Waves In Metamaterials Research Articles

Characteristics of band gaps of a metamaterial plate with membrane-type resonators based on the energy approach

Local resonance metamaterials have garnered substantial interest in recent years due to their potential to effectively control low-frequency noise and vibration. This study proposes a new metamaterial plate with double mass membrane-type resonators (DMMRs). Combining polynomial fitting and virtual spring method, the natural characteristics of the resonator and the dispersion surfaces of the metamaterial plate are obtained. Results show the proposed metamaterial plate exhibits multiple band gaps, resulting from the cancellation of shear forces in the plate by the reaction forces generated by the first two resonances of the resonators. Parametric analysis is performed to obtain the variation patterns of the band gaps, where approximate models of the resonator are adopted to explain the effects of the parameters. It is found that the occurrence and width of the two band gaps are closely related to the mass ratio between the masses on the resonator and the substrate plate. Furthermore, finite element analysis is conducted to verify the effectiveness of the theoretical derivation, as well as the suppression effect of the metamaterial plate. The findings demonstrate the advantages of the metamaterial plate in vibration control and band gap tuning. The study provides guidance for the design and analysis of elastic wave metamaterials.

Nonlocal interactions on dynamic growth of an inclusion in locally resonant elastic wave metamaterials

Nonlocal interactions on dynamic growth of an inclusion in locally resonant elastic wave metamaterials

Nonlocal topological states in elastic wave metamaterials with active feedback control

Topological elastic wave metamaterials provide a new mechanism to tune wave energy and provide engineering applications which are difficult to realize by traditional structures. This work reports topological characteristics of nonlocal elastic wave metamaterials with active feedback control. The effects of nonlocal connection on band structures and dynamic behaviors of rectilinear lattices are studied. Then, the honeycomb lattice with nonlocal interactions is investigated, which realizes interface transmission and hybrid order topological states. The introduction of active feedback control systems can change the Young’s modulus of nonlocal metamaterials, which flexibly tune the topological characteristic of elastic waves. According to finite element simulation and experiment, the interface transmission and hybrid order can be generated by active feedback control, which agrees with theoretical predictions.

Diode behaviors of curved elastic wave metamaterials with a nonlinear granular chain

Diode behaviors of curved elastic wave metamaterials with a nonlinear granular chain

Rayleigh waves in an elastic half-space with a hard sphere-filled metasurface

In spite of extensive recent research on surface waves in metamaterials, Rayleigh waves with a metasurface layer filled with coated or uncoated hard spheres seem to be explored. In this work, based on an effective medium model for hard sphere-filled metacomposites, an analysis is given for Rayleigh surface waves of an elastic half-space covered by a thin metasurface layer filled with coated or uncoated hard spheres. Explicit Rayleigh wave speed-frequency relation is derived, and the lower and upper bounds of bandgap for Rayleigh waves are determined explicitly. Several examples based on physically relevant material constants are discussed, with clear general conclusions on Rayleigh waves with a thin elastic layer filled with coated or uncoated hard spheres.

Propagation of Dirac waves through various temporal interfaces, slabs, and crystals

We investigate the influence of the temporal variations of various medium parameters on the propagation of Dirac-type waves in materials where the quasiparticles are described by a generalized version of the pseudospin-1/2 Dirac equation. Our considerations also include the propagation of electromagnetic waves in metamaterials with the Dirac-type dispersion. We focus on the variations of the scalar and vector potentials, mass, Fermi velocity, and tilt velocity describing the Dirac cone tilt. We derive the scattering coefficients associated with the temporal interfaces and slabs analytically and find that the temporal scattering is caused by the changes of the mass, Fermi velocity, and vector potential, but does not arise from the changes of the scalar potential and tilt velocity. We also explore the conditions under which the temporal Brewster effect and total interband transition occur and calculate the change in total wave energy. We examine bilayer Dirac temporal crystals where parameters switch between two different sets of values periodically and prove that these systems do not have momentum gaps. Finally, we assess the potential for observing these temporal scattering effects in experiments.

High-Performance and Flexible Metamaterial Wave Absorbers with Specific Bandwidths for the Microwave Device

In this paper, we proposed a high-performance electromagnetic-wave metamaterial absorber which can be used directly for 5G technology. The absorber exhibits a high performance in a tailored frequency range of 28 ± 1 GHz. At both transverse-electric and transverse-magnetic polarization, the absorption exceeds 99% when the electromagnetic wave is incident normally, and the absorption keeps being over 97% as the incident angle increases even to 45 degrees. The absorber is flexible, and it is very suitable for mass production because the production process is simple. In addition, the minimum dimension of the meta-structure is only 0.2 mm, and the cost is relatively low. Similarly, another high-performance metamaterial absorber with a tailored bandwidth at the center frequency of 77 GHz, which is relevant to self-driving cars, was also prepared by a minimal adjustment to the original structure.

Second-order topological corner states in two-dimensional elastic wave metamaterials with nonsymmorphic symmetries

This paper investigates the higher-order topological behavior of elastic wave metamaterials composed of L-shaped pillars attached to a plate. In this system, the multi-dimensional topological transitions can be developed for physical transfer among the corner, edge, and bulk elastic wave modes by tuning the rotation angle of the L-shaped pillars. Different from the four degenerate corner states in the symmorphic system, these corner states in this metamaterial evolve into two doublets because of the lack of mirror symmetries. With the energy highly trapped at the corners, it thus can immediately realize elastic resonators/sensors with high-quality factors. Besides, the coupling effect between corner and edge states is analyzed in the multi-dimensional topological system. The edge–corner coupling effect could be applied to relevant fields, such as high-sensitive detection, elastic energy harvesting, and optomechanical sensing.

Sound transmission of active elastic wave metamaterial with double locally resonant substructures surrounded by external mean flow

The elastic wave metamaterial with active feedback control is presented to discuss its dynamic effective parameter and sound transmission properties. Both studies are initiated from the local resonance with the active feedback control and dynamic structural response. The acoustic-structure coupling of the metamaterial with resonators and orthogonal stiffeners are analyzed with effects of the external mean flow. Different analytical methods are used to derive the effective mass density and sound transmission loss (STL) of the elastic wave metamaterial. The effective density is obtained by the dynamic effective medium method firstly. And the second one applies the spatial harmonic expansion method with the principle of virtual work for the STL based on the Bloch–Floquet theorem and Poisson summations. The effective mass density shows frequency-dependent properties and appears positive and negative values in a certain frequency region simultaneously. This research also illustrates both characteristics can be tuned by the active feedback control with the acceleration and displacement feedback control actions. Numerical results of coupled structures show that the changes of transmission characteristics in the certain frequency region are consistent with the effective mass density properties of uncoupled unit cell structure. In addition, influences of the lattice constants, incident angles and Mach number on the STL are illustrated and discussed.

Nonreciprocal Transmission of Non-collinear Mixing Wave in Nonlinear Elastic Wave Metamaterial

Nonreciprocal Transmission of Non-collinear Mixing Wave in Nonlinear Elastic Wave Metamaterial

Elastic wave propagation in a single-layered hexagonal boron nitride metamaterial

Wave propagation in a single-layered hexagonal boron nitride (h-BN) metamaterial is investigated by molecular dynamics (MD) simulation and the finite element method (FEM). The molecular model for a single-layered h-BN metamaterial is established. The transmission performance of elastic waves in metamaterials is simulated by the MD method. The MD simulation results show that the metamaterial has an elastic wave bandgap in the frequency range of THz. The edge states in the bandgap region are found by the MD method and FEM, and the wave propagation is confined to the boundary only. The results obtained by the FEM roughly agree with those of MD simulations. The difference in the bonding structures between the atoms at the boundary and interior of the metamaterial results in the differences between the FEM and MD results. The size effect on the bandgap structure is studied by comparing the transmission curves of the metamaterial with different unit cell sizes. The size effect becomes more substantial with decreasing feature size of the metamaterial. This work can be helpful for the vibration suppression of nanoelectromechanical systems.

Novel Optical Soliton Waves in Metamaterials with Parabolic Law of Nonlinearity via the IEFM and ISEM

Here, the miscellaneous soliton solutions of the generalized nonlinear Schrödinger equation are considered that describe the model of few-cycle pulse propagation in metamaterials with parabolic law of nonlinearity. The novel analytical wave solutions to the mentioned nonlinear equation in the sense of the nonlinear ordinary differential transform equation are obtained. The techniques are the improved exp − Γ ϖ function method and the improved simple equation method. The nonlinear ordinary transform to concern the generalized Schrodinger equation to convert it for a solvable integer-order differential equation is used. After the successful implementation of the presented methods, the exact solitary wave solutions in the form of trigonometric, rational, and hyperbolic functions are obtained. Hence, the presented methods are relatable and efficient to solve nonlinear problems in mathematical physics.

A review of elastic plate wave metamaterials

超材料指具有超越天然材料性能的人工材料，因其独特的物理性质及广泛的应用领域受到人们的关注。固体中的弹性波被广泛应用于无损检测、无线通讯、无源传感等领域，具有重要的应用价值。不同于流体声波，固体中的弹性波由于存在纵波与横波的耦合及模式转换，更难进行精确操纵，这就给超材料的应用提供了很好的舞台。本文以弹性波中极具代表性的板波作为焦点，较为系统地回顾了板波超材料的发展历史、主要研究进展及其在未来信息功能器件发展方向的潜力。

Intelligent meta-imagers: From compressed to learned sensing

Computational meta-imagers synergize metamaterial hardware with advanced signal processing approaches such as compressed sensing. Recent advances in artificial intelligence (AI) are gradually reshaping the landscape of meta-imaging. Most recent works use AI for data analysis, but some also use it to program the physical meta-hardware. The role of “intelligence” in the measurement process and its implications for critical metrics like latency are often not immediately clear. Here, we comprehensively review the evolution of computational meta-imaging from the earliest frequency-diverse compressive systems to modern programmable intelligent meta-imagers. We introduce a clear taxonomy in terms of the flow of task-relevant information that has direct links to information theory: compressive meta-imagers indiscriminately acquire all scene information in a task-agnostic measurement process that aims at a near-isometric embedding; intelligent meta-imagers highlight task-relevant information in a task-aware measurement process that is purposefully non-isometric. The measurement process of intelligent meta-imagers is, thus, simultaneously an analog wave processor that implements a first task-specific inference step “over-the-air.” We provide explicit design tutorials for the integration of programmable meta-atoms as trainable physical weights into an intelligent end-to-end sensing pipeline. This merging of the physical world of metamaterial engineering and the digital world of AI enables the remarkable latency gains of intelligent meta-imagers. We further outline emerging opportunities for cognitive meta-imagers with reverberation-enhanced resolution, and we point out how the meta-imaging community can reap recent advances in the vibrant field of metamaterial wave processors to reach the holy grail of low-energy ultra-fast all-analog intelligent meta-sensors.

Tunable three-dimensional nonreciprocal transmission in a layered nonlinear elastic wave metamaterial by initial stresses

In this work, the three-dimensional (3D) propagation behaviors in the nonlinear phononic crystal and elastic wave metamaterial with initial stresses are investigated. The analytical solutions of the fundamental wave and second harmonic with the quasi-longitudinal (qP) and quasi-shear (qS1 and qS2) modes are derived. Based on the transfer and stiffness matrices, band gaps with initial stresses are obtained by the Bloch theorem. The transmission coefficients are calculated to support the band gap property, and the tunability of the nonreciprocal transmission by the initial stress is discussed. This work is expected to provide a way to tune the nonreciprocal transmission with vector characteristics.

Broadband modulation of terahertz wave polarization states with flexible metamaterial

In this work, we study the broadband manipulation of polarization states of terahertz (THz) waves with flexible metamaterial both theoretically and experimentally. Firstly, we construct a chiral THz metamaterial with asymmetric L-shaped metal-dielectric-metal structure, generating a series of electric dipoles via its interacting with terahertz waves. By changing the geometric parameters of the structure, the time responses of the electric dipoles in the two orthogonal directions are effectively modulated. Consequently, the chiral metamaterial efficiently converts linearly polarized terahertz wave into a circularly polarized one. The radiation of the metamaterial remains almost unaffected by the changing of the incident angle, which indicates that this chiral metamaterial can be used to realize a flexible terahertz circularly-polarized wave plate. Further, we present the working principle of this flexible terahertz circularly-polarized wave plate at the bending state based on the equivalent circuit model. Moreover, we fabricate a flexible metamaterial wave plate by using polymers as the dielectric layer. When the linearly polarized light is incident on the metamaterial, the circularly polarized output can be achieved in a wide frequency range of 0.46–0.62 THz. The polarization conversion remains quite stable even if the sample is bent. This flexible terahertz metamaterial wave plate is expected to be applied to 6G communication, molecular detection, etc.

Design of vibration isolators by using the Bragg scattering and local resonance band gaps in a layered honeycomb meta-structure

In this study, a vibration isolator is designed using the Bragg scattering and local resonance band gaps in a layered honeycomb meta-structure. Various studies have been conducted on the noise and vibration problems of engineering structures by utilizing the band gaps in phononic crystal meta-materials. However, no study on the application of phononic crystal meta-materials to the design of vibration isolators has been published due to the large lattice constant and narrow band gap. To overcome the difficulties of realization in vibration isolators, a layered honeycomb meta-structure is proposed in this study. The proposed meta-structure consists of a layered square honeycomb structure and a local resonator placed inside the honeycomb core. A transfer matrix model based on the effective mass is developed to comprehend the mechanism of band gap formation. Furthermore, a strategy for designing an ultra-wide low-frequency coupled band gap is established analytically. Then, a four-layer honeycomb meta-structure is designed and fabricated based on the proposed design strategy. Experimental results demonstrate the successful realization of an ultra-wide coupled band gap with the introduction of the resonators with meticulously selected parameters. Finally, the designed meta-structure is applied to a vibration isolator, and the vibration isolation performance is verified experimentally. This work has broad engineering application prospects and is of high significance for promoting the implementation of elastic wave meta-materials in the engineering field.

Full-silica metamaterial wave plate for high-intensity UV lasers

Bringing light–matter interactions into novel standards of high-energy physics is a major scientific challenge that motivated the funding of ambitious international programs to build high-power laser facilities. The major issue to overcome is to avoid laser intensity heterogeneities over the target that weaken the light–matter interaction strength. Laser beam smoothing aims at homogenizing laser intensities by superimposing on the target laser speckle intensities produced by orthogonal left and right circularly polarized beams. Conventional wave plates based on anisotropic crystals cannot support the laser fluences of such lasers, and the challenge is now to design wave plates exhibiting a high laser induced damage threshold (LIDT). Fused silica exhibits high LIDT, but its isotropic dielectric permittivity prevents effects on polarization retardance. Metamaterials have been widely investigated to tailor the phase and polarization of light but with plasmonic or high-refractive-index materials, and applying this approach with silica is highly challenging due to the weak optical contrast between silica and air or vacuum. Here we design and fabricate a silica-based metasurface acting almost like a quarter-wave plate in the UV spectral range, fulfilling the numerous constraints inherent to high-power laser beamlines, in particular, high LIDT and large sizes. We numerically and experimentally demonstrate that fused silica etched by deep grooves with a period shorter than the wavelength at 351 nm operates the linear-to-quasi circular polarization conversion together with a high transmission efficiency and a high LIDT. The high aspect ratio of the grooves due to the short period imposed by the short wavelength and the deepness of the grooves required to overcome the weak optical contrast between silica and air is experimentally obtained through a CMOS compatible process.

Discrete scattering and meta-arrest of locally resonant elastic wave metamaterials with a semi-infinite crack

Previous investigations on wave scattering and crack propagation in the discrete periodic structure are concentrated on the conditional mass–spring model, in which the internal mass is not included. In this work, elastic wave metamaterials with local resonators are studied to show the scattering of elastic waves by a semi-infinite crack and the arrest behaviour. The influences of internal mass–spring structure are analysed and the discrete Wiener–Hopf method is used to obtain the displacement solution. Numerical calculations are performed to show that the dynamic negative effective mass and band gaps can be observed owing to the local resonance of the internal mass. Therefore, the scattering of an elastic wave with a specific frequency by a semi-infinite crack can be avoided by tuning the structural parameters. Moreover, the energy release ratio which characterizes the splitting resistance is presented and the meta-arrest performance is found. It is expected that this study will increase understanding of how to control the scattering characteristics of elastic waves by a semi-infinite crack in locally resonant metamaterials and also help to improve their fracture resistance.

Transient Invisibility and Cloak of Impact Elastic Wave in Piezoelectric/Piezomagnetic Metamaterials

Based on the scattering cancellation technique, a piezoelectric cloaking is designed, which can make the piezomagnetic cylinder invisible to transient elastic waves. Following the Laplace transform, the piezoelectric cloaking mechanism is presented and dynamic stress concentration factor (DSCF) is derived by the plane wave expansion method. The numerical method of the inverse Laplace transformation is used to show the cloaking behavior that besides the invisible phenomenon, the DSCF is also reduced by the cloak. The piezoelectric parameter plays a positive role on enhancing the object invisibility and improving the stress distribution. These results can offer the fundamental design and application of elastic wave metamaterials.