Hybridization of backward acoustic waves in piezoelectric plates

The phenomenon of hybridization of the backward acoustic waves propagating in a piezoelectric crystal plate has been studied. In an electrically free plate (in particular, of potassium niobate) with a crystal orientation for which a sagittal plane is the symmetry plane, the dispersion curves of backward acoustic waves exhibit points of intersection and hybridization is absent. However, for a small change in the direction of wave propagation, the dispersion curves exhibit “repulsion” and the waves become coupled. The degree of hybridization is quantitatively evaluated in terms of the hybridization coefficient, which is defined as the ratio of the total mutual energy density and the total energy density of the interacting waves. It is demonstrated that the extent of repulsion of the dispersion curves for the interacting waves is determined by the dependence of the hybridization coefficient on the product of the plate thickness and the wave frequency.     

Shear-horizontal acoustic waves in piezoelectric plates bordered with conductive liquid

The influence of a conductive liquid on the characteristics of shear-horizontal acoustic waves of zeroth order (SH0 mode) propagating in thin piezoelectric plates of lithium tantalate, lithium niobate, and potassium niobate was investigated. Experimental results obtained for SH0 mode devices fabricated on lithium niobate plates are found to be in good agreement with theory. The data presented in this paper is useful for a proper design of various acoustic wave sensors operating in contact with conductive liquids.     

The power flow angle of acoustic waves in thin piezoelectric plates

The curves of slowness and power flow angle (PFA) of quasi-antisymmetric (A0) and quasi-symmetric (S0) Lamb waves as well as quasi-shear-horizontal (SH0) acoustic waves in thin plates of lithium niobate and potassium niobate of X-,Y-, and Z-cuts for various propagation directions and the influence of electrical shorting of one plate surface on these curves and PFA have been theoretically investigated. It has been found that the group velocity of such waves does not coincide with the phase velocity for the most directions of propagation. It has been also shown that S0 and SH0 wave are characterized by record high values of PFA and its change due to electrical shorting of the plate surface in comparison with surface and bulk acoustic waves in the same material. The most interesting results have been verified by experiment. As a whole, the results obtained may be useful for development of various devices for signal processing, for example, electrically controlled acoustic switchers.     

The peculiarities of propagation of the backward acoustic waves in piezoelectric plates

The characteristics of backward acoustic waves in piezoelectric plates under different electrical boundary conditions were investigated. It has been shown that electrical shorting of the plate leads to increasing and decreasing the phase velocity for backward and forward branches, respectively. The peculiarities of the hybridization effect of backward waves were studied.     

Exact analysis of the propagation of acoustic waves in multilayeredanisotropic piezoelectric plates

Exact analysis of the propagation of acoustic waves in multilayered piezoelectric plates is performed using the transfer matrix method. A general technique for analyzing layered piezoelectric resonators under thickness and lateral field excitation is presented and is applied to the study of zinc oxide on silicon thin film resonators. Both one and two-dimensional analysis with general material anisotropy is performed, and a simplified method for incorporating thin conducting electrodes on the plate's free surfaces is presented. The general methodology described is summarized into efficient algorithms to aid in the implementation of the procedures and some computational aspects are discussed. Results are presented for cutoff behavior as well as general dispersion characteristics for two and three layered plates     

Propagation of QSH (quasi shear horizontal) acoustic waves in piezoelectric plates

The characteristics of QSH (quasi shear horizontal) acoustic waves propagating in thin plates of Y-cut, X-propagation lithium niobate are investigated theoretically and experimentally. The fractional velocity change (Deltanu/nu) produced by electrical shorting of the surface is calculated as a function of the normalized plate thickness h/lambda (h=plate thickness, lambda=acoustic wavelength). It was found that values of Deltanu/nu as high as 0.18 could be obtained. Experimental measurements show good agreement with theory. The properties of QSH waves propagating in the presence of a perfectly conducting electrode separated from the piezoelectric plate by a small air gap have been studied theoretically and experimentally. It was found that by varying the height of the gap, the phase shift through a 3.2-MHz QSH wave delay line can be varied by more than 230 degrees . We have also theoretically investigated the influence of a thin layer of arbitrary conductivity on the velocity and attenuation of the QSH wave. Calculations show that the variations in these parameters can be as high as 18% and 5 dB per wavelength for a change in layer surface conductance from 10(-7) to 10(-5) S. Results obtained in this paper confirm the attractive properties of QSH waves for a variety of sensing and signal processing applications.     

Gravimetric sensitivity of acoustic waves in thin piezoelectric plates in the presence of liquids

The effect of a dielectric weight load on the zero-order acoustic modes in a thin piezoelectric plate of lithium tantalate (LiTaO₃) was theoretically studied, and the change in this sensitivity in the presence of a liquid was estimated. The gravimetric sensitivity has a complicated frequency spectrum and also depends on the plate thickness and on the load material. The presence of a liquid can significantly increase the sensitivity of zero-order acoustic modes in a piezoelectric plate with respect to a dielectric weight load.     

New method of change in temperature coefficient delay of acoustic waves in thin piezoelectric plates

As is well-known, the development of high-effective and thermostable acoustic devices assumes using the acoustic waves with high coefficient of electromechanical coupling (K2) and low temperature coefficient of delay (TCD). At present, it also is well-known that fundamental shear horizontal (SH0) acoustic waves in thin piezoelectric plates possess by significantly more electromechanical coupling compared to surface acoustic waves (SAW) in the same material. However, although the value of TCD of SH0 waves is insignificantly less than for SAW, this is not enough for development of thermostable devices. This paper suggests a new way of decreasing TCD of SH0 waves in piezoelectric plates at a high level of electromechanical coupling. This way assumes to use the structure containing the piezoelectric plate and liquid with the special dependence of permittivity on temperature. Theoretical and experimental investigation showed that, for SH0 wave in YX LiNbO3 plate at hf = 700 m/s (h = plate thickness, f = wave frequency) the presence of butyl acetate can decrease the value of TCD by six times at K2 = 30%. In a whole the obtained results open the wide prospect of using SH0 wave in thin piezoelectric plate for development of high effective and thermo-stable acoustic devices.     

Resonance reflection of acoustic waves in piezoelectric bi-crystalline structures

The paper studies the bulk wave reflection from internal interfaces in piezoelectric media. The interfaces of two types have been considered. Infinitesimally thin metallic layer inserted into homogeneous piezoelectric crystal of arbitrary symmetry. Rigidly bonded crystals whose piezoelectric coefficients differ by sign but the other material constants are identical. Analytic expressions for the coefficients of mode conversion have been derived. An analysis has been carried out of specific singularities arising when the angle of incidence is such that the resonance excitation of leaky interface acoustic waves occurs. The conditions for the resonance total reflection have been established. The computations performed for lithium niobate (LiNbO3) illustrate general conclusions.     

Bleustein-Gulyaev-Shimizu surface acoustic waves in two-dimensional piezoelectric phononic crystals

In this paper, we present a study on the existence of Bleustein-Gulyaev-Shimizu piezoelectric surface acoustic waves in a two-dimensional piezoelectric phononic crystal (zinc oxide, ZnO, and cadmium-sulfide, CdS) using the plane wave expansion method. In the configuration of ZnO (100)/CdS(100) phononic crystal, the calculated results show that this type of surface waves has higher acoustic wave velocities, high electromechanical coupling coefficients, and larger band gap width than those of the Rayleigh surface waves and pseudosurface waves. In addition, we find that the folded modes of the Bleustein-Gulyaev-Shimizu surface waves have higher coupling coefficients.     

Matrix algorithms for modeling acoustic waves in piezoelectric multilayers

Matrix algorithms for modeling acoustic waves in piezoelectric multilayers are presented. All the algorithms considered are capable of resolving the numerical instability of transfer matrix at high frequency-thickness product. The formulation of basic matrices for the algorithm building blocks, and the development of recursive algorithms for the stack matrices, are systematically presented for both the conventional scattering and impedance matrices as well as the more recent hybrid matrix. Many variants of the algorithms are discussed, along with their respective usefulness and deficiency. Comparisons are made in their computational efficiency and numerical stability. For unconditional stability throughout large and small thicknesses, both scattering and hybrid matrix algorithms are applicable. For most efficiency, the algorithms that synergize both scattering and hybrid or impedance submatrices are superior, using surface matrix approach. Other aspects of algorithms such as formula conciseness, physical insight, versatility in incorporating boundary conditions, etc., are also noted.     

Spatial dispersion of short surface acoustic waves in piezoelectric ceramics

Summary This work explores the effect of the electric field gradient in the constitutive behavior of elastic dielectrics by analyzing the anti-plane surface waves propagating over a half-space of polarized ceramics. The obtained frequency equation shows that the gradient effect makes the surface waves dispersive, although they are known to be non-dispersive according to the classical theory of linear piezoelectricity that neglects the gradient effect. This analysis further shows that there exists a microstructural characteristic length, comparing to which the dispersion is significant for short waves while negligible for long waves. This suggests that the dispersion may have significant effects for very small surface acoustic wave devices operating with high-frequency short waves.     

Surface acoustic waves propagating over a rotating piezoelectric half-space

Surface acoustic waves (SAW) propagating over a piezoelectric half-space rotating at a constant angular rate about a fixed axis are analyzed using the linear theory of piezoelectricity, including Coriolis and centrifugal forces. Rotation sensitivity, the rotation induced change of wave speed, is studied. The dependence of the rotation sensitivity on the orientation of the rotation axis and the orientation of the material is examined. Numerical results for polarized ceramics PZT-5H are presented to show the detailed characteristics of the rotation sensitivity. The implications of the numerical results are discussed for different applications     

Attenuation of acoustic normal modes in piezoelectric plates loaded by viscous liquids

Attenuation cac versus viscosity eta of adjacent liquid is measured for each normal mode n generated in 30 different plates of commercially available, piezoelectric crystals with thickness-to-wavelength ratio in the range h/lamda = 0.6 - 2.5. Two modes with an optimal combination of sensitivity (0.1 dB/mm x cP), insertion loss (<35 dB), and stop-band rejection (>15 dB) are found in liquid-loaded 128 degrees Y,X + 90 degrees - LiNbO3 with h/lamda = 1.67. Both modes are suited for viscosity measurements and other sensing tasks in viscous liquids. They have predominantly longitudinal displacement and large propagation velocity v(n), about 15,000 m/s.     

On the existence of surface acoustic waves on piezoelectric substrates

The existence of surface waves on anisotropic materials was proven under fairly general conditions by Lothe and Barnett in 1976. But, until now, the status of surface waves on piezoelectric materials has remained unresolved. This paper presents general existence theorems for surface waves on piezoelectric substrates. It is demonstrated that for short circuit boundary conditions a surface wave solution must exist under virtually any circumstances. However, for a free surface, comparatively stringent existence conditions are required. Numerical examples are given for both free and shorted surfaces, and it is demonstrated that, in some situations, a surface wave solution may not exist for free surface propagation. The existence proofs were developed as a result of theoretical work on Green function modeling, which is now the preferred technique for rigorous SAW and pseudo-SAW device analysis. The mechanisms of the existence proofs and the associated mathematical results give great insight into the structure and properties of the Green functions and include many results that are directly relevant to device analysis     

Finite element formulation of smart piezoelectric composite plates coupled with acoustic fluid

In the context of noise and vibration reduction by passive piezoelectric devices, this work presents the theoretical formulation and the finite element (FE) implementation of vibroacoustic problems with piezoelectric composite structures connected to electric shunt circuits. The originalities of this work concern (i) the formulation of the electro-mechanical-acoustic coupled system, (ii) the implementation of an accurate and inexpensive laminated composite plate FE with embedded piezoelectric layers connected to resonant shunt circuits, and (iii) the development of an efficient fluid-structure interface element. Various results are presented in order to validate and illustrate the performance of the proposed fully coupled numerical approach.     

Propagation of thickness-twist waves through a joint between two semi-infinite piezoelectric plates

We study the propagation of thickness-twist waves through a joint between two semi-infinite piezoelectric plates of crystals with 6-mm symmetry or polarized ceramics. An exact solution from the three-dimensional equations of piezoelectricity is obtained. The solution shows the cutoff of certain waves and the presence of localized electromechanical fields near the joint. The results are of fundamental importance to the understanding and design of resonators and other devices made from plates of these materials, in particular thin film resonators of ZnO and AlN.     

The peculiarities of energy characteristics of acoustic waves in piezoelectric materials and structures

This paper is devoted to detailed theoretical investigation of energy density and power flow of homogeneous (bulk) and inhomogeneous (surface and plate) plane acoustic waves in piezoelectric materials and structures. The analysis of these waves in different materials of various crystallographic orientations allowed us to establish some energy regularities. These regularities are the same for instantaneous energy characteristics of homogeneous waves and for time-average energy characteristics on unit of aperture of inhomogeneous waves if the electrical energy and power flow in vacuum are taken into account. It has been shown that, for strong piezoactive waves, the electric energy density may exceed the mechanical energy density more than three times.     

The energy density and power flow of acoustic waves propagating in piezoelectric materials

It is shown that, for a plane bulk acoustic wave propagating in arbitrary piezoelectric media, the densities of mechanoelectrical and electromechanical energies are always equal in absolute value and have opposite signs. However, in general, the mechanoelectrical and electromechanical power flows of such a wave calculated by the traditional expression for the Poynting vector do not compensate each other, although the total density of these energies is always equal to zero. A discovered discrepancy based on the dissymmetry of piezoelectric constants with respect to the electrical and mechanical indexes may cause difficulties for calculation of important parameters for practical applications such as energy transport velocity of acoustic waves in piezoelectric materials.     

Tonpilz piezoelectric transducers with acoustic matching plates for underwater color image transmission

Tonpilz piezoelectric transducers with multiple acoustic matching plates are suitable for color image acoustic transmission, to achieve wideband low-ripple characteristics as well as high-efficiency high-power transmitting capability. The design method for the transducers was investigated on the basis of multiple-mode filter synthesis theory. For transducers with single, double, and triple matching plates, optimum specific acoustic impedances and lengths were calculated. Moreover, based on this design method, a 24 kHz array comprising nine identical transducers with single matching plates was built and evaluated. As a result, this array showed high-efficiency, low-ripple, and wideband characteristics. Excellent agreement between theoretical values and experimental results was obtained. A field test was carried out on color image transmission from a 3500 m sea depth, using the fabricated array, during which good color images were received.