Anomalous dispersion of electromagnetic eigenwaves in a sandwich structure with a gap

A system of two different isotropic dielectric plates aligned parallel to each other and separated by a gap is considered. For a sufficiently large gap, electromagnetic eigenwaves in the plates are virtually independent and dispersion curves for the studied system are characterized by an infinite set of intersections. A decrease in the gap thickness leads to coupling between the wave fields and the disappearance of the intersection points due to divergence of the dispersion curves. Each of the dispersion curves of the spectrum transformed under the action of coupling is formed by a set of adjacent portions of initially independent branches corresponding to different plates. A gradual change in the frequency along one of the new dispersion curves results in a periodic displacement of the localization zone of the wave field from one plate to the other.     

SH surface acoustic wave propagation in a cylindrically layered piezomagnetic/piezoelectric structure

SH surface acoustic wave (SH-SAW) propagation in a cylindrically layered magneto-electro-elastic structure is investigated analytically, where a piezomagnetic (or piezoelectric) material layer is bonded to a piezoelectric (or piezomagnetic) substrate. By means of transformation, the governing equations of the coupled waves are reduced to Bessel equation and Laplace equation. The boundary conditions imply that the displacements, shear stresses, electric potential, and electric displacements are continuous across the interface between the layer and the substrate together with the traction free at the surface of the layer. The magneto-electrically open and shorted conditions at cylindrical surface are taken to solve the problem. The phase velocity is numerically calculated for different thickness of the layer and wavenumber for piezomagnetic ceramics CoFe₂O₄ and piezoelectric ceramics BaTiO₃. The effects of magnetic permeability on propagation properties of SH-SAW are discussed in detail. The distributions of displacement, magnetic potential and magneto-electromechanical coupling factor are also figured and discussed.     

Propagation of surface acoustic waves in a piezoelectric medium with a periodic groove structure

A system of equations is formulated to describe the propagation of surface acoustic waves in a piezoelectric substrate whose surface has a periodic structure formed by transverse grooves. Dependences of the reflection coefficient and the wave velocity on the geometry of the periodic structure (the width and the depth of the grooves) are obtained in a wide range of variation of these parameters for five different orientations in various piezoelectric crystals (quartz, lithium niobate, lithium tantalate, and langasite).     

Hybridization of acoustic waves in piezoelectric plates

The interaction (hybridization) of different types of acoustic waves of zero and higher orders propagating in lithium niobate piezoelectric plates is theoretically investigated. Different crystallographic orientations of the plates and different directions of wave propagation in them are considered. It is shown that, for an electrically free plate with the propagation direction along any of the crystallographic axes, the dispersion curves have intersection points and hybridization is absent. However, when the propagation direction slightly changes or when one of the plate surfaces is short-circuited, the dispersion curves separate and the waves become coupled. A quantitative coefficient characterizing the degree of wave hybridization with allowance for both mechanical and electric coupling is introduced. It is shown that the dependence of this coefficient on the product of the plate thickness by the wave frequency determines the extent of separation of the dispersion curves of interacting waves. The phenomenon under study is of both fundamental and practical interest, for example, in connection with the problem of an efficient excitation of nonpiezoactive acoustic waves in piezoelectric plates.     

Anomalous absorption of bulk shear sagittal acoustic waves in a layered structure with viscous fluid

It is demonstrated theoretically that the absorptivity of bulk shear sagittal waves by an ultra-thin layer of viscous fluid between two different elastic media has a strong maximum (in some cases as good as 100%) at an optimal layer thickness. This thickness is usually much smaller than the penetration depths and lengths of transverse and longitudinal waves in the fluid. The angular dependencies of the absorptivity are demonstrated to have significant and unusual structure near critical angles of incidence. The effect of non-Newtonian properties and non-uniformities of the fluid layer on the absorptivity is also investigated. In particular, it is shown that the absorption in a thin layer of viscous fluid is much more sensitive to non-zero relaxation time(s) in the fluid layer than the absorption at an isolated solid-fluid interface.     

压电条SH声辐射场研究

具有一定宽度和厚度的无穷长压电条置于均匀各向同性半空间上, 压电条在电激励下产生机械振动从而在整个空间产生声场. 将压电条取为6mm晶系, 其对称主轴沿长度方向. 针对这 种压电换能器结构, 深入研究了SH波的激发和辐射特性. 首先将压电条中的声场展开为傅里 叶级数, 而将压电条下的无界半空间中的声场展开为傅里叶积分, 然后根据边界条件得到了 整个空间中声场的求解方案, 通过数值模拟计算了声场的分布特性, 并和传统方法进行了定 量的对比和分析. 最后采用最陡下降法(鞍点法)研究并得到了压电条声辐射场的远场近似表 达式, 分析了声场的指向性规律. 结果表明只有当频率f和压电条宽度a的乘积 fa<1 kHz·m 时, 传统方法得到的结果是可靠的，当频率升高时，压电条内应力和位移呈振荡式分布，频率愈高振荡愈激烈，且与传统方法的差异愈大.本文对声学微系统与声传感器件的研究具有 重要意义. 关键词： 压电条 6mm晶系 表面位移 指向性因子     

Shear surface acoustic waves in the stratified structure piezoelectric—High-temperature granular superconductor

The interaction of a Gulyaev-Bluestain surface wave with a granular high-temperature superconducting (HTSC) medium has been investigated. For piezoelectrics of symmetry 4mm and 6mm, dispersion equations have been derived that describe the characteristics of surface acoustic waves (SAWs). The temperature dependences of the SAW attenuation and phase have been calculated forZnO andBa ₂Si₂TiO₃ crystals. It is shown that at temperatures higher than the critical temperature an attenuation jump and a phase shift are observed. The effect intensifies with increase in the electromechanical coupling coefficient and with decrease in the thickness of the HTSC film. For theBa ₂Si₂TiO₃ crystal the attenuation jump and phase shift are11 dB/cm and38 deg/cm, respectively, at a frequency of820 MHz. The results obtained can also be generalized for periodic HTSC structures and can be used to design frequency-selective devices and fast-response bolometric photodetectors. Tomsk State University of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 49–52, April, 1999.     

Power-mode theorems for guided acoustic waves in piezoelectric media

Relationships between complex power flow pseudo energy, propagation constant and complex frequency are presented for acoustic waves in piezoelectric media. These relationships are essentially energy-power equations which apply to anisotropic, nonconservative, dispersive, linear systems, analogous to those obtained by Chorney and Penfield for guided electromagnetic waves. At vanishing piezoelectric coupling the powermode theorems split into a proper electromagnetic set and a proper mechanical set. By differentiating the power-mode equations with respect to the complex frequency further results are obtained linking the group velocity with power flow and energy storage. Conclusions may be drawn from these expressions regarding the signature of the dispersion (forward or backward waves). The equipartition of pseudo energy is established at cut-off, and the vanishing of the complex power flow at resonance. Examples including wave propagation in lossless and lossy media are included.     

Propagation of Bleustein-Gulyaev waves in a prestressed layered piezoelectric structure

Based on the theories of nonlinear continuum mechanics, piezoelectricity and elastic waves in solids, theoretical analysis of Bleustein-Gulyaev surface acoustic wave propagation in a prestressed layered piezoelectric structure are described. Numerical calculations are performed for the case that the layer and the substrate are identical LiNbO(3) except that they are polarized in opposite directions. It is found that an almost linear behavior of the relative change in phase velocity versus the initial stress is obtained for both surface electrically free and shorted cases. Potential applications in the design of acoustic wave devices are suggested.     

Parametric excitation of helicon and acoustic waves in piezoelectric semiconductor-plasma

The parametric excitation of a helicon and an acoustic wave in a piezoelectric semiconductor-plasma in the presence of a strong magnetic field has been investigated using the coupled mode theory. The expressions for the threshold value of the electric field required for the onset of instability and for the growth rate well above the threshold have been obtained. It is observed that an acoustic wave of higher frequency and higher phase velocity than that of the pump wave cannot be excited. The analysis has been applied to the case of n type InSb sample where the threshold value of the electric field is found to be of the order 5.2 × 10³ Vm^?1 and the growth rate at an electric field 5.2 × 10⁴ Vm^?1 is of the order of 8.7 × 10¹⁰ sec^?1.     

Parametric excitation of acoustic waves in piezoelectric solid state magnetoplasma

Absolute instability of the acoustic wave (excited parametrically) has been explored on the basis of the Bers and Briggs criterion in the presence of a large transverse static magnetic field. In the magnetoplasma threshold the electric field decreases to about 0.4 times the value at zero magnetic field.     

On the density of surface acoustic waves and surface thermodynamics in a piezoelectric

Piezoelectricity introduces new modes and modifies part of the elastic vibrational spectrum for both bulk and surface waves. This has a direct bearance on surface thermodynamics. A simple phenomenological model is studied analytically and exactly. This bears out the basic physics involved and allows for a quick and easy estimate of the changes to be expected, which turn out to be substantial.     

Bleustein-Gulyaev waves in a functionally graded piezoelectric material layered structure

This work presents a theoretical study of the propagation behavior of Bleustein-Gulyaev waves in a layered structure consisting of a functionally graded piezoelectric material (FGPM) layer and a transversely isotropic piezoelectric substrate. The influence of the graded variation of FGPM coefficients on the dispersion relations of Bleustein-Gulyaev waves in the layered structure is investigated. It is demonstrated that, for a certain frequency range of Bleustein-Gulyaev waves, the mechanical perturbations of the particles are restricted in the FPGM layer and the phase velocity is independent of the electrical boundary conditions at the free surface. Results presented in this study can not only provide further insight on the electromechanical coupling behavior of surface waves in FGPM layered structures, but also lend a theoretical basis for the design of high-performance surface acoustic wave (SAW) devices. Supported by the National Natural Science Foundation of China (Grant No. 10632060), the National Basic Research Program of China (Grant No. 2006CB601202), the National 111 Project of China (Grant No. B06024), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20070698064)     

利用声波控制超短脉冲的色散

 声光互作用器件声光可编程色散滤波器（AOPDF）是一种实时的色散补偿器件，它可用于飞秒啁啾脉冲放大系统。通过耦合模理论推导，得到了输出脉冲的群延迟与调制声波的频率、啁啾、带宽等参数的关系，并且对用2.5cm长的LiNbO₃作为声光晶体的AOPDF补偿飞秒光脉冲的色散进行了数值模拟，得到了对中心波长为800 mm的钛宝石飞秒激光色散补偿特性及所需声波的频率和啁啾参数。     

Specific propagation directions of acoustic waves for piezoelectric and nonpiezoelectric media

I reanalyze the problem of the existence of longitudinal normals inside the symmetry planes of piezoelectric crystals belonging to the symmetry class mm2. The equations determining components of longitudinal normals situated outside the symmetry planes for media of this symmetry are discussed. It is proven that nonpiezoelectric media of rhombic symmetry could have 4 or 8 distinct acoustic axes. Examples of nonpiezoelectric elastic media of monoclinic symmetry without acoustic axes are given. The method of determination of the components of acoustic axes for piezoelectric media of arbitrary symmetry is presented. With the help of this method, I discuss the problem of acoustic axes for piezoelectric media of the symmetry class mm2. The text was submitted by the author in English.     

Temperature-stable orientations in LGS and LGN piezoelectric crystals for surface acoustic waves

The temperature characteristics of surface acoustic waves (SAW) propagating in LGS and LGN crystals are numerically analyzed. The optimal orientations that correspond to the zero value of the first-order temperature coefficient of delay (TCD) for SAW propagating in these crystals are considered. The second-order TCD for SAW is calculated for a wide range of operating temperatures. It is shown that the temperature dependences of the material constants of LGS and LGN crystals are strongly nonlinear. The characteristics of SAW propagating in a structure that consists of an isotropic layer overlying an LGS or LGN piezoelectric crystal are numerically calculated. It is shown that, in the presence of a thin aluminum layer of a certain thickness on the crystal surface, in some cases it is possible to extend the operating temperature range within which the TCD for SAW is equal to zero.     

Love waves in a layered functionally graded piezoelectric structure under initial stress

Abstract

To study the effect of initial stress on the propagation behavior of Love waves in a layered functionally graded piezoelectric structure, a mathematical model is established. The piezoelectric layer is taken as exponentially graded material where as half-space is taken as simply elastic substratum. The coupled electromechanical field equations are solved analytically to obtain the mechanical displacements and electrical potential functions for the piezoelectric layer and elastic substrate. The dispersion relations are obtained for electrically open and short cases. The higher mode Love wave propagation has been considered. For numerical interpretation of the results, four sets of piezoelectric layer and elastic substrate have been taken into consideration. Graphical representation reveals about the effect of initial stress and the effect of inhomogeneity parameter on the phase velocity against wave number for electrically open and electrically short cases, respectively.     

The effect of initial stress on the propagation behavior of SH waves in piezoelectric coupled plates

This study analytically investigates the propagation of shear waves (SH waves) in a coupled plate consisting of a piezoelectric layer and an elastic layer with initial stress. The piezoelectric material is polarized in z-axis direction and perfectly bonded to an elastic layer. The mechanical displacement and electrical potential function are derived for the piezoelectric coupled plates by solving the electromechanical field equations. The effects of the thickness ratio and the initial stress on the dispersion relations and the phase and group velocities are obtained for electrically open and mechanically free situations. The numerical examples are provided to illustrate graphically the variations of the phase and group velocities versus the wave number for the different layers comparatively. It is seen that the phase velocity of SH waves decreases with the increase of the magnitude of the initial compression stress, while it increases with the increase of the magnitude of the initial tensile stress. The initial stress has a great effect on the propagation of SH waves with the decrease of the thickness ratio. This research is theoretically useful for the design of surface acoustic wave (SAW) devices with high performance.