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It is known that Lamb waves in homogeneous traction-free plates can propagate with arbitrary phase velocity, spanning the admissible speed interval (0; + ∞) . However, as the current research shows, Lamb waves propagating in two-layered traction-free plates may have 'forbidden' phase velocities, at which no Lamb waves can propagate. The analysis is based on the approach comprising Cauchy complex formalism and the exponential fundamental matrix method. [ABSTRACT FROM AUTHOR]

The analytical and geometrical conditions for the possible appearance of the infinite group velocity (IGV) points belonging to the dispersion curves of Lamb waves propagating in traction-free plates are studied by a combined method comprising Cauchy sextic formalism and the exponential fundamental matrix method. According to the obtained geometrical condition, the IGV corresponds to the coincidence of a tangent line to any of the dispersion curves with a straight line passing through the origin. The developed technique is demonstrated by applying to the analysis of Lamb wave dispersion in three-layered plates with a soft inner core. [ABSTRACT FROM AUTHOR]

This research aims to measure the material parameters and porosity of the resin matrix composite material produced by hot moulding process under various pressures. The laser ultrasonic technique has been used as the measurement technique and the guided wave dispersion relationship was obtained in the resin matrix. In the resin substrate, the single-layer flat plate Lamb wave model was applied to inversely calculate the material parameters and compared with tensile test and traditional ultrasonic measurements. In the woven composite laminate, the specimens were produced with different porosity using the hot pressing moulding process, scanned with computed tomography to confirm the porosity under different pressure and the dispersion curve changes were observed using the laser ultrasonic technique. Result showed that the inversely calculated thickness of pure resin test pieces were consistent with the laser ultrasonic measurement within an error of 5%. The elastic modulus of inverse calculation and the actual tensile test values showed within 12% of error. In the woven fibre composite, the dispersion curve obtained by the laser ultrasonic measurement showed that, as the porosity increases, the dispersion curve tends to shift to a lower wave velocity. In addition to that, the porosity of the woven composite is not changed under different hot pressing pressures. The computed tomography scanning indicated that the pores are mostly concentrated in the overlap of the carbon fibre weaving and extended along the fibre warp and weft directions, showing cross-shaped pores. [ABSTRACT FROM AUTHOR]

Lamb and Rayleigh waves-based dispersion analysis has been carried out for non-destructive surface wave testing of different slab-like structures involving a concrete roof slab, a concrete floor, a concrete pavement, and an asphaltic pavement. An impact was generated by gently striking the slab's free surface with a hammer. A method has also been given to generate the governing (predominant) dispersion mode in the case of Rayleigh wave propagation considering the complex nature of the dispersion function $\vert {{ D}\lpar {c\comma \; \kappa } \rpar } \vert$ | D (c , κ) | ; $c$ c and $\kappa$ κ refer to phase velocity and wavenumber, respectively. The theoretical dispersion plots generated from the inversion analysis by varying the values of different input parameters were subsequently closely matched with the corresponding obtained field dispersion images for different cases in order to back compute the elastic profile of the slab/pavement. For developing the dispersion images, the Park's wavefield transformation method was employed. For checking the thicknesses of the different layers, cylindrical cores were also extracted. The study is expected to be useful for evaluating different slab-like structures, including pavements, by using surface wave-based non-destructive tests. [ABSTRACT FROM AUTHOR]

Lamb and Rayleigh waves-based dispersion analysis has been carried out for non-destructive surface wave testing of different slab-like structures involving a concrete roof slab, a concrete floor, a concrete pavement, and an asphaltic pavement. An impact was generated by gently striking the slab's free surface with a hammer. A method has also been given to generate the governing (predominant) dispersion mode in the case of Rayleigh wave propagation considering the complex nature of the dispersion function $\vert {{ D}\lpar {c\comma \; \kappa } \rpar } \vert$ | D (c , κ) | ; $c$ c and $\kappa$ κ refer to phase velocity and wavenumber, respectively. The theoretical dispersion plots generated from the inversion analysis by varying the values of different input parameters were subsequently closely matched with the corresponding obtained field dispersion images for different cases in order to back compute the elastic profile of the slab/pavement. For developing the dispersion images, the Park's wavefield transformation method was employed. For checking the thicknesses of the different layers, cylindrical cores were also extracted. The study is expected to be useful for evaluating different slab-like structures, including pavements, by using surface wave-based non-destructive tests. [ABSTRACT FROM AUTHOR]

The acoustic waves of higher orders propagating in a layered structure consisting of a silicon plate coated with piezoelectric ZnO and/or AlN films were used for the development of a sensor with selective sensitivity to liquid viscosity η in the range of 1–1500 cP. In that range, this sensor possessed low sensitivity to liquid conductivity σ and temperature T in the ranges of 0–2 S/m and 0–55 °C, respectively. The amplitude responses insensitive to the temperature instead of the phase were used to provide the necessary selectivity. The sensor was based on a weak piezoactive acoustic wave of higher order. The volume of the probes sufficient for the measurements was about 100 μL. The characteristics of the sensors were optimized by varying the thicknesses of the structure layers, number of layers, wavelength, wave propagation direction, and the order of the acoustic waves. It was shown that in the case of the layered structure, it is possible to obtain practically the same selective sensitivity toward viscosity as for acoustic waves in pure ST, X quartz. The most appropriate waves for this purpose are quasi-longitudinal and Lamb waves of higher order with in-plane polarization. It was found that for various ranges of viscosity η = 1–20 cP, 20–100 cP, and 100–1500 cP, the maximum sensitivity of the appropriate wave is equal to 0.26 dB/cP, 0.087 dB/cP, and 0.013 dB/cP, respectively. The sensitivity of the waves under study toward the electric conductivity of the liquid is much less than the sensitivity to liquid viscosity. These two responses become comparable only for very small η < 2 cP. The waves investigated have shown no temperature responses in contact with air, but in the presence of liquid, they increase depending on liquid properties. The temperature dependence of liquid viscosity is measurable by the same sensors. The results obtained have shown the possibility of designing acoustic liquid viscosity sensors based on multilayered structures. The set of possible acoustic waves in layered structures possesses modified propagation characteristics (various polarization, phase velocities, electromechanical coupling coefficients, and attenuations). It allows choosing an optimal acoustic wave to detect liquid viscosity only. [ABSTRACT FROM AUTHOR]

In this study, a new method for determining the elastic constants of isotropic plates using Lamb wave fundamental modes is presented. This method solves the inverse problem, where the elastic constants (Young's modulus and Poisson's ratio) of the plate were estimated by measuring the phase velocities of the Lamb wave using the Rayleigh–Lamb equations to find the solution and determining the phase velocities of the A0 and S0 modes using a new method. The suitability of the proposed method for determining the elastic constants was evaluated using simulated and experimental signals propagating on an aluminum plate. The theoretical modeling on the aluminum 7075-T6 plate shows that the proposed method allows the determination of the Poisson ratio with a relative error not exceeding 2% and Young's modulus with a relative error not exceeding 0.5%. The experimental measurements of an aluminum plate of known thickness (2 mm) and density (2685 kg/m3) confirmed the suitability of the proposed method for the measurements of elastic constants. In the proposed method, the processing of ultrasonic signals can be performed in real-time, and the values of the elastic constants can be obtained immediately after scanning the required distance. [ABSTRACT FROM AUTHOR]

New designs based on S0 Lamb modes in AlN thin layer resonating structures coupled with the implementation of structural elements in SiO2, are theoretically analyzed by the Finite Element Method (FEM). This study compares the typical characteristics of different interdigital transducer (IDTs) configurations, involving either a continuous SiO2 cap layer, or structured SiO2 elements, showing their performance in the usual terms of electromechanical coupling coefficient (K2), phase velocity, and temperature coefficient of frequency (TCF), by varying structural parameters and boundary conditions. This paper shows how to reach temperature-compensated, high-performance resonator structures based on ribbon-structured SiO2 capping. The addition of a thin diamond layer can also improve the velocity and electromechanical coupling coefficient, while keeping zero TCF and increasing the solidity of the membranes. Beyond the increase in performance allowed by such resonator configurations, their inherent structure shows additional benefits in terms of passivation, which makes them particularly relevant for sensing applications in stern environments. [ABSTRACT FROM AUTHOR]

The problem of acoustic wave propagation in a predeformed compressible elastic layer interacting with a layer of viscous compressible fluid is considered. The study is based on the three-dimensional equations of the linearized theory of finite strain elasticity for an elastic layer and the three-dimensional linearized Navier–Stokes equations for a layer of viscous compressible fluid. The problem statement and the approach based on the general solutions of linearized equations for the elastic body and the fluid are applied. The dispersion equation describing the propagation of harmonic waves in a hydroelastic system in a wide frequency range for a thick layer of fluid is obtained. The effect of prestresses, as well as the thickness of the elastic body and fluid layers, on the phase velocities and damping factors of generalized Lamb modes is analyzed. The developed approach and the results obtained make it possible to establish the limits of applicability of models based on different variants of the theory of small initial deformations, classical elasticity theory, and the perfect fluid model for wave processes. Numerical results are plotted and analyzed. [ABSTRACT FROM AUTHOR]

Lamb waves are extensively used in non-destructive tests (NDT) to detect corrosion and another defects in thin plates. Several NDT methods require to compute the phase velocity of the Lamb wave, which depends on the frequency. In this work we show the potential of the combination of the phase velocity method (PVM) with the finite element method (FEM) for computing the phase velocity dispersion curve of an ultrasonic pulse traveling in a transversally annular isotropic thin plate. The FEM-PVM is based on the numerical solution of the wave propagation equations for several selected frequencies. To solve these equations, a second order difference scheme is used to discretize the temporal variable, while spatial variables are discretized with FEM. The open software FreeFem++ is used with quadratic triangular elements to compute the displacements. The phase velocity for a given frequency is obtained from the computed displacements at few points on the top of the plate. Repeating the procedure for several frequencies we compute a sample of points that are fitted to obtain an approximation of the phase velocity dispersion curve. A deeper understanding on the behavior of the phase velocity dispersion curve with respect to the plate curvature is obtained as result of an extensive experimentation with annular isotropic plates of two materials. [ABSTRACT FROM AUTHOR]

On 15 January 2022, the Hunga volcano produced a massive explosion that generated perturbations in the entire atmosphere. Nonetheless, signatures in the mesosphere and lower thermosphere (MLT) have been challenging to identify. We report MLT horizontal wind perturbations using three multistatic specular meteor radars on the west side of South America (spanning more than 3,000 km). The most notorious signal is an exceptional solitary wave with a large vertical wavelength observed around 18 UT at all three sites, with an amplitude of ∼50 m/s mainly in the westward direction. Using a customized analysis, the wave is characterized as traveling at ∼200 m/s, with a period of ∼2 hr and a horizontal wavelength of ∼1,440 km in the longitudinal direction, away from the source. The perturbation is consistent with an L1 Lamb wave mode. The signal's timing coincides with the arrival time of the tsunami triggered by the eruption. Plain Language Summary: The eruption of the Hunga volcano in January 2022 had a widespread impact on the atmosphere, affecting various layers. We describe a perturbation in horizontal winds caused by the event, which was observed over the west coast of South America by three different meteor radar systems separated by more than 3,000 km between them. The perturbation behaved similarly in the altitude range of 80–100 km, and the wave parameters observed were consistent with high‐order Lamb wave solutions from simulations carried out using the Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension. This finding complements other studies that have explored the impacts of the eruption on different atmospheric levels. Overall, this study provides valuable insights into the complex and far‐reaching effects of volcanic eruptions on the atmosphere. Key Points: Hunga eruption generated extreme horizontal wind perturbations at 80–100 km of altitude over South AmericaThe signal was detected almost simultaneously by three multistatic meteor radar systems spanning more than 3,000 kmThe perturbation had a period of ∼2 hr, a horizontal phase velocity of ∼200 m/s, and a horizontal wavelength of ∼1,440 km [ABSTRACT FROM AUTHOR]

A class of antisymmetric solutions of Lamb wave equations with zero strains and stresses on the surface, so-called internal Lamb waves, is studied. Two types of such solutions are found: the first corresponds to the Lamé phase velocity; the second, to phase velocities exceeding the velocity of the expansion wave in an unbounded medium. It is proved that internal waves with the same phase velocity form series, while the frequencies of members of one series are multiples of the frequency of the first member of the series. The same is true for wavenumbers. The profiles of deformed plates and distributions of the maximum stress and shear values are presented. [ABSTRACT FROM AUTHOR]

The propagation of bending waves in a plate resting on a two-parameter elastic foundation is considered. In contrast to the classical Kirchhoff model, the mathematical model used here takes into account not only the kinetic and potential energies of bending vibrations, but also the kinetic energy due to the inertia of rotation of the plate elements during bending. The dispersion equation, phase velocity, energy transfer velocity, and energy characteristics of waves propagating in the plate are analyzed depending on the ratio of the coefficients determining the shear and compression stiffness of the elastic foundation. Conditions are found under which waves with phase and group velocities having opposite directions (frequently called "backward" waves), can exist in the plate. It is demonstrated that such waves significantly change the behavior of the energy flux. In addition, relations are found that relate the kinematic and average energy characteristics of the waves. [ABSTRACT FROM AUTHOR]

The application of non-stationary Lamb wave signals is a promising tool in various industrial applications where information about changes inside a structure is required. Phase velocity is one of the Lamb wave parameters that can be used for inhomogeneities detection. The possibility of reconstructing the segment of the phase velocity in a strong dispersion range using only two signals is proposed. The theoretical study is performed using signals of the A0 mode propagating in an aluminium plate at a frequency of 150 kHz, 300 kHz, 500 kHz and 900 kHz. The experiment was carried out at a value of 300 kHz. The studies conducted indicated that the maximum distance between two signals, at which the time-of-flight can be measured between the same phase points, is the main parameter for the two signals technique application. Theoretical and experimental studies were performed, and the mean relative error was calculated by comparing the obtained results with those calculated via the SAFE method. In the theoretical study, the mean relative error of 0.33% was obtained at 150 kHz, 0.22% at 300 kHz, 0.23% at 500 kHz and 0.11% at 900 kHz. The calculated mean relative errors δ c p h = 0.91 % and δ c p h = 1.36 % were obtained at different distances in the experimental study. The results obtained show that the estimation of the phase velocity in dispersion ranges using only two received signals was a useful tool that saved time and effort. [ABSTRACT FROM AUTHOR]

• Thermoelastic Lamb waves in functionally graded nanoplates are studied based on integral form of modified nonlocal theory. • The Legendre polynomial approach is improved based on the proposed iterative solution integration method. • The escape frequency, which appears in differential model of modified nonlocal theory, does not exist in the integral one. • Nonlocal effect on attenuation is more notable than that on phase velocity. • Nonlocal effect strengthens attenuations before their peak frequency, but then weakens them. Based on the integral form of the modified nonlocal theory, the dispersion and attenuation characteristics of thermoelastic Lamb waves in functionally graded material nanoplates are investigated. The improved Legendre polynomial series approach is presented to conquer the difficulty of the very time-consuming integration calculation, which contains the nonlocal factor, the Legendre polynomials, rectangular window function and their derivative. An iteration solution integration method is derived by using the properties of Legendre polynomials and the integration by parts. The proposed approach possesses the advantages of a small scale of the characteristic matrix and can directly obtain the complex wave number solutions without iteration. Comparisons with the available data indicate the validity of the proposed approach. Numerical examples show that the nonlocal effect on attenuation is more notable than that on phase velocity, especially at the frequency of the maximal attenuation. Besides, the nonlocal effect is very weak at the low frequency. Importantly, the escape frequency, which appears in the results from the differential form of modified nonlocal theory, does not exist in the integral form of modified nonlocal theory. In fact, the escape frequency originates from the approximate transformation from integral model to differential model. [ABSTRACT FROM AUTHOR]

In nonlinear ultrasonic damage detection, the appropriate Lamb wave mode to accurately characterise the nonlinearity attributed to the material damage should be selected important. However, an effective mode is more difficult to select practically as impacted by the dispersion and multi-mode characteristic of the Lamb wave. In this study, based on the dispersion curve of Lamb waves, the modes meeting the second harmonics and third harmonics phase velocity matching were given, and the nonlinear cumulative effects exerted by different modes on fatigue cracks were compared. In addition, an investigation was conducted on the amplitude change of the second and third harmonics signal of the identical fatigue damage. The results show that the harmonic amplitude decreases with the increase of the fatigue crack length. The third harmonics under the two modes are more sensitive to fatigue damage than the second harmonics. Moreover, the amplitude of the third harmonic excited by S1 mode exceeds that of the other mode. As the fatigue crack length increases, the relative second- and third-order nonlinear coefficients generated by S1 mode have approximately the same trend, first increasing and then decreasing. The results reveal that the third harmonic under S1 mode could more effectively characterise fatigue damage. [ABSTRACT FROM AUTHOR]

Dispersion curves are plotted and the propagation of generalized Lamb waves over a wide range of frequencies is studied based on the linearized three-dimensional Navier–Stokes equations for the layer of viscous compressible fluid and the linear equations of classical elasticity for the elastic layer. The effect of the viscosity of the fluid, the thickness of the elastic and liquid layers on the phase velocity and the damping factor of generalized Lamb modes is analyzed in the case of a thick liquid layer. For all modes, there are elastic layers of certain thickness for which the effect of the viscosity of the fluid on the phase velocity and the damping factors of the mode is minimum. It is also found out that for some modes, there are both certain thickness and thickness intervals for which the effect of the fluid viscosity on the phase velocity and the damping factors of these modes is significant. In the case of a strongly stiff material of the elastic layer, for some modes, there is a layer thicknesses (frequencies) for which the viscosity of the fluid does not affect the phase velocities of these modes. The approach and the results allow us to establish the limits of applicability of models of wave processes based on the model of a perfect compressible fluid. The numerical results are presented in the form of curves and are analyzed. [ABSTRACT FROM AUTHOR]

The influence of the quality of welding thin steel sheets on the physical and mechanical properties of electric steel has been studied using Lamb waves. It is shown that Lamb waves excited in the zero symmetric mode are an effective source of information about the state of the material both in the welded joint of the plates and in the zone of base metal not affected by thermal influences. Markers of the quality of welded joints are determined. It is established that the most informative parameters are the phase velocity of a Lamb wave and its amplitude. Based on velocity measurements, macroscopic anisotropy of the acoustic properties of the material is found. It is assumed that the origin of this anisotropy is due to residual stresses arising in the technological process of processing steel sheets. The results obtained are of interest for specialized quality control of butt joints in thin steel sheets. [ABSTRACT FROM AUTHOR]

Early detection of defects inside a rail is of great significance to ensure the safety of rail transit. This work investigated the ability of ultrasonic guided waves (UGWs) to detect internal defects in a rail head. First, the model of UGW propagation in rail, which has an irregular cross-section, was constructed based on the semi-analytical finite element (SAFE) method. Fundamental characteristics, such as wavenumber, phase or group velocity, and wave structure inside the rail, were then calculated. Following modal and vibration energy distribution analysis, a guided wave mode that is sensitive to transverse fissure (TF) defects was selected, and its excitation method was proposed. The effectiveness of the excitation method was confirmed by simulations performed in the ABAQUS software. According to the simulation data, the dispersion curve calculated by using the two-dimensional Fourier fast transform (2D-FFT) coincided well with that of the SAFE method. After that, the sensitivity of the selected mode to internal rail defects was validated and its ability to locate defects was also demonstrated. Finally, the effects of excitation frequency, defect size, and vertical and horizontal defect depth on the reflection waveforms were investigated. [ABSTRACT FROM AUTHOR]

Lamb waves are often used for damage detection in structures. Hot-spot monitoring via wave focusing is considered in this study, which can be achieved by using a plano-concave aspherical lens. Once attached to the plate, the lens modifies the effective plate thickness, and therefore changes the Lamb wave characteristics, such as wavenumber and phase velocity, providing a convenient way of controlling Lamb waves. Another possibility for focusing Lamb waves is to use multiple actuators and design dispersion pre-compensated excitation signals with an embedded time delay. These two approaches can be combined together. We conducted numerical simulations using the time-domain spectral element method based on the 3D elasticity theory and demonstrated that the A0 mode of Lamb waves could be focused on the desired focal point. We compared the efficacies of the plano-concave lens approach, the dispersion pre-compensated focusing approach, and a combination of both approaches, emphasizing the advantages and disadvantages of each method. [ABSTRACT FROM AUTHOR]

The 2D-FFT is described as a traditional method for signal processing and analysis. Due to the possibility to determine the time and frequency (t,f) domains, such a method has a wide application in various industrial fields. Using that method, the obtained results are presented in images only; thus, for the extraction of quantitative values of phase velocities, additional algorithms should be used. In this work, the 2D-FFT method is presented, which is based on peak detection of the spectrum magnitude at particular frequencies for obtaining the quantitative expressions. The radiofrequency signals of ULWs (ultrasonic Lamb waves) were used for the accuracy evaluation of the method. An uncertainty evaluation was conducted to guarantee the metrological traceability of measurement results and ensure that they are accurate and reliable. Mathematical and experimental verifications were conducted by using signals of Lamb waves propagating in the aluminum plate. The obtained mean relative error of 0.12% for the A0 mode (160 kHz) and 0.05% for the S0 mode (700 kHz) during the mathematical verification indicated that the proposed method is particularly suitable for evaluating the phase-velocity dispersion in clearly expressed dispersion zones. The uncertainty analysis showed that the plate thickness, the mathematical modeling, and the step of the scanner have a significant impact on the estimated uncertainty of the phase velocity for the A0 mode. Those components of uncertainty prevail and make about ~92% of the total standard uncertainty in a clearly expressed dispersion range. The S0 mode analysis in the non-dispersion zone indicates that the repeatability of velocity variations, fluctuations of the frequency of Lamb waves, and the scanning step of the scanner influence significantly the combined uncertainty and represent 98% of the total uncertainty. [ABSTRACT FROM AUTHOR]

Guided wave propagation and its dispersion phenomenon of infinite solid elastic rods are encountered in several applications including, mechanical and civil engineering fields. In this paper, the elastic stress wave propagation in the axisymmetric circular cross-section of a high strength steel wire with cylindrical waveguide is investigated using a semi-analytical finite element (SAFE) method. The error analyses are carried out on fundamental modes, namely, flexural F (n , m) , longitudinal L (0 , m) , and torsional T (0 , m) modes. The theoretical framework for finite element (FE) discretization is established for the cylindrical waveguide. A three-node triangular linear element is used for solving SAFE dispersion solutions such as the wavenumber-frequency curve, phase velocity, and group velocity curves. The convergence and accuracy of the method are analyzed by comparing it with the calculation results of the transcendental Pochhammer frequency equation, and the meshing criterion is proposed. The use of higher-order (quadratic) elements are proposed for lower computational burden and effective method for solving eigenvalue problems. The effect of using 6-node triangular quadratic elements in the SAFE method for improving frequency accuracy is discussed in a detailed manner by proposing the meshing criterion. The calculation accuracy of a quadratic element semi-analytical discretization exceeds that of a linear element discretization with four times its radial circumference. The statistical histograms are demonstrated to prove the results of the proposed semi-analytical discretization method which can be used for solving cylindrical waveguides. [ABSTRACT FROM AUTHOR]

Zero-Group-Velocity (ZGV) guided mode has recently received particular attention because of its highly sensitive to structural changes, such as defects. Parallel to ZGV, in the present work, we introduce a new guided mode so-called Minimum-Group-Velocity (MGV) that is a remarkable phenomenon in defect detection applications. Strictly speaking, when any two phase-velocity dispersion curves of Lamb modes approach each other without overlapping, we observe this new mode in group-velocity dispersion curves. It is worth noting that this MGV mode has never been addressed in literature. We compute the Lamb-like modes in asymmetric viscoelastic sandwich plates using the Stiffness Matrix Method (SMM). We show that the change in properties of this sandwich can dramatically affect frequency ranges associated with ZGV and MGV modes. However, a linear correlation between phase velocities and this change on viscoelastic properties is discussed, where we observed an interconnection phenomenon in the dispersion curves. This interconnection happens between specific points on the dispersion curves, each corresponding to a ZGV- or MGV-mode. On the other hand, we verify that the detection of changes in level of viscoelastic properties or variations in the thickness of the buffer viscoelastic layer is possible within a limited segment of the damped mode curve. [ABSTRACT FROM AUTHOR]

• Under stress-free and clamped boundary conditions, SH waves within a thin micropolar plate display both symmetric and skew-symmetric modes. However, these modes are notably absent under mixed boundary conditions. Similarly, P-SV waves can also generate both modes. Notably, both SH and P-SV waves exhibit dispersive characteristics. • The dispersion relationship governing SH-waves under mixed boundary conditions remains unique, regardless of which surface of the plate is stress-free or clamped. Notably, an intriguing transition point emerges in the phase velocity trend for SH waves under mixed boundary conditions. Preceding this point, the phase velocity decreases with an increasing wave number; however, beyond this point, the trend reverses. This phenomenon strongly suggests a non-linear relationship between phase velocity and plate properties under mixed boundary conditions. • The phase velocities of both SH and P-SV waves exhibit a direct correlation with both the plate thickness and the characteristic length parameter of micropolar plate. • The coupling number demonstrates a positive correlation with the phase velocity of SH waves under stress-free and clamped conditions, along with a similar relationship observed in the phase velocity of P-SV waves. The effects of the coupling number on the phase velocity of SH waves under mixed boundary conditions are particularly intriguing. In this scenario, the phase velocity initially rises and then declines with higher coupling numbers, with more noticeable impacts observed in the lower wave number range. This insight significantly contributes to a better comprehension of vibration behavior in thin plates under diverse conditions. • It is observed that number of modes increases with the increase in non-dimensional wavenumber. The observed phenomenon suggests that, across all modes, the phase velocity undergoes a reduction and eventually stabilizes at a constant value with an increasing wave number. Additionally, as the wavenumber increases, higher modes emerge with an augmented phase velocity. Studying wave propagation characteristics in plates is vital for comprehending the material dynamics to enhance the strength of structures and for optimizing the effectiveness of non-destructive testing devices. Micropolar elasticity displays microcontinuum behavior by integrating rotational and coupling effects through displacements and micro-rotations. The present study thoroughly investigates horizontally polarized shear waves (SH) within a thin micropolar plate by employing diverse boundary conditions namely stress-free, clamped, and mixed conditions. Shear horizontal waves propagate within a plate by shearing the material along the surface, excluding any motion in perpendicular direction. Moreover, for a more comprehensive grasp of wave behavior in a micropolar plate, the study investigates P-SV type waves under plane strain conditions. Analytical techniques are utilized to derive the dispersion relations for SH and P-SV type waves in a micropolar plate. Graphical representations are provided to showcase the impacts of various micropolar parameters such as coupling number, characteristic length, and plate thickness on the phase velocities of SH and P-SV type waves. The study also includes a dispersion analysis of the multimode aspect of SH and P-SV waves. This thorough investigation can significantly augment the comprehension of wave propagation phenomena within plate-like structures. [ABSTRACT FROM AUTHOR]

This study investigates nonlocal and surface effects on the dispersion behaviors of Shear horizontal (SH) waves in piezoelectric(PE)-piezomagnetic(PM) bilayer systems. The interface between these two layers is imperfectly bonded. The general governing equations are derived from the nonlocal magnetoelectroelastic (MEE) theory by adding an inherent length. The G-M model and generalized Young-Laplace equations have been used to incorporate surface effects into the boundary conditions of the bilayer systems. The closed-form dispersion equation is obtained analytically for electrically open and magnetically short conditions. Numerical solutions are utilized to investigate the effects of nonlocal scale parameters and surface parameters on SH surface wave propagation. Contrary to the results of classical theory, the coupling effects of nonlocal small-scale and surface piezoelectricity are more significant than individual effects. Also, it has been observed that the imperfectness parameter across the interface and the thickness ratio of the bilayer significantly affect the phase velocity. Moreover, 2D and 3D plots of the mode shapes of field variables for the propagation of SH waves are presented graphically. These results are validated by conducting analyses excluding nonlocal effects. This allows us to isolate the specific impact of surface effects in the piezoelectric–piezomagnetic bilayer system, drawing connections to existing results and enhancing the robustness of our findings. This study provides valuable insights into complex wave dynamics, helping to optimize the performance and functionality of such smart composites in various engineering applications. • Theoretical study of the propagation of SH wave in bilayer plate is investigated. • The coupling influence of surface piezoelectricity and nonlocality are discussed. • Thickness ratio of bilayer plates and imperfect interface have significant impacts. • Mode-shape plots of field variables for the SH wave are presented graphically. • This study provides valuable insights into complex wave dynamics in nanostructures. [ABSTRACT FROM AUTHOR]

Determining Lamb wave dispersion curves when measuring phase and group velocity values at a fixed frequency is now a common and relevant task. In most cases, in order to solve such a problem, it is necessary to know the exact properties of the material, particularly its thickness. In experimental methods, Lamb wave parameters are evaluated directly from the test materials. This paper proposes a new and simple experimental algorithm for A0 mode group and phase velocity determination based on signal filtering and zero-crossing estimating. The main idea is to capture the zero-crossing instances of the signals closest to the signal envelope peaks and use these time instances to determine the phase and group velocities. The reliability of the proposed method was evaluated using simulated and experimental signals propagating in an aluminum plate. Theoretical modeling has shown that the proposed method enables the calculation of the A0 mode group and phase velocities with a mean relative error of less than 0.7%. An accuracy of 0.8% was observed during the experimental measurements. [ABSTRACT FROM AUTHOR]

Experimental characterization of Lamb waves in plate-like structures overcomes the intrinsic limits of a priori semianalytical finite element simulations, where material inaccuracies and nonidealities cannot be easily considered. Unfortunately, the experimental extraction of guided wave dispersion curves, and especially their polar representation along different directions of propagation at a given frequency, is not trivial. In nonisotropic materials, such analysis is a key aspect for a reliable and robust characterization of the behavior of waves. In this work, by exploiting scanning laser Doppler vibrometer measurements with narrowband excitation, two different signal processing methods for the extraction of the wavenumber polar representation at the excitation frequency are investigated and characterized. The first method is based on a distance regularized level set (DRLSE) algorithm, widely used in image processing and computer vision but, to the best of the author’s knowledge, never used in the Lamb waves’ field. The second method is based on the 2-D sparse wavenumber analysis which exploits the wavefield sparse representation in the wavenumber domain. With a precise and reliable extraction of the wavenumber characteristic in the ${k}$ -space, the polar representations at the excitation frequency of phase and group velocities can be estimated. The former, by exploiting the well-known wavenumber–frequency relation, the latter, instead, by computing numerical derivative among wavenumbers at multiple frequencies. The methodology has been validated on three different composite plates with different degrees of nonisotropy properties. The results show the effectiveness of the two methods, highlighting the advantages and disadvantages of both. [ABSTRACT FROM AUTHOR]

Dispersion of Lamb waves propagating in stratified and functionally graded (FG) plates is analyzed by a newly developed variant of Cauchy sextic formalism. Comparative analysis of Lamb wave dispersion in stratified, FG, and homogenized plates reveals a substantial discrepancy in dispersion properties of the studied media, making the use of homogenization techniques almost meaningless, with the only exception at the limiting phase velocity that corresponds to vanishing frequency. At the same time, dispersion curves in the stratified plates converge to the corresponding curves in the FG plate at the increasing number of the stratification layers. [ABSTRACT FROM AUTHOR]

We have implemented a 1D and 2D simulation of excitation and propagation of Lamb waves in Al/AlN/(100)-diamond and Al-IDT/AlN/(100)-diamond piezoelectric layered structures (the last in a SAW resonator configuration), respectively. The distribution of elastic displacements in Lamb waves of different orders has been calculated, the mode types have been identified, and the dispersion dependences of the phase velocities have been studied including the excitation at ultrahigh frequencies. The phase velocity values calculated using the 1D and 2D models are in good agreement with those determined experimentally. We have shown that, above a synchronism frequency of an IDT, resonances which occur in these structures, are determined by excitation of Lamb waves in a substrate. The quality factor of these resonances is extremely higher than that on surface acoustic waves. This is confirmed by the experimental data. The amplitude-frequency responses and frequency dependences of the quality factor calculated using the 2D model are in good agreement with the experiment. [ABSTRACT FROM AUTHOR]

Theoretical study of the effect of uniaxial pressure on the propagation characteristics of plate modes as Lamb and SH waves in a lithium niobate plate is carried out. A change in the effective crystalline symmetry, as well as the effective elastic constants under the pressure influence, has been derived. The controlling coefficients describing the pressure influence on the plate modes’ phase velocities are calculated for the various applications of uniaxial pressure. The uniaxial pressure influence on the hybridization of the elastic waves is discussed. [ABSTRACT FROM AUTHOR]

Objective: Estimating the elasticity distribution in the cornea is important because corneal elasticity is usually influenced by corneal pathologies and surgical treatments, especially for early corneal sclerosis. Because the thickness of the cornea is typically less than 1 mm, high-resolution ultrasound elastography as well as the Lamb wave model is required for viscoelastic property estimation. In the present study, an array high-frequency ultrasound (HFUS) elastography method based on ultrafast ultrasound imaging was proposed for estimating the viscoelastic properties of porcine cornea. Methods: The elastic wave was generated by an external vibrator, after which the wave propagation image was obtained using a 40-MHz array transducer. Viscoelasticity estimation was performed by fitting the phase velocity curve using the Lamb wave model. The performance of the proposed HFUS elastography system was verified using 2-mm-thick thin-layer gelatin phantoms with gelatin concentrations of 7% and 12%. Ex vivo experiments were carried out using fresh porcine cornea with artificial sclerosing. Results: Experimental results showed that the estimated elasticity was close to the standard value obtained in the phantom study when the Lamb wave model was used for elasticity measurement. However, the error between the standard elasticity values and the elasticity values estimated using group shear wave velocity was large. In the ex vivo eyeball experiments, the estimated elasticities and viscosities were respectively 9.1 ± 1.3 kPa and 0.5 ± 0.10 Pa·s for a healthy cornea and respectively 15.9 ± 2.1 kPa and 1.1 ± 0.12 Pa·s for a cornea with artificial sclerosis. A 3D HFUS elastography was also obtained for distinguishing the region of sclerosis in the cornea. Conclusion: The experimental results demonstrated that the proposed HFUS elastography method has high potential for the clinical diagnosis of corneal diseases compared with other HFUS single-element transducer elastography systems. [ABSTRACT FROM AUTHOR]

• The method of multiple scales is applied to analysis of internally resonant guided waves. • The amplitudes of the internally resonant guided waves are nonlinearly dependent to propagation distance. • The propagation-distance dependence of the amplitudes is affected by detuning parameters. Taking into account damping effects, the propagation-distance dependence of the amplitude of nonlinear guided waves arising from an internal resonance was investigated. In the analysis of Lamb-wave propagation, we introduced nonlinear quadratic effects derived from both geometric and material nonlinearities, referred to as classical nonlinearities, and damping effects by expressing the Lamé constants as complex numbers. Assuming a small detuning from the phase matching condition with respect to wavenumber and frequency, and using the method of multiple scales and self-adjointness of the governing equations with boundary conditions, the amplitude equations describing the nonlinear coupling of the two wave modes are derived as solvability conditions. This derivation also provides both physical and mathematical insights into both the phase and group velocity matching conditions. Numerical results obtained from these amplitude equations show that because of the nonlinear coupling an internal resonance between the two modes can occur under the above matching conditions. Without detuning, one mode increases monotonically in amplitude while the other decreases monotonically. Nevertheless, their changes gradually decrease with propagation distance, and each amplitude converges to a finite value. However, with wavenumber and frequency detuning, both amplitudes increase and decrease cyclically with propagation distance, resulting in a weakening of this resonance. Furthermore, results with damping effects show an attenuation of both amplitudes with propagation distance, which limits the distance resonance waves can propagate. [ABSTRACT FROM AUTHOR]

An improved Legendre polynomial series approach (AILPSA) is presented to investigate the circumferential thermoelastic Lamb wave in a fractional order orthotropic cylindrical plate. In the AILPSA, the analytical integration is developed based on the orthogonality and recursive properties of the Legendre polynomial to simplify the integral computation involved in the solving progress. As a consequence, the computational efficiency is improved significantly. Results are compared with those from the previous article to confirm the validity of the introduced method. Using the AILPSA, guided wave characteristics in various fractional order orthotropic cylindrical plates are investigated by solving the eigenvalues and eigenvectors of the system of algebraic equations. The influences of fractional order and radius‐thickness ratio on dispersion curve and displacement, temperature amplitudes are illustrated. The results show that the fractional order almost has no effect on the phase velocities of quasi‐elastic wave modes, but has notable effect on their attenuations. A smaller fractional order means a smaller temperature amplitude for the quasi‐elastic wave mode, but means a larger temperature amplitude for the thermal wave mode. A smaller radius thickness ratio indicates a smaller attenuation and a larger temperature amplitude. [ABSTRACT FROM AUTHOR]

We investigate guided (Lamb) waves in a human cadaver skull through experiments and computational simulations. Ultrasonic wedge transducers and scanning laser Doppler vibrometry are used respectively to excite and measure Lamb waves propagating in the cranial bone of a degassed skull. Measurements are performed over a section of the parietal bone and temporal bone spanning the squamous suture. The experimental data are analyzed for the identification of wave modes and the characterization of dispersion properties. In the parietal bone, for instance, the A0 wave mode is excited between 200 and 600 kHz, and higher-order Lamb waves are excited from 1 to 1.8 MHz. From the experimental dispersion curves and average thickness extracted from the skull computed tomography scan, we estimate average isotropic material properties that capture the essential dispersion characteristics using a semi-analytical finite-element model. We also explore the leaky and non-leaky wave behavior of the degassed skull with water loading in the cranial cavity. Successful excitation of leaky Lamb waves is confirmed (for higher-order wave modes with phase velocity faster than the speed of sound in water) from 500 kHz to 1.5 MHz, which may find applications in imaging and therapeutics at the brain periphery or skull-brain interface (e.g., for metastases). The non-leaky A0 Lamb wave mode propagates between 200 and 600 kHz, with or without fluid loading, for potential use in skull-related diagnostics and imaging (e.g., for sutures). [ABSTRACT FROM AUTHOR]

A surface acoustic wave (SAW)-driven acoustofluidic chip of high energy efficiency is proposed through model analysis. The chip supports propagation of Lamb waves in the lid above a fluid-filled channel. Eigenmode resonance in the on-chip channel is then achieved by coupling both the SAWs and the Lamb waves into the fluid. Specifically, the phase velocity of the Lamb mode equals the SAW speed along the substrate, and the leaky angles of both match that required by the expected channel mode. Compared to resonant SAW acoustofluidics (RSA), Lamb wave coupled RSA can make the energy tripled or higher. Meanwhile, the obtained resonance frequency deviates very slightly from the designed value, limiting the error to 0.5, while RSA chips exhibit errors as high as 5.7. The proposed design protocol can help to promote the energy efficiencies and contain the in-channel temperature rise and resonance frequency deviations in SAW acoustofluidics. [ABSTRACT FROM AUTHOR]

The authors have carried out an experimental and theoretical study of the propagation of surface acoustic waves (SAW)—Rayleigh, Sezawa and SH-modes, as well as Lamb waves in Me-IDT/AlN/(100) diamond (Me = Pt, Al) piezoelectric layered structures with a SAW resonator configuration. The types of modes are identified and the dispersion curves of the phase velocities and electromechanical coupling coefficients for SAW and Lamb waves are obtained. The excitation of Lamb waves up to a frequency of 7.3 GHz was observed experimentally. The resonance curves for Lamb waves have a higher quality factor Q compared to surface acoustic waves propagating on the same substrates. At a frequency of about 7 GHz, the loaded Q-factor reaches 3400, while the quality parameter Q × f = 2.4 × 1013 Hz. An unusual effect of a significant increase in the Q-factor of Lamb waves with the frequency increasing from 760 at 1.5 GHz to 3400 at 7 GHz is noted. [ABSTRACT FROM AUTHOR]

In the context of Bak's model, guided waves in a 1-D hexagonal piezoelectric quasi-crystal plate are investigated by applying the Legendre polynomial method. Three cases of quasi-periodic directions are discussed. The dispersion curves, phonon, and phason displacement distributions are illustrated. Some new wave phenomena are revealed: The phase velocity of Lamb wave phason modes decreases as the phonon–phason coupling parameters, R i , increase. Phason displacements and the electric potential have consistent distributions with those of phonon displacement components in the quasi-periodic direction. These obtained results lay the theoretical basis for the design and optimization of piezoelectric devices. [ABSTRACT FROM AUTHOR]

• Guided-wave propagation is characterized in 3D-printed plates with different infills. • A method to calculate phase velocity from the wave's time-spatial plot is introduced. • A method to experimentally determine dispersion curves and identify 5+ modes is shown. • Dispersion, slowness, tuning, and attenuation are highly affected by infill density. • Reference propagation characteristics for a wide range of infills are made available. Thanks to its many advantages, additive manufacturing (AM) is witnessing a gigantic shift from small applications to the production of complex industrial components, including safety–critical applications like aerospace and civil construction. This arises the need to develop accurate and robust technologies for evaluating and monitoring the structural integrity of AM components. The objective of this study is to comprehend how ultrasonic guided waves (GWs) propagate in 3D-printed poly(lactic acid) (PLA) plates of different infill densities. The experimental investigation involves five intact PLA plates printed with infill densities ranging from 20 to 100% at a step of 20%. A scanning laser Doppler vibrometer was used to visualize GW propagation by performing full-wavefield area-scans. Spatial-time, frequency-wavenumber, and wavenumber-wavenumber analyses were performed to scrutinize the available GW modes and their slowness profiles within the anisotropic structure. In addition, the tuning of the fundamental Lamb-wave (LW) modes at different excitation frequencies was examined, and the amplitude attenuation of the generally most pronounced mode (A 0 mode) was investigated for different infill densities at an excitation of 50 kHz. A reference methodology is presented to experimentally identify more than five propagating modes in the frequency-wavenumber domain then obtain their phase-velocity dispersion curves. Significant variations are observed in the dispersion characteristics when lowering the infill density leading to the appearance of more modes at lower cutoff frequencies and drops in both the group and phase velocities in most of the cases. A complex behavior of the guided waves was observed in the dispersion curves of the 20%-infill plate, with possible mode interruptions/disturbance at an excitation frequency beyond 70 kHz. The appearance of shear-horizontal modes is noticed/strengthened at oblique propagation directions which may be attributed to mode conversion of the LW modes after obliquely interacting with the internal structure of the plates. Though high wave attenuation is a characteristic of the used polymer material, this attenuation is further increased at lower infill densities. The tuning behavior of the fundamental LW modes is also shown to be significantly affected by the infill density. The presented results can serve as reference propagation and dispersion characteristics for researchers working on similar materials and geometries. Such knowledge and understanding can be particularly useful for GW-based structural healthy monitoring of AM structures. [ABSTRACT FROM AUTHOR]

• The tensile and shear elastic moduli of the plates can be estimated using the S 0 and A 0 modes. • The phase velocity of the S 0 mode depends only on the equivalent tensile elastic modulus and in-plane Poisson's ratio, whereas the phase velocity of the A 0 mode depends almost only on the equivalent shear elastic modulus. • The in-plane Poisson's ratio of cross-ply laminates changes sufficiently small to neglect its effect on the phase velocities of the S 0 mode. This paper proposes a simple and effective Lamb wave-based measurement method for the elastic moduli of cross-ply composite plates, considered equivalent to a single-layer orthotropic plate with nine independent elastic constants. The effects of theses constants on the phase velocities of the fundamental S 0 and A 0 modes are investigated. The phase velocity of the S 0 mode depends only on the equivalent tensile elastic modulus and in-plane Poisson's ratio in the low-dispersive frequency-thickness product regime, whereas the phase velocity of the A 0 mode depends almost only on the equivalent shear elastic modulus. Moreover, the in-plane Poisson's ratio of cross-ply laminates changes sufficiently small to neglect its effect on the phase velocities of the S 0 mode. Therefore, the tensile and shear elastic moduli of the plates can be estimated using the S 0 and A 0 modes, and the mapping relations between the phase velocities of these modes and the elastic moduli are established. The proposed approach has been numerically and experimentally tested on cross-ply carbon fiber reinforced laminates, and validated by theoretical values and conventional tensile tests. [ABSTRACT FROM AUTHOR]

This paper proposes a damage detection method based on an improved DAS imaging algorithm by introducing time difference due to anisotropy of composite material. First, the finite element characteristic frequency method is used to obtain the dispersion curve of the composite plate, and the validity of the dispersion curve is verified. Next, the average phase velocity of the Lamb wave at mixed modes in the composite plate is obtained by two-dimensional Fourier transform (2-D FFT). The mixed modal group velocity is calculated according to the corresponding phase velocity, the mean change rate of the phase velocity and the dispersion curve obtained by simulation. The time difference due to anisotropy of composite material is investigated, and the damage location is estimated by the delay-and-sum (DAS) imaging algorithm. Experiments on carbon fiber multilayer composite plates verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The problem of the propagation of acoustic waves in a layer of a compressible viscous fluid that interacts with an elastic half-space is solved using the three-dimensional linear equations of classical elasticity theory for the solid and the three-dimensional linearized Navier–Stokes equations for the compressible viscous fluid. The problem statement and approach based on the application of the general solutions of linear equations for elastic bodies and linearized equations for the fluid are employed. The dispersion equation describing the propagation of quasi-Lamb waves in the hydroelastic system is derived. Dispersion curves for normal waves in a wide frequency range are plotted. The effect of the thickness of the liquid layer on the phase velocities and attenuation coefficients of acoustic waves is analyzed. It is shown that the influence of fluid viscosity on the parameters of the wave process is associated with the properties of wave localization. Using the developed approach and obtained results, the limits of the applicability of the models of wave processes based on the model of an ideal fluid are established. The numerical results are presented in the form of graphs and analyzed. [ABSTRACT FROM AUTHOR]

The constant velocity one-dimensional wave theory has been commonly used to determine the pile lengths from the impulse response testing results for several years. In this paper, the three-dimensional guided wave theory was introduced to extract more information from the impulse response spectra on five concrete piles. Combined with resonance concept, this guided wave-based approach was developed to simply and efficiently identify the length estimates with 3% or less errors, similar to those of the conventional one-dimensional wave-based approach. Moreover, the guided wave theory provides more individual resonant frequencies insight over that of the one-dimensional wave theory. All the experimental phase velocities at their corresponding resonant frequencies have a good consistency with the guided wave prediction curve at frequencies up to 5000 Hz. The resulting scattering also presents a slightly decrease trend with frequency. The overall analysis indicates that the guided wave theory can give more useful information than that of the one-dimensional wave theory. In future, one can use this inverse computation approach to evaluate unknown pile lengths. [ABSTRACT FROM AUTHOR]

Summary: The present study focuses on estimating material nonlinearity and consequently remaining useful life of fatigued specimens using the amplitude‐ and physics‐based material nonlinearity parameters evaluated for Lamb wave motion in plate specimens. The amplitude‐based nonlinearity parameter depends on amplitudes of the Lamb wave harmonics generated due to material nonlinearity. Here, it is employed to estimate the inherent and dislocation induced material nonlinearities for different stages of fatigue. The cumulative effect is obtained from the strict matching of phase and group velocities of the S1 − S2 mode pair. The physics‐based nonlinearity parameter is obtained from the higher order elastic coefficients, plastic coefficients, and substructural evolution parameters. It does not depend on wave propagation distance; however, it depends on percent fatigue life. Thus, it is used to construct a theoretical nonlinearity curve. A spectral amplitude normalization technique is given to systematically evaluate the material nonlinearity, once the Lamb wave data over different wave propagation distances are known either from experiments or from simulations. The values of amplitude‐based nonlinearity parameter thus estimated through the simulation and experiments for different fatigue stages are then plotted onto the obtained theoretical nonlinearity curve. A reasonably good agreement is seen between the fatigue life estimations given by both the nonlinearity parameters. Thus, the amplitude‐based nonlinearity parameter obtained from the Lamb wave response can be effectively used to estimate the remaining useful life of the fatigued plate specimens. [ABSTRACT FROM AUTHOR]

Burst wave lithotripsy is a method to noninvasively fragment urinary stones by short pulses of focused ultrasound. In this study, physical mechanisms of stone fracture during burst wave lithotripsy were investigated. Photoelasticity imaging was used to visualize elastic wave propagation in model stones and compare results to numerical calculations. Epoxy and glass stone models were made into rectangular, cylindrical, or irregular geometries and exposed in a degassed water bath to focused ultrasound bursts at different frequencies. A high-speed camera was used to record images of the stone during exposure through a circular polariscope backlit by a monochromatic flash source. Imaging showed the development of periodic stresses in the stone body with a pattern dependent on frequency. These patterns were identified as guided wave modes in cylinders and plates, which formed standing waves upon reflection from the distal surfaces of the stone model, producing specific locations of stress concentration in the models. Measured phase velocities compared favorably to numerically calculated modes dependent on frequency and material. Artificial stones exposed to bursts produced cracks at positions anticipated by this mechanism. These results support guided wave generation and reflection as a mechanism of stone fracture in burst wave lithotripsy. [ABSTRACT FROM AUTHOR]

The propagation of quasi-Lamb waves in a prestrained compressible elastic layer that interacts with a half-space of a compressible ideal fluid and in a prestrained compressible elastic half-space that interacts with a layer of an ideal compressible fluid is studied. Use is made of the three-dimensional linearized equations of the theory of elasticity of finite deformations for the compressible elastic solid and the three-dimensional linearized Euler equations for the compressible ideal fluid. A problem statement and an approach based on the general solutions of the linearized equations for elastic solid and fluid are used. The dispersion equations that describe the propagation of quasi-Lamb waves in hydroelastic systems over a wide frequency range are derived. The effect of the initial stresses and the thicknesses of the elastic layer and liquid layer on the phase velocities of quasi-Lamb modes is analyzed. A criterion of the existence of quasi-Lamb waves in hydroelastic waveguides is proposed. The developed approach and the obtained results make it possible to establish the limits of applicability of the models of wave processes based on different theories of small initial deformations, as well on the classical theory of elasticity. The numerical results are presented in the form of graphs and are analyzed. [ABSTRACT FROM AUTHOR]

In this paper, we have presented the dispersion curve of Lamb waves in an aluminum plate with a periodic rectangular corrugation experimentally. A mode selection method was applied to generate Lamb waves in the region of the corrugated periodic structure using a moving continuous wave laser, and the signal can be detected at any point in the excitation region. The relationship between the phase velocity and the frequency is observed. It is found that the intensity distribution of the dispersion curves in the experimental results is related to the slope of the dispersion curves as well as the selection of the detection point. Vibrations at a series of locations were detected, reflecting the change in energy that Lamb waves undergo in the process of propagation through the periodic structure, which is different from the existing method of single-point excitation and detection. The spatial distribution of the mode amplitude at the resonances points, in particular induced by the Bragg reflection, has been studied. [ABSTRACT FROM AUTHOR]

This paper studies the propagation of symmetric and antisymmetric Lamb waves along a 1 mm thick iodic acid plate (HIO3) in the 1–50 MHz frequency range. The Lamb mode propagation along three crystallographic planes was theoretically investigated, for two mutually orthogonal propagation directions. Several frequencies were found that correspond to Lamb modes with zero group velocity (ZGV) and non-null phase velocity values. The first symmetric Lamb mode, S1, was found to possess only one ZGV point, regardless of the propagation direction; higher order symmetric and antisymmetric modes with up to four ZGV points were found, depending on the propagation plane. The dependence of the ZGV frequencies on each elastic constant (c11, c13, c33, c55) of the HIO3 plate material was also investigated by changing the constant values by 5% and 10%. It was found that c33 and c55 affect the number of the ZGV points, while c11 and c13 affect the frequency of the ZGV points. The existence and frequencies of the ZGV points are strongly dependent on the proximity of standing longitudinal and transverse waves at nearby cutoff frequencies. [ABSTRACT FROM AUTHOR]

Optical breakdown of water is used as a sound source to excite a broadband set of leaky Lamb waves in submerged aluminum plates. The source is shown to simultaneously excite guided modes spanning 0.1–5 MHz in frequency and 0–0.8 mm−1 in wavenumber. The measured response overlaps well with dispersion curves for Lamb waves in the plates, revealing strong coupling to both symmetric and antisymmetric modes. The strongest responses arise when a mode's phase velocity approximately equals the plate's compressional wave velocity. These results are shown to arise from an interplay of the sensing geometry, guided wave speeds, and signal processing. Finally, implications for non-contact sensing are discussed. [ABSTRACT FROM AUTHOR]