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Acoustic black hole (ABH) structures are widely used for vibration and acoustic waves control due to their ability to guide the zero reflection of elastic waves and the concentration of wave energy. However, ABH can hardly suppress the ultra-low-frequency waves. We propose the acoustic cloister to break the low-frequency limit of the cutoff frequency and realize the perfect ABH effect while suppressing the ultra-low frequency waves. Thus, the waves can be localized within this structure and realize the ultra-low frequency ultra-broadband bandgap. We theoretically elaborate the bandgap mechanism of the acoustic cloister and demonstrate the good robustness of the acoustic cloister, which is beneficial for generating stable ultra-low frequency nonlinear bandgaps. Nonlinear buckling theory has been applied to explain the ultra-low frequency nonlinear bandgaps of 3–22 and 24–28 Hz that appear in the experiments, which reduces the wave transmission by 20–40 dB, and it has been demonstrated that the bending stresses appeared in the experiments can generate and greatly extend ultra-low frequency bandgaps. In torsional excitation experiments, the acoustic cloister structure attenuates wave transmission in the 3–100 Hz range by 10–80 dB. Our work makes a significant contribution to advances in vibration and acoustic wave control. [ABSTRACT FROM AUTHOR]

Based on the quantum valley Hall effect analogy, this work proposes a phononic crystal plate with ligament-type beams to obtain the topological valley transmission of elastic waves. A pure Bragg degenerate state appears in the high-frequency region with a resonator introduced. By rotating the central scatterer and the beams, the mirror symmetry is broken to form a topological bandgap. Subsequently, this work finds that two selective edge states also appear beside the commonly non-trivial crossing edge states in the topological bandgap by calculating the projected band and eigenvalue spectrum of the supercell with different valley Hall phases phononic crystals. Their appearance is due to band separation of the topological edge states caused by an increase in the rotation angle. Both selective edge states can transmit topologically in specific paths. They will help further to broaden the width of the frequency band of topological transmission. Besides, an elastic wave splitter is designed and demonstrated numerically, which can form two channels and three channels in different frequency bands. With the topological selective edge state disappearing, a topological corner state exists in the edge bandgap. This work provides a theoretical reference for practical applications of broadband elastic wave topological transmission and elastic energy trapping. [ABSTRACT FROM AUTHOR]

Recently, the mode conversion of elastic waves has attracted much attention, due to its scientific significance and potential applications. The applications based on the high mode conversion efficiency were also explored in many fields. However, because of the complexity of elastic waves, the existing structures for the high efficient conversion of elastic waves are relatively complicated, and there are also some limitations in the practical design. Here, we report the extraordinary mode conversion of elastic waves through asymmetric brass plates partitioned by subwavelength cuts. It is demonstrated that high efficiencies (90%) and one-way conversions between transversal waves and longitudinal waves are achieved by the structured solid plate at the resonant frequency, which leads to the striking unidirectional transmission of elastic waves. Analyzing the resonant fields demonstrates that the intrinsic modes within the individual pieces derived by the cuts are responsible for this abnormal wave conversion. The simple scheme for wave conversion presented here may have potential applications, such as non-invasive flow sensing. [ABSTRACT FROM AUTHOR]

This study illustrates the successful achievement of tunable defect bands in one-dimensional defective phononic crystals (PnCs) through the incorporation of piezoelectric defects with synthetic negative capacitances (SNCs) for the first time. The efficacy of SNCs in creating tunable bandpass filters across a broad frequency range is thoroughly examined using the proposed analytical and numerical models. A newly developed electroelastically coupled transfer matrix that incorporates SNCs is presented, considering either series or parallel connection between bimorph piezoelectric elements. Defect band and transmittance analyses are conducted using the transfer matrix and S-parameter methods. Two key findings emerge from this investigation. First, when the total equivalent capacitance of the bimorph piezoelectric elements and SNC becomes zero, the defect band representing the point-symmetric defect-mode shape can be customized throughout the entire phononic bandgap. Second, the constant transmittance value, resembling short-circuit conditions, highlights the remarkable ability of SNCs to tune defect bands without energy dissipation, paving the way for fully tunable bandpass filters. To propel this research forward, future investigations could explore expanding the design space with double defects, adopting enhanced modeling techniques to account for lateral and shear effects, developing a control algorithm for the automatic optimization of SNC values in actively tunable bandpass filters, and incorporating artificial intelligence into design methods for piezoelectric defects with electrical connections. [ABSTRACT FROM AUTHOR]

This paper presents the design of a single-phase solid phononic crystal (PnC) structure featuring a regular hexagonal perforation pattern. The structure manifests three negative refraction bands, encompassing one for transverse waves and two for longitudinal waves, thereby enabling simultaneous control of shear and longitudinal waves. Due to the high symmetry of the triangular lattice, the equal frequency curves corresponding to the negative refraction band approach circular shapes, suggesting a nearly isotropic negative refraction effect. This negative refraction effect is achieved through specific mass resonance modes closely related to the porous structure designed in this paper. Initially, we analyze the band structure of the PnC, followed by designing the PnC plate structure to achieve negative refraction control for transverse waves at a frequency of 32.4 kHz, with a negative refraction index of −1. Additionally, negative refraction control for longitudinal waves is attained at frequencies of 44 and 64.54 kHz. Subsequently, we scrutinize the influence of various conditions on negative refraction, including different structural parameters, incident angles, and operating frequencies, while verifying the robustness of the designed phonon crystal structure. Leveraging the negative refraction characteristics of the structure, we construct an elastic wave lens to achieve perfect imaging of shear and longitudinal waves. Finally, employing finite element simulation and analyzing focusing imaging characteristics with different source positions, we validate that the results closely align with theoretical expectations. The solid PnC structure designed in this study holds significant potential for applications in the fields of elastic wave imaging. [ABSTRACT FROM AUTHOR]

The time-modulated active medium with linear independent frequency conversion method has been demonstrated to enable wave orientation and reconstruction. However, due to the symmetric scattering field, this technique requires intricate microcircuit designs. To overcome this limitation, this paper proposes a tunable piezoelectric metasurface based on acoustic black holes (ABHs) to redirect flexural wave reflections. The system can convert an incident flexural wave into a reflected wave of any direction and frequency. This is accomplished through the linear time modulation of the sensing signal, which breaks the constraints of Snell's law inherent in traditional designs and is insensitive to the incident amplitude. The coupling of the ABH damping system with a linear independent frequency conversion mechanism allows for the conversion of an incident flexural wave into a reflected wave in any direction and frequency while also eliminating the influence of second harmonic reflection on the wave field and simplifying the time modulation circuit. In addition, this paper demonstrates arbitrary angle reflection, focusing, beam splitting, and frequency conversion of the incident wave. By improving the flexibility of elastic wave manipulation, this paper introduces a new approach for active control of elastic waves and provides a design method that can be employed in a variety of applications ranging from vibration protection of engineering structures to vibration sensing and evaluation. [ABSTRACT FROM AUTHOR]

Elastic metamaterials with double negativity can manipulate the propagation of elastic waves at sub-wavelength scales by inducing multiple resonances to achieve different negative effective parameters. Numerous efforts have been made to control the dynamic behavior by directly tuning the frequency range of double negativity in elastic metamaterials. This study examines the impact of tensile loads on double negativity in relation to ligament inclination angle. The findings will aid in the direct tunability of double negativity in single-phase chiral metamaterials. The study examines a simple single-phase four-ligament chiral unit with low-order double negativity. The presence of double negativity was verified through band structure analysis and calculation of the four effective dynamic parameters. Additionally, the effects of two geometrical factors on the frequency ranges of negative parameters were investigated through parametric scanning. The results indicate that the frequency range of double negativity reaches its maximum at a ligament inclination angle of around 45° and disappears as the angle approaches 65°. Given that the ligament inclination angle of the unit cells can be easily altered by external tension, this intriguing outcome is leveraged to achieve the emergence and vanishing of double negativity. This characteristic is confirmed through the examination of negative refraction phenomena via simulation examples. [ABSTRACT FROM AUTHOR]

Mode coupling and conversion between longitudinal and transverse modes are ubiquitous and universal in elastic waves, presenting a challenge in realistic applications such as nondestructive evaluation and geological exploration, where independent and separate manipulation of each mode is demanded. In this article, we propose a design of elastic metalens that can realize a high-efficiency focusing for the longitudinal wave and a V-shaped converging pattern for the transverse wave at the same time. The metalens is constructed from a metagrating, where each meta-atom has a simple configuration and renders high diffraction efficiency even for large steering angles, enabled by concurrent utilization of grating diffraction theory and advanced optimization algorithms. Interestingly, an arbitrary energy splitting ratio between the reflected longitudinal and transverse waves can be obtained by precisely controlling the coupling strength and conversion efficiency between them, providing improved flexibility and adaptability to various application environments. Two illustrative examples with a sharp focusing effect and tailored conversion efficiency are explicitly demonstrated, with a 50/50 energy splitting ratio between the longitudinal and transverse waves in the first case, and a 70/30 ratio in the second one. [ABSTRACT FROM AUTHOR]

We report an experimental study of surface acoustic wave (SAW) localization and propagation in random metasurfaces composed of Al scatters using pump–probe spectroscopy. Thanks to this technique, wideband high frequency acoustic modes are generated, and their dynamical propagation directly from inside of the media with a high (micrometric) spatial resolution is enabled. During SAW propagation, part of the acoustic wavefront energy is trapped within free areas between the scatterers, acting as cavities. The spectral content of the localized modes of a few GHz is found to depend on the shape and size of the cavities but also on the landscape seen by the wave during its propagation before arriving inside them. The experimental results are supported by numerical simulations using the finite element method. This study is the phononic part of a more global research on the co-localization of elastic and optical waves on random metasurfaces, with the main objective of enhancing the photon–phonon interaction. Applications could range from the design of acousto-optic modulators to ultrasensitive sensors. [ABSTRACT FROM AUTHOR]

We present a framework for the inverse design of spatially graded phononic materials based on ray tracing. Spatial grading of phononic materials allows the unit cell to vary smoothly in space. Compared to periodic architectures, spatial grading opens up a vast design space that promises new capabilities for manipulating elastic and acoustic waves. However, the use of spatial grading to control wave propagation has been limited to simple gradings, largely due to the bottleneck of modeling efficiency, and to the long-wavelength limit of low frequencies. In this work, ray tracing is exploited as an efficient alternative, around which we develop an optimization framework based on the adjoint state method toward the flexible inverse design of graded phononic materials. We demonstrate the design of graded mass-spring networks for objectives including focusing all directions of a point source, broadband focusing of a plane wave, and frequency sorting. These objectives are out of reach of periodic phononic materials, highlighting the high potential of spatially graded phononic materials. Moreover, our results demonstrate the importance of wave dispersion, which is classically neglected in the long-wavelength limit of elastodynamics. [ABSTRACT FROM AUTHOR]

The introduction of metamaterials has provided new possibilities to manipulate the propagation of waves in different fields of physics, ranging from electromagnetism to acoustics. However, despite the variety of configurations proposed so far, most solutions lack dynamic tunability, i.e. their functionality cannot be altered post-fabrication. Our work overcomes this limitation by employing a photo-responsive polymer to fabricate a simple metamaterial structure and enable tuning of its elastic properties using visible light. The structure of the metamaterial consists of graded resonators in the form of an array of pillars, each giving rise to different resonances and transmission band gaps. Selective laser illumination can then tune the resonances and their frequencies individually or collectively, thus yielding many degrees of freedom in the tunability of the filtered or transmitted wave frequencies, similar to playing a keyboard, where illuminating each pillar corresponds to playing a different note. This concept can be used to realize low-power active devices for elastic wave control, including beam splitters, switches and filters. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'. [ABSTRACT FROM AUTHOR]

This paper presents a study of wave propagation through an infinite periodic structure that consists of elastic Timoshenko beams interconnected with rigid bodies. This is a generalized approach in which the beams are not coaxial and the centre of mass of each rigid body is placed away from the intersection of their neutral axes. An analytical approach is used by applying the transfer matrix method (TMM), along with the Floquet–Bloch theorem for elastic wave propagation. Subsequent parametric analysis is performed with visualization of resulting band diagrams of a representative structure. These results are verified through comparison with solutions obtained using the finite-element method (FEM). In this manner, a comprehensive dynamical analysis of tailored metastructures is provided. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'. [ABSTRACT FROM AUTHOR]

The geometric phase provides important mathematical insights to understand the fundamental nature and evolution of the dynamic response in a wide spectrum of systems ranging from quantum to classical mechanics. While the concept of geometric phase, which is an additional phase factor occurring in dynamical systems, holds the same meaning across different fields of application, its use and interpretation can acquire important nuances specific to the system of interest. In recent years, the development of quantum topological materials and its extension to classical mechanical systems have renewed the interest in the concept of geometric phase. This review revisits the concept of geometric phase and discusses, by means of either established or original results, its critical role in the design and dynamic behaviour of elastic waveguides. Concepts of differential geometry and topology are put forward to provide a theoretical understanding of the geometric phase and its connection to the physical properties of the system. Then, the concept of geometric phase is applied to different types of elastic waveguides to explain how either topologically trivial or non-trivial behaviour can emerge based on the geometric features of the waveguide. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'. [ABSTRACT FROM AUTHOR]

Periodic wave barriers have been widely used to manipulate elastic waves propagating in saturated and single-phase soil due to their attenuation zone properties. However, it is difficult to promote application of periodic barriers in unsaturated soils due to their complex constitutive relationship. In this study, manipulation of surface waves by periodic in-filled trench barriers in unsaturated soil has been studied based on the periodic theory. The dispersion relations of a periodic structure for surface waves in unsaturated soil are determined. The attenuation mechanism of evanescent surface waves is revealed. Next, the effects of several key parameters of unsaturated soil on the attenuation zones of the periodic in-filled trench barriers are comprehensively discussed. It is found that in a particular range for material parameter, the surface waves are attenuated over the entire frequency range due to the viscosity of fluid. Finally, a periodic in-filled trench barrier is designed according to a field test of ground vibration induced by a train, and its performances in mitigating surface waves propagating in unsaturated and saturated soils are conducted and compared by conducting analysis in time domain. This investigation provides a new insight for manipulating surface waves by periodic barriers. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'. [ABSTRACT FROM AUTHOR]

In this work, the Schwarz primitive unit cell is used as the building block of different types of metastructures for steering and focusing elastic vibrations. The emergence of a Bragg-type bandgap when constructing a two-dimensional plate from such unit cells is experimentally validated. It is demonstrated that increasing both mass and porosity of the Schwarz primitive leads to a decrease in the frequency of the out-of-plane propagating wave targeted in this study. By arranging these modified Schwarz primitive unit cells in constant and graded layouts, two-dimensional plates with an embedded metabarrier and a metalens are numerically designed. The metabarrier protects an interior area of the plate from the propagating waves on a wide frequency band (approx. 1.4–3.4 kHz). Equally, the refractive index profile necessary for gradient index lenses is obtained via a progressive variation of the added mass or, alternatively, the porosity of the unit cell over a rectangular area. For the first time, bending of the out-of-plane mode towards the focusing point is practically validated in a challenging mesoscale experiment requiring the assembly of different three-dimensional printed sections of the plate. The increased porosity design is advantageous not only in terms of overall lightweight, but also towards additive manufacturing as it requires less material. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'. [ABSTRACT FROM AUTHOR]

Peridynamics describes the material in a non-local form and is very suited for the simulation of dynamic fracture. However, one significant effect regarding dynamic fracture is the correct handling of elastic deformation, like the pressure and tension waves inside a body, due to dynamic boundary conditions like an impact or impulse. Many peridynamic material formulations have been developed with differences in this regard. This study investigates the elastic wave propagation characteristics of bond-based, ordinary state-based, continuum kinematics-inspired peridynamics and a local continuum consistent correspondence formulation. Multiple parameters of a longitudinal pressure wave inside an elastic bar are studied. While all formulations demonstrate adequate wave propagation handling, all except the correspondence formulation are sensitive to incomplete horizons. The local continuum consistent formulation does not suffer from the surface effect and models the wave propagation with perfect accuracy. [ABSTRACT FROM AUTHOR]

This paper presents a novel locally resonant metamaterial structure and proposes a method to analyze its elastic wave dispersion properties. The structure is conceived as a multiple beam system with parallel beams transversely interconnected by periodic arrays of small resonators, each consisting of a spring-mass-spring subsystem in parallel with a couple of springs. Inserting the resonators between the beams, instead of attaching them as external appendages like in some alternative examples of locally resonant beams in the literature, makes the structure appealing for practical realization and use; furthermore, hosting several arrays of resonators gives the possibility to open multiple band gaps. The proposed method is a homogenization approach for flexural wave dispersion analysis, which removes the equations for the resonators from the set governing the dynamics of the system and reverts the original structure to an equivalent one featuring a tri-diagonal effective mass matrix with frequency dependent terms. The advantage of the homogenization approach is twofold: (1) it demonstrates that the band gaps arise in the frequency ranges where the effective mass matrix is negative definite, generalizing the well-established concept of band gaps attributable to negative mass effects in single locally resonant beams; (2) it provides dispersion curves and band gaps very efficiently, and the band gaps are identified upon calculating the eigenvalues of the tri-diagonal effective mass matrix. Analytical expressions of the band gap edges are obtained for the baseline case of a double beam system, to be readily used for design. Additionally, the exact transfer matrix method in conjunction with the Bloch theorem is formulated as alternative to the homogenization approach for wave dispersion analysis. Finally, the proposed concept of locally resonant structure and pertinent homogenization approach are validated by calculating the transmittance properties of the corresponding finite structure, via the standard finite element method. [ABSTRACT FROM AUTHOR]

Multicomponent seismic technology utilizes the kinematic and dynamic characteristics of reflected P‐waves and converted S‐waves to reduce ambiguity in seismic exploration. The imaging and inversion accuracy of P‐SV‐converted waves are important in determining whether multicomponent seismic exploration can achieve higher exploration accuracy than conventional P‐wave exploration. Pre‐stack inversion of P‐SV‐converted waves requires precise input of P‐SV‐converted wave angle‐domain common‐image gathers. Consequently, the P‐SV‐converted wave angle‐domain common‐image gather extraction accuracy will significantly affect the P‐SV‐converted wave inversion accuracy. However, existing methods for extracting P‐SV‐converted wave angle‐domain common‐image gathers are constrained by issues such as the P‐ and S‐wave crosstalk artefacts, low‐frequency noises and inaccurate calculation of P‐wave incident angles, leading to poor imaging accuracy. We study an angle‐domain cross‐correlation imaging condition and address three key issues based on this condition: the decoupling of P‐ and S‐waves, the separation of up‐going and down‐going waves and the precise calculation of P‐wave incident angles. Our strategies facilitate high‐precision extraction of P‐SV‐converted wave angle‐domain common‐image gathers using elastic wave reverse‐time migration. In this paper, first, we employ the first‐order velocity‐dilatation‐rotation elastic wave equations to decouple P‐ and S‐waves automatically during source and receiver wavefield extrapolations. Second, we calculate the optical flow vectors of P‐ and S‐waves to ensure stable calculations of wave propagation directions. Based on this, we obtain up‐going and down‐going waves of P‐ and S‐waves. Meanwhile, we calculate the incident angle of the source P‐wave using geometric relations. Lastly, we apply the angle‐domain imaging condition to achieve high‐precision extraction of P‐SV‐converted wave angle‐domain common‐image gathers. Model examples demonstrate the effectiveness and advantages of the proposed method. [ABSTRACT FROM AUTHOR]

As an essential component of urban infrastructure construction, polyethylene (PE) pipelines face the challenging task of underground detection due to the complex and dynamic nature of the subsurface environment, diverse installation paths, and the inherent insulating properties of PE materials. In order to address the non-excavation detection of buried PE pipelines, this paper proposes an acoustic method based on the long short-term memory (LSTM) neural network. The study begins by analyzing the propagation and reflection mechanisms of elastic waves in the pipe-soil coupling system, and a impact excitation source is designed to generate the excitation signal. After establishing the experimental environment and collecting experimental data, a comprehensive analysis is conducted, and the LSTM neural network is employed for data classification to determine the presence of buried PE pipelines. Through neural network training, accurate identification of the PE pipeline's existence and prediction of its burial depth are achieved, providing an efficient and reliable solution for buried PE pipeline detection. The practical results demonstrate the significant application prospects of the combined acoustic method and LSTM neural network in buried PE pipeline detection. This research contributes a novel solution to the field of non-destructive PE pipeline detection, with both theoretical and practical implications. [ABSTRACT FROM AUTHOR]

Hydrogen has become a popular alternative energy to traditional fossil fuels due to its potential to contribute to a more sustainable future. It is recognized that the safety, efficiency, and economic aspects of hydrogen storage and transportation play an important role in the hydrogen energy industry. The development and commercialization of hydrogen energy are currently hindered by the structural integrity issue associated with hydrogen storage tanks. To tackle this structural integrity issue, a tangible structural health monitoring (SHM) technology is entailed for the health management of hydrogen storage tanks. Currently, flexible transducers are increasingly used to construct sensing systems and facilitate the deployment of SHM methods due to their superior properties such as conformality, low profile, and lightweight. This paper provides an overview of the SHM methods based on flexible sensing technology for hydrogen storage tanks. The most common damage modes caused by diverse factors during the service life for four types of hydrogen storage tanks are first summarized. The burgeoning flexible sensing technologies with corresponding damage characterization methods (including strain-based and elastic wave-based methods) are reviewed, and their applications in storage tanks are also discussed. On this basis, potential advancements and research topics regarding SHM systems based on flexible sensing technology for hydrogen storage tanks are discussed, and it is expected that flexible sensing technology will play a game-changing role in the future construction of SHM systems for hydrogen storage tanks. [Display omitted] • Flexible sensors are suitable for the SHM application of hydrogen storage tanks. • The sensor array and composite sensor-structure approaches are introduced. • Flexible piezoelectric transducers can provide guided waves with mode tuning. • Applying ultrasonic guided wave method to composite pressure vessels is limited. [ABSTRACT FROM AUTHOR]

The entry and propagation of pores inside an adhesive interface between an elastomer and a rigid sphere were studied experimentally and simulated numerically. It was shown that mutually interacting events involving attachment-detachment of different segments of the elastomer to the indenter resulted in non-trivial patterns of spatially distributed contacts between them, which were additionally influenced by air penetration of the pores. [ABSTRACT FROM AUTHOR]

The interior inverse elastic scattering problem is considered in this paper. The scattering in the cavity is illuminated by an time-harmonic elastic point source at fixed frequency. The boundary of the cavity is assumed to be a small and smooth perturbation of some circle. In this paper, we are interested in the reconstruction of the boundary according to the measured data on a closed curve inside the cavity. In implementation, we split the displacement field into compressional and shear waves by the Helmholtz decomposition. Then we use coordinate transformation, power series expansion based on perturbed parameters and Fourier expansion of corresponding power series coefficients to simplify the original boundary value problem to a successive sequence of one-dimensional boundary value problem. We linearize the inverse problem by eliminating the higher-order terms in the power series expansion; and design a reconstruction algorithm by the explicit relationship between the Fourier coefficients of the boundary function and the total field. In order to obtain better resolution, we also use a nonlinear correction method in the numerical experiments. The numerical results have shown the effectiveness and the stableness of the proposed method. [ABSTRACT FROM AUTHOR]

Defect state of phononic crystals (PCs) has attracted fast-growing attention due to wave energy localization, which can serve as an effective means of controlling elastic waves. In this paper, we investigate the defect state of a one-dimensional (1D) broadband controllable pillared PC beam consisting of pillared permanent magnets on an aluminium beam through numerical simulations and experiments. First, the width and position of the band gap are altered by adjusting the height of the magnetic pillars’. Then, building on this foundation, we successfully observe the controllable defect states of longitudinal waves at the defects of pillared PC beams through a simple adjustment of the height of the defective magnetic pillars’. Finally, we conduct an experimental validation to confirm the feasibility of the localization behavior of elastic waves in the pillared PC system. This research offers a straightforward method to dynamically control the defect state of PCs and enhance the applications for defected PCs, spanning novel filters, defect detectors, and broadband energy harvesting. [ABSTRACT FROM AUTHOR]

There has been a considerable number of studies on the reflection and transmission of plane waves in anisotropic elastic half-spaces. However, the obtained formulas of the reflection and transmission coefficients are implicit, and the numbers of reflected and transmitted waves are undetermined. In this paper, the reflection of qP waves from an orthotropic elastic layer overlying an orthotropic elastic half-space is considered. It has been proved that an incident qP wave always creates two reflected waves, one qP wave and one qSV wave, and the reflection angle of the reflected qP wave is equal to the incident angle. Based on this fact, formulas for the reflection coefficients have been derived by using the transfer matrix method along with the effective boundary condition technique. It should be noted that, different from the previously obtained implicit formulas, these formulas are totally explicit functions of the incident angle, the (dimensionless) layer thickness and the material parameters of the half-space and the layer. Since the obtained formulas are totally explicit, they will be useful in various practical applications, especially in nondestructively evaluating the mechanical properties of deposited layers. [ABSTRACT FROM AUTHOR]

It is clear that there is a relationship between time and space in nanostructures that are always attacked by waves with wavelengths within the intrinsic characteristic length of the nanostructure. Also, the viscoelastic behavior of nanostructures is affected by this relationship between nonlocal time and nonlocal space. It is worth noting that the conventional tempo-spatially decoupled nonlocal viscoelasticity does not give accurate results regarding the viscoelastic response of these structures. Hence, herein and for the first time, a novel fractional nonlocal time–space strain gradient viscoelasticity is implemented to be able to give a correct answer in addressing the dispersion of elastic waves inside functionally graded material (FGM) viscoelastic nanoplates. The constructive equations of this theory are based on the theory of nonlocal strain gradient elasticity. The properties of the FGM studied in this research are obtained by the power-law model, and the kinematic relations are extracted based on the refined higher-order plate theory. Subsequently, motion equations are written using Hamilton's principle and solved analytically. The results of this work reveal that an increase in the nonlocal parameter can reduce the loss factor in a remarkable way due to the coupling between the nonlocalities in the spatial and temporal domains. [ABSTRACT FROM AUTHOR]

In this work, the effects of interaction between elastic and plasma-thermal waves are studied in the framework of the hyperbolic two-temperature theory. The basic equations are formed during the photo-excitation processes in the context of the photothermal theory. A laser pulse illuminates the outer surface of a semiconductor medium whose thermal conductivity is variable. Three different models of the generalized photo-thermoelasticity theory are applied to a 2D deformation problem. The integral transforms technique are used to solve the problem by applying the double transforms Fourier and Laplace. The inversion of Fourier and Laplace transforms is obtained according to Honig and Hirdes technique. The thermal, mechanical and recombination plasma loads are utilized at the medium-free surface to attain the complete solutions of the main physical fields. A comparison between the three different models of thermoelasticity is performed; in addition, the influence of some physical parameters are studied. Si material has been utilized as an example to ensure the validity of the attained solution. [ABSTRACT FROM AUTHOR]

The dispersion of elastic shear waves in multilayered bodies is a topic of extensive research due to its significance in contemporary science and engineering. Anti-plane shear motion, a two-dimensional mathematical model in solid mechanics, effectively captures shear wave propagation in elastic bodies with relative mathematical simplicity. This study models the vibration of elastic waves in a multilayered inhomogeneous circular membrane using the Helmholtz equation with fractional-order infusion, effectively leveraging the anti-plane shear motion equation to avoid the computational complexity of universal plane motion equations. The method of the separation of variables and the conformable Bessel equation are utilized for the analytical examination of the model's resulting vibrational displacements, as well as the dispersion relation. Additionally, the influence of various wave phenomena, including the dependencies of the wavenumber on the frequency and the phase speed on the wavenumber, respectively, with the variational effect of the fractional order on wave dispersion is considered. Numerical simulations of prototypical cases validate the formulated model, illustrating its applicability and effectiveness. The study reveals that fractional-order infusion significantly impacts the dispersion of elastic waves in both single- and multilayer membranes. The effects vary depending on the membrane's structure and the wave propagation regime (long-wave vs. short-wave). These findings underscore the potential of fractional-order parameters in tailoring wave behavior for diverse scientific and engineering applications. [ABSTRACT FROM AUTHOR]

The features of the occurrence and propagation of transverse deformation waves in the elastic lithosphere–viscous asthenosphere system under nonisothermal conditions are studied in the approximation of a thin layer. In this case, the phase transition at the boundary of the layers plays an essential role due to temperature and pressure disturbances. The qualitative and quantitative properties of the propagation of disturbances of thermomechanical fields have been studied in the long-wave approximation. It is shown that, due to the energy supply from the nonisothermal asthenosphere, weakly attenuated wave packets can occur, which spread over thousands of kilometers with a characteristic speed of about 100 km/year. This makes it possible to consider them as a possible trigger mechanism for the massive emission of methane from frozen sedimentary rocks into the atmosphere. [ABSTRACT FROM AUTHOR]

In aspects of its simple configuration and tunability, piezoelectric-based metasurface has benefited over its mechanical counterpart in adaptive wavefront manipulation. By tuning the circuitry elements in the shunting circuits properly, the equivalent material properties of the metasurface can be modified to attain a complete 2 π phase shift and to maintain high transmission at desired working frequencies. In this paper, a piezoelectric-based elastic metasurface with hybrid shunting circuits ( NC – LC – NC shunts) are proposed to adaptively control the propagation of flexural waves. Through tuning of negative capacitance and inductance simultaneously, the proposed elastic metasurface can cover a phase shift ranging from 0 − 2 π while having a high transmission ( ≥ 0.7). It is discovered that any similar metasurface structural design with solely single shunting circuit presently available could not achieve the same results as the proposed elastic metasurface. In addition, analytical modeling based on equivalent Young's modulus is developed and a finite element model is built to study the transmission and phase shift of the proposed metasurface. It is demonstrated numerically that the proposed piezoelectric-based elastic metasurface is capable of performing switchable functionalities, such as wave refraction and focusing, at different working frequencies (3500 Hz, 5000 Hz, etc.). Utilization of hybrid shunting circuits in designing a more compact metasurface design. Establish an analytical model based on equivalent Young's modulus to predict effective range of circuitry elements. Build a finite element model to study the transmission and phase shift of the piezoelectric-based metasurface. Cover a full 2 π phase shift and maintain high transmission through tuning negative capacitance and inductance simultaneously. Perform switchable functionalities at different working frequencies. [ABSTRACT FROM AUTHOR]

• A multifunctional mechanical model with both amplified illusion and cloaking properties is proposed. • The amplified function can make a small object to produce the same displacement distribution as a large object. • Intelligent control system with the detective and control functions is introduced. • Effectively broaden the effective frequency range of structure in 3300Hz×4400 Hz and 1200Hz×3100 Hz. • The cloaking characteristics of the structure are verified through theoretical, numerical and experimental analysis. Illusion device can make an object to produce a field distribution different from its own, offering potential applications in diverse fields. In this work, we propose a multifunctional metamaterial with intelligent control systems, which exhibits amplified illusion and cloaking characteristics for detecting or hiding objects over different frequency ranges. The amplification function allows a small object to generate the same displacement distribution as a larger object, while the cloaking function renders an object invisible and undetectable. Simulation and experimental results demonstrate the exceptional amplification and cloaking properties of the multifunctional configuration. In contrast to single-function structures like cloaking and focusing, which can only fulfill a specific function, designing a multifunctional structure capable of achieving two or more properties within a single configuration presents a significant challenge. [ABSTRACT FROM AUTHOR]

The elastic wave bandgap (BG) properties of locally resonant phononic crystal (LRPC) make it has great potential in the research and development of damping composite material and the application of vibration control engineering. However, the number of BG of the traditional LRPC is only one, the BG frequency range is too concentrated, and the multi-frequency BGs is not opened, so the application in practical engineering is limited. In response to the above issues, this paper designs a concentric ring cement-based locally resonant phononic crystal (CRCBLRPC) composite material, and studies and analyzes its BG characteristics. Firstly, the improved plane wave expansion method (IPWEM) and finite element method (FEM) are used to calculate the band structure of the CRCBLRPC. Secondly, the transfer function and BG mechanism of CRCBLRPC are calculated using FEM. Then, the factors affecting the BG of CRCBLRPC are analyzed. Finally, an equivalent model of spring-mass system is proposed to theoretically estimate the BG range of CRCBLRPC. The results show that the CRCBLRPC opens multi-frequency and low frequency BGs within the 200 Hz frequency band, and the number of BGs is more than that of the traditional LRPC. Within the BG frequency range, the CRCBLRPC has a good inhibition effect on vibration. Among them, the density of the scatterer and the elastic modulus of the coating layer are the main factors affecting the BG of the CRCBLRPC. The established spring-mass system equivalent model can accurately calculate the BG range of the CRCBLRPC. The research content and related conclusions of this paper provide new perspectives and insights for the study and design of LRPC composite materials with multi-frequency and low frequency BGs, and can also provide new ideas and methods for solving low frequency vibration in practical engineering. [ABSTRACT FROM AUTHOR]

Seismic surface waves carry significant energy that poses a major threat to structures and may trigger damage to buildings. To address this issue, the implementation of periodic barriers around structures has proven effective in attenuating seismic waves and minimizing structural dynamic response. This paper introduces a framework for seismic surface wave barriers designed to generate multiple ultra-low-frequency band gaps. The framework employs the finite-element method to compute the frequency band gap of the barrier, enabling a deeper understanding of the generation mechanism of the frequency band gap based on vibrational modes. Subsequently, the transmission rates of elastic waves through a ten-period barrier were evaluated through frequency–domain analysis. The attentional effects of the barriers were investigated by the time history analysis using site seismic waves. Moreover, the influence of the soil damping and material damping are separately discussed, further enhancing the assessment. The results demonstrate the present barrier can generate low-frequency band gaps and effectively attenuate seismic surface waves. These band gaps cover the primary frequencies of seismic surface waves, showing notable attenuation capabilities. In addition, the soil damping significantly contributes to the attenuation of seismic surface waves, resulting in an attenuation rate of 50%. There is promising potential for the application of this novel isolation technology in seismic engineering practice. [ABSTRACT FROM AUTHOR]

Rainbow trapping, observed in elastic waves, has attracted considerable scientific interest owing to its potential applications in energy harvesting, buffering, and wavelength-division multiplexing devices. However, previous approaches have often necessitated complex geometric modifications to the scatterer, such as altering dimensions or shifting along diagonals to corners, limiting practical utility. Here, we realize the coupled topological edge states (CTESs) of elastic waves in a two-dimensional (2D) solid phononic crystal (PC) with inversion center changes. Changing the inversion center along the x or y directions by a specific distance can induce the topological phase transition. The topological edge states (TESs) arise at the interface by combining PCs with different topologies positioned adjacent to each other. Furthermore, it is demonstrated that TES exhibits topological robustness against defects. By introducing a gradient into the PC structure by altering the geometrical parameters of scatterers along the interface, the topological rainbow trapping of elastic waves is achieved. Finally, the CTES are generated by the interaction between TESs of different interfaces, which can lead to coupled topological rainbow trapping in phononic heterostructures with different displacement parameters along the multiple interface gradient. Our results pave the way for manipulating the symmetric and antisymmetric topological modes of elastic waves in topologically coupled waveguides, which offers potential applications in selective filtering and multiband waveguiding. [ABSTRACT FROM AUTHOR]

Non-invasive assessment of the electrical activation pattern can significantly contribute to the diagnosis and treatment of cardiac arrhythmias, due to faster and safer diagnosis, improved surgical planning and easier follow-up. One promising path is to measure the mechanical contraction via echocardiography and utilize this as an indirect way of measuring the original activation pattern. To solve this demanding inversion task, we make use of physics-informed neural networks, an upcoming methodology to solve forward and inverse physical problems governed by partial differential equations. In this study, synthetic data sets were created, consisting of 2D excitation waves coupled to an isotropic and linearly deforming elastic medium. We show that for both focal and spiral patterns, the underlying excitation waves can be reconstructed accurately. We test the robustness of the method against Gaussian noise, reduced spatial resolution and projected tri-planar data. In situations where the data quality is heavily reduced, we show how to improve the reconstruction by additional regularization on the wave speed. Our findings suggest that physics-informed neural networks hold the potential to solve sparse and noisy bio-mechanical inversion problems and may offer a pathway to non-invasive assessment of certain cardiac arrhythmias. [ABSTRACT FROM AUTHOR]

The conventional theory of elastic-wave propagation is based on classical elastodynamics, assuming linear small deformations of particles. However, recent observations of seismic rotation have revealed significant disparities between actual rotational motions induced by earthquakes in focal areas and near fields compared to theoretical calculations and simulations. Considering the nonlinearity may be the main cause of the discrepancies and based on classical elastodynamic principle, we derive seismic elastic-wave equations with Green strain tensor without the linear small deformation assumption, a different way from using complex nonlinear constitutive relation and try to interpret the mechanism of seismic rotation. By simulating and analyzing translational and rotational components subjected to the three basic and typical vibrating sources, namely, isotropic (ISO), double couple (DC), and compensated linear vector dipole (CLVD), represented by moment tensors, we investigate the wavefield differences between elastic-wave equations based on linear and nonlinear geometric relations and quantify the differences in homogeneous elastic full-space model. Subsequently, we simulate two observed six-component Taiwan earthquakes and compare their differences caused by nonlinear simulations. The results indicate that linear approximation errors are more pronounced in seismic ISO and CLVD sources. And the nonlinearity of small deformation has a more pronounced effect on rotational motions deduced by strong earthquakes. Also, the nonlinear mechanics of seismic rotation can attribute to the complex propagation paths and source mechanisms simultaneously. [ABSTRACT FROM AUTHOR]

Metamaterials (MMs), which include phononic crystals (PCs) as a particular type, exhibit anomalous wave propagation properties through artificial design of topologies or lattice forms of unit‐cells. Recent advancements in MMs signify an ascendant research trend, providing promising design ideas and means for unprecedented wave propagation properties. The imperative for on‐demand, real‐time active control of wave propagation underscores the significance of tunable manipulation of acoustic/elastic waves, promoting the design and development of tunable MMs. Furthermore, the versatility of intelligent materials and their ongoing development and innovation contribute significantly to the emergence of diverse intelligent MMs. This comprehensive survey provides an overview of recent advancements and current research trends in the interdisciplinary field of intelligent MMs with electro‐/magneto‐mechanical couplings. The primary objective of the review is to emphasize significant progress in agile manipulation of acoustic/elastic waves in electro‐/magneto‐mechanical coupled MMs, followed by an in‐depth exploration of intelligent metasurfaces, topological MMs, non‐Hermitian parity‐time symmetric wave systems, odd elastic MMs, and spatiotemporally modulated MMs. Special emphasis is given to multi‐field coupling effects. The review concludes with a summary and outlines potential prospects, offering a timely and informative guide for future studies on actively tunable PCs and MMs in practical engineering applications. [ABSTRACT FROM AUTHOR]

AbstractIn this paper, we study the propagation of surface waves on an A-shape metasurface, whose structure of the unit-cell is composed regularly of an A-shape surface column (made of steel), a thin magnetorheological plate and a soft thick rubber base. On the basis of the commercial program COMSOL Multiphysics, finite element method (FEM) analyses are carried out. The localization of elastic waves surrounding the surface allows surface waves to be distinguished among various complex wave modes. By adjusting the geometry, the A-shape surface column can be transformed from snowflake to A-shape. Owing to the C3v symmetry system, a Dirac cone of surface wave is observed in a snowflake metasurface. When the surface column changes to A-shape, the C3v symmetry is broken, making the Dirac cone vanish and a new band gap of surface waves arise. The band gap can be opened or closed by changing a geometric parameter, which determines the shape of the surface column changing from gadarene A-shape to snowflake or even upturned A-shape. Furthermore, we discover that although the topological phases of the gadarene A-shape and upturned A-shape metasurfaces are opposite, they share overlapped band gaps. Based on this phenomenon, we design a topological insulator for surface waves, whose super-cell is composed of gadarene A-shape units and upturned A-shape units. Through the calculation of the super-cell band structure, we observe the topologically protected interface states (TPISs). Subsequently, we design several waveguides whose paths are controllable. Up to now, most of the existing metasurfaces are made of passive materials, whose properties cannot be adjusted in real time, making them inconvenient for engineering applications when external conditions are changed. Therefore, we use tunable magnetorheological elastomer (MRE) to control the properties of the topological insulators. The stiffness of the surface layer can be converted by applying a magnetic field, which makes the topological metasurface controllable. These intelligent topological insulators may find important applications in the design of surface acoustic wave (SAW) devices. [ABSTRACT FROM AUTHOR]

This paper introduces a structural design which has superior energy harvesting ability. The proposed structure is based on the ability of most periodic structures to prohibit elastic waves from propagating in a specific frequency range of the phonon band gap. By leading into acoustic black hole (ABH) units and utilizing the energy concentration characteristics of the ABH structure, the filtering effect can be made more significant. These two characteristics can produce significant strain and energy localization, which is conducive to energy harvesting. In this paper, we obtained ABH unit capable of producing broadband gaps by adjusting the geometric parameters of the ABH structure, and chose a cantilever as the research object for energy harvesting, by applying a piezoelectric patch on the unit located near the fixed end to gain a broader application in the actual situation. The results show that the beam combining the energy concentration characteristics of band gap and ABH structure has a significant improvement in energy harvesting efficiency. Optimization on the parameters of ABH unit shows that the band gap characteristic of the periodic ABH structure can further optimize the energy harvesting efficiency of practical energy harvesters, and opens up a new possibility of energy harvesting of ABH structure. [ABSTRACT FROM AUTHOR]

Unconsolidated, undrained triaxial deformation tests were performed on sandy facies Opalinus Clay at 50 MPa confining pressure to characterize the effect of water and microfabric orientation on the deformation behavior, mechanical properties, and P-wave velocity evolution. Dry and wet (≈ 8 and > 95% initial water saturation, respectively) samples with 12.6 ± 0.4 vol% porosity were deformed parallel and perpendicular to the bedding direction at a constant strain rate of 5 × 10–6 s−1. Dry samples revealed semi-brittle behavior and exhibited strain localization at failure, while deformation was more ductile at saturated conditions, promoting stable, slow faulting. Peak strength, Young's modulus, and number of cumulative acoustic emissions decreased significantly for wet samples compared to dry samples; the opposite was observed for Poisson's ratio. P-wave velocity anisotropy was significantly altered by differential stress, primarily due to the interplay between pore and fracture closure and stress-induced microcrack formation. For samples that were deformed perpendicular to bedding, we observed a reduction and reversal of P-wave velocity anisotropy with increasing differential stress, whereas anisotropy of parallel samples increased. The results suggest that water saturation reduces the pressure at the brittle-ductile transition and that the elastic properties and anisotropy of sandy facies Opalinus Clay can be significantly altered in an anisotropic stress field, e.g., adjacent to fault zones or tunnel excavations. Changes in elastic anisotropy are primarily controlled by the orientation between the pre-existing microfabric and the maximum principal stress direction, stress magnitude, and the degree of water saturation. Highlights: The presence of water reduces compressive strength, stiffness and P-wave velocity anisotropy of sandy facies Opalinus Clay, accompanied by increasing strain delocalization, promoting stable, slow faulting during triaxial deformation Triaxial deformation alters the elastic wave velocity anisotropy and symmetry of sandy facies Opalinus Clay, depending on water content and on the orientation of bedding relative to loading direction Changes in elastic anisotropy are mainly controlled by the closure of pores and microcracks and the formation of stress-induced fractures [ABSTRACT FROM AUTHOR]

Modelling seismic wavefields in complex 3-D elastic media is the key in many fields of Earth Science: seismology, seismic imaging, seismic hazard assessment and earthquake source mechanism reconstruction. This modelling operation can incur significant computational cost, and its accuracy depends on the ability to take into account the scales of the subsurface heterogeneities varying. The theory of homogenization describes how the small-scale heterogeneities interact with the seismic waves and allows to upscale elastic media consistently with the wave equation. In this study, an efficient and scalable numerical homogenization tool is developed, relying on the similarity between the equations describing the propagation of elastic waves and the homogenization process. By exploiting the optimized implementation of an elastic modelling kernel based on a spectral-element discretization and domain decomposition, a fully scalable homogenization process, working directly on the spectral-element mesh, is presented. Numerical experiments on the entire SEAM II foothill model and a 3-D version of the Marmousi II model illustrate the efficiency and flexibility of this approach. A reduction of two orders of magnitude in terms of absolute computational cost is observed on the elastic wave modelling of the entire SEAM II model at a controlled accuracy. [ABSTRACT FROM AUTHOR]

Quantum computing has attracted considerable attention in recent years because it promises speedups that conventional supercomputers cannot offer, at least for some applications. Though existing quantum computers (QCs) are, in most cases, still too small to solve significant problems, their future impact on domain sciences is already being explored now. Within this context, we present a quantum computing concept for 1-D elastic wave propagation in heterogeneous media with two components: a theoretical formulation and an implementation on a real QC. The method rests on a finite-difference approximation, followed by a sparsity-preserving transformation of the discrete elastic wave equation to a Schrödinger equation, which can be simulated directly on a gate-based QC. An implementation on an error-free quantum simulator verifies our approach and forms the basis of numerical experiments with small problems on the real QC IBM Brisbane. The latter produce simulation results that qualitatively agree with the error-free version but are contaminated by quantum decoherence and noise effects. Complementing the discrete transformation to the Schrödinger equation by a continuous version allows the replacement of finite differences by other spatial discretization schemes, such as the spectral-element method. Anticipating the emergence of error-corrected quantum chips, we analyse the computational complexity of the best quantum simulation algorithms for future QCs. This analysis suggests that our quantum computing approach may lead to wavefield simulations that run exponentially faster than simulations on classical computers. [ABSTRACT FROM AUTHOR]

Film/substrate structures are often seen in nature and engineering and their characteristic mechanical behaviors facilitating widespread application prospects. Surface patterns of film/substrate structures significantly affect the propagation of elastic waves. This paper investigates elastic wave propagation in the thin film/substrate periodic structure with sinusoidal surface patterns through the uniaxial tension. Based on the Bloch wave theory and numerical simulation, diverse bandgaps are triggered and the overall frequency range of the bandgaps shifts upward with the increase of the tensile strain, which demonstrates that tensioning the bilayer is a reliable and robust way for manipulating bandgaps. Band properties and bandgap evolution by various geometric and material parameters are discussed systematically, including various surface sinusoidal amplitudes, thickness of the substrate and various density or modulus ratio. The underlying mechanism of the exciting results in reversal design and regulation of structural geometry is revealed and is explained by using the spring-mass model. This work can provide new thought and insight for controlling wave propagation and promoting potential applications of the film/substrate systems and devices. [ABSTRACT FROM AUTHOR]

• The reflection/transmission of seismoelectric waves propagating through a sandwiched structure are studied. • A new fractional order viscoelastic model with two attenuation peaks at seismic and sonic frequencies is established. • The seismoelectric effects have noticeable influences on EM wave while negligible influences on seismic waves. • The porosity and the viscoelasticity of solid frame have evident influences on both elastic waves and EM waves The seismoelectric waves generated in a fluid-saturated porous interlayer and the reflection/transmission characteristics at the interfaces of sandwiched structure are studied in this paper. Aiming to describe the strong attenuation and dispersion simultaneously at seismic and sonic frequencies, a new fractional viscoelastic model for the solid skeleton is introduced to the Pride's seismoelectric coupling theory. Using the interfacial continuity of stress, displacements, magnetic and electric fields, the reflection/transmission coefficients are determined. The numerical results are provided and shown graphically. The effects of seismoelectric coupling and the viscoelastic characteristics of solid skeleton on the reflection and transmission of seismoelectric waves are mainly studied. It is observed that the thickness, porosity and the viscoelastic characteristics of solid skeleton have evident effects not only on the electromagnetic waves but also on the seismic waves. [ABSTRACT FROM AUTHOR]

Seismic exploration has caught widespread attention in metal ore exploration due to its higher resolution. However, the presence of topography and complex underground structures in metal ore exploration complicates seismic records. Therefore, it is essential to apply a numerical simulation method suitable for metal ore exploration to study the propagation law of seismic waves in shallow and ore-forming zones, providing reliable theoretical support for multi-component seismic techniques. In particular, the presence of topography generates strong-amplitude surface waves, scattered waves, and converted waves, which consistently distort seismic records and affect the imaging accuracy of the metallogenic belts. Additionally, the propagation of seismic waves is also affected by the anisotropy and viscoelasticity of the underground medium. This paper proposes an elastic wave finite-difference numerical simulation method suitable for irregularly topographical and complex medium conditions, named the comprehensive parameter correction method, which implements a free-surface boundary condition based on the concept of medium averaging. It is algorithmically simple and implies no additional computational costs. Meanwhile, the results obtained by this method are highly consistent with those of the spectral element method, demonstrating its accuracy. By presenting several numerical simulation cases and illustrating the impact of topography and medium conditions on seismic records, this paper demonstrates the necessity of considering irregularly topographical and complex medium conditions in metal ore exploration. In conclusion, the numerical simulation method we propose provides a solid theoretical foundation for the application of seismic exploration methods in metal ore exploration. [ABSTRACT FROM AUTHOR]

Sedimentary strata typically exhibit the characteristics of transverse isotropy (VTI) with a vertical axis of symmetry. However, fractures in sedimentary strata tend to produce anisotropic closure due to horizontal in situ stress, resulting in pronounced orthorhombic anisotropy in VTI media under such stress conditions and influencing the propagation behavior of seismic waves. Previous studies have primarily focused on the elastic wave velocity anisotropy induced by applied stress in isotropic background media, neglecting the impact of VTI background media on the anisotropy induced by horizontal in situ stress and the response characteristics of seismic wave propagation. To address these gaps, we first establish the effective elastic stiffness tensor of VTI media under horizontal in situ stress using nonlinear acoustoelastic theory. Then, we derive the accurate and linearized approximate equations for P-wave seismic reflectivity of VTI media under horizontal in situ stress, based on wave equations and scattering theory, respectively. Finally, we compare and analyze the characteristics of orthorhombic anisotropic seismic response induced by horizontal in situ stress at various types of elastic reflection interfaces. Our results demonstrate that the linearized approximation of the seismic reflection response characteristics closely aligns with the accurate equations under conditions of small stress below 10 MPa, effectively capturing the azimuth-dependent orthorhombic anisotropy induced by horizontal in situ stress in VTI media. The results of this study also provide a novel theoretical approach and valuable insights into the seismic prediction of in situ stress. [ABSTRACT FROM AUTHOR]

Elastic metamaterials with unusual elastic properties offer unprecedented ways to modulate the polarization and propagation of elastic waves. However, most of them rely on the resonant structural components, and thus are frequency-dependent and unchangeable. Here, we present a reconfigurable 2D mechanism-based metamaterial which possesses transformable and frequency-independent elastic properties. Based on the proposed mechanism-based metamaterial, interesting functionalities, such as ternary-coded elastic wave polarizer and programmable refraction, are demonstrated. Particularly, unique ternary-coded polarizers, with 1-trit polarization filtering and 2-trit polarization separating of longitudinal and transverse waves, are first achieved. Then, the strong anisotropy of the proposed metamaterial is harnessed to realize positive-negative bi-refraction, only-positive refraction, and only-negative refraction. Finally, the wave functions with detailed microstructures are numerically verified. [ABSTRACT FROM AUTHOR]

Incident particles in the Klein tunnel phenomenon in quantum mechanics can pass a very high potential barrier. Introducing the concept of tunneling into the analysis of phononic crystals can broaden the application prospects. In this study, the structure of the unit cell is designed, and the low frequency (< 1 kHz) valley locked waveguide is realized through the creation of a phononic crystal plate with a topological phase transition interface. The defect immunity of the topological waveguide is verified, that is, the wave can propagate along the original path in the cases of impurities and disorder. Then, the tunneling phenomenon is introduced into the topological valley-locked waveguide to analyze the wave propagation, and its potential applications (such as signal separators and logic gates) are further explored by designing phononic crystal plates. This research has broad application prospects in information processing and vibration control, and potential applications in other directions are also worth exploring. [ABSTRACT FROM AUTHOR]

To address the incompatibility between high environmental adaptability and deep subwavelength characteristics in conventional local resonance metamaterials, and overcome the deficiencies in the stability of existing active control techniques for band gaps, this paper proposes a design method of pure metal vibration damping metamaterial with continuously tunable stiffness for wideband elastic wave absorption. We design a dual-helix narrow-slit pure metal metamaterial unit, which possesses the triple advantage of high spatial compactness, low stiffness characteristics, and high structural stability, enabling the opening of elastic flexural band gaps in the low-frequency range. Similar to the principle of a sliding rheostat, the introduction of continuously sliding plug-ins into the helical slits enables the continuous variation of the stiffness of the metamaterial unit, achieving a continuously tunable band gap effect. This successfully extends the effective band gap by more than ten times. The experimental results indicate that this metamaterial unit can be used as an additional vibration absorber to absorb the low-frequency vibration energy effectively. Furthermore, it advances the metamaterial absorbers from a purely passive narrowband design to a wideband tunable one. The pure metal double-helix metamaterials retain the subwavelength properties of metamaterials and are suitable for deployment in harsh environments. Simultaneously, by adjusting its stiffness, it substantially broadens the effective band gap range, presenting promising potential applications in various mechanical equipment operating under adverse conditions. [ABSTRACT FROM AUTHOR]

A novel hollow star-shaped chiral metamaterial (SCM) is proposed by incorporating chiral structural properties into the standard hollow star-shaped metamaterial, exhibiting a wide band gap over 1 500 Hz. To broaden the band gap, solid single-phase and two-phase SCMs are designed and simulated, which produce two ultra-wide band gaps (approximately 5 116 Hz and 6 027 Hz, respectively). The main reason for the formation of the ultra-wide band gap is that the rotational vibration of the concave star of two novel SCMs drains the energy of an elastic wave. The impacts of the concave angle of a single-phase SCM and the resonator radius of a two-phase SCM on the band gaps are studied. Decreasing the concave angle leads to an increase in the width of the widest band gap, and the width of the widest band gap increases as the resonator radius of the two-phase SCM increases. Additionally, the study on elastic wave propagation characteristics involves analyzing frequency dispersion surfaces, wave propagation directions, group velocities, and phase velocities. Ultimately, the analysis focuses on the transmission properties of finite periodic structures. The solid single-phase SCM achieves a maximum vibration attenuation over 800, while the width of the band gap is smaller than that of the two-phase SCM. Both metamaterials exhibit high vibration attenuation capabilities, which can be used in wideband vibration reduction to satisfy the requirement of ultra-wide frequencies. [ABSTRACT FROM AUTHOR]

Multilayered van der Waals (vdW) materials have attracted increasing interest because of the manipulability of their superior optical, electrical, thermal, and mechanical properties. A mass-spring model (MSM) for elastic wave propagation in multilayered vdW metamaterials is reported in this paper. Molecular dynamics (MD) simulations are adopted to simulate the propagation of elastic waves in multilayered vdW metamaterials. The results show that the graphene/MoS2 metamaterials have an elastic wave bandgap in the terahertz range. The MSM for the multilayered vdW metamaterials is proposed, and the numerical simulation results show that this model can well describe the dispersion and transmission characteristics of the multilayered vdW metamaterials. The MSM can predict elastic wave transmission characteristics in multilayered vdW metamaterials stacked with different two-dimensional (2D) materials. The results presented in this paper offer theoretical help for the vibration reduction of multilayered vdW semiconductors. [ABSTRACT FROM AUTHOR]