The Experimental Registration of the Evanescent Acoustic Wave in YX LiNbO3 Plate

Evanescent acoustic waves are characterized by purely imaginary or complex wavenumbers. Earlier, in 2019 by using a three dimensional (3D) finite element method (FEM) the possibility of the excitation and registration of such waves in the piezoelectric plates was theoretically shown. In this paper the set of the acoustically isolated interdigital transducers (IDTs) with the different spatial periods for excitation and registration of the evanescent acoustic wave in Y-cut X-propagation direction of lithium niobate (LiNbO3) plate was specifically calculated and produced. As a result, the possibility to excite and register the evanescent acoustic wave in the piezoelectric plates was experimentally proved for the first time. The evanescent nature of the registered wave has been established. The theoretical results turned out to be in a good agreement with the experimental ones. The influence of an infinitely thin layer with arbitrary conductivity placed on a plate surface was also investigated. It has been shown that the frequency region of an evanescent acoustic wave existence is very sensitive to the changes of the electrical boundary conditions. The results obtained may be used for the development of the method of the analysis of thin films electric properties based on the study of evanescent waves.

Electric Current Distribution During Electromagnetic Braking in Continuous Casting

The electromagnetic brake (EMBr) is a well-known and widely applied technology for controlling the melt flow in the continuous casting (CC) of the steel. The effect of a steady (DC) magnetic field (0.31 T) in a CC mold is numerically studied based on the GaInSn experiment. The electrical boundary conditions are varied by considering a perfectly insulating/conductive mold or the presence of a conductive solid shell, which is experimentally modeled by 0.5 mm brass plates. An intense current density (up to 350 kA/m2) is induced by the EMBr magnetic field in the form of loops. The electric current loop tends to close either inside the liquid bulk or through the conductive solid. Based on the character of the induced current loop closures, the turbulent flow is affected as follows: (i) it becomes unstable in the insulated mold, forming 2D self-inducing vortex structures aligned with the magnetic field; (ii) it is strongly damped for the conductive mold; and (iii) it exhibits transitional behavior with the presence of a solid shell. The application of the obtained results for the real CC process is discussed and validated.

Linear piezoelectricity

This chapter presents the elements of linear piezoelectricity including mechanical and electrostatic balance laws and coupled mechanical electrical constitutive relations. The thermodynamically consistent constitutive relations are determined from a coupled electromechanical energy balance argument and expressions are given alternately considering the electric field and the electric displacement as independent fields. Appropriate electrical boundary conditions are also discussed. The theory is also specialized to poled piezoceramics. A chapter appendix provides a brief discussion of Maxwell’s equations for electromagnetics and energy transport in the quasi-static limit. A second chapter appendix discusses the properties of third order tensors.

Love-Type Wave in PMN-PT Single Crystal Layered Structures with Periodic Undulations

Love-type wave propagation has been studied in a layered structure consisting of a thin layer of PMN-PT single crystal deposited on an elastic half-space. The weakly periodic undulations of the upper surface of the layered system and the common interface between the PMN-PT layer and the elastic substrate are considered. The PMN-PT single crystal is poled along the [011]_c direction so that the macroscopic symmetry is orthonormal mm2. The dispersion relations for electrically open and shorted circuits are obtained. The effects of various parameters including corrugation, undulatory, position and electrical boundary conditions on dispersion properties of Love-type waves are discussed. The results show that corrugations of the surface and the interface play a dominant role in the propagation of a Love-type wave, especially, the interfacial corrugation can produce an anomalous dispersion in the case of an electrically shorted condition. The surface corrugation enhances the phase velocity of a Love-type wave while the interface corrugation reduces the phase velocity in the range of relatively smaller wavenumber, and these variations gradually tend to vanish with increase in wavenumber. The undulatory parameter and the position parameter present a secondary impact on the dispersion behaviors of a Love-type wave compared with the corrugation parameters, both of them slightly enhance the phase velocity. The obtained results can offer some fundamentals for improving the efficiency and sensitivity of the interface response in the design and application of piezoelectric SAW devices.

Thermal Conductivities of PZT Piezoelectric Ceramics under Different Electrical Boundary Conditions

<p>Physical properties of polycrystalline lead-zirconate-titanate (PZT) changes according to electrical boundary conditions and poling. This paper reports the thermal properties of poled and unpoled PZT's in the poling direction for open circuit and short circuit conditions. The authors found that the short-circuit condition exhibited the largest thermal conductivity than the open-circuit condition. In the relationship between these two thermal properties, the authors propose the "electrothermal" coupling factor k^κ₃₃, which is similar to the electromechanical coupling factor k₃₃ relating the elastic compliances under short- and open-circuit conditions. On the other hand, the thermal conductivity of the unpoled specimen exhibits the lowest thermal conductivity, in comparison with the poled specimens, which suggests the importance of phonon mode scattering on the thermal conductivity with respect to elastic compliance.</p>

Static Electromechanical Characteristics of Piezoelectric Converters with various Thickness and Length of Piezoelectric Layers

The paper presents the analysis of electromechanical characteristics of piezoelectric converters subjected to an electric field and mechanical load. The analyses were performed based on a method consisting implementation of special segments responsible for electrical boundary conditions to a homogeneous beam. Constitutive equations were developed, allowing one to obtain static electromechanical characteristics for piezoelectric actuators with freely defined boundary conditions and geometry. Moreover, based on constitutive equations obtained, a particular solution for cantilever transducer subjected to concentrated force has been developed. The resulting analytical solution was compared with the data available in the literature, and the developed FEM solution. Furthermore, the influence of factors such as relative length, thickness and location of particular piezoelectric layers on electromechanical characteristics of the transducer was defined.