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Abnormal noise is a key factor affecting automobile ride comfort, and the localisation of abnormal noise sources is critical for noise control. Herein, a mathematical model is proposed for the localisation of automobile door rattle sources based on Lamb wave propagation theory, Morlet wavelet transform, and the principle of time-reversal focus positioning. The cause of vibration signal wave packet aliasing was explored through thin plate impact simulation, and narrow-band signal extraction was then determined. The influence of the initial generation time T 0 of the rattle signal on the positioning imaging was obtained through a rattle noise source localisation test, and the signal imaging discrimination method at time T 0 was proposed. Verification test results showed that the maximum positioning error of the automobile door rattle noise source was no greater than 3.2 cm, and the average positioning error was 2.01 cm, which confirmed the feasibility of the proposed method for locating the rattle noise source in the automobile door. [ABSTRACT FROM AUTHOR]

The Lamb shift, one of the most fundamental interactions in atomic physics, arises from the interaction of H atoms with the electromagnetic fluctuations of the quantum vacuum. The energy shift has been computed in a variety of ways. The energy shift, as Feynman, Power, and Milonni demonstrated, equals the change in the vacuum energy in the volume containing the H atoms due to the change in the index of refraction arising from the presence of the H atoms. Using this result and a group theoretical calculation of the contribution to the Lamb shift from each frequency of the vacuum fluctuations, in this paper we obtain an expression for the region of the vacuum energy for each frequency ω around the H atom due to the Lamb shift. This same field plays an essential role in the van der Waals force. We show the ground state atom is surrounded by a region of positive vacuum energy that extends well beyond the atom for low frequencies. This region can be described as a steady state cloud of vacuum fluctuations. For energies E = ℏ ω less than 1 eV, where ℏ is the reduced Planck constant and ω is frequency, the radius of the positive energy region is shown to be approximately 14.4/E Å. For a vacuum fluctuation of wavelength, λ , the radius is (α / 2 π) λ , where α is the fine-structure constant. Thus, for long wavelengths, the region has macroscopic dimensions. The energy–time uncertainty relation predicts a maximum possible radius that is larger than the radius based on the radiative shift calculations by a factor of 1 / 4 α . [ABSTRACT FROM AUTHOR]

The load-bearing capacity is a pivotal consideration in the design of offshore renewable energy structures. This paper aims to address the technical challenges associated with the additional wave loads caused by the integrated devices in a hybrid system for the multi-purpose utilization of coastal renewable energy. A self-protected hybrid wind-wave energy system is proposed, in which an oscillating water column (OWC) device is attached at a monopile foundation of an offshore wind turbine. In the meantime, the OWC is connected by a submerged horizontal perforated plate at its exterior shell, which is expected to minimize the wave loads on the system. The hydrodynamic performance of the system is investigated. A novel approach is developed to model the wave interaction with the hybrid system. This efficient approach removes the necessity of decomposing the wave-scattering field into diffraction and pressure-dependent radiation components. Detailed numerical computation is then conducted for both regular and irregular sea states. Various hydrodynamic properties related to the system, such as wave energy harvesting, wave force/moment, and free-surface elevation, have been evaluated. Numerical results manifest the feasibility of imposing a negligible effect on the high wave energy harvesting while reducing the high wave loads by manipulating the submerged horizontal perforated plate. The impact of the perforated plate on the dominant wave energy harvesting in the long-period region is found to be trivial. In contrast, it can affect the high bending moment in the short-period region, which causes a reduction of greater than 15%. [ABSTRACT FROM AUTHOR]

The Lamb wave time-reversal method (TRM) has been widely proposed as a baseline-free technique for Structural health monitoring (SHM) of plate/shell-type structures. Still, its efficacy has never been tested under a variable environment. The present study examines the conventional TRM and establishes that it is unsuitable for baseline-free detection and sizing of damage under varying temperatures since the damage index (DI) is prone to change with temperature rise and generally has low sensitivity to damage. The investigation is performed for block mass-type and notch-type defects using experiments and numerical simulations. The study further tests the refined time-reversal method (RTRM), presented recently, against the same objective. This technique uses Lamb waves of the best reconstruction frequency to probe the structure, at which the reconstructed signal in a healthy plate undergoes minimum deviation from the input signal. It considers an extended wave packet for computing the DI instead of using the main mode alone. We show that this process leads to the lowest DI for undamaged plates and the highest sensitivity to damage. Also, the DI remains almost unchanged during temperature change, irrespective of the damage type, size, and plate thickness. It makes the RTRM very effective for baseline-free identification and sizing of damage under varying temperatures. [ABSTRACT FROM AUTHOR]

The 2022 Hunga Tonga-Hunga Ha'apai eruption generated tsunamis that propagated across the Pacific Ocean. Along the coast of Japan, nearshore amplification led to amplitudes of nearly 1 m at some locations, with varying peak tsunami occurrence times. The leading tsunami wave can generally be reproduced by Lamb waves, which are a type of air-pressure wave generated by an eruption. However, subsequent tsunamis that occurred several hours after the leading wave tended to be larger for unknown reasons. This study performs multi-scale numerical simulations to investigate subsequent tsunami waves in the vicinity of Japan induced by air pressure waves caused by the eruption. The atmospheric pressure field was created using a dispersion relation of atmospheric gravity wave and tuned by physical parameters based on observational records. The tsunami simulations used the adaptive mesh refinement method, incorporating detailed bathymetry and topography to solve the tsunami at various spatial scales. The simulations effectively reproduced the tsunami waveforms observed at numerous coastal locations, and results indicate that the factors contributing to the maximum tsunami amplitude differ by region. In particular, bay resonance plays a major role in determining the maximum amplitude at many sites along the east coast of Japan. However, large tsunami amplification at some west coast locations was not replicated, probably because it was caused by amplification during oceanic wave propagation rather than meteorological factors. These findings enhance our understanding of meteotsunami complexity and help distinguish tsunami amplification factors. [ABSTRACT FROM AUTHOR]

Structural Health Monitoring (SHM) techniques have an important role in the performance of mechanical structures. In particular, piezoelectric transducers (PZT) have been employed for establishing damage detection processes in SHM systems. However, despite their wide use, there is limited information in the literature regarding important characteristics for SHM applications, such as the shape, dimensions and frequencies to use, which can affect the performance of the system used to detect the damage. This article investigates longitudinal and flexural waves for applications using circular piezoelectric transducers bonded to thin plates. The methodology allows one to obtain optimal frequencies to create and capture both types of waves and understand the influence of the geometric characteristics of these transducers on the damage detection. Numerical simulations are carried out to show that a change in the parameters of the piezoelectric transducers can maximize the waves amplitudes incoming at the sensor. Results from experimental tests are presented to demonstrate the proposed methodology. New equations are introduced and they compute output voltage and determine optimal frequencies to monitor the structure. The findings contribute to establishing a more efficient design of a damage detection process involving plate-like structures in SHM systems based on wave propagation. [ABSTRACT FROM AUTHOR]

This paper aims at numerical finite element (FEM) research of guided Lamb waves propagation in multidirectional composite plates. All simulations were conducted in the Abaqus/CAE software by using the dynamic/explicit solver. The material considered in this work was carbon/epoxy composite laminate with [90⁰/θ/θ/θ/-θ/-θ/-θ/90⁰] stacking sequence where θ set was equal 0⁰, 30⁰, 45⁰, 60⁰ and 90⁰. The main goal of the analysis was to evaluate the influence of fiber orientation angles θ on propagation behavior of the separate symmetric S0 and asymmetric A0 Lamb wave modes. Numerical model was created by using the C3D8R brick element. The Lamb waves were generated by using concentrated force with 200 kHz frequency. The acoustic signal generated by travelling wave was registered at two nodes that representthe acoustic emission sensors. Obtained results were presented in tabular form where separate mode velocities were collected and on the normalized displacement versus time plots depicted registered wave signals. In addition, the contour diagrams and through-thickness deformations plots were created to present behavior of the extensional and the flexural modes. The greatest value of the S0 mode velocity was obtained for unidirectional laminates whereas the lowest for composite plate with 45⁰ fiber orientation angle. The asymmetric mode found to generate slightly greater deformation of plate in XZ plane than the symmetric. Recognition of the Lamb wave behavior in multidirectional laminates will allow to better planning the experimental acoustic emission tests. [ABSTRACT FROM AUTHOR]

In this Letter, we provide an experimental demonstration of amplitude-dependent dispersion tuning of surface acoustic waves interacting with nonlinear resonators. Leveraging the similarity between the dispersion properties of plate edge waves and surface waves propagating in a semi-infinite medium, we use a setup consisting of a plate with a periodic arrangement of bead-magnet resonators along one of its edges. Nonlinear contact between the ferromagnetic beads and magnets is exploited to realize nonlinear local resonance effects. First, we experimentally demonstrate the nonlinear softening nature and amplitude-dependent dynamics of a single bead-magnet resonator on both rigid and compliant substrates. Next, the dispersion properties of the system in the linear regime are investigated. Finally, we demonstrate how the interplay of nonlinear local resonances with plate edge waves gives rise to amplitude-dependent dispersion properties. The findings will inform the design of more versatile surface acoustic wave devices that can passively adapt to loading conditions. [ABSTRACT FROM AUTHOR]

Due to its multi-mode and dispersion characteristics, Lamb waves cause interference to signal processing, which profoundly limits their application in nondestructive testing. To resolve this issue, firstly, based on the traditional EMAT, a horizontal polarization periodic permanent magnet electromagnetic acoustic transducer (HP-PPM-EMAT) was proposed. A 2-D finite element model was then developed to compare magnetic flux density, Lorentz force, and signal strength between the traditional EMAT and the HP-PPM-EMAT. The simulation results show that the HP-PPM-EMAT enhances the A0 mode Lamb wave (A0 wave) and suppresses the S0 mode Lamb wave (S0 wave). Finally, the influence of structural parameters of the HP-PPM-EMAT on the total displacement amplitude ratio of A0 and S0 was investigated using orthogonal test theory, and the width of magnet units was improved based on the orthogonal test. The results show that the total displacement amplitude ratio of A0 to S0 of the improved HP-PPM-EMAT can be improved by a factor of 7.74 compared with that of the traditional Lamb wave EMAT, which can produce higher-purity A0 mode Lamb waves. [ABSTRACT FROM AUTHOR]

The ultrasonic guided lamb wave approach is an effective non-destructive testing (NDT) method used for detecting localized mechanical damage, corrosion, and welding defects in metallic pipelines. The signal processing of guided waves is often challenging due to the complexity of the operational conditions and environment in the pipelines. Machine learning approaches in recent years, including convolutional neural networks (CNN) and long short-term memory (LSTM), have exhibited their advantages to overcome these challenges for the signal processing and data classification of complex systems, thus showing great potential for damage detection in critical oil/gas pipeline structures. In this study, a CNN-LSTM hybrid model was utilized for decoding ultrasonic guided waves for damage detection in metallic pipelines, and twenty-nine features were extracted as input to classify different types of defects in metallic pipes. The prediction capacity of the CNN-LSTM model was assessed by comparing it to those of CNN and LSTM. The results demonstrated that the CNN-LSTM hybrid model exhibited much higher accuracy, reaching 94.8%, as compared to CNN and LSTM. Interestingly, the results also revealed that predetermined features, including the time, frequency, and time–frequency domains, could significantly improve the robustness of deep learning approaches, even though deep learning approaches are often believed to include automated feature extraction, without hand-crafted steps as in shallow learning. Furthermore, the CNN-LSTM model displayed higher performance when the noise level was relatively low (e.g., SNR = 9 or higher), as compared to the other two models, but its prediction dropped gradually with the increase of the noise. [ABSTRACT FROM AUTHOR]

In this paper, a radial gradient seismic metamaterial (RGSM) is proposed. The structural unit cell is composed of an external square soil embedded with a triangular-cross-sectioned steel ring, which is filled at different angles of multiple steel rings to form a supercell. The dispersion curve and attenuation spectrum of the unit cell are calculated by the finite element method, and the opening mechanism of the band gap is explained by analyzing the modes at the band gap boundary. The influence of geometric parameters and material parameters on the band gap is further studied, and the optimized supercell radial gradient seismic metamaterial (OS-RGSM) structure is designed through structure and parameter optimization. The ultra-low broadband excellent band gap in the range of 2.35–20 Hz for seismic Lamb waves is realized, and its three-dimensional frequency response and displacement field diagram are calculated. In addition, the attenuation characteristics of the optimized supercell seismic metamaterial on the seismic surface wave are calculated and analyzed. It is found that the attenuation can reach more than 50% in the ultra-low frequency range of 3.5–9 Hz. The seismic wave barrier is verified by the vibration transmission characteristics of RGSM under finite period and dynamic time history analysis. The results show that RGSM can effectively shield from seismic Lamb waves in the ultra-wideband with the starting frequency of 2.35 Hz and can also effectively attenuate the seismic surface wave in semi-infinite space. [ABSTRACT FROM AUTHOR]

This study presents novel analytical solutions for analyzing wave dissipation effect and bottom flow field characteristics of permeable submerged horizontal plates through physical model trials. The experimental results show that a solid submerged horizontal plate effectively attenuates wave cycles, with a greater periodic attenuation effect at smaller submerged depths. However, this attenuation effect becomes reduced or less pronounced after a certain threshold. Selecting an optimal opening ratio becomes key to achieving the desired cycle attenuation. When the inundation depth of the horizontal plate is large, the wave dissipation effect is weak. Reducing the opening rate can improve the wave dissipation effect, but only to a certain extent. Under irregular wave actions, the velocity field of the submerged horizontal plate is uniformly distributed. The relative submerged depth has minimal effect on the maximum flow velocity and root mean square flow velocity. Increasing the wave height and increasing the open holes on a plate can improve the flow velocity at the bottom of the plate. However, increasing the opening ratio also leads to insignificant changes in flow velocity. A correlation between the transmission coefficient of the open plate and the maximum flow velocity has also been determined. The findings of this paper serve as a research foundation for the implementation of submerged horizontal plate wave dissipation structures in engineering. [ABSTRACT FROM AUTHOR]

Wave energy converters together with flexible breakwaters not only provide shelter to the energy devices against wave attacks but also offer improved performance, longer survivability and lower costs. Thus, in the present work we are interested to investigate the interaction of linear water waves with an array of three thin vertical plates, comprising of two plate wave energy converters and one flexible breakwater, submerged in water of finite depth in a two dimensional space. The plate in the middle of the setup is a flexible plate of variable thickness, and on either side of it are piezoelectric plate wave energy converters with constant thickness. The problem is solved by converting the associated boundary value problem into a system of coupled integral equations. A modified form of the energy balance equation is derived, which results due to the presence of the two piezoelectric plates. We investigate how the structural properties of the piezoelectric plates like their submergence depths, plate lengths, distance from the breakwater and different edge conditions can affect the wave attenuation and wave power absorption efficiency. Further, it is also examined how the presence of the non-uniform flexible plate with different flexibility and lengths can improve the performance of the system. It is analysed that shorter sized piezoelectric plate wave energy converters in the presence of non-flat flexible plate offer higher wave power absorption efficiency at lower frequencies. • Wave power absorption by two vertically submerged piezoelectric plates is studied. • A non-uniform flexible plate is also included in the setup. • A modified form of the energy balance equation is derived. • Various physical quantities are investigated for efficient performance of the system. • Elastic plate helps reduce wave transmission and increase power absorption efficiency. [ABSTRACT FROM AUTHOR]

Most cracks do not grow straight due to the inhomogeneity of material properties. Furthermore, quantifying structural damage using Lamb waves is difficult due to uncertain crack shape. Here, we present a newly developed finite element model to simulate the propagation of Lamb waves in a cracked plate to quantify the influence of crack size and orientation on the characteristics of Lamb wave propagation. This model includes a piezoelectric actuator and sensor to generate and receive the tone-burst signals of Lamb wave. The damping coefficient of the finite element model was calibrated with the experimental data of plates without a crack. The Lamb wave propagation simulations were performed with various crack sizes, crack orientations, and distances between the actuator and sensor. Our model was utilized to investigate the influence of crack orientation on damage quantification based on the signal phase change and normalized amplitude. We successfully evaluated the effect of the incident angle of the crack, crack size, and distance between the sensors on the change of the plate wave signal characteristics. The signal characteristics obtained from our novel finite element model can be used to develop a quantification model to estimate the crack size, direction, and distance from the sensor. [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]

In the present paper, an auxetic tape composed of modified star-shaped unit cells is used to filter the propagation of elastic waves in two-dimensional structures. The pattern of the designed bandgaps and their capability to mitigate wave propagation is experimentally and numerically studied. First, the architecture of the conventional star-shaped unit cell is introduced, and according to the Bloch's theorem the phononic bandgaps are calculated for the one unit cell. The unit cells' dimensions are designed to provide a wide phononic bandgap over the low-frequency range of 400–1700 Hz. The geometry of the conventional star unit cell is modified toward two modified stars to enhance low-frequency bandgaps. These unit cells are then used as a filter tool in a two-dimensional panel, and they are numerically simulated using the finite element method. Excitation is locally applied to the panel, and a layer of phononic crystal surrounds its location. It is shown that the lattice band is capable of trapping waves inside the bounded area and can remarkably suppress the propagation of waves. Numerical results and the bandgap formation obtained from Bloch's theorem are verified with the results measured from an experiment. [ABSTRACT FROM AUTHOR]

We investigated forced Lamb waves using the method of multiple scales and Green's function method. With the former method, we derived a solvability condition containing terms describing forced effects. In Lamb waves problems, the solvability condition is a first-order partial differential equation in contrast to the governing equations describing Lamb waves, which are second-order partial differential equations and boundary conditions. With the latter method, we obtained the Green's function for the solvability condition. This way of deriving the Green's function is easier than solving the governing equations for Lamb waves. Finally, we obtained the amplitudes of the forced Lamb waves using the Green's function. The proposed method may be used to obtain the amplitudes from arbitrary forced distributions in both the time and space domains. Furthermore, the method may be used to obtain the frequency and wave number responses that take into consideration the detuning effects and may be used to consider dispersion effects. As a result, we found out that some kind of resonance occurs when the relation between input position and time delay corresponds to the group velocity of the input propagation mode. Solutions obtained by our method were verified using the frequency-domain-based integral transform method. [ABSTRACT FROM AUTHOR]

SUMMARY: The 15 January 2022 eruption of the Hunga–Tunga volcano generated a Lamb pressure wave propagating all over the globe and triggering a tsunami throughout the planet. A first atmospheric wave arrived 16 hr after the eruption on the French Mediterranean coasts and propagated southward. A second one originating from Africa was observed 4 hr later with an attenuated amplitude. The first wave can be roughly defined either by a N wave or a sinusoid signal with a period close to 50 min and an amplitude of 130 Pa. In the Mediterranean Sea, the tsunami was recorded by almost all standard coastal tide gauges or pressure gauges. The French tide gauge stations recorded water waves with amplitudes ranging from a few centimetres to 10 cm and with periods ranging from 10 min to 1 hr. Numerical simulation of the tsunami is performed by the operational code Taitoko for different atmospheric sources. Non-linear shallow water equations are solved by a finite-difference method, using the nested multigrid approach. The tsunami is generated by calculating analytically the atmospheric pressure gradient in the momentum equations. Comparisons of time-series between numerical solutions and records are satisfactory for most tide-gauges along the French Mediterranean coast. Sensitivity analysis on the atmospheric source and on the resolution is performed. For most tide-gauge stations, numerical results show that the wave forms depend first on local resonance phenomena. [ABSTRACT FROM AUTHOR]

Guided ultrasonic waves are used for the inspection of multilayered composite aerospace structures. Calculating the corresponding dispersion diagrams is challenging for thick-walled composites with more than 100 layers, such as in modern rocket booster pressure vessels. The Dispersion Calculator (DC) is an open source software for calculating such dispersion diagrams and mode shapes of guided waves. Attenuation caused by viscoelasticity and fluid-loading makes the dispersion curve tracing much more difficult than in the nonattenuated case because the modal solutions are sought in the complex wavenumber plane. The tracing problem is mastered by a reliable algorithm. Whereas leaky Lamb and Scholte waves in coupled and decoupled cases are modeled using the stiffness matrix method, shear horizontal (SH) waves are traced using the transfer matrix method without facing the numerical instability. Through implementation of mode family specific dispersion equations in both matrix techniques for nonattenuated and attenuated cases, symmetric, antisymmetric, and nonsymmetric leaky Lamb, Scholte, and SH waves can be traced separately with better efficiency and robustness. The capabilities of DC are demonstrated by calculating dispersion diagrams and mode shapes for a viscoelastic composite with 400 layers immersed in water. Results are compared against DISPERSE (Imperial College London, London, UK) for selected cases. [ABSTRACT FROM AUTHOR]

Hunga Tonga-Hunga Ha'apai climactic eruption on January 15, 2022, released enormous energy that affected the ionosphere over the Pacific Rim. We analyzed ionospheric disturbance following volcanic eruptions using near-field (<1000km), regional (1000–5000 km), and far-field (5000–12000 km) global positioning system (GPS) observations. The results indicate that the near-field ionospheric perturbation that occurred 8–15 min after the cataclysmic eruption was mainly derived from the shock wave (~1000 m/s) generated by the blast, while the low-frequency branch with long-distance propagation characteristics over the regional and the far-field was mainly associated with atmospheric Lamb waves (~330 m/s). Moreover, the amplitude of disturbance and background total electron content (TEC) are related proportionally. The intensity of the volcanic eruption and the background ionospheric conditions determine the magnitude of ionospheric responses. TEC perturbations were invisible on the reference days. Furthermore, the source location and onset time were calculated using the ray tracing technique, which confirms that the Tonga event triggered the ionospheric anomaly beyond the crater. Finally, the change in the frequency of the perturbations coincided with the arrival of the initial tsunami, implying the generation of a meteotsunami. [ABSTRACT FROM AUTHOR]

Crack imaging is attractive in the community of nondestructive testing and structural health monitoring of plate-like structures. However, most existing research focuses on the imaging of single crack, while limited work has been reported for the imaging of multiple cracks. To this end, the application of the Lamb wave-based technique is presented in this paper to image the multiple cracks. The antisymmetric mode (A0) of Lamb wave propagation in the thin plate is simulated using the numerical finite element method, and a circular piezoelectric sensor array is considered to capture the Lamb wave signals. The damage index taking into account the attenuation of the reflected signal amplitude is proposed using the reflection signals from the cracks, and the Hilbert transform is used to extract the information of damage. The damage scanning map is constructed to show the damage location in the plate. The proposed damage identification algorithm based on Lamb wave propagation is also used to detect two cracks in the thin plates. The consideration of wave attenuation improves the identification of multiple cracks. The proposed damage identification algorithm using a phased piezoelectric sensor array shows its potential to locate the cracks in thin plates. [ABSTRACT FROM AUTHOR]

The field of an SV-source of transverse waves in a solid homogeneous layer with free boundaries is found. In addition to transverse waves, longitudinal waves arise at these boundaries. The total field in the layer is characterized by scalar and vector potentials. Due to the axial symmetry of this field, the vector potential has only an angular component. The integral representation of the potentials was obtained by the Fourier–Bessel method. Based on residue theory, the field in the layer is represented as the superposition of cylindrical Lamb modes. The amplitudes of these modes are calculated. [ABSTRACT FROM AUTHOR]

In order to solve the problem of Lamb wave dispersion and multi-mode restriction in plate structure and its practical application in ultrasonic nondestructive testing technology, a method based on Bloch-Floquent theory and finite element characteristic frequency method is used to calculate the dispersion curve of plate structure containing mode information in real and pure imaginary wave number domains. Based on the Bloch-Floquent periodic boundary conditions, the dispersion curves of infinite steel plate structures in irreducible Brillouin region and pure imaginary wave number domain are quickly calculated. In this study, Bloch-Floquent extension and Fourier transform are used to obtain the real wave number information of each characteristic mode and overcome the aliasing problem of dispersion curve. In this study, the modal identification is carried out according to the out-of-plane displacements of the upper and lower surfaces of each mode, and the complete dispersion relation of the steel plate is obtained. The calculated results of this method are in good agreement with those obtained by solving the dispersion equation with the traditional dichotomy method, which verifies the validity of this method. [ABSTRACT FROM AUTHOR]

Optical security films have gained a lot of attention due to its potential application in authentication services. Electrode-free optical devices are in demand along with electrode devices due to its secure access to the decryption key and ability to hide information from public access. Our concern in this study is the examination of electrode-free optical security film. In such devices, hidden information can be viewed in black/white contrast or controlled birefringent colours, which are produced by patterned phase plate and polariser. In particular, we develop the model of stratified anisotropic media for theoretical description of reflective characteristics of optical security films. Our theoretical results are compared with experimental observations. Blue and yellow birefringent colours of supertwisted nematic liquid crystal cell are achieved by using theory of optical characteristics in anisotropic media and partial coherence. This theoretical analysis suggests new openings in the optimisation of liquid crystal security films. [ABSTRACT FROM AUTHOR]

The flow kinematics and impacting pressures on a suspended horizontal plate under extreme waves were investigated experimentally. Three different stages of extreme waves, unbreaking, incipient breaking, and broken, were separately generated using a dispersive focusing method. The flow field kinematics around the plate during the slamming process was measured using a combination of particle image velocimetry and bubble image velocimetry techniques. We found that for aerated areas, there are significant differences in flow patterns under different conditions. The velocity distribution in aeration areas is more discrete. The slamming peak on the upper surface is influenced greatly by the aeration effect, resulting in the maximum slamming peak of the unbreaking case being 3.8 kPa, which is 0.41 times larger than that of the incipient-breaking case and 1.12 times larger than that of the broken case. However, for the area below the plate, the slamming force and flow evolution under different types of breaking exhibit similarity. [ABSTRACT FROM AUTHOR]

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We numerically and experimentally demonstrate super-resolution focusing of the lowest anti-symmetric (A0) mode Lamb waves in a thin aluminum plate. The subwavelength focusing/imaging is achieved by exploiting the anisotropy in phononic crystal (PC) lattices and amplification of evanescent waves. To this end, we embedded a PC flat lens in the aluminum plate, consisting of holes arranged in a square lattice formation. We revealed that the bound slab phonon modes amplify evanescent waves, as previously observed for electromagnetic and acoustic waves. Hence, the slab mode helps propagate subwavelength information through the PC lens to reach the near-field image formed due to negative refraction and result in the high resolution image. [ABSTRACT FROM AUTHOR]

Anomalies in reflection from periodic structures, well known in optics, result from either the transition from specular reflection to diffraction of light (Rayleigh's anomaly) or by coupling to the leaky surface mode supported by the structure (Wood's anomaly). Experimental observation and detailed analysis of both kinds of anomalies are presented here in the case of antisymmetric Lamb wave (A0) incidence at the 1D periodic structure located along the edge of the elastic plate. A structure with a strong phononic effect has been chosen, which enables the separation of both effects in terms of frequency. Another distinct feature of elastic waves in the periodic structure considered in this work is the existence of several localized modes, which leads to the multiple Wood's anomalies. Here, we report the experimental observation of double Wood's anomaly in addition to the Rayleigh's type of anomaly. [ABSTRACT FROM AUTHOR]

The solution of wave problems is usually connected with significant difficulties. One of the effective methods for solving these problems is the method of integral transformations. However, even if we use this method, then it is sometimes impossible to obtain a solution in the final form or at least in the form suitable for subsequent numerical calculations. By using an example of analysis of the process of propagation of waves in a plate from a spherical source, we propose a method for overcoming these difficulties. Simplification of the problem is realized by splitting the total wave into elementary components with respect to the wave numbers and complex frequencies. The solution is reduced to the possibility of numerical calculations on a computer. The practical application of these calculations can be useful, in particular, for the analysis of the data obtained by the acoustic-emission method. [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]

Recently Lamb wave devices have originated as an alternate acoustic device for high‐frequency wireless sensing applications. Their potential for sensing devices, including biomedical diagnostics and environmental monitoring as a wireless and passive device, calls for further analysis of the device with higher sensitivity. ZnO‐based sensor has always been of research interest due to its biocompatibility, sensing abilities, and yet cost‐effectivity. A Lamb wave device based on ZnO/SiO2/Si membrane has been theoretically simulated using finite element analysis method (FEM) to study the higher modes, as higher working frequency leads to higher sensitivity of the device toward sensing applications. Optimized properties are identified and utilized for the fabrication of Lamb wave devices. It is observed that for optimized parameters of ZnO/SiO2/Si Lamb device, higher antisymmetric modes are not only advantageous for high sensitivity applications but also more stable within the given operating conditions. Experimentally obtained results indicate close matching with theoretical results. [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]

Electronic circuits must address electromagnetic interference due to high-speed transmissions and simultaneous switching actions. This paper proposes a design of novel planar EBG structure L Bridge with embedded slit type with 3 × 3 array fashion, which can be used in a plane layer of a printed circuit board to reduce simultaneous switching noise (SSN). Two sets of pattern such as alternate structure and entire embedded pattern are considered and measured the cut-off frequencies. The performance of the structure is simulated, experimentally verified using R&S®ZVH Vector Network Analyser for the frequency range 0.1 to 10 GHz and compared the outcomes. It is observed that for the −50 dB of noise depth, proposed structure is achieved 1.6 GHz to 10 GHz as lower and upper cut-off frequency. In addition, this concluded the noise suppression using equivalent circuit model and parallel plate wave guide theory. Signal integrity on this structure is also analysed with single-ended and differential mode signal transition. Eye pattern is generated and compared for measuring and validating the signal quality while using this EBG structure. [ABSTRACT FROM AUTHOR]

In the field of structural health monitoring, Lamb Wave has become one of the most widely used inspection tools due to its advantages of wide detection range and high sensitivity. In this paper, a new damage detection method for honeycomb sandwich structures based on frequency spectrum and Lamb Wave Tomography is proposed. By means of simulation and experiment, a certain number of sensors were placed on the honeycomb sandwich plate to stimulate and receive the signals in both undamaged and damaged cases. By Lamb Wave Tomography, the differences of signals before and after damage were compared, and the damage indexes were calculated. Furthermore, the probability of each sensor path containing damage was analyzed, and the damage image was finally realized. The technology does not require analysis of the complex multimode propagation properties of Lamb Wave, nor does it require understanding and modeling of the properties of materials or structures. In both simulation and experiment, the localization errors of the damage conform to the detection requirements, thus verifying that the method has certain feasibility in damage detection. [ABSTRACT FROM AUTHOR]

• Bending edge wave is studied in a thin transversely isotropic viscoelastic plate supported by a viscoelastic foundation. • The nonlocal elasticity theory is used to extract the micro-scale effect on the travelling edge wave. • The Kirchhoff plate theory and the sinusoidal waveform are considered to obtain the closed-form solution. • It is observed that due to the present of viscosity in the foundation the speed of the wave is reduced. The analysis consists of the dynamic behaviour of a thin semi-infinite functionally graded plate under bending edge wave propagation. The plate is made of transversely isotropic materials supported by an elastic foundation. A quadratic variation of the properties of the materials is used to examine the behaviour of the FGM (Functionally Graded Materials) plate in the bending edge wave propagation. The Eringen differential form is employed to transition from non-local to local elasticity. The parameter entailed in the differential form is used to extrapolate the microstructure's impact on the bending edge wave propagation in the functionally graded plate. Additionally, the surface elasticity theory is included to investigate the surface effects on the dispersion of edge wave. The viscosity effect of the plate and the foundation are taken into consideration while formulating the problem. To develop the kinematics of FGM plates, the Kirchhoff plate theory is considered. The motion of the plate is taken along the transverse direction of the plate. The viscoelastic theory proposed by Kelvin-Voigt is used to formulate the mathematical theory of the proposed model. A coupled equation corresponding to the moments and shear forces has been obtained while formulating the plate equation of motion. The rotatory inertia effect is neglected due to the small deflection of the plate. The numerical simulation presented in the paper shows the influence of the viscosity of the elastic foundation, surface effects, non-local elasticity, and the density of the materials on the natural frequency of bending edge wave propagation. [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]

The conventional CBL/VDL sonic log, sector bond log and ultrasonic pulse echo log all are unable to be used to accurately evaluate the quality of well cementing with light-weight cement slurries. To deal with this problem and improve the accuracy of evaluating the quality of well cementing with light-weight cement slurries, an ultrasonic Lamb wave well logging instrument for cementing job quality evaluation was developed based on ultrasonic “pulse-echo” detection mechanism. A model was established describing the relationship among the bending Lamb wave attenuation rate, the vertical echo resonance efficiency and the sonic impedance of medium outside casing. A chart was developed to evaluate the solid-liquid-gas three phase media. With the model and the chart, a new method for evaluating the quality of well cementing based on ultrasonic Lamb wave was developed in connection with light-weight calibration well logs. This new method can be used to effectively evaluate the quality of well cementing with lightweight cement slurries and detect the height of the cement return, thus having solved the difficulties encountered with the lightweight slurries. This technology has provided a clue for examining and evaluating the quality of well cementing with light-weight cement slurries. Meanwhile, the ultrasonic Lamb wave well cementing job quality log instrument can also be used to evaluate the casing eccentricity and casing wear, the results of which can be used as a basis for evaluating the quality of well cementing and the integrity of the wellbore. This new technology will have a broad application prospect. [ABSTRACT FROM AUTHOR]

This paper proposes a method to realize ideal lithium niobate (LiNbO3) A1 resonators. By introducing subwavelength through-holes between the interdigital transducer (IDT) electrodes on the LiNbO3 surface, all unfavorable spurious modes of the resonators can be suppressed completely. It is convenient and valid for various IDT electrode parameters and different LiNbO3 thicknesses. Also, this method does not require additional device fabrication steps. At the same time, these through-holes can greatly reduce the suspended area of the LiNbO3 thin film, thus significantly improving the design flexibility, compactness, mechanical stability, temperature stability, and power tolerance of the resonators (and subsequent filters). It is expected to become an important means to promote the practical application of LiNbO3 A1 filters and even all Lamb waves filters. [ABSTRACT FROM AUTHOR]

We present the design, fabrication, and experimental test of a THz all-dielectric phase shifter plate. The design consists of two wave plate zones coupled in a perpendicular orientation with respect to each other. A large surface area device is realized by an additive manufacturing technique using Acrylonitrile Butadiene Styrene (ABS). Its characteristics are analytically evaluated and experimentally measured in the THz band using time domain spectroscopy and imaging routines. The proposed design enables the creation of quasi-ideal phase retardation in between the two planes with good uniformity on a large surface area. We also achieve the flexibility to select the plane of symmetry around the chosen central axes of choice with a sensitive control over the electromagnetic field polarization direction without inducing any temporal shifts in between the wave front components of the traversed beam. Due to its inherent simplicity and robustness, the phase shifter can be easily scaled at higher frequencies and potentially used in several advanced applications, including free-electron laser (FEL) systems where an accurate polarization control of high intensity beams is required. [ABSTRACT FROM AUTHOR]

The hollow cylinder with a large diameter is the typical shell structure in major engineering applications such as aviation, aerospace, ocean, and so on. Unlike the geometric properties of transportation pipe, the shell structure has a large size and short length. It is relatively difficult to detect damage globally. According to the abovementioned characteristics, a damage localization method based on helical sensor network is proposed in the current research work to locate the internal damage in large-scale hollow cylinder in which the sensors are arranged on the outer surface of the structure. The wavefront theory about flexural modes is fully explored to determine helical sensor network which is suitable for the full frequency spectrum and avoids the approximate estimation to the wave in plate. The flexible sensing paths and single mode excitation in helical sensor network also provide more possibilities for the damage localization in hollow cylinder. The verification method of circumferential orders based on the Fourier transform is developed by the normal mode expansion approach. To apply the helical sensor network of flexural mode in damage localization, the effective loading length of flexural modes is investigated using simulation. And the simulation and experiment both are conducted to locate the internal damage in hollow cylinders and verify the credibility of proposed localization method. The scale parameter and sensing path number are further investigated to determine the effect on location accuracy. [ABSTRACT FROM AUTHOR]

Composite structures are widely used for aerospace applications but are prone to barely visible impact damage from low velocity impacts. Guided wave measurements using sparse arrays of distributed sensors provide an important structural health monitoring (SHM) tool for detecting and localizing impact damage in composites. However, the anisotropy of composites needs to be considered as it can affect guided wave propagation and scattering, impacting imaging performance. Improved defect characterization can be achieved by considering the scattering characteristics for the signal processing. Scattering around two different damage types for multiple incident wave directions in a quasi-isotropic carbon fiber reinforced polymer (CFRP) panel were investigated. Full 3D Finite Element (FE) simulations were compared to the measured scattered guided wave field at an artificial insert delamination. Permanent magnets mounted on an undamaged region of the plate were used as scattering targets and both numerical and experimental scattering patterns were compared to the delamination results. Strong directional dependency was observed for both damage types, with energy focusing along the fiber directions of the outer ply layers. For the delamination, mostly forward scattering is observed for all incident wave directions, whereas the magnet blocked forward wave transmission and scattered wave energy in all directions. 2D scattering matrices were calculated, demonstrating distinct scattering behavior for each damage type. Implications of anisotropy and angular scattering on SHM guided wave sparse array imaging are discussed. [ABSTRACT FROM AUTHOR]

Driven by the rapid advancement in manufacturing technologies, engineering structures with complex geometries are increasingly applied in various industries, posing challenges to the applicability and adaptability of existing structural health monitoring methods based on guided ultrasonic waves. To fulfill the characterization of defects in complex structures, a novel approach featuring a conjunction of zero-group-velocity (ZGV) Lamb waves and polarized poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) transducers is proposed. In this approach, the PVDF-TrFE solvent is deposited and in situ polarized on the structure surface to form thin and flexible coatings, with which the ZGV waves can be excited efficiently and measured reliably. On this basis, the defect can be characterized by investigating the defect-induced alteration in ZGV wave features. In experimental validations, disbond defects in multilayer bonded structures are evaluated using the ZGV waves measured with fabricated PVDF-TrFE transducers. For the first time, the ZGV waves are measured in a contact and in situ manner. Compared with conventional noncontact measurement of ZGV waves, the proposed approach features a remarkably improved reliability, convenience for narrowband excitation, immunity to measurement uncertainty and capability of in situ monitoring. The proposed approach can advance the ZGV wave-based methods toward the in situ health monitoring and enable the defect evaluation in emerging complex structures. [ABSTRACT FROM AUTHOR]

Based on the barometric data recorded by the seismic monitoring network on the Chinese mainland, Lamb wave periods and relative arrival times of 462 stations are obtained with the aid of Meyer's wavelet decomposition, Welch's periodogram spectrum estimation and waveform cross-correlation. By extracting the seismic Rayleigh waves of two seismic stations in the South Pacific and comparing them with the synthetic seismograms, the occurrence time of the first two large volcanic eruptions and the largest volcanic eruption are credibly deduced, and then the travel times and propagation speeds of the Lamb waves are obtained. In order to further explain the attributes of the pressure disturbance associated with the complex acoustic gravity wave (AGW) phases on pressure, a series of numerical simulations with the QSSP program are applied to yield highly similar waves corresponding to the barometric records, which indicates that the eruption source may contain more than 10 sub-events within an hour. According to our detailed analyses, major conclusions are obtained as follows: (1) Although the primary pressure disturbance of the Tonga volcanic eruption appears to be a simple bulge, it is in fact a complex wave composed of multiple eruptions. The largest eruption occurred about 13 min after the first large eruption. (2) In addition to the propagation of the traditional Lamb mode, the Pekeris mode phase that propagates with a lower speed is also observed in some stations, and its amplitude is about a fifth of the Lamb wave. The Pekeris waves may have been more significantly delayed as they traveled against the westerly wind due to their much shorter periods and lower velocities. (3) The group velocity of the Lamb wave is about 308 m/s. Its average period is 70 min, and the wavelength is about 1300 km. The arrival time deviation at each station is negatively correlated with the difference in the near-surface air temperature between North and South China. However, accurately estimating the parameters of the Pekeris waves or the antipodal Lamb waves is challenging due to their low signal-to-noise ratio (SNR), even though the horizontal propagation speed of the Pekeris wave toward China is estimated to be approximately 225 m/s. (4) Much shorter periods and later arrivals at the stations within 200 km of Beijing may be related to the significant cooling (i.e. 12 °C temperature drop), which occurred from Ulantoba, Outer Mongolia, to Beijing beginning at noon on January 15 (Beijing time). [ABSTRACT FROM AUTHOR]

Locally resonant metasurfaces can control the propagation of Lamb wave modes in a plate. The resonator is typically designed through frequency matching: adjusting its geometry and/or materials properties by trial and error until its resonance frequency matches the frequency of the target Lamb wave mode. We demonstrate that although frequency matching appears effective for controlling the A 0 wave mode, it may fail in the case of the S 0 mode. This paper proposes a fundamentally different approach to design a specific metasurface to forbid the propagation of a prescribed Lamb wave mode in a plate. The proposed approach is based upon manipulating the boundary conditions on the top surface of the plate. Different types of Cauchy boundary conditions applied to the surface are shown to control the reflections and mode conversions of low-frequency A 0 and S 0 Lamb waves. Even a small patch with the modified boundary conditions can be effective. Finally, we show that a local "clamping" resonator that assimilates Cauchy boundary conditions on the surface of the plate changes the plate dispersion characteristics resulting in mode conversion and reflection. This finding provides a rational procedure to design a specific metasurface. The surface-mounted resonators enable control of wave propagation in plates without compromising structural integrity, are easily installed, and can be retrofit to the existing planar structures. The numerical results agree well with the experimental results reported in the literature. [ABSTRACT FROM AUTHOR]

A flexoelectric actuator represents a new approach for exciting Lamb waves in plate structures and, thus, can be potentially used for active structural health monitoring systems and microsensors. This paper analytically investigated the performance of a flexoelectric actuator for Lamb wave excitation. The constitutive equation for a thin plate flexoelectric structure was derived using the thermodynamics theory. A significant size effect could be demonstrated by the constitutive equation, which suggests a greatly enhanced curvature excitation performance at a small dimension. The interaction between the ideally bonded flexoelectric actuator with the plate could be simplified into two pairs of pin force and pin moment under the assumption of a weak coupling condition. The strain and the displacement responses to the pin-force and pin-moment pairs were obtained using the integral transform techniques and residue calculus. The pin-moment component mainly yielded an antisymmetric Lamb wave mode, while the pin force was reminiscent of its piezoelectric counterpart. The tuning of either a symmetric or an antisymmetric mode could be achieved by choosing an appropriate excitation frequency. The response under a five-cycle Hanning-window toneburst excitation signal was compared with the finite element analysis results and good agreement between them was found. [ABSTRACT FROM AUTHOR]

Research into the use of nonlinear ultrasonic guided waves for nondestructive evaluation is expanding at a high rate because of the great potential benefit that they possess for early detection of material degradation. However, development of inspection and testing strategies is complicated because (i) the underlying physical principles are complex, (ii) there is a broad spectrum of possible solutions but only a limited number that have been shown to be effective, and (iii) the nonlinearity is weak and thus its measurement is challenging. This Tutorial aims to provide a foundation for researchers and technology-transitioners alike, to advance the application of nonlinear ultrasonic guided waves and ultimately transform how the service lives of structural systems are managed. The Tutorial focuses on the physical principles of nonlinear ultrasonic guided waves leading to the so-called internal resonance conditions that provide a means for selecting primary waves that generate cumulative secondary waves. To detect material degradation, we are primarily interested in nonlinearity stemming from the material itself, which is represented as hyperelastic. For the special case of plates, internal resonance points have been identified and case studies are presented to illustrate some of the applications. The Tutorial has one new result not published in a research paper; finite element simulation of energy transfer from shear-horizontal primary waves to symmetric Lamb waves at the second harmonic. [ABSTRACT FROM AUTHOR]

Abstract Pinhole corrosion is difficult to discover through conventional ultrasonic guided waves inspection, particularly for micro-sized pinholes less than 1 mm in diameter. This study proposes a new micro-sized pinhole inspection method based on segmented time reversal (STR) and high-order modes cluster (HOMC) Lamb waves. First, the principle of defect echo enhancement using STR is introduced. Conventional and STR inspection experiments were conducted on aluminum plates with a thickness of 3 mm and defects with different diameters and depths. The parameters of the segment window are discussed in detail. The results indicate that the proposed method had an amplitude four times larger than of conventional ultrasonic guided waves inspection method for pinhole defect detection and could detect micro-sized pinhole defects as small as 0.5 mm in diameter and 0.5 mm in depth. Moreover, the segment window location and width (5−10 times width of the conventional excitation signal) did not affect the detection sensitivity. The combination of low-power and STR is more conducive to detection in different environments, indicating the robustness of the proposed method. Compared with conventional ultrasonic guided wave inspection methods, the proposed method can detect much smaller defect echoes usually obscured by noise that are difficult to detect with a lower excitation power and thus this study would be a good reference for pinhole defect detection.

The possibility to steer floating cells dispersed in water by means of flexural plate waves (FPWs) generated by a 9 mm $\times9$ mm piezoelectric MEMS transducer has been explored. The MEMS transducer has a squared cavity etched out in a silicon substrate formed by a 6 mm $\times6$ mm composite diaphragm made of a piezoelectric aluminum nitride (AlN) layer on top of a doped silicon plate. The piezoelectric layer can be electrically actuated by means of metal interdigital transducers (IDTs) placed over the AlN film at the diaphragm edges. Cell alignment has been sought for by inducing standing FPWs in the diaphragm and in the contacting water layer in the cavity by the one-dimensional (1D) acoustic field pattern obtained by exciting two IDTs located symmetrically with respect to the diaphragm centre. The working principle has been validated by means of 2D finite element modelling and simulations. The MEMS transducer has been fabricated using the PiezoMUMPs process and experimentally tested by exploiting a tailored front-end electronic circuit. Inactive fibroblast cells with an approximate diameter of $15~\mu \text{m}$ have been dispersed in demineralized water within the cavity at a concentration in the order of 105 cells/ml. By applying sinusoidal excitation signals to faced IDTs with zero phase shift and peak amplitude of 10 V, lines of cells spaced by half wavelength $\lambda $ /2 = $56~\mu \text{m}$ have been achieved at 12.5 MHz, in good agreement with theoretical predictions and simulation results.