Composite Metamaterials Research Articles

Ultra-Broadband Sound Absorbing Materials Based on Periodic Gradient Impedance Matching

Ultra-broadband sound absorption with periodic gradient impedance matching is of great concern in the research of acoustic materials. This study investigates the impedance matching of composite acoustic metamaterials comprising micro-perforated plates (MPPs) and subsequent Fabry–Pérot(FP) channels. Based on the impedance matching theory, ultra-broadband sound absorption has been realized through a design with 36 channels whose thickness is only 50 mm. Also, the average sound absorption coefficient of 88% and an absorption frequency bandwidth (490–4000 Hz) can be achieved by preserving the matching impedance. Furthermore, by changing the thickness of the perfect absorber being 100 mm, the average sound absorption coefficient can reach greater than 90% in the frequency range of 250–4500 Hz. The proposed structure is validated analytically and experimentally. This work can help with designing and improving the method of acoustic metasurfaces and especially have the potential in ultra-broadband sound absorber designs.

Nonlocal composite metamaterial in calculation of near-field thermal rectification.

We consider the near-field radiative heat transfer (NFRHT) between a semi-infinite polar dielectric plate and a composite metamaterial containing semiconductor nanoparticles with spatial dispersion or nonlocality. We show that the enhancement of near-field heat radiation is found owing to the strong coupling of surface phonon polaritons (SPhPs) excited between polar dielectric plate and air, and localized surface plasmon polaritons (LSPPs) in the composite metamaterials. The introduction of nonlocality is helpful to enhance the NFRHT and even the rectification efficiency significantly when the temperature difference is small. For a large volume fraction of semiconductor nanoparticles, the thermal rectification efficiency can be larger than 90% at a small temperature difference within 150 K. Our findings may pave a way for thermal devices based on composite metamaterial containing semiconductor nanoparticles.

Active multifunctional composite metamaterials with negative effective mass density and negative effective modulus

In this paper, a new composite metamaterial structure with negative effective mass density, negative effective modulus, and an ultralarge Poisson’s ratio is designed for vibration isolation, wave filtering, programmable construction of waveguides and negative refraction. This metamaterial can achieve vibration isolation in different frequency ranges using the shunting circuits. In two-dimensional metamaterial plate, a negative longitudinal modulus can be achieved by designing a model with an ultralarge Poisson’s ratio. This metamaterial can serve as wave filter when both shear and longitudinal waves are presented simultaneously. Wave propagation in the metamaterial can be controlled by switching of the shunting circuits. In this way, waveguides can be created programmatically. The phenomenon of negative refraction is also achieved in this metamaterial. Through control of the shunting circuits, this multifunctional metamaterial can be applied to vibration isolation, wave filtering, programmable waveguide construction, and negative refraction without changing its geometric structure.

Design and optimization of three-dimensional composite multilayer cylindrical pentamode metamaterials for controlling low frequency acoustic waves

For three-dimensional pentamode metamaterials, it is of great significance to realize underwater low frequency acoustic wave control. Therefore, in order to compare with traditional double-cone pentamode metamaterials, two multilayer composite cylindrical three-dimensional pentamode metamaterials with low frequency and broad band gaps are proposed in this paper. By using pentamode metamaterials with lattice constants on the order of centimeters, the phononic band gaps below 60 Hz and the single-mode area below 30 Hz can be obtained. In addition, compared with asymmetrical double-cone locally resonant pentamode metamaterials, the lower edge frequency, relative bandwidth and figure of merit of the first phononic band gap can be reduced by up to 61.4%, 10.3% and 40.6%, respectively. It will provide reference and guidance for the engineering application of pentamode metamaterials in controlling the ultra-low frequency broadband acoustic waves, vibration and noise reduction.

Modeling the flexoelectric effect via the reduced micromorphic model

This paper aims to demonstrate how the flexoelectric effect can be incorporated into the reduced micromorphic model, where materials can be designed and fabricated with complex structures that possess electric properties. These kinds of materials are known as composite metamaterials with properties that do not exist in nature such as the flexoelectric effect phenomena. These phenomena take place when both negative and positive charges move to occupy new positions inside the materials where the new positions of these charges depend on the applied external mechanical or electrical fields. The new arrangements of charges produce a spontaneous polarization inside the material that fades when removing the applied fields. According to the classical theory of elasticity, the spontaneous polarization is mathematically related to a macro-scale measure. In the present work, instead of the macro-scale, we use a micro-scale measure to formulate the polarization phenomena. This formulation is achieved by employing the variation technique for the internal energy functional and the virtual work done by the external fields. The field equations and the concomitant boundary conditions are also obtained. Moreover, the constitutive relations are presented in terms of internal state variables. Finally, an application is made in one-dimension and the results are presented in figures with physical explanation.

Continuous carbon fiber reinforced composite negative stiffness mechanical metamaterial for recoverable energy absorption

This study investigated negative stiffness (NS) mechanical metamaterials, which are potential in the energy absorption field. However, critical drawback of low specific energy absorption in traditional NS mechanical metamaterials limits them to be applied. In this paper, a reusable continuous carbon fiber reinforced polymer (CFRP) composite NS mechanical metamaterial was proposed and fabricated. A combination of compression tests and numerical simulations have been carried out to gain a comprehensive understanding of the structural quasi-static mechanical properties. Repeatability of the metamaterial was then verified by cyclic compression. The results of quasi-static test show that the metamaterial has excellent reusability characteristics and good energy absorption capability. In addition, the effect of the structural parameters on the mechanical properties was revealed using the experimentally verified numerical model. Moreover, by dint of the numerical model, the effect of stacking sequence of the metamaterial on the mechanical properties was also investigated, and the correctness of the curved beams adopted 0° stacking sequence in this paper was proved. Finally, plate-impact tests were performed to investigate the cushion performance of this metamaterial. The metamaterial structure shows good impact resistance without the occurrence of any plastic deformation. The research has guiding significance for the design of impact-resistant metamaterials.

Ensemble learning: a bidirectional framework for designing data-driven THz composite metamaterials

Metamaterials present revolutionary routes to manipulate the behavior of electromagnetic waves. The well-designed metamaterial can exhibit exotic functionalities, such as perfect absorption, holography, beam steering, optical nonlinear generation, and various functional interfaces. However, those designs currently rely on trial-and-error and case-by-case numerical simulations to achieve target responses, which usually requires huge computing resources and expertise related to metamaterials. In this study, we propose a machine-learning-assisted bidirectional ensemble learning framework for designing composite metamaterial absorbers at 0.3–2.0 THz. The proposed framework is a guide to reveal the intricate and nonintuitive relationship between a composite metamaterial structure and its absorption spectrum from previously known datasets, which circumvents the limitation of numerical simulation. This framework not only effectively realizes the forward prediction of the absorption spectrum, but also can retrieve composite metamaterial structure parameters from a given spectrum.

Super-resolution scanning imaging based on metal-dielectric composite metamaterials.

We propose super-resolution scanning imaging by using a metamaterial composed of a silver-silicon dioxide composite covered by a layer of chromium containing one slit and a silicon dioxide substrate. By simulating a distribution of energy flow in the metamaterial for an H-polarized wave, we find that the output beam exhibits focusing accompanied with good directional radiation, which is able to be designed as a super-resolution scanning probe. We also demonstrate numerically super-resolution imaging by scanning our designed metamaterial over a sub-wavelength object.

A Review on the History and Current Literature of Metamaterials and Its Applications to Antennas & Radio Frequency Identification (RFID) Devices

Metamaterials are artificially engineered novel substances (or matter) that exhibit properties not found in nature. One of the earliest examples of a metamaterial structure is the split-ring resonator. This article is a current review of metamaterials, what it is, its classification, and its applications towards the field of antennas and radio frequency identification (RFID) devices. There are two major types of metamaterial antennas: leaky-wave antennas, and resonant antennas. Antennas can be made from composite right-left handed metamaterials, or antennas can be loaded with a metamaterial screen such as a shelled electrically small antenna (ESA) fed by coax. Metamaterial resonators can aid in reducing the antenna size, help improve the gain, improve the directivity, improve the return loss, and control the radiation pattern (by loading the antenna with a tunable unit). Recent advances in printing and fabricating technologies have allowed for use of metamaterial antennas in wearable gadgets and textiles; and can be used in conjunction with RFID devices and tags to advance and aid (emergency) equipment used by first responders.

Band gap tuning through microscopic instabilities of compressively loaded lightened nacre-like composite metamaterials

Large deformation effects give the opportunity for tuning and manipulating the dynamic properties of periodic microstructured materials, including those related to vibration control and band gap phenomena. We investigate the wave propagation properties in bioinspired nacre-like composite metamaterials subjected to uniaxial loading processes, also considering the onset of instabilities at the microscopic and macroscopic scales. The dynamic response of a new 2D lightened brick-and-mortar microstructure containing periodically arranged cavities is investigated, by analyzing the propagation of elastic waves superimposed on a deformed state by means of a Bloch-wave analysis. The band gap properties of the proposed advanced metamaterial were investigated in terms of spectral quantities as a function of the main geometrical parameters and of the level of applied deformations. Numerical results have shown that the elastic wave propagation is strongly influenced by the prestress state inducing microscopic instability, thus providing new opportunities to design periodic bioinspired composite metamaterials characterized by wave absorption capabilities as a function of microstructural evolution.

Two-Dimensional Composite Acoustic Metamaterials of Rectangular Unit Cell from Pentamode to Band Gap

Pentamode metamaterials have been receiving an increasing amount of interest due to their water-like properties. In this paper, a two-dimensional composite pentamode metamaterial of rectangular unit cell is proposed. The unit cells can be classified into two groups, one with uniform arms and the other with non-uniform arms. Phononic band structures of the unit cells were calculated to derive their properties. The unit cells can be pentamode metamaterials that permit acoustic wave travelling or have a total band gap that impedes acoustic wave propagation by varying the structures. The influences of geometric parameters and materials of the composed elements on the effective velocities and anisotropy were analyzed. The metamaterials can be used for acoustic wave control under water. Simulations of materials with different unit cells were conducted to verify the calculated properties of the unit cells. The research provides theoretical support for applications of the pentamode metamaterials.

Polarization-dependent broadband absorber based on composite metamaterials in the long-wavelength infrared range.

Capturing polarization information has long been an important topic in the field of detection. In this study, two polarization-dependent broadband absorbers based on a composite metamaterial structure were designed and numerically investigated. Unlike in conventional metamaterial absorbers, the bottom metallic film is functionalized to achieve a polarization response or broadband absorption. The simulation results show that the type I absorber exhibits TM polarization-dependent broadband absorption (absorptivity>80%) from 8.37 µm to 12.12µm. In contrast, the type II absorber presents TE polarization-dependent broadband absorption (absorptivity>80%) from 8.23 µm to 11.93 µm. These devices are extremely sensitive to the change of polarization angle. The absorptivity changes monotonically with an increase of the polarization angle, but it is insensitive to oblique incidence. This design paves the way for realizing broadband polarization-dependent absorption via a simple configuration. It has bright prospects in thermal detection applications and imaging fields.

Fiber-reinforced composite metamaterials for mode conversion of elastic waves

Metamaterials are a class of man-made composites that can realize extraordinary wave phenomena and can be designed through exploiting anisotropy of elastic media. Anisotropy, as is known, is also an inherent characteristic of classical composites. Therefore, there is a great potential that the anisotropy of classical composites can be utilized to achieve extraordinary manipulation of elastic waves. To this end, we propose a concept of fiber-reinforced composite metamaterials, which attains extraordinary wave properties with rationally designed ply angles. Specifically, we consider the phenomenon of transmodal Fabry–Perot interference. This phenomenon, which can transfer wave energy between longitudinal and transverse modes solely and maximally, requires that the interferometer should attain unique anisotropy. Based on the transmodal interference theory and the classical lamination theory, the composite metamaterials are designed and validated numerically and experimentally. We note that the base material properties of each layer can significantly affect the metamaterial design, and an anisotropy index is introduced to investigate the effects. Our work broadens the applications of classical composites and offers a new way to design metamaterials.

Free vibration analysis of PLA based auxetic metamaterial structural composite using finite element analysis

The unique engineered material termed Metamaterials is not seen naturally and were made artificially by repeating unit cell geometry in multiple directions to form a structural composite metamaterial. The present research is to investigate the three types of uniform architecture metamaterials i.e square, auxetic and honeycomb along with three of its hybrids i.e square-auxetic, auxetic-honeycomb and square-honeycomb. All the modelled metamaterials samples were imported to Ansys modal analysis section and free vibration analysis is performed under the workbench graphic user interface via the finite element method. The materials for the simulation test is PLA (polylactic acid) adopted. The results like natural frequency and mode shapes are extracted from the simulation. It was observed that among hybrids the highest natural frequency was seen for auxetic-square hybrid geometry i.e 858 Hz at 3rd natural frequency, which decreased to 35 and 44% when compared to square-honeycomb, auxetic-honeycomb respectively. The emerging area potential application of hybrid PLA auxetic metamaterial includes robotics, aerospace, nautical, sports and bio-medical industries.

Composite trampoline metamaterial with enlarged local resonance bandgap

The engineered resonance phenomena by artificial structures have opened a new frontier in modern science and technology. Artificial structures such as pillared phononic crystals and metamaterials are emerging domain due to their surface resonance features that are governed by periodic array of pillars embedded on a host plate. The dual aspects of pillared structure exhibiting both Bragg and local resonance bandgaps make it a prominent choice for wave manipulation in general and vibration isolation in particular. The present study proposes pillared-plate structure based composite trampoline metamaterial that can exhibit ultrawide local resonance bandgap with relative bandwidth around 100%, confirmed by numerical and experimental approaches. The study establishes that composite nature of the pillar together with trampoline effect caused by drilling periodic array of holes in the host plate can enhances the effective mass density and reduce the plate stiffness, respectively that eventually lead to enlarged local resonance bandgap. The evolution of composite design with trampoline effect from parent pillar-plate structure is also fully discussed through wave dispersion and frequency response studies, and the widening of local resonance bandgap is demonstrated. By a parametric study, the effect of geometric parameters on the reported bandgaps is elaborated. Both numerical and experimental results validate the effectiveness of composite trampoline pillar-plate structure in attenuating bulk waves over broadband frequency spectrum. The new findings reported here provide another perspective on the dynamical characteristics and usefulness of pillared metamaterials for wave manipulation and subwavelength vibration attenuation.

A Microvascular‐Based Multifunctional and Reconfigurable Metamaterial

AbstractNearly all‐natural and synthetic composites derive their characteristic attributes from a hierarchical makeup. Engineered metamaterials exhibit properties not existing in natural composites by precise patterning, often periodically on size scales smaller than the wavelength of the phenomenon they influence. Lightweight fiber‐reinforced polymer composites, comprising stiff/strong fibers embedded within a continuous matrix, offer a superior structural platform for micro‐architectured metamaterials. The emergence of microvascular fiber‐composites, originally conceived for bioinspired self‐healing via microchannels filled with functional fluids, provides a unique pathway for dynamic reconfigurable behavior. Demonstrated here is the new ability to modulate both electromagnetic and thermal responses within a single structural composite by fluid substitution within a serpentine vasculature. Liquid metal infiltration of varying density micro‐channels alters polarized radio‐frequency wave reflection, while water circulation through the same vasculature enables active‐cooling. This latest approach to control bulk property plurality by widespread vascularization exhibits minimal impact on structural performance. Detailed experimental/computational studies, presented in this paper, unravel the effects of micro‐vascular topology on macro‐mechanical behavior. The results, spanning multiple physics, provide a new benchmark for future design optimization and real‐world application of multifunctional and adaptive microvascular composite metamaterials.

Dissipative dual-phase mechanical metamaterial composites via architectural design

Dual-phase mechanical metamaterials, fabricated as a hybrid of two architected lattice materials with different mechanical properties and bioinspired patterning, have been shown to exhibit improved combination of properties, such as enhanced reinforced strength and toughness. In this study, we specifically examine the selection of the reinforcement phase, specifically involving the effects of its structural architecture, in terms of connectivity and interfacial structure, on the resulting mechanical properties and deformation mechanisms of such dual-phase lattice composites. The composites are simply fabricated using selected laser melting based additive manufacturing. Using quasi-static compression tests and simulation studies, we find that enhancing the role of the reinforcement phase (RP), connection phase (CP) and their interfaces, by employing more trusses distributed along the loading direction, can dramatically improve mechanical properties and energy absorption. By such architectural design of the connection phase, the specific stiffness, specific strength, and specific energy absorption of the dual-phase lattice composites can be optimized, respectively by 77%, 7% and 51% compared to the unreinforced matrix phase lattices. This suggests that the design space of mechanical metamaterials can be significantly expanded by architectural and phase selection together with bioinspired phase patterning.

Compression behaviours of 3D-printed CF/PA metamaterials: Experiment and modelling

This study characterises the compressive behaviours of 3D-printed carbon fibre (CF) reinforced polyamide (PA) composite metamaterials with negative Poisson's ratio (NPR) or enhanced effective elastic modulus (EEEM), which were designed via a multidisciplinary approach and additively manufactured with fused filament fabrication. The continuous carbon reinforced PA (CCF/PA) metamaterials are compared to those made of short carbon fibre reinforced PA (SCF/PA) when subjected to in-plane compression. A numerical model based on continuum damage mechanics is developed to describe the response and failure of the 3D-printed CCF/PA composites while another one based an elastic-plastic model is developed for the 3D-printed SCF/PA parts. For metamaterials with NPR, the stiffness, peak force, energy absorption (EA) and specific energy absorption (SEA) of CCF/PA metamaterials are respectively 152.1%, 90%, 107.6% and 86%, respectively, larger than those of SCF/PA, while the SCF/PA metamaterials can reach a greater NPR (about −0.3) than CCF/PA (−0.2 ~ −0.1). For composites with EEEM, the stiffness, peak force, EA and SEA of CCF/PA are significantly improved by 433.3%, 183.3%, 228.7% and 208.2%, respectively, in comparison to those of SCF/PA. Based on experimental observation and numerical simulation, matrix failure is found to be predominant for CCF/PA NPR and EEEM composites.

Spectral entropy and strain energy trends in composite mechanical metamaterials

The strain energy and spectral (Shannon) entropy distributions in composite lattices made of core and reinforcement components are investigated by conducting numerical experiments on a set of indefinitely tall lattice strips subjected to a point surface load. The spectral entropy measures the complexity of the strain energy spectrum as it transforms with distance from the loaded surface. The spectral entropy behavior is tailored by adjusting the degree of anisotropy in the lattices. Isotropic continuum-like responses exhibited enhanced spectral entropy decay near the loaded surface and were associated with dispersion of strain energy over a wide spatial area of the lattice. Highly anisotropic responses showed a slow entropy decay at the surface and the localization of strain energy. Interestingly, with sufficient distance from the loaded surface, all lattice designs exhibited the same asymptotic rate of entropy decay, and this rate also was similar to an isotropic continuum material behavior. This implies in practice that any exotic properties of metamaterials determined by their modal selectivity are generally better pronounced in the vicinity of loads, and that they tend to diminish on the periphery of these interesting material systems.

Binary masses manipulation with composite bilayer metamaterial

Flexible and efficient mass manipulation is of critical importance in multiple fields of industrial separation, membrane science, chemical production, and biotechnology. Owing to the extensive investigation of transformation optics/thermodynamics, some pioneering attempts of mass diffusion metamaterial are proposed to motivate the traditional techniques. However, most of the current works are dependent on specific spatial transformations, thus leading to the conventional imperfects of transformation-based metamaterial in mass manipulations. Here, we propose a bilayer meta-device for binary masses manipulation (O2 and N2) by directly solving static Fick’s law. Only homogeneous media are employed in such design owing to the independence of spatial transformations. The O2 avoiding and N2 concentrating behaviors with non-distortion concentration fields reveal the manipulative significance. The findings may promote the research on mass diffusion metamaterial towards easy obtainment, and open up an avenue for innovating the conventional mass manipulation techniques.