Search

The lithographically tunable and small size features of Lamb wave resonators (LWRs) take a bright future for their use in high frequency narrow band filters. Resonant frequency drift due to temperature variation has a large impact on the narrower passband and a temperature coefficient of frequency (TCF) closer to 0 can broaden the stable temperature range of the resonator. This paper proposes a method of etching grooves in the area of the piezoelectric layer not covered by the Interdigital transducer (IDT) electrodes to improve the temperature stability of the Lamb resonator. Through the finite element method and theoretical analysis, the phase velocity, group velocity, and TCF dispersion curve of different modes of the resonator with groove structure were determined. The reason for the change of TCF under different normalized thicknesses of AlN was explained through the conversion of the LWR from a contour mode resonator (CMR) to a Cross-Sectional Lamé Mode Resonator. Simulation and test have shown that etching grooves have the effect of reducing TCF by adjusting the electromechanical coupling coefficient. The test shows that 205 nm-depth grooves can lower the TCF of the S0 mode IDT-Open LWR from −13.3 to −5.1 ppm/°C and S1 mode from −36.8 to −9.0 ppm/°C, respectively. The TCF of S0 and S1 mode LWRs decreased by 61.7% and 75.5%, respectively, after 205 nm groove etching. The groove etching method greatly raises the temperature stability of the LWR, enabling Lamb wave filters to operate stably over a wider temperature range. [ABSTRACT FROM AUTHOR]

In this paper, a new Stroh formalism for gradient electro-mechanics is derived for the first time, which is both mathematically concise and numerically powerful, applicable to generally coupled anisotropic material systems. Based on this new formalism, the complicated Lamb wave in flexoelectric and piezoelectric plates is investigated. The dispersion equation is obtained by solving the eigenvalue problem along with the unconditionally stable dual-variable and position method. From the obtained dispersion equation, the dispersion curves and mode shapes of the Lamb wave are calculated by the 1D form of the multidimensional moduli ratio convergence method. Two important and interesting features are observed from our analysis: One is the difference in the mode shape symmetry between the piezoelectric and flexoelectric cases, and the other is the size-dependent property of the flexoelectric effect as observed by nondimensionalization. These features are further illustrated by comparing the dispersion curves and wave-mode shapes among the three different material models (purely piezoelectric, purely flexoelectric, and flexoelectric and piezoelectric coupled). The newly derived Stroh formalism offers a robust, concise, and unified approach for dealing with strain gradient electro-mechanic materials with crystal systems of general anisotropy. The present work also explains the physical mechanism of symmetry breaking observed, as induced by flexoelectric coupling in piezoelectric materials. [ABSTRACT FROM AUTHOR]

Real-time monitoring of structural health status is very important for supersonic aircraft, since the long-term operation in harsh service environments, such as high temperatures, can cause potential damage. Structural health monitoring (SHM) based on lamb wave has been approved to be a critical technique for the reliable operation of supersonic aircraft, but is limited by the operating temperature of conventional piezoelectric sensors, which makes it difficult to meet the high-temperature monitoring requirements. The BiFeO 3 –BaTiO 3 ceramics exhibit excellent piezoelectric properties and high Curie temperature (T c), making them promising for high-temperature SHM of supersonic aircraft. Here, we fabricated a piezoelectric sensor using 0.67BiFeO 3 -0.33BaTiO 3 -0.25%molMnO 2 (BF33BTMN-025) ceramic, which exhibits a piezoelectric charge constant (d 33) of 135 pC/N at room temperature and a T c of 448 °C. The BF33BTMN-025 ceramic sensor operates effectively at temperatures up to 200 °C and maintains stable damage monitoring sensitivity as well. Compared with Pb(Zr, Ti)O 3 (PZT), BaTiO 3 (BTO) and other piezoelectric sensors commonly used in SHM field, the BF33BTMN-025 ceramic sensor has a higher operating temperature and a comparable sensitivity. Our work demonstrates that the BF33BTMN-025 ceramic sensor can be employed as piezoelectric sensor for high-temperature SHM, which has a wide application potential in the field of real-time monitoring of supersonic aircraft. [ABSTRACT FROM AUTHOR]

Thin-film lithium niobate is an attractive material for RF acoustic devices because of its high electromechanical coupling. However, due to the large coupling and the high anisotropy, thin-film lithium niobate resonators are prone to accidental resonances called spurious modes. These modes compromise the frequency response of the resonators, limiting their use in filter and oscillator applications. In this work, we present a novel method of spurious mode suppression through a special edge treatment etch process. Two thin-film lithium niobate resonators were fabricated, one with smooth sidewalls and one with the edge treatment. It was found that the edge-treated resonators show a weaker spurious mode response. This is potentially a new way to mitigate spurious resonances, a major issue in lithium niobate Lamb wave devices. [ABSTRACT FROM AUTHOR]

Highly efficient and spectrally pure single photon sources are desirable in fundamental studies of quantum physics and in many varied applications like in quantum metrology and quantum cryptography. 2D semiconductor colloidal quantum wells (CQWs) are quite appropriate as nanoscale photon sources because of their giant oscillator strengths and large absorption cross sections. The integration of such sources with dielectric metasurfaces exhibiting narrow resonances provides an excellent platform for highly efficient light‐matter interactions and the development of on‐chip light sources with high spectral purity. Here details on the use of capillary filling method are reported to achieve photonic coupling of CQWs to a metasurface resonator (MSR) featuring a square‐lattice geometry of holes on a slab‐waveguide to achieve strongly enhanced and almost spectrally pure emission of ≈3% of the original out‐of‐plane emission line‐width of the quantum emitters at room temperature. Long‐range exciton‐mediated photon transport facilitated by in‐plane slab waveguide modes is demonstrated and a theoretical basis to explain all the experimental data including that in terms of the MSR‐modified Lamb shifts and Purcell decays is provided. The results demonstrate a new platform with emergent photonic properties and suggest possibility of their use in on‐chip photonic quantum information processing. [ABSTRACT FROM AUTHOR]

Background Propose Method Results Conclusions The skin is the largest organ of the human body and serves distinct functions in protecting the body. The viscoelastic properties of the skin play a key role in supporting the skin‐healing process, also it may be changed due to some skin diseases.In this study, high‐frequency ultrasound (HFUS) elastography based on a Lamb wave model was used to noninvasively assess the viscoelastic anisotropy of human skin.Elastic waves were generated through an external vibrator, and the wave propagation velocity was measured through 40 MHz ultrafast HFUS imaging. Through the use of a thin‐layer gelatin phantom, HFUS elastography was verified to produce highly accurate estimates of elasticity and viscosity. In a human study involving five volunteers, viscoelastic anisotropy was assessed by rotating an ultrasound transducer 360°.An oval‐shaped pattern in the elasticity of human forearm skin was identified, indicating the high elastic anisotropy of skin; the average elastic moduli were 24.90 ± 6.63 and 13.64 ± 2.67 kPa along and across the collagen fiber orientation, respectively. The average viscosity of all the recruited volunteers was 3.23 ± 0.93 Pa·s.Although the examined skin exhibited elastic anisotropy, no evident viscosity anisotropy was observed. [ABSTRACT FROM AUTHOR]

Highly efficient surface acoustic wave (SAW) transducers offer significant advantages for microfluidic atomization. Aiming at highly efficient atomization, we innovatively accomplish dual-surface simultaneous atomization by strategically positioning the liquid supply outside the IDT aperture edge. Initially, we optimize Lamb wave transducers and specifically investigate their performance based on the ratio of substrate thickness to acoustic wavelength. When this ratio h / λ is approximately 1.25, the electromechanical coupling coefficient of A0-mode Lamb waves can reach around 5.5% for 128° Y-X LiNbO3. We then study the mechanism of droplet atomization with the liquid supply positioned outside the IDT aperture edge. Experimental results demonstrate that optimized Lamb wave transducers exhibit clear dual-surface simultaneous atomization. These transducers provide equivalent amplitude acoustic wave vibrations on both surfaces, causing the liquid thin film to accumulate at the edges of the dual-surface and form a continuous mist. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced polymers (CFRPs) are widely used in the fabrication of solid rocket motor casings due to their exceptional performance. However, the bonding interface between CFRP and viscoelastic materials (rubber) is prone to debonding damage during service and storage under complex environmental conditions, which poses a significant threat to the structural integrity and reliability of the engine. Existing nondestructive testing (NDT) methods, such as X-ray imaging, infrared thermography, and ultrasonic testing, although somewhat effective, exhibit significant limitations in detecting interfacial defects in deep or multilayered composite materials, particularly under the challenging conditions of service and storage. This study proposes an innovative method based on active Lamb wave energy analysis and introduces the Damage Evolution Factor (DEF), specifically designed to detect and evaluate interfacial debonding defects in CFRP–rubber bonded structures within solid rocket motors during service and storage. Through numerical simulations and experimental validation, we selected the A0 mode Lamb wave, which is more sensitive to interfacial damage, as the incident wave and excited it on the surface of the structure. Displacement time-history response signals at observation points under different damage models were extracted and analyzed, and DEF values were calculated. The results show that DEF values increase with the size of the interfacial debonding damage. Similar trends were observed in experimental studies, further validating the effectiveness of this method and demonstrating that DEF can be used for the quantitative evaluation of interfacial debonding defects in CFRP–rubber bilayer bonded structures. [ABSTRACT FROM AUTHOR]

• The 2022 Tonga eruption confirmed that explosions can produce air-driven tsunamis • Lamb waves from large explosions are one way to generate and drive global tsunamis • Airbursts from comets and asteroids can produce tsunamis by atmospheric coupling • Several mechanisms are proposed for air-driven tsunami generation and amplification • Impact plume collapse, vortices, and steam blowoff are hypothetical tsunami sources [ABSTRACT FROM AUTHOR]

Guided waves propagating in mechanical structures have proved to be an essential technique for applications, such as structural health monitoring. However, it is a well-known problem that when using non-stationary guided wave signals, dispersion, and high-order vibrational modes are excited, it becomes cumbersome to detect and identify relevant information. A typical method for the characterization of these non-stationary signals is based on time–frequency (TF) mapping techniques. This method produces 2D images, allowing the study of specific vibration modes and their evolution over time. However, this approach has low resolution, increases the size of the data, and introduces redundant information, making it difficult to extract relevant features for their accurate identification and classification. This paper presents a method for identifying discontinuities by analyzing the data in the TF maps of Lamb wave signals. Singular Value Decomposition (SVD) for low-rank optimization and then perform foreground feature extraction on the maps were proposed. These foreground features are then analyzed using Principal Component Analysis (PCA). Unlike traditional PCA, which operates on vectorized images, our approach focuses on the correlation between coordinates within the maps. This modification enhances feature detection and enables the classification of discontinuities within the maps. To evaluate unsupervised clustering of the dimensionally reduced data obtained from PCA, we experimentally tested our method using broadband Lamb waves with various vibrational modes interacting with different types of discontinuity patterns in a thin aluminum plate. A Support Vector Machine (SVM) classifier was then implemented for classification. The results of the experimental data yielded good classification effectiveness within reasonably low computational time despite the large matrixes of the TF maps used. [ABSTRACT FROM AUTHOR]

Functionally gradient material (FGM) in service often experience temperature variations that can affect the propagation characteristics of guided waves. This investigation aims to study the propagation of thermoelastic guided waves in the FGM plate. A computational method for the state vector and Legendre polynomials hybrid approach, which is proposed based on the Green–Nagdhi theory of thermoelasticity. The heat conduction equation is introduced into the governing equations, and optimized using univariate nonlinear regression for arbitrary gradient distributions of the material components. To study their dispersion characteristics, a non-hierarchical calculation for the dispersion curves of FGM plates versus temperature is realized. In addition, a frequency domain simulation model is developed and compared with theoretical data to evaluate the accuracy and feasibility of the proposed theory. Then, the influence of Legendre orthogonal polynomial cut-off order on dispersion curve convergence is investigated. Subsequently, the shift of the gradient index and temperature variation on the fundamental mode in dispersion curve is analyzed. The results indicate that changes in both gradient index and temperature lead to a systematic shift in the phase velocity of fundamental modes in the low frequency range. Meanwhile, anti-symmetric modes exhibit higher sensitivity. On this basis, the study can provide theoretical support for the acoustic non-destructive characterization of FGM plates versus temperature. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) is a non-destructive technique that relies on monitoring naturally occurring sources of high frequency ultrasound in components and structures. Ultrasonic waves propagate in the form of different wave modes—for instance Lamb waves in thin plates, or Rayleigh and P- and S- waves in bulk structures. Those wave modes have different properties, but also contain information regarding the source of the naturally occurring wave. Manually, the wave modes can be recognized by comparing a time–frequency representation of the signal to the dispersion curves expected in the tested object. For analyzing a large number of signals, this manual mode recognition becomes a tedious process. This paper proposes a method to automate the wave mode recognition based on some minimal knowledge of the occurring wave modes. As inputs, only the propagation speed of the possible wave modes and the source position need to be provided along with a limited set of reference wavelets for each wave mode. Cross-correlation of a signal with a reference wavelet of a mode reduces the signal to a limited number of peaks that may delineate the start of the mode. Using other signals from the same event but from different sensors, velocities are calculated for each peak in order to select the peak that corresponds to the arrival of the mode under investigation. To validate the method, a dataset was recorded based on four types of out-of-plane sources: Hsu-Nielsen sources of 0.3 and 0.5 mm, sensor pulse signals and AEs from melting ice. Since the presented dataset was recorded on a plate, the aim of the validation was to recognize the zero-order symmetrical and anti-symmetrical Lamb modes. The results of the proposed mode recognition method applied to this dataset are compared with results from manual mode recognition. For Hsu-Nielsen sources, the succes rate is found to be above 95%. For narrow-band pulsed signals or for AEs from melting ice with a low signal-to-noise ratio, succes rates between 75 and 80% relative to manual mode recognition are reported. [ABSTRACT FROM AUTHOR]

The use of Lamb waves within a guided wave (GW)–based scheme holds promise toward monitoring and nondestructive evaluation (NDE) of plate structures. Their short wavelength enables interaction with small defects and they can travel long distances, thus offering extensive spatial coverage. In boosting the performance of these schemes for more advanced damage identification tasks, such as precise damage localization and quantification, the fusion of measurement data with models is advantageous. Such a hybrid scheme, which relies on the inclusion of engineering models, is hampered by the short wavelengths of GW-based schemes. Short wavelengths require a fine discretization of numerical models in space and in time, which results in high computational costs. In alleviating this issue, we propose a reduced-order model (ROM) relying on exploitation of the frequency response function (FRF) principle, which is parameterized with respect to the positioning of local defects. Through appropriate coordinate transformations, the surrogate, constructed based on the matching pursuit (MP) algorithm, can exploit the mechanical properties of the wave so that only a small amount of training simulations are needed. The efficacy of the proposed surrogate is demonstrated in a synthetic inverse setting, using a particle swarm optimization (PSO) strategy. [ABSTRACT FROM AUTHOR]

In addressing the challenging issue of impact source localization for large-scale anisotropic stiffened compartmental cylindrical shell structures, this paper presents a novel impact localization method. The method is based on a time-reversal virtual focusing triangulation approach and does not rely on prior knowledge of the structure or specific measurements of wave velocity. By employing energy power filtering to select key sensors, wavelet packet decomposition is utilized to extract narrowband Lamb wave signals, which are then synthesized. Further enhancement of signal recognition is achieved through time-reversal amplification techniques. Experimental results demonstrate that under non-motorized operating conditions, this method achieves an average error of 0.89 m. Under motorized operating conditions, the average error is 1.12 m. Although the presence of background noise leads to an increase in error, the overall localization performance is superior to traditional triangulation methods. Additionally, selecting the top three sensors in terms of energy power ranking can more accurately record impact response. [ABSTRACT FROM AUTHOR]

Reconfigurable coupled-resonator elastic waveguides are formed using defects composed of threaded rods, fixed with nuts and attached to a perforated two-dimensional phononic crystal slab. The resonant frequency of the defect can be tuned continuously within a complete phononic bandgap by adjusting the length of the threaded rod. Straight waveguides are formed from a line of defects. Phononic circuits are created by coupling three parallel straight waveguides. Through precise manipulation of the length of the threaded rod assembly, frequency demultiplexing of Lamb waves is achieved. Numerical and experimental results are found to be in good agreement. This work is of significance for the practical design of phononic devices including reconfigurable circuits. [ABSTRACT FROM AUTHOR]

The lowest-order shear horizontal (SH0) guided wave in a plate is crucial for nondestructive testing and structural health monitoring due to its nondispersive nature. However, mode conversion at the interface for the SH0 wave complicates the received information and increases the difficulty of signal analysis. In this work, an elastic metasurface is proposed to suppress mode conversion at the interface and to reflect the SH0 wave directionally. The metasurface comprises a series of rectangular elements with a specific phase gradient covering the 2 π phase range. The effectiveness of the proposed metasurface is confirmed through finite element simulations and experimental validation. The results indicate that the metasurface can significantly reduce the amplitude of the reflected lowest-order symmetric Lamb wave when compared to the reflection without the metasurface, while simultaneously allowing the reflected SH0 wave to propagate at the designed angle. Furthermore, the metasurface maintains its functionality for SH0 wave with incident angles varying from 0° to 25°. This study provides a viable approach for suppressing mode conversion and modulating the reflection behavior of SH0 wave, which is expected to find applications in nondestructive testing and structural health monitoring. [ABSTRACT FROM AUTHOR]

When an ultrasonic pulse propagates in a thin plate, nonlinear Lamb waves with higher harmonics and a zero-frequency component (ZFC) will be generated because of the nonlinearity of materials. The ZFC, also known as the static displacement or static component, has its unique application on the evaluation of early-stage damages in the elastic symmetrical undulated plate. In this study, analysis of the excitation mechanism of the ZFC and the second harmonic component (SHC) was theoretically and numerically investigated, and the material early-stage damage of a symmetrical undulated was characterized by studying the propagation of nonlinear Lamb waves. Both the ZFC and SHC can be effectively employed in monitoring the material damages of the undulated plate in its early stage. However, several factors must be considered for the propagation of the SHC in an undulated plate because of the geometric curvature and interference between the second harmonics during propagation, preventing efficient application of this technique. If the fundamental wave can propagate in the plate regardless of the plate boundary conditions, an accumulative effect always exists for the ZFC in a thin plate, indicating that the ZFC is independent of the structural geometry. This study reveals that the ZFC-based inspection technique is more efficient and powerful in characterizing the damages of a symmetrical undulated plate in the early stage of service compared to the second harmonic method. [ABSTRACT FROM AUTHOR]

For practical engineering structures, fatigue is one of the main factors affecting their safety and durability. Under long-term service conditions, the minor damage will be affected by fatigue loading and expand to macroscopic cracks, affecting the structure's service performance. Based on the sensitivity of Lamb waves to minor and initial damage, a damage monitoring method for fatigue crack propagation is proposed. By carrying out fatigue crack propagation tests under constant amplitude loading, the Paris equation of 316L steel and damage signals at different crack growth stages were obtained. Combined with damage monitoring tests and finite element analysis, the relationship between the phase damage index (PDI), amplitude damage index (ADI), signal correlation coefficient, and fatigue crack propagation length was studied. Compared with PDI and ADI, the signal correlation coefficient is more sensitive to crack initiation, which can be selected as the damage monitoring index in the initial stage of crack growth. With the increase of fatigue crack propagation length, the peak time of the direct wave signal gradually moves backward, which shows an obvious phase change. In the whole fatigue crack growth stage, PDI and crack length show a monotonically changing trend. By using the stress intensity factor as the conversion parameter, a prediction model of the fatigue crack propagation rate based on PDI was established. Compared to the fatigue crack propagation rate measured by experiments, the relative error of the predicted results is 10%, which verifies the accuracy of the proposed damage monitoring method. [ABSTRACT FROM AUTHOR]

In this paper, to determine the efficacy of the porous bed on damping far-field wave energy, the wave dynamics around a circular plate is studied. By combining the appropriate boundary conditions, the unknown potential is attained for the free surface and the plate-covered region. The Bessel series solution is attained further, by employing the matched eigenfunction expansion technique. Wave force excitation on the circular plate, deflection of the plate, and flow distribution is calculated and examined to comprehend the efficacy of the current investigation. Moreover, the motion of the plate is assessed in the time domain. The study reveals a substantial reduction in wave amplitude on the plate's leeward side because of the energy dissipation by the porous bed. Also the study concludes that for intermediate values of porosity with larger wavenumbers, approximately 50% of wave power is dissipated with respect to incident wave power. [ABSTRACT FROM AUTHOR]

Anomalous guided waves appearing at a non-semisimple degeneracy of the fundamental matrix are observed and analyzed in the framework of the Cauchy sextic formalism. The non-semisimple degeneracy condition is explicitly constructed for the most general case of Lamb waves propagating in a traction-free layer with arbitrary elastic anisotropy. A new type of dispersion equation and the corresponding dispersion solution are obtained. The connection with surface waves of the non-Rayleigh type is discussed. [ABSTRACT FROM AUTHOR]

The scattering of flexural waves in piezoelectric thin plates with defects effects the electro-mechanical coupling property. Theoretical analysis for flexural waves is lack of a suitable decoupling function. Here, we have developed a method based on applied electric field to make a solution of the dynamic moment concentration factor (DMCF) for flexural waves scattering problems. The DMCFs of the piezoelectric materials have been found that it is significantly larger than those of the ordinary elastic materials because of electro-mechanical coupling. In the region of low frequency, DMCFs have a dependence on applied electric field and independent on the incident angle. Those opposite phenomena are observed as the frequency increasing. Those results provide theoretical guidance for dynamic analysis and strength design of piezoelectric material structures. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, an active ultrasound-based touchscreen technology is presented for real-time monitoring of multiple contacts on a glass panel of 20 × 19 cm. Both fundamental Lamb wave modes are generated by sending a linear chirp between 50 and 100 kHz to a single piezoelectric ceramic lead zirconate titanate. Measurement is performed using four piezoelectric ceramic lead zirconate titanate elements, and real-time localization and detection are performed on a system on module i.MX 8 M Nano. Results show that Lamb waves can be used for real-time multi-touch detection and localization on both sides of the panel. Moreover, the prototype developed allows for relative pressure measurement. [ABSTRACT FROM AUTHOR]

This study numerically analyzes a submerged horizontal plate (SHP) device subjected to both regular and irregular waves. This device can be used either as a breakwater or a wave energy converter (WEC). The WaveMIMO methodology was applied for the numerical generation and wave propagation of the sea state of the Rio Grande coast in southern Brazil. The finite volume method was employed to solve conservation equations for mass, momentum, and volume fraction transport. The volume of fluid model was employed to handle the water-air mixture. The SHP length (Lp) effects were carried out in five cases. Results indicate that relying solely on regular waves in numerical studies is insufficient for accurately determining the real hydrodynamic behavior. The efficiency of the SHP as a breakwater and WEC varied depending on the wave approach. Specifically, the SHP demonstrates its highest breakwater efficiency in reducing wave height at 2.5Lp for regular waves and 3Lp for irregular waves. As a WEC, it achieves its highest axial velocity at 3Lp for regular waves and 2Lp for irregular waves. Since the literature lacks studies on SHP devices under the incidence of realistic irregular waves, this study significantly contributes to the state of the art. [ABSTRACT FROM AUTHOR]

AbstractThe study explores the propagation of symmetric and antisymmetric fundamental Lamb waves in laminated composite strips, employing multi-field piezo-elastic plate models. The findings indicate the necessity of employing higher-order kinematic models to enhance the accuracy of wave propagation assessments. To further optimize computational efficiency, node-dependent kinematic models are utilized. The research delves into the tradeoff between reducing computational costs and maintaining result accuracy demonstrating a reduction of up to 60% in computational expenses in simple models while keeping the error below 1%. Two-dimensional wave propagation in laminated composite plates was further considered, expanding the scope due to material orthotropy. [ABSTRACT FROM AUTHOR]

The first asymmetric mode (A1 mode) lamb wave resonator (LWR) with a resonant frequency of 6 GHz based on Z-cut lithium niobate (LN) films is presented. An asymmetric electrode structure with different-sized electrode pads in the center and edged regions has been proposed, which can be used to optimize the distribution of the electric field and decrease acoustic impedance mismatch to improve the target mode. Experiment results reveal that LWRs with an asymmetric electrode structure can successfully enhance the A1 mode, achieving a high effective electromechanical coefficient ( k eff 2 ) of 26%, a quality factor (Q) of 1123, and an excellent figure-of-merit (FOM = k eff 2 ∙ Q) of 262. It demonstrates that asymmetric electrode structure provides a new way to suppress the spurious modes for LWRs and shows a great application prospect in wide-bandwidth and low-loss filters used in the sub-6 G frequency range. [ABSTRACT FROM AUTHOR]

Ultrasonic guided waves, which are often generated and detected by piezoelectric transducers, are well established to monitor engineering structures. Wireless solutions are sought to eliminate cumbersome wire installation. This work proposes a method for remote ultrasonic-based structural health monitoring (SHM) using mechanoluminescence (ML). Propagating guided waves transmitted by a piezoelectric transducer attached to a structure induce elastic deformation that can be captured by elastico-ML. An ML coating composed of copper-doped zinc sulfide (ZnS:Cu) particles embedded in PVDF on a thin aluminium plate can be used to achieve the elastico-ML for the remote sensing of propagating guided waves. The simulation and experimental results indicated that a very high voltage would be required to reach the threshold pressure applied to the ML particles, which is about 1.5 MPa for ZnS particles. The high voltage was estimated to be 214 Vpp for surface waves and 750 Vpp for Lamb waves for the studied configuration. Several possible technical solutions are suggested for achieving ultrasonic-induced ML for future remote SHM systems. [ABSTRACT FROM AUTHOR]

The submarine volcano Hunga Tonga–Hunga Ha'apai erupted explosively on January 15, 2022, offering a unique opportunity to investigate interactions between the atmosphere and ionosphere caused by Lamb and Pekeris waves. However, the resonance of Pekeris waves has not been previously detected. In this study, we applied a multi-point monitoring approach focusing on the lower ionosphere and atmospheric electric field. Here we show observed oscillations of 100–200 s in manmade transmitter signals and the magnetic and atmospheric electric fields, which were caused by Pekeris waves. However, no corresponding changes with the period of 100–200 s in atmospheric pressure due to Pekeris waves were observed on the ground. A simulation of neutral wind revealed Pekeris waves oscillating near the mesopause, suggesting resonance. Therefore, the oscillation in atmospheric electric field is interpreted that the resonance in the lower ionosphere was projected onto the Earth's surface via a global electric circuit. [ABSTRACT FROM AUTHOR]

Using dense global navigation satellite system data and brightness temperature data across the New Zealand and Australia regions, we tracked the propagation of traveling ionospheric disturbances (TIDs) associated with the 15 January 2022 Tonga volcanic eruptions. We identified two shock wave-related TIDs and two Lamb wave-related TIDs following the eruptions. The two shock wave-related TIDs, propagating with velocities of 724–750 and 445–471 m/s, respectively, were observed around New Zealand and Australia within a distance of 3500–6500 km from the eruptive center. These shock wave-related TIDs suffered severe attenuation during the propagation and disappeared more than 6500 km from the eruptive center. Based on the TEC data from the nearest ground-based receivers, we estimated the onset times of two main volcanic explosions at 04:20:54 UT ± 116 s and 04:24:37 UT ± 141 s, respectively. The two shock wave-related TIDs were most likely generated by these two main volcanic eruptions. The two Lamb wave-related TIDs propagated with velocities of 300–370 and 250 m/s in the near-field region. The Lamb wave-related TIDs experienced minimal attenuation during their long-distance propagation, with only a 0.17% decrease observed in the relative amplitudes of the Lamb wave-related TIDs from the near-field to far-field regions. [ABSTRACT FROM AUTHOR]

The Lamb waves in nematic elastomer plates are investigated by adopting the viscoelasticity theory in the hydro-dynamic (low frequency) limit. The Legendre polynomial series approach is employed to obtain the complex wave number solutions to characterize the wave propagation and attenuation. Some unique Lamb wave characteristics are revealed. Results show that the cutoff frequencies of all Lamb modes vanish due to the high viscoelasticity. Except for A0 mode, each mode has a minimal attenuation frequency. Besides, the attenuation of nematic phase is thousands of times greater than the isotropic phase, which would be significant in designing damping applications. [ABSTRACT FROM AUTHOR]

The possibility of using the Digital Image Correlation (DIC) technique, along with Lamb wave analysis, was investigated in this study for damage detection and characterization of polymer carbon fiber (CFRP) composites with the help of numerical modeling. The finite element model (FEM) of the composite specimen with artificial damage was developed in ANSYS and validated by the results of full-field DIC strain measurements. A quantitative analysis of the damage detection capabilities of DIC structure surface strain measurements in the context of different defect sizes, depths, and orientation angles relative to the loading direction was conducted. For Lamb wave analysis, a 2D spatial-temporal spectrum analysis and FEM using ABAQUS software were conducted to investigate the interaction of Lamb waves with the different defects. It was demonstrated that the FEM updating procedure could be used to characterize damage shape and size from the composite structure surface strain field from DIC. DIC defect detection capabilities for different loadings are demonstrated for the CFRP composite. For the identification of any composite defect, its characterization, and possible further monitoring, a methodology based on initial Lamb wave analysis followed by DIC testing is proposed. [ABSTRACT FROM AUTHOR]

We report on the experimental demonstration of aluminum scandium nitride (AlScN)-on-cubic silicon carbide (3C-SiC) Lamb wave resonators (LWRs) realized via microelectromechanical systems (MEMS) technology, operating at high temperature (T) up to T = 800 °C, while retaining robust electromechanical resonances at ∼27 MHz and good quality factor of Q ≈ 900 even at 800 °C. Measured resonances exhibit clear consistency and stability during heating and cooling processes, validating the AlScN-on-SiC LWRs can operate at high T up to 800 °C without noticeable degradation in moderate vacuum (∼20 mTorr). Even after undergoing four complete thermal cycles (heating from 23 to 800 °C and then cooling down to 23 °C), the devices exhibit robust resonance behavior, suggesting excellent stability and suitability for high-temperature applications. Q starts to decline as the temperature exceeds 400 °C, which can be attributed to energy dissipation mechanisms stemming from thermoelastic damping and intrinsic material loss originating from phonon–phonon interactions. [ABSTRACT FROM AUTHOR]

Several studies on functionally graded materials (FGMs) have been done by researchers, but few studies have dealt with the impact of the modification of the properties of materials with regard to the functional propagation of the waves in plates. This work aims to explore the effects of changing compositional characteristics and the volume fraction of the constituent of plate materials regarding the wave propagation response of thick plates of FGM. This model is based on a higher-order theory and a new displacement field with four unknowns that introduce indeterminate integral variables with a hyperbolic arcsine function. The FGM plate is assumed to consist of a mixture of metal and ceramic, and its properties change depending on the power functions of the thickness of the plate, such as linear, quadratic, cubic, and inverse quadratic. By utilizing Hamilton's principle, general formulae of the wave propagation were obtained to establish wave modes and phase velocity curves of the wave propagation in a functionally graded plate, including the effects of changing compositional characteristics of materials. [ABSTRACT FROM AUTHOR]

This paper presents a novel crack size estimation method based on dilated convolution and time series fine tuning using in‐situ Lamb wave. The contributions of this proposed method are twofold: (1) a dilated convolution‐based neural network which is an effective representation learning methods with larger receptive fields for periodic signals and (2) a crack length adjustment approach based on previous estimations with a time series fine tuning method. The time series fine tuning method utilizes the monotonicity of the crack length with respect to time. A new evaluation metric has been adopted, which considers prediction errors, time errors, and monotonicity errors. The proposed method outperforms the previous feature extraction‐based methods with or without time series fine tuning in this new evaluation metric. Highlights: Crack estimation method using deep learning and time series fine tuning was proposed.The neural network using a combination of dilated convolution and long short‐term memory (LSTM) network was designed.The proposed method outperformed prior manual feature extraction‐based approaches. [ABSTRACT FROM AUTHOR]

We performed a stability analysis of a 2D wave-plate coupling system equipped with memory viscoelastic damping. The study highlights the unique functionality of the damping mechanism, which operates indirectly and exclusively within either the wave or plate subsystem. The opposing subsystem receives dissipative signals indirectly through the coupling component. The primary objective of this study was to determine whether the indirect memory damping is sufficient to ensure the overall stability of the coupled system. To address this question, a frequency domain analysis was employed to establish explicit decay rates of the coupled system. Notably, a polynomial decay rate is observed when the memory damping is applied solely to either the plate or wave subsystem, which provides a conclusive answer to the posed question. [ABSTRACT FROM AUTHOR]

Guided ultrasonic wavefield propagation imaging (GUPI) is useful for visualizing hidden flaws in aerospace thin-walled structures, but the need for subjective signal processing involving three-dimensional Fourier transformation to increase the visibility of subtle flaws hinders its wider acceptance. A high-resolution wavenumber bandpass filter capable of consolidating subtle flaw-relevant information from a wide frequency band using only two-dimensional Fourier transformation was proposed. The filter overturns the long-standing belief that modes must be separated based on narrow-band data acquisition or processing to achieve high flaw visibility. Its characteristics and advantages were experimentally demonstrated through enhanced visualization of hidden wall-thinning flaws of a plate specimen. Its strength was further demonstrated through the first GUPI visualization of a partially loosened bolt, with unprecedented clarity to discern bolt tightness levels. The results conclusively proved that the proposed filter significantly enhances the resolution of GUPI within a structured processing framework. [ABSTRACT FROM AUTHOR]

Plate-like structures, including composite material plates, are extensively employed in major engineering structures such as aerospace, high-speed rail, and civil engineering. The growing utilization of curved panel structures and the increasing complexity of these structures have emphasized the need for flexible sensors capable of efficient signal front-end reception. Addressing the limitations of conventional sensors made of brittle piezoelectric materials in adhering to the surface of structures for health monitoring, a self-developed flexible dielectric elastomer-interdigital transducer (DE-IDT) array is employed to achieve damage imaging in isotropic aluminum curved panel structures and orthotropic composite material plates using linear frequency modulation (chirp) signal excitation. In addition, a proposed fusion method is utilized to obtain weighted imaging results, and evaluation and analysis are performed using relevant indicators. Experimental findings highlight the improved imaging accuracy achieved through phased array data fusion using the linear chirp signal, attributed to its wideband characteristics and ability to capture more damage signals. Moreover, the effectiveness of the circular DE-IDT array for damage detection and imaging in curved panel structures and composite material plates is successfully verified. [ABSTRACT FROM AUTHOR]

This paper presents a damage sparse imaging method using multipath-scattered Lamb waves. It leverages a large number of echoes and reverberations in the recorded signal that may be usually ignored in conventional methods. First, reflections of Lamb waves at free edges are viewed as waves transmitted from a virtual transducer which is located at the mirror point of the actual one. On this basis, an optimized transducers-layout strategy is proposed based on the multipath propagation model of the Lamb wave. Benefiting from that, the direct damage-scattered wave and several waves scattered by both the damage and edges could be separately identified in the time domain, and further, each wave could be matched with a sensing path (either actual or virtual) in the expanded sensor network. Subsequently, a dictionary is constructed from the Lamb wave propagation and scattering model. By solving the sparse reconstruction problem, the pixel value of each point in the region of interest is obtained, and the whole area can be finally visualized. The proposed method is validated using experiments conducted on an aluminum plate with simulated damages. Results show that the damages can be correctly detected and accurately localized with only a single transmitter–receiver pair. [ABSTRACT FROM AUTHOR]

Topological data analysis (TDA) is a powerful and promising tool for data analysis, but yet not exploited enough. It is a multidimensional method which can extract the topological features contained in a given dataset. An original TDA-based method allowing to monitor the health of structures when equipped with piezoelectric transducers (PZTs) is introduced here. Using a Lamb wave based Structural Health Monitoring (SHM) approach, it is shown that with specific pre-processing of the measured time-series data, the TDA (persistent homology) for damage detection and classification can be greatly improved. The TDA tool is first applied directly in a traditional manner in order to use homology classes to assess damage. After that, another method based on slicing the temporal data is developed to improve the persistence homology perception and to leverage topological descriptors to discriminate different damages. The dataset used to apply both methods comes from experimental campaigns performed on aeronautical composite plates with embedded PZTs where different damage types have been investigated such as delamination, impacts and stiffness reduction. The proposed approach enables to consider a priori physical information and provides a better way to classify damages than the traditional TDA approach. In summary, this article demonstrates that manipulating the topological the features of PZTs time-series signals using TDA provides an efficient mean to separate and classify the damage natures and opens the way for further developments on the use of TDA in SHM. [ABSTRACT FROM AUTHOR]

Nonlocal and quantum mechanical phenomena in noble metal nanostructures become increasingly crucial when the relevant length scales in hybrid nanostructures reach the few-nanometer regime. In practice, such mesoscopic effects at metal–dielectric interfaces can be described using exemplary surface-response functions (SRFs) embodied by the Feibelman d-parameters. Here we show that SRFs dramatically influence quantum electrodynamic phenomena – such as the Purcell enhancement and Lamb shift – for quantum light emitters close to a diverse range of noble metal nanostructures interfacing different homogeneous media. Dielectric environments with higher permittivities are shown to increase the magnitude of SRFs calculated within the specular-reflection model. In parallel, the role of SRFs is enhanced in noble metal nanostructures characterized by large surface-to-volume ratios, such as thin planar metallic films or shells of core–shell nanoparticles, for which the spill-in of electron wave functions enhances plasmon hybridization. By investigating emitter quantum dynamics close to such plasmonic architectures, we show that decreasing the width of the metal region, or increasing the permittivity of the interfacing dielectric, leads to a significant change in the Purcell enhancement, Lamb shift, and visible far-field spontaneous emission spectrum, as an immediate consequence of SRFs. We anticipate that fitting the theoretically modelled spectra to experiments could allow for experimental determination of the d-parameters. [ABSTRACT FROM AUTHOR]

On 15 January 2022, the largest eruption of the Hunga‐Tonga volcano in recorded history produced a plume registered by multi‐parametric instruments around the world. However, the far‐field hydrogeological responses to Lamb waves from this eruption remain underexplored. We studied the responses of groundwater to the volcanic eruption in the far‐field over 8,700 km, including 274 wells. Results show that the Lamb waves with a speed of 316 m/s affects the groundwater system, leading to similar fluctuations in well water level (WL) and opposite phase fluctuation in borehole strain. Different wells exhibit diverse responses in WL amplitudes, possibly for heterogeneities in local aquifer systems. Gain values of 5 wells that simultaneously measure atmospheric pressure, borehole air pressure, borehole strain and WL are consistent with results obtained through cross‐power spectrum estimation. This work demonstrates a novel response in far‐field groundwater systems induced by Lamb waves and expects application for aquifer parameter estimation. Plain Language Summary: The massive eruption of the Hunga‐Tonga volcano on 15 January 2022 generated shock waves in the Earth's atmospheric layer, known as Lamb waves, which propagated at the boundary of air and the solid Earth. While many studies reported multi‐parameter responses during or after the eruption, the response of the groundwater system has not been studied. In this study, we found that Lamb waves from the volcano eruption induced similar phase responses in the water levels of 256 wells within the 274‐well network and opposite phase responses in borehole strain in mainland China. Additionally, the Lamb wave induced a possible time lag in the response of well water level (WL) and horizontal strain, which may be caused by different hydraulic properties of the wells. In the five wells with common observations, the calculated atmosphere pressure sensitivity is consistent with previous studies. The response of well WL to the Lamb wave is obviously different compared to that observed during co‐seismic events and Earth tides. Key Points: The Lamb wave from the Hunga‐Tonga volcano eruption induces similar phase responses in the water level (WL) of 256 wells in the far fieldResponses of well WL and borehole strain to the Lamb wave show a possible time‐delay relative to that of atmosphere pressureThe incorporation of the WL parameter and horizontal transverse strain is recommended to calibrate the appropriate models [ABSTRACT FROM AUTHOR]

AbstractProcess-induced initial gradient stress is inevitable during the fabrication of fiber reinforced polymer (FRP) composites. In this research, governing wave equations with variable coefficients are established for FRP plates under initial gradient stress, based on the acoustoelastic theories. The Legendre polynomial (LP) method is utilized to derive the solving algorithm. The dispersion curves are obtained without layer slicing, which provides a more realistic analysis model for gradient stress. The accuracy and convergence of the proposed method are discussed through numerical examples. The influences of initial gradient stress on dispersion slowness curves of Lamb and SH waves are analyzed, considering the parabolic initial gradient stress distribution, in which it’s common in the manufacturing process of FRP composites. The effect of initial gradient stress distribution on the phase velocity is investigated in detail. The influence of the anisotropic effect of FRP on guided wave propagation under initial gradient stress is discussed. The numerical analysis shows that the behavior of guided waves is influenced not only by the initial gradient stress but also dominated by propagation direction in anisotropic FRP composite plates. These results can provide a useful reference for the testing based on guided waves for FRP composite, especially when the initial gradient stress is encountered. [ABSTRACT FROM AUTHOR]

Three-dimensional magneto-optical traps (3D-MOTs) are an integral component of atomic clocks, quantum computers, and other cold-atom science applications. Due to the dependence on bulk optics and lasers, conventional 3D-MOTs occupy a large volume, limiting their portability. Efforts to build 3D-MOTs using integrated photonics promise to reduce the size and weight of these systems allowing applications beyond the lab. However, the need for counterpropagating beams to facilitate 4- and 6-beam geometries necessitates free-space mirrors and quarter wave plates (QWPs) that limit integration. Replacing these mirrors and QWPs with planar retroreflecting metasurfaces provides a route to achieving a complete 3D-MOT within an integrated package. Here, we report on the design and demonstration of a retroreflecting metasurface for 3D-MOTs that operates at large angles and preserves circular polarization. Specifically, we utilize Bayesian optimization to design an amorphous silicon (a-Si) on gold metasurface for high efficiency polarization-insensitive retroreflection of 780 nm circularly polarized light at 54.7°. Numerical simulations demonstrate maintenance of circular polarization after highly efficient retroreflection ( ϵ − 1 = 1.10 , R − 1 = 0.86). Experimentally, we demonstrate similarly excellent performance at 736 nm at 50.3 ° ( ϵ − 1 = 1.04 , R − 1 = 0.73) and show that deviation from the target design is due to oxidation of the a-Si metaelements. We conclude by discussing mitigation strategies for future devices and propose a corrective optic for the currently fabricated device. This work represents a step toward the miniaturization of 3D-MOTs and expansion of cold-atom science beyond the laboratory. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries are essential for the development of consumer electronics and electric vehicles due to their high energy density, low self-discharge rate, and easy maintenance. To optimize the performance of lithium-ion batteries and meet the battery requirements of devices, it is necessary to charge the batteries at a faster rate. Therefore, this paper proposes a five-stage constant current charging method based on Lamb wave depolarization to enhance the charging efficiency. Specifically, the orthogonal experimental method is first used to determine the near-optimal value of the charging current in each stage of the five-stage constant current charging process. Subsequently, Lamb waves are introduced during the charging process of each constant current charging stage. Compared with the traditional five-stage constant current charging method, the five-stage constant current charging method based on Lamb wave depolarization improves the charging efficiency. The charging efficiency of the five-stage constant current charging method based on Lamb wave depolarization with an excitation voltage peak-to-peak amplitude Vpp of 120 and an excitation duration of 6 min is 20% higher than that of the traditional five-stage constant current charging method. The weakening of the polarization effect is positively correlated with the Lamb wave excitation voltage. In addition, the five-stage constant current charging method based on Lamb wave depolarization is superior to the five-stage constant current shelving depolarization charging method and the five-stage constant current negative pulse depolarization charging method in improving the charging efficiency. [ABSTRACT FROM AUTHOR]

Early damage in metal materials is primarily characterized by microdefects, such as microcracks and micropores. In this study, we developed a novel approach for quantitatively assessing the microdefect damage degree in dual-phase bainite–ferrite (B + F) X80 pipeline steel using ultrasound nonlinear parameters. A finite element analysis model with micron-scale three-dimensional ellipsoidal defects was established based on the Gurson–Tvergaard–Needleman material damage theory. The propagation process of Lamb waves in the model was simulated to investigate the interaction mechanism between microdefects and Lamb waves and explore the quantitative relationship between ultrasound nonlinearity and microdefect damage degree, which can be characterized by the size and number of microdefects. Furthermore, to validate the simulation findings, an ultrasound testing experiment was designed to evaluate the microdefect damage in (B + F) X80 pipeline steel. The results demonstrate that when Lamb waves propagate through microdefects, their amplitude is attenuated, resulting in changes in ultrasound nonlinear parameters. Within a specific range, the nonlinear coefficient of Lamb waves increases with an increase in microdefect length and number of microdefects but decreases with an increase in microdefect width. This finding holds significant value for evaluating damage degree and predicting the service life of X80 pipeline steel. [ABSTRACT FROM AUTHOR]

We introduce a Lamb-wave medium with tunable propagation velocities, which are controlled by a two-dimensional heating pattern produced by a laser beam. We utilized it to demonstrate that waves in an appropriately designed medium can propagate in the form of concentric squares, in contrast to the circular patterns typically emitted by a point source in a homogeneous two-dimensional medium. In order to avoid the concentration of wave energy in the middle of the sides of the squares, we propose two alternatives: a square wave that either rotates or exponentially decelerates as it expands. Additionally, we present how circular waves can be transformed into spiral waves utilizing the same tunable medium. The described experimental platform offers a new tool to generate shaped pulses for ultrasonic applications, which has the potential to improve the efficiency of energy and information transport. [ABSTRACT FROM AUTHOR]

In this paper, piezoceramic-based excitation of shear horizontal waves is investigated. A thickness-shear d15 piezoceramic transducer is modeled using the finite-element method. The major focus is on the directivity and excitability of the shear horizontal fundamental mode with respect to the maximization of excited shear and minimization of Lamb wave modes. The results show that the geometry of the transducer has more effect on the directivity than on the excitability of the analyzed actuator. Numerically simulated results are validated experimentally. The experimental results show that transducer bonding significantly affects the directivity and amplitude of the excited modes. In conclusion, when the selected actuator is used for shear excitation, the best solution is to tailor the transducer in such a way that at the resonant frequency the desired directivity is achieved. [ABSTRACT FROM AUTHOR]

This study focuses on investigating hard-magnetic soft materials, characterized by magnetoactive polymers containing magnetically polarized particles as fillers. The research utilizes the Gent model of hyperelasticity to analyze the propagation of Lamb waves in a magnetically induced deformed compressible plate. In this investigation, we explore both finite deformations and incremental wave propagation in nonlinear hard-magnetic soft materials. The main objective is to formulate the elastic tensor and relevant wave equations within the framework of Lagrangian space. To assess the dispersion characteristics of the guided wave, the study introduces and discusses an extension of the semi-analytical finite element (SAFE) method. Using this numerical approach, the research further examines the effects of magnetic flux densities and its orientation with respect to wave propagation direction on the dispersion characteristics of the fundamental Lamb modes. The study starts by examining the limiting case of the neo-Hookean material model to explain such inherent dependencies. These dependencies are then further emphasized by including the strain-stiffening effect that the Gent material model describes. The research findings reveal the presence of a threshold applied magnetic flux, beyond which the Gent-type material may undergo a snap-through instability, resulting in changes in the dispersion characteristics of the fundamental symmetric Lamb mode. [ABSTRACT FROM AUTHOR]

This article proposes a framework for the damage assessment of and effect of temperature variations in laminated composites using Lamb waves and unsupervised autonomous features. A network of piezoelectric transducers is employed to generate data for 18 health states of a laminated composite plate. The data is processed with sparse autoencoder (SAE) for unsupervised autonomous features. The discriminative capabilities of the extracted features are confirmed by processing the feature space in the supervised and unsupervised frameworks of machine learning. The confusion matrices of supervised learning provided physical insights into the problem. The feature space was also visualized in two dimensions in an unsupervised manner through principal component analysis (PCA), which revealed physically consistent results for the effect of temperature variations, damage of different severity levels, and the undamaged paths between the actuator and sensors. The healthy state data and information on the paths between the actuator and sensors was processed via SAE for damage localization. The proposed approach can be employed for the autonomous assessment of composite structures for the presence of damage and variations of operating temperatures while using both supervised and unsupervised machine learning algorithms. [ABSTRACT FROM AUTHOR]