Plate Acoustic Waves Research Articles

I-2 Integrated High Temperature Longitudinal, Shear, and Plate Acoustic Wave Transducers(Device application (English session))

I-2 Integrated High Temperature Longitudinal, Shear, and Plate Acoustic Wave Transducers(Device application (English session))

Investigation of the phase velocities of guided acoustic waves in soft porous layers

A new experimental method for measuring the phase velocities of guided acoustic waves in soft poroelastic or poroviscoelastic plates is proposed. The method is based on the generation of standing waves in the material and on the spatial Fourier transform of the displacement profile of the upper surface. The plate is glued on a rigid substrate so that it has a free upper surface and a nonmoving lower surface. The displacement is measured with a laser Doppler vibrometer along a line corresponding to the direction of propagation of plane surface waves. A continuous sine with varying frequencies was chosen as excitation signal to maximize the precision of the measurements. The spatial Fourier transform provides the wave numbers, and the phase velocities are obtained from the relationship between wave number and frequency. The phase velocities of several guided modes could be measured in a highly porous foam saturated by air. The modes were also studied theoretically and, from the theoretical results, the experimental results, and a fitting procedure, it was possible to determine the frequency behavior of the complex shear modulus and of the complex Poisson ratio from 200 Hz to 1.4 kHz, in a frequency range higher than the traditional methods.

Amplification of acoustic waves in piezoelectric semiconductor plates

Two-dimensional equations for coupled extensional, flexural and thickness-shear motions of thin plates of piezoelectric semiconductors are obtained systematically from the three-dimensional equations by retaining lower order terms in power series expansions in the plate thickness coordinate. The two-dimensional equations are specialized to crystals of 6 mm symmetry and are simplified by thickness-shear approximation. Propagation of thickness-shear waves and their amplification by a dc electric field are analyzed.

General relationships for guided acoustic waves in anisotropic plates

Some universal identities for plane elastic waves in free and clamped homogeneous plates of arbitrary anisotropy are obtained and analysed. Insight is gained by linking the dispersion of guided–wave phase velocity (or, more precisely, its derivative in wavenumber or frequency) to the Stroh matrix, i.e. to the coefficients of the governing system of wave motion equations in the sextic form, on the one hand, and to the energetic parameters, on the other. The derivation also involves the residues of the plate admittance (Gree9s function in the transform domain) along a dispersion branch. Combining these complementary perspectives enables a general criterion for increasing or decreasing trends in the dispersion branches and provides useful interpretations of the difference between the phase velocity and the in–plane group velocity. Explicit examples at low, high and cut–off frequencies are presented. Limitations for the case of transversely inhomogeneous plates are discussed.

Nonlinear Acoustoelastic Interactions of Lamb Waves with LiNbO<sub>3</sub> Films Deposited on Sapphire Substrates

The influence of a biasing electric field on the propagation of the lowest-order antisymmetrical a0 Lamb wave modes in a bi-layered piezoelectric plate is investigated in this paper. It is found that the velocity shifts for the a0 mode due to presence of the bias field on the 10- µm LiNbO3 film structure are comparable with those observed in surface acoustic waves and Lamb waves in LiNbO3 plates. The fractional change in phase velocity of the layered piezoelectric structure is a linear function of the biasing electric field and can be used in voltage sensors.

Investigation of acoustic waves of higher order propagating in plates of lithium niobate

This paper presents theoretical investigation of higher order acoustic plate waves propagating in single crystals of lithium niobate. The dependencies of wave velocity and electromechanical coupling coefficient of antisymmetric, symmetric, and shear horizontal modes on the parameter hf ( h=plate thickness, f=operating frequency) are calculated as a function of propagation direction on X-, Y-, and Z-cut lithium niobate plates. It is found that several modes can provide values of K 2 that are much greater than can be obtained with surface acoustic waves (SAWs). For example, K 2 as high as 0.26 and 0.38 can be obtained from SH 1 and A 2 modes, respectively. This compares with a maximum value of K 2=0.055 for SAWs. It is further shown that there are several crystal cut and propagation directions that can allow efficient excitation and detection of a single mode with minimal interference due to other modes.

Motion of microscopic grains in a periodic potential of plate acoustic waves

We report on a novel method of charge particle transport. It is based on the application ofa moving electrostatic potential and an oscillating friction force to the particle which occur dueto acoustic waves travelling in a piezoelectric medium. ZnS grains placed onto the surface of aY-cut,Z-propagatingLiNbO3 plate experience a sequence of jumps in the forward and in the backward directions withrespect to the phase velocity of the plate wave. The jump probability appears to changewith the Lamb mode supported by the plate and the sign of the grain charge. We presentcomputed spatial profiles of the piezoelectric potential and the displacement components onthe surface of the plate for the two lowest resonant modes of Lamb waves. The occurrenceof the grain motions is then explained by the presence of the electrical and frictionforces, and good qualitative correspondence of the theory and experiment is found.

Hybridization of acoustic waves in piezoelectric plates

The conditions for hybridization of the zero-order and high-order acoustic waves propagating in a piezoelectric crystal plate have been studied. The dependence of the phase velocity of the hybrid waves on the parameter hf (h is the plate thickness and f is the wave frequency) is established for the potassium niobate and lithium niobate plates possessing various crystallographic orientations and conductivities. It is found that hybridization takes place when the conductivity of a thin surface layer exceeds a certain critical value, which can vary within broad limits depending on the plate material and orientation. The degree of dispersive repulsion of the coupled modes grows with increasing electromechanical coupling coefficient.

Technique of Measurements of Elastic Wave Attenuation Parameters

Certain methodical aspects of using one of the active methods of acoustic testing of materials and products, namely, measurements of the frequency dependence of the attenuation coefficient are considered when the dependence of recorded results on the physical differences between the measurement channels is eliminated. The attenuation coefficients of transverse and longitudinal ultrasonic waves are estimated under the laboratory conditions and the problems of predicting the remaining lifetime on the basis of attenuation of surface acoustic waves in plates subjected to alternating bending in the low-cycle fatigue domain are discussed.

Acoustic wave properties of CVD diamond

Diamond is a material which displays exceptional electronic, thermal, tribological, elastic and acoustic properties. These exceptional properties make diamond extremely difficult to characterize. In particular, diamond displays the highest acoustic velocities of any material making it an ideal candidate for acoustic wave devices. The acoustic properties of CVD diamond have not been successfully characterized by conventional acoustic techniques. This has led to a lack of process control for production of standardized CVD diamond and has hindered development of diamond devices because of a lack of knowledge of diamond acoustic properties. This paper examines recent progress in characterization of acoustic properties of CVD diamond, with a particular emphasis on the propagation of laser-generated surface acoustic waves in polycrystalline plates and what it reveals about the properties and microstructure of polycrystalline black, white and highly oriented CVD diamond samples.

Reflection of normal acoustic waves in thin plates from a grating with a periodically distributed mechanical load

Reflection of zero-order normal acoustic waves excited in a thin piezoelectric plate from a set of conducting strips of a finite thickness is studied both theoretically and experimentally. The analysis shows that the effects produced by the short-circuiting of the plate surface and by the elastic load on the impedance ratio of adjacent plate segments are in opposition to each other. These effects can be commensurable, and, hence, for each wave type, there is a certain value of the strip thickness at which the reflection coefficient becomes equal to zero. The experimental results obtained for a shear horizontal normal wave (an SH0 wave) propagating in a lithium niobate plate are in good agreement with the theory and justify the use of the equivalent-circuit model in analyzing the properties of reflectors of the type under study.

Improved equivalent circuits for acoustic plate wave devices

This paper presents improved equivalent circuits for the analysis and design of acoustic plate wave devices. The method uses a mixed equivalent circuit for the interdigital transducer consisting of both active and passive sections placed on the surface of a piezoelectric plate. The values of the various circuit elements are obtained by carrying out a best fit between theoretical and experimental frequency dependence of the real and imaginary parts of transducer input impedance. Knowledge of the equivalent circuit parameters allows one to optimize design of the devices. The method has been successfully employed for the design of one-port shear-horizontal wave resonators on Y– X lithium niobate plates. The proposed method can also be utilized for determining acoustic wave velocity with high accuracy.

Dispersion of surface acoustic waves in polycrystalline diamond plates

Abstract Five free-standing polycrystalline diamond plates were grown by electron-assisted hot filament CVD on molybdenum using different deposition parameters. The homogeneity of the elastic properties was studied for each side of the samples by surface acoustic waves (SAWs) using pulsed laser excitation and piezoelectric detection. From the velocities of the longitudinal acoustic bulk waves (LABWs) and SAWs, values of the Poisson ratio of approximately ν=0.14±0.06 were obtained. The Young's modulus varied between E =928±40 GPa and E =1098±43 GPa. Anomalous dispersion of the SAWs on the nucleation side was observed in some samples. In addition the mean velocity of the SAWs was generally higher on the nucleation side than on the growth side. This indicates that the elastic properties changed considerably during the growth process. Measurements of the grain size by scanning electron microscopy (SEM), of the phase purity by Raman spectroscopy, and the texture by X-ray diffraction (XRD) were performed in order to estimate the contribution of different effects to the dispersion and the side dependence of the SAW velocities. In addition Fourier transform infrared (FTIR) spectroscopy was applied to study the influence of the hydrogen content.

Conditions for anomalous acousto-optical diffraction by backward propagating acoustic waves.

Experimental evidence is given of acoustic plate waves, whose group velocity is contradirected with respect to the phase velocity, through a determination of the acoustic wavelength dependence on frequency, in a limited range of frequencies. The dependence dLambda/dOmega>0 between wavelength and frequency is experimentally verified, as the required condition for acousto-optical diffraction, where higher frequency components would scatter light into smaller diffraction angles.

A Continuous Sensor to Measure Acoustic Waves in Plates

An active fiber composite tape with segmented electrodes was modeled for use as a continuous sensor for structural health monitoring of plate structures. The material has unidirectional piezoceramic fibers with interdigital electrodes on the top and bottom surfaces and is poled in the fiber direction. The elastic response of a plate with the modeled sensor was computed in closed form at small time steps, and the coupled piezoceramic constitutive equations were solved. Wave propagation responses and the corresponding sensor voltages were computed in the simulations. The simulations indicate that the continuous sensor can detect damage to the plate based upon high frequency wave propagation characteristics. A continuous sensor comprised of monolithic piezoceramic patches was built and tested to measure simulated acoustic emissions on panel structures. The monolithic patches were used to simplify fabrication of the sensor. The sensor detected simulated acoustic emissions in a fiberglass panel using only one channel of data acquisition. The continuous sensor can potentially reduce the cost, complexity, number of channels of data acquisition, and the weight of monitoring instrumentation to a level where it becomes practical to perform health monitoring on large structures.

A Continuous Sensor to Measure Acoustic Waves in Plates

A Continuous Sensor to Measure Acoustic Waves in Plates

Investigation of acoustic waves in thin plates of lithium niobate and lithium tantalate

The general properties of fundamental antisymmetric A0, symmetric S0, and shear horizontal SH0 acoustic waves propagating in thin piezoelectric plates have been theoretically investigated on samples of lithium niobate (LiNbO3) and lithium tantalate (LiTaO3). The results obtained will be useful for a proper development of various physical, chemical, and biological sensors and devices for signal processing based on plate acoustic waves.

Characteristics of acoustic plate waves in potassium niobate (KNbO 3) single crystal

This paper presents detailed theoretical investigation of three fundamental acoustic wave modes propagating in thin plates of single crystal potassium niobate. The wave velocity and Δv/ v, the fractional velocity change produced by electrical shorting of the surface, are calculated for all propagation directions on the surfaces of X-, Y-, and Z-cut plates. It is found that acoustic plate waves can provide extremely large values of electromechanical coupling coefficient. This property makes these waves very attractive for use in a variety of sensor and signal processing applications.

Acoustic waves in piezoelectric plates bordered with viscous and conductive liquid

The influence of a viscous or conductive liquid on the characteristics of acoustic waves propagating in thin piezoelectric plates is investigated theoretically as well as experimentally. Experimental results are found to be in good agreement with the theoretical calculations. The data presented in this paper is essential for the proper design of various acoustic wave sensors operating in contact with viscous and/or conductive liquids.

On the theory of wave propagation in anisotropic plates

A theoretical framework is developed which describes wave propagation in infinite homogeneous elastic plates of unrestricted anisotropy. The approach exploits the propagator matrix which is the exponential of the fundamental elasticity matrix underlying Stroh9s formalism of anisotropic elastodynamics. The matrices of plate impedance and admittance are introduced, and their analytical properties are established, which appear fruitful for computing and analysing the plate wave spectra. On this basis, the dispersion equation can be cast into the form of a real equation involving the monotonic function, whose zeros and poles are the wave velocities in a given plate subjected to different boundary conditions (traction–free or clamped faces). It is proved that three fundamental wave branches exist for any orientation of wave propagation in an anisotropic plate with traction–free faces, and that those branches are missing if one or both faces are clamped. The intrinsic symmetry of the wave motion in an arbitrary plate is revealed. The general formalism is applied to elaborate the long–wavelength low–frequency approximation for a (thin) free plate of unrestricted anisotropy. The frequency–dispersive wave velocities, displacements and tractions at the onset of the fundamental wave branches are derived explicitly. The conditions for the extreme velocity values and some other useful universal connections are determined for an arbitrary thin plate, and exemplified for specific anisotropy cases.