Metamaterial Structure Research Articles

A well-posed and microstructure-emerged homogenization method for nonlocal metamaterial truss

The classical multiscale homogenization methods can only take into account the pure microstructural effect, resulting in the inability to accurately capture the nonlocal interactions emerged from the underlying microstructures of metamaterial structures. This paper explores the nonlocal interplay mechanism that emerged from artificial microstructures and develops a well-posed and microstructure-emerged homogenization method capable of capturing microstructure-emerged nonlocality that is strictly related to its extrinsic and intrinsic length scales. First, we propose a novel nonlocal concentrated element model that accounts for both the pure microstructural effect and the nonlocal interaction mechanism to describe the static response of metamaterial trusses. This model not only considers the pure microstructural effect but also further considers the nonlocal interaction, thus providing a more comprehensive description of the static response of metamaterial trusses. Then, based on the nonlocal concentrated element model, a microstructure-emerged homogenization method is developed for metamaterial trusses with an accuracy comparable to that of high-fidelity numerical methods. Since the developed homogenization method is well-posed, a closed-form solution for the displacement of the metamaterial truss is obtained. High-fidelity finite element simulations show that the effective moduli of different metamaterial trusses have significant nonlocal effects, especially for metamaterial trusses with high porosity. Results indicate that the microstructure-emerged homogenization method provides a robust and accurate representation of the metamaterial truss, significantly outperforming the classical multiscale homogenization methods that only consider pure microstructural effects.

Tensegrity‐Inspired Pre‐Stress Control for Programmable Multistability and Stiffness in Mechanical Metamaterials

AbstractMechanical metamaterials have considerable application potential, but are often limited to single applications owing to material and manufacturing constraints. To achieve a “single structure, multiple applications” goal, this study presents a multifunctional metamaterial structure. The metamaterial cells gain significant deformation and recovery abilities by incorporating the concept of a tensegrity structure to balance flexibility and rigidity and using a rigid‐flexible fabrication process. Inspired by cat‐tongue barbs and Hooke's law, an innovative pre‐stress programming structure is designed for integrated fabrication, enabling multilevel pre‐stress control for each cell. This programmable stress allows the twin‐cell array to transition in situ from monostable to bistable states and provides multilevel critical‐force functions for bistable states. After assembling a nine‐cell array, the structure offers a wide range of adjustable stiffness levels, enabling soft‐rigid transitions and varied force‐displacement responses without the need for additional tools. It also allows controlled collapse ratios and deformation through stiffness control. Additionally, the nine‐cell array features isotropy with a Poisson ratio of v = −1 and clear indentation resistance. This approach is promising for applications such as adjustable energy dissipators, automotive equipment, and passive safety.

Analysis of hyperbolic crystals with non-square lattice for improving acoustic energy harvesting

Abstract With the increase in the production of small and low-power electrical devices, there has been an increased focus on creating a useful power source to replace the battery. The energy contained in acoustic waves is one of the attractive energy sources for powering low-power devices. The design and fabrication of metamaterials is one of the effective methods of harvesting acoustic energy that has recently attracted the attention of many researchers. As is presented in this article, the aim is to design and fabricate a novel metamaterial structure with optimal dimensions to improve acoustic energy harvesting in a specific frequency range using a piezoelectric patch. In this metamaterial, hyperbolic crystals with non-square lattice have been used for the first time. This analysis is simulated using the 3D version of Comsol software 6.0. In addition, artificial neural networks and genetic algorithms were used to select the optimal parameters. The results showed that using the non-square lattice of the hyperbolic crystal, more average energy can be harvested in the frequency range of 3310-4325 Hz than in the metamaterial with the cylindrical crystal. Furthermore, the maximum amount of voltage and power extraction with an optimal electrical resistance of 10 kΩ in the metamaterial with the hyperbolic crystals at a frequency of 3374.71 Hz is equal to 27.26 mV and 74.33 nW, respectively, which is much larger compared to the metamaterial with the cylindrical crystals under the same mass and conditions. The simulation results are compared and validated with the experimental results by fabricating the present metamaterial and conducting laboratory tests.

Novel metamaterial wave barrier structure with multiple frequency wide band gaps for rail transit vibration isolation

As a new kind of artificial composite material, locally resonant phononic crystal (LRPC) can attenuate and suppress the propagation of elastic waves in certain frequency range, which has a broad application prospect and value in the field of vibration and noise control. The traditional LRPC can only open one band gap (BG), but the vibration and noise in practical engineering are often multi-band, so the traditional LRPC cannot effectively cover the target frequency range, and the efficiency of vibration and noise reduction is greatly limited. In response to the shortcomings of traditional LRPC, this paper designs a novel locally resonant phononic crystal with multiple primitive cell combination structure (LRPCWMPCCS), which is a locally resonant supercell structure composed of five types of locally resonant single primitive cells. Firstly, the band structure of the LRPCWMPCCS is calculated using the finite element method, and compared with the band structure of traditional LRPC. Secondly, the frequency response function of the LRPCWMPCCS is calculated to evaluate its attenuation effect on elastic waves in the BG frequency range, and the generation mechanism of its locally resonant BG is explored by analyzing the displacement field and energy distribution characteristics at the BG edge. Then, the equivalent model of the LRPCWMPCCS is established for theoretical calculation of the BG range. Finally, the vibration isolation performance of LRPCWMPCCS wave barrier in practical engineering is analyzed, and the application prospects of the LRPCWMPCCS are discussed. The results show that the LRPCWMPCCS designed in this paper can open the multifrequency BGs, and the BGs width is wider. The number of BGs opened is positively correlated with the type of primitive cells inside the LRPCWMPCCS. Within the BG frequency range, the LRPCWMPCCS has a good attenuation effect on vibration waves, with attenuation values exceeding 20 dB. The spring-mass system equivalent model of the LRPCWMPCCS can accurately calculate its BG range and has good accuracy. The LRPCWMPCCS wave barrier has remarkable control and attenuation effect on vibration. Among them, the maximum vibration acceleration of traditional LRPC wave barrier and LRPCWMPCCS wave barrier is reduced by 18.51% and 39.50%, respectively. The relevant research results of this paper have great value and prospects in the design of LRPC with multifrequency and wide BGs, which can also provide a new method and idea for solving vibration and noise problems.

Dynamically Tunable Terahertz Multiple Plasmon‐Induced Transparency and Slow Light in Planar Metamaterials With Rectangular Interrupted Graphene

ABSTRACTA novel planar monolayer graphene metamaterial structure containing rectangular interrupted graphene is proposed. Dynamically tunable multiple plasmon‐induced transparency (PIT) and slow light are obtained within the terahertz band through destructive interference between continuous dark and interrupted bright modes. Two distinct graphene types function as the optical dark and bright modes, and continuous graphene array is the nonradiative dark mode, whereas interrupted graphene array is the broad linewidth bright mode, respectively. Given the existence of graphene structure in the continuous state, continuous graphene Fermi level is dynamic tuned through the simple use of the bias voltage. Expressions of n‐order coupled mode theory (CMT) are correctly deduced, with CMT fitting theoretical analysis being identical to finite‐difference time‐domain numerical simulation based on dual‐ and triple‐PIT results for n = 3 and n = 4 cases, respectively. The continuous graphene Fermi level increases within 0.7–1.1 eV; the group index of the dual‐PIT system is maintained within 475.1–801.6, while that of the triple‐PIT system is 583.3–886.3. Additionally, the maximal group index is as high as 886.3 at 1.1 eV, indicating that an outstanding slow light device is established. Consequently, these proposed structures and research outcomes can guide the design of multichannel optical filters, excellent slow light devices, and dynamically tunable optical modulators.

Study on band-gap characteristics and formation mechanism of four-ligament chiral elastic metamaterials

Abstract Chiral elastic metamaterials, owing to their exceptional properties distinct from conventional materials and their superior mechanical performance, exhibit significant potential for applications in vibration reduction, noise suppression, energy absorption, and cushioning. To address the challenge of low-frequency vibration control, this paper proposes a dual-component chiral elastic metamaterial structure with four ligament elements. The study explores the bandgap characteristics and elastic wave propagation behavior of this structure within the 1000 Hz frequency range. By analyzing the vibration modes of the unit cell and calculating the group and phase velocities of elastic waves, the physical mechanism underlying bandgap formation is elucidated. The results demonstrate that the proposed four-ligament chiral elastic metamaterial exhibits excellent bandgap properties, with the bandgap covering more than 80.4% of the frequency range below 1000 Hz. This highlights its capability for low-frequency elastic wave control and offers a theoretical reference for the design of novel vibration reduction and noise suppression structures, as well as for low-frequency elastic wave regulation.

Design and analysis of a far-infrared metamaterial perfect absorber with sensing applications

In this paper, we present an analysis and design of a metamaterial as the perfect absorber and refractive index sensor in the far-infrared (IR) region, utilizing the finite element method (FEM). The structure consists of a metal resonator on a silicon dielectric with a bottom copper layer beneath the dielectric. Our results demonstrate that the designed structure achieves nearly perfect absorption of transverse electric (TE) polarization at a resonance wavelength of λ r =9.40µm. This occurs because of the perfect impedance matching condition, which achieves a 99.47% absorption efficiency. This condition is also sensitive to the angle of incidence and causes minimal reflection at the resonating wavelength of λ r . This characteristic makes the designed metamaterial structure suitable for use as a sensor. The structure enables maximum electric field confinement in the gap region (g) of the split ring resonator (SRR) at the metal-dielectric interface. The resonance wavelength can be effectively tuned and optimized by varying the gap size (g), dielectric material, dielectric thickness (t d ), copper layer thickness (t c ), and incident angle of the metamaterial absorber (MA). The absorption peak shows a highly sensitive response to changes in the refractive index of the surrounding medium, with a sensitivity of 1600 nm/RIU. This absorber, with its excellent absorption in the far-IR spectrum, holds promising potential for applications in energy harvesting and IR sensing.

Rectangular ring resonator-based symmetrically engineered metamaterial absorber for electromagnetic interference shielding in the S and C bands

Abstract This research aims to investigate the use of metamaterial (MM) structures in S and C bands for efficient EMI shielding. The designed MM absorber consists of four rectangular ring resonators (RRR) made of copper separated by a 1.3 mm thick FR-4 dielectric layer with dimensions of 15 mm × 15 mm and a ground layer of annealed copper with a thickness of 0.035 mm. The simulated results demonstrate two absorption peaks at 4.1 GHz and 6.8 GHz, with absorption values of 99.9% and 96%, respectively. The properties of the reflection coefficient are investigated using a circuit model of the MM absorber, and the electromagnetic wave absorption mechanism is further studied by examining the surface current, H-field, and E-field distributions at absorption peaks. The metamaterial (MM) absorber exhibits almost perfect absorption across a significant angle of incidence and polarisation angle up to 60 degrees. The suggested MM design provides dual-band shielding characteristics with a -10 dB reflection coefficient (S11) at 4.0-4.14 GHz and 6.83-6.89 GHz. Furthermore, the Metamaterial (MM) absorber offers a shielding efficiency of > 20 dB in all bands, according to the theoretical analysis. The MM’s 99% absorption and shielding capability makes it suitable for a wide range of high-potential applications.

The use of geometrical nonlinear local resonators to enhance the vibration control performance of metamaterial structures

Abstract Metamaterials has become an exciting solution for structural noise and vibration reduction in many engineering applications. Acoustic metamaterials are structures built using repetitive assemblies of identical elements to explore either Bragg-scattering or localized resonance to control mechanical waves. They present frequency bands in which waves do not freely propagate, named bandgaps, allowing acoustic and vibration attenuation at one or multiple targeted frequency ranges. If properly designed and implemented, the inclusion of a nonlinear stiffness can result in resonance frequency shifts that broaden the attenuation frequency band. This work investigates the influence of an array of lightweight nonlinear local resonators (NLR) realized via additive manufacturing on the low-frequency bandgap formation of a metamaterial beam. The NLR uses the high-static-low-dynamic stiffness (HSLDS) concept, which introduces geometric nonlinearity. The proposed model is validated through simulation and experimental analysis. The NLR results in a broadened and shifted attenuation band to lower frequencies without the necessity of adding extra mass to the resonator. This investigation contributes to understanding improvements provided by nonlinear elements for vibration control in metastructures.

Metamaterial structure impacts on stress and bending fatigue lifetime of additive-manufactured 3D-printed PLA specimens

Metamaterial structure impacts on stress and bending fatigue lifetime of additive-manufactured 3D-printed PLA specimens

Lattice-like Mechanical Metamaterials Structure Design Method Based on Convolutional Neural Network and NSGA-II Algorithm

Abstract Lattice-like mechanical metamaterials have excellent mechanical properties such as ultra-low density, high specific strength, and high energy absorption, and have broad application prospects in key components of platforms such as armored vehicles, helicopters, and aerospace vehicles. Aiming at the problem of inverse design of superstructure cellular structures, a study on the design method of cellular structures was carried out. Firstly, based on the uniqueness of cellular structural characteristics and the principle of comprehensive information, the cellular structural characteristic matrix and the cellular macroscopic mechanical characteristic matrix of coupled cellular configuration and structural parameters were proposed respectively; then, with the cellular structural characteristic matrix as input data and the macroscopic mechanical characteristic matrix of the cell as output data, a superstructure material performance prediction model based on convolutional neural network was established; further, with the minimum error between the specified target value and the predicted value of the macroscopic mechanical characteristic parameter as the criterion, a multi-objective optimization function was established; finally, the performance prediction model was combined with the fast non-dominated algorithm (NSGA-II algorithm) with elite retention strategy to construct a superstructure cellular structure design model, and the effectiveness of the structural design model was verified by case studies.

A Low-Coupling Broadband MIMO Array Antenna Design for Ku-Band Based on Metamaterials

In response to the demand for broadband antennas in 5G mobile communications, this paper proposes a compact broadband multiple-input multiple-output (MIMO) antenna array. By chamfering a radiation patch and adding parasitic patches, the antenna is miniaturized while also expanding its bandwidth. The mutual coupling between the two antenna elements is reduced by loading a double-layer metamaterial decoupling structure above the elements which consists of an open resonating ring and a square ring. The antenna is simulated and measured using the three-dimensional electromagnetic simulation software HFSS and a vector network analyzer. The results show that the proposed antenna has a good radiation performance of <i>S</i><sub>11</sub> < -10 dB in the operating band of 12.11–13.99 GHz (relative bandwidth of 14.41%). Furthermore, the isolation of the proposed MIMO antenna array in the operating band is improved by more than -18.8 dB on loading the metameterial structure, indicating that the array antenna is suitable for use in the Ku-band.

Coupling Enhancement of Wireless Power Transfer System Using Double Square SR Metamaterial

In the work presented in this paper, the performance of a wireless power transfer system is shown to be enhanced by means of a metamaterial slab utilized as a reflector. The metamaterial slab investigated is a 2D design consisting of a 5 × 5 array of double square split ring resonator cells. It has a near-field mu-near-zero (MNZ) and mu-negative (MNG) characteristic near the target frequency of 2.4 GHz. The array is physically compact having an area of 12.5 × 12.5 cm2. The WPT system considered in the given work is a system of two 10-turn coils separated by a distance of 20 mm. Considerable improvement in the performance is observed in terms of S-parameters and the coupling coefficient after the application of the metamaterial slab reflector. Measurements performed on the fabricated prototype validate the potentiality of the proposed metamaterial structure for improving the efficiency of a wireless power transfer system.

Analyzing vibration transmission through cantilever systems using biomechanical and impact-responsive metamaterial structures

Vibration control in cantilever systems is a critical challenge in various engineering applications, where unwanted vibrations can lead to structural fatigue, reduced performance, and potential failure. This study investigates the effects of integrating biomechanical and impact-responsive metamaterials into cantilever systems to mitigate vibration transmission. The metamaterials, characterized by their adaptive stiffness and energy-absorbing properties, are strategically embedded in key structural components such as the arms, joints, and base. Through experimental analysis, this work assesses the reduction in vibration amplitude, shifts in natural frequency, enhanced damping capacity, energy absorption during impact, and strain reduction at critical points. The results show that the metamaterial-enhanced system achieves significant reductions in vibration amplitude, up to 40%, and increases in natural frequency by over 30%, minimizing the risk of resonance. Additionally, the damping ratio is improved by as much as 53%, while the energy absorption during impact is increased by up to 26%. Strain reduction at critical points reaches 24%, contributing to improved mechanical resilience. These findings demonstrate the potential of biomechanical and impact-responsive metamaterials in enhancing the dynamic performance of cantilever systems, offering a new approach to vibration mitigation in engineering applications.

Enhancing Wireless Power Transfer Performance Based on a Digital Honeycomb Metamaterial Structure for Multiple Charging Locations

Enhancing the efficiency is an essential target of the wireless power transfer (WPT) technology. Enabling the WPT systems requires careful control to prevent power from being transferred to unintended areas. This is essential in improving the efficiency and minimizing the flux leakage that might otherwise occur. Selective field localization can effectively reduce the flux leakage from the WPT systems. In this work, we propose a method using a digital honeycomb metamaterial structure that has a property operation as a function of switching between 0 and 1 states. These cavities were created by strongly confining the field by using a hybridization bandgap that arose from wave interaction with a two-dimensional array of local resonators on the metasurface. A WPT efficiency of 64% at 13.56 MHz was achieved by using the metamaterial and improved to 60% compared to the system without the metamaterial with an area ratio of Rx:Tx~1:28. Rx is the receiver coil, and Tx is the transmitter one.

Non-Hermitian ideal Weyl photonic metamaterials and polarization-momentum resolved ultrahigh absorption.

In the past decade, there has been a significant surge of interest in investigating non-Hermitian Hamiltonians, particularly in photonics. The eigenvalues of general non-Hermitian Hamiltonians are complex and possess unique topological features such as exceptional degeneracy. The introduction of non-Hermitian perturbations into Weyl semimetals can transform Weyl points into exceptional rings characterized by multiple topological invariants. However, the ideal realization of Weyl rings within practical three-dimensional structures has remained a significant challenge. In this work, we extend artificial photonic metamaterial structures that can transform ideal Weyl points into non-Hermitian exceptional rings. We show the associated intriguing polarization-momentum ultrahigh absorption, which enables what we believe to be a new device application in non-Hermitian photonics. Our study not only proposes the practical model for ideal non-Hermitian photonic Weyl exceptional rings but also opens the gate of non-Hermitian scattering characterization.

Thermal Regulation of the Acoustic Bandgap in Pentamode Metamaterials

This study used the finite element method to investigate the acoustic bandgap (ABG) characteristics of three-dimensional pentamode metamaterial (PM) structures under the thermal environment, and a method for controlling the PM ABG based on external temperature variation is also proposed. The results indicate that the complete acoustic bandgap can be obtained for a PM in the thermal environment, which makes the PM combine the bandgap characteristics of phononic crystals. More than that, the bandwidth and locations of ABGs can be effectively manipulated by controlling the temperature. Considering the softening effect of thermal stresses, the ABG gradually moves to lower frequencies as the temperature increases. Based on this, different degrees of ABG tunability can be achieved by changing the thermal environment to propagate or suppress acoustic waves of different frequencies. This work provides the possibility for PMs to realize intelligent regulation of the bandgap.

Bi-directional homogenization method for the design of multi-scale mechanical metamaterials

Bi-directional homogenization method for the design of multi-scale mechanical metamaterials

Study on Bandgap of Two‐Dimensional Square Lattice Acoustic Metamaterial with Multiembedded Cores

Acoustic metamaterials have been widely studied for their excellent ability of vibration isolation. In this article, a 2D square lattice acoustic metamaterial structure with multiembedded cores is proposed. Based on Bloch's theorem and finite element method, the band structures and bandgap properties of the structure are calculated and analyzed, and the vibration isolation ability of the structure is investigated. The effects of structural parameters on the bandgap property are analyzed. Thus, the anisotropy of the structure is also analyzed by the contours of phased velocity and group velocity. The results show that the structure has significant bandgap properties and vibration isolation. The second‐order similarity ratio has significant effects on the bandgap property. Via increasing the second‐order similarity ratio, the total bandgap width and low‐frequency bandgap width are widened. In addition, the structure has significant anisotropy, and the energy of elastic wave propagates at the direction of 45° and 135°. The research in this article supplements the design and research of 2D lattice acoustic metamaterials and makes a beneficial exploration for future engineering applications.

Epsilon negative dynamic coded THz metamaterial beamformer for digital information encryption

Light propagation facilitates digital information encryption by utilizing Epsilon Negative (ENG) metamaterials as a medium. Achieving the desired encryption hinges on synchronizing two pivotal features: the phase difference and the epsilon shifting of the metamaterials. The proposed metamaterial is intricately designed to represent digital bit 1 (states 0 and 1), contingent upon the arrangement of material multilayers within the metamaterial device. Specifically, state 1 is fashioned through a combination of Graphene and Gold, while state 0 is solely represented by Graphene on a metamaterial structure. The developed structure exhibits right hand metamaterial (epsilon of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:+$$\\end{document}7.20) for state 0 and plasma metamaterial (epsilon \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:-$$\\end{document}6.94) for state 1 at 8.6 THz. Notably, the phase difference between 0 and 1 states is around \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:90^\\circ\\:$$\\end{document}. Primarily leveraging the synchronized combination phase and epsilon as the key design parameters for the metamaterial array, the beamforming pattern enables beam steering within the angular range of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:+30^\\circ\\:$$\\end{document} to \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:-30^\\circ\\:$$\\end{document}. Secondly, employing a sophisticated material addition strategy involving Gallium Arsenide (GaAs) systematically manipulates the sidelobe in specific directions, thereby providing a mechanism to modulate the sidelobe and concurrently augment spatial resolution. After preparing the metamaterial coded (MC) lens, the source, lens and receiver strategically encrypt the scanning image, employing techniques including Doppler compression and 2D discrete Fourier transform. The proposed MC lens offers applicability like image encryption, security scanning, conveyor systems, hyperlenses and modern cryptography.