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 characteristics of fundamental shear-horizontal acoustic waves in structure “nanocomposite polymeric film-vacuum gap-piezoelectric plate”

AbstractRecently it has been shown that SH0 wave in structure “piezoelectric plate-nanocomposite polymeric film with Fe nanoparticles” is characterized by the low TCD (∼15 ppm/C) and high value of K2 (∼32%). However in the case of the acoustical contact of polymeric material with the plate such structure possesses significant attenuation of the acoustic wave (∼1dB/λ). In order to avoid this effect it was suggested to use the structure containing the gap between the polymeric film and plate. As the result of theoretical analysis the dependencies of SH0 wave velocity versus relative thickness of vacuum gap were obtained. It has been found that there exist such values of gap and dielectric permittivity of the nanocomposite material when the value of TCD of SH0 wave significantly decreases. At that the attenuation connected with the dissipation factor is practically absent

Surface roughness effects on vibration characteristics of AT-cut quartz crystal plate

With the miniaturization and high-frequency requirements of quartz crystal resonators (QCRs), microscopic issues affecting operating performance, e.g., the surface roughness, are receiving more and more attention. In this study, the surface roughness is considered as a Gaussian distribution, and mode coupling properties of AT-cut QCRs is systematically investigated under different temperature environments with the aid of two-dimensional thermal field equations. The resonant frequency, frequency-temperature curves, and mode shapes of QCRs are obtained through the partial differential equation (PDE) module of COMSOL Multiphysics software for free vibration analysis. For forced vibration analysis, the admittance response and phase response curves of QCRs are calculated via the piezoelectric module. The results from both free and forced vibration analyses demonstrate that surface roughness reduces the resonant frequency of QCRs. Additionally, mode coupling is more likely to occur in a crystal plate with a surface roughness, leading to activity dip and reduced working performance of QCRs, which should be avoided in device fabrication

A systematic tomography framework for thickness mapping of pipes using helical guided waves

Pipe wall loss caused by corrosion is of growing interest in the petrochemical industry. A systematic tomography framework using helical guided waves is developed in this paper to conduct a thickness mapping. In this work, the thickness under investigation is reconstructed using an objective function derived from the acoustic Helmholtz equation. The main approach consists of two parts. Firstly, the parametric dictionary is designed to separate the overlapped guided waves travelling in helical paths. After that, the scattering field can be extracted as the input of the distorted born iteration method. The imaging result is exemplified numerically and experimentally, with the strengths and drawbacks explained thoroughly. Remarkably, the thickness error of the simple defect is still within 0.5 mm when the input data is poor. A clear qualitative description of complex defects can be achieved through iterations even in the absence of an initial objective function. The framework established in this paper contributes a comprehensive imaging algorithm and the corresponding signal processing approach, all of which are conducive to providing some reference for engineering applications in nondestructive testing and structural health monitoring

Guided acoustic waves at periodically structured edges: Linear modes and nonlinear generation of Lamb and surface waves

Acoustic waves are investigated which are guided at the edge (apex line) of a wedge-shaped elastic body or at the edge of an elastic plate. The edges contain a periodic sequence of modifications, consisting either of indentations or inclusions with a different elastic material which gives rise to high acoustic mismatch. Dispersion relations are computed with the help of the finite element method. They exhibit zero-group velocity points on the dispersion branches of edge-localized acoustic modes. These special points also occur at Bloch-Floquet wavenumbers away from the Brillouin zone boundary. Deep indentations lead to flat branches corresponding to largely non-interacting, Einstein-oscillator like vibrations of the tongues between the grooves of the periodic structure. Due to the nonlinearity of the elastic media, quantified by their third-order elastic constants, an acoustic mode localized at a periodically modified edge generates a second harmonic which partly consists of surface and plate modes propagating into the elastic medium in the direction vertical to the edge. This acoustic radiation at the second-harmonic frequency is investigated for an elastic plate and a truncated sharp-angle wedge with periodic inclusions at their edges. Unlike nonlinear bulk wave generation by surface acoustic waves in an interdigital structure, surface and plate mode radiation by edge-localized modes can be visualized directly in laser-ultrasound experiments

The multi-field coupled vibration analysis of AT-cut quartz crystal resonators with parallelism error

During the fabrication of quartz crystal resonators (QCRs), parallelism error is inevitably generated, which is rarely investigated. In order to reveal the influence of parallelism error on the working performance of QCRs, the coupled vibration of a non-parallel AT-cut quartz crystal plate with electrodes is systematically studied from the views of theoretical analysis and numerical simulations. The two-dimensional thermal incremental field equations are solved for the free vibration analysis via the coefficient-formed partial differential equation module of the COMSOL Multiphysics software, from which the frequency spectra, frequency–temperature curves, and mode shapes are discussed in detail. Additionally, the piezoelectric module is utilized to obtain the admittance response under different conditions. It is demonstrated that the parallelism error reduces the resonant frequency. Additionally, symmetry broken by the non-parallelism increases the probability of activity dip and is harmful to QCR’s thermal stability. However, if the top and bottom surfaces incline synchronously in the same direction, the influence of parallelism error is tiny. The conclusions achieved are helpful for the QCR design, and the methodology presented can also be applied to other wave devices

Local modulation of electrical distributions in bent PS fibers via multi-segmented layered structures

Piezoelectric semiconductor fibers are the foundation of nanogenerators, nano-force sensors, and other nanodevices. Regulating the local piezopotential characteristics inside the PS fiber is crucial for its piezoelectric performance. However, due to the extremely small size of nanofibers, this is quite challenging. In this study, we propose a method for modulating local electrical distribution of bent PS fibers using a multi-segmented layered structure. The field equations for bent PS fibers are derived, and the effect of a non-uniform additional layer’s discontinuity in material properties and thickness distributions on the distributions of strain, potential, and charge carrier concentration fields within the fiber are investigated. Results from theoretical studies and case studies indicate that the discontinuity of material coefficients or the thickness in the attached layer allows the local piezopotential distribution of the bent fiber to be effectively tuned by external forces. In the bent fibers, the potential and carrier concentration in the intermediate region no longer remain constant, but instead, localized potential wells and barriers, or plateau-like regions of high and low potential, start to form along the axial direction, and they are symmetric with respect to the strain neutral axis. The discontinuity of various material coefficients in the attached layer has different effects on the local potential changes in the bent fiber. Local potentials of arbitrary form can be controlled through different material and thicknesses distribution combinations of the attached layer. The findings of this study provide important guidance for modulating the local electrical distributions of PS fibers and offer new insights and design ideas for nanoscale piezoelectric devices