depending on the character of the change of the coating properties, is studied. Peculiarities of the surface waves' behaviour at different combinations of the coating and substructure materials are investigated. It is demonstrated, that by means of a special change of the coating properties it is possible to obtain the structure, on the surface of which Love waves or Bleustein-Gulyaev waves (BGW) are propagated, or the structure in which surface waves are absent in a definite frequency range. © 2018 IEEE.