Multifunctional Metamaterials Research Articles

Multifunctional Metamaterial with Reconfigurable Electromagnetic Scattering Properties for Advanced Stealth and Adaptive Applications.

The rapid development of radar detection systems has led to an increased sensitivity to the electromagnetic (EM) scattering properties of detected targets. Flexible and adaptable EM scattering properties significantly enhance the survivability of battlefield weapons. This paper presents the design of a novel multifunctional metamaterial with reconfigurable EM scattering properties based on a bistable curved beam. In addition to the cushioning and energy absorption properties of curved beams, the metamaterial achieves more than 90% EM absorption in the frequency range of 2.17-17.31GHz, with a relative thickness of only 0.09λL. The bistable nature of the metamaterial allows it to switch between different states. Moreover, combined with the digital coding, this metamaterial can continuously adjust the absorbing bandwidth and further enhance the EM absorption rate within a specific frequency band range. If applied to satellite configurations, the developed metamaterial significantly reduces the radar cross section and offers potential applications in reconfiguring EM scattering properties, when applied to satellite configurations. By actively controller and reconstructing the EM scattering properties at certain frequency points, the metamaterial can achieve camouflage, providing innovative solutions for future stealth technology, electronic countermeasures, and deception jamming in radar detection.

Multifunctional Metamaterial for Asymmetric Transmission and Perfect Absorption in Terahertz Region

Multifunctional Metamaterial for Asymmetric Transmission and Perfect Absorption in Terahertz Region

Multifunctional metamaterials for simultaneous sound absorption and flexural vibration isolation

Controlling the noise and vibration simultaneously in some engineering scenes is extremely essential to eliminate harmful effects on the humans and equipments. To overcome this challenge, a multifunctional metamaterial plate with both airborne sound absorbtion and flexural vibration isolation simultaneously is investigated theoretically, numerically, and experimentally. The plate consists of a host plate and a Helmholtz resonator, where Helmholtz resonance is used to absorb sound waves and its external solid domain plays as role of a local resonator to isolate the flexural vibrations. The theoretical models were established to characterize the mechanism of the sound absorption and vibration isolation. The experimental results demonstrated that the proposed metamaterial plate can achieve perfect sound absorption at 649 Hz and a flexural wave band gap at 289–470 Hz. Besides, although the sound absorption and vibration isolation functions are integrated in the same component, our theory identifies several critical geometrical parameters which can manipulate the absorption peak and the flexural wave bandgap, allowing us to design its frequency of multiple functions as desired. This work provides a promising solution for noise and vibration reduction in engineering.

A numerical study of a multifunctional metamaterial with efficient terahertz absorption and low infrared emission

Abstract In this study, a multifunctional metamaterial is proposed to effectively absorb terahertz (THz) radiation and shield against infrared (IR) emissions. The device comprises an IR shielding layer made of ZnS and SiO2, and a terahertz absorbing layer utilizing a ‘graphene—SiO2—gold’ sandwich-like structure. The properties of the metamaterial are investigated using the full-vector finite element method. The results indicate that the emissivity of the device is below 0.1 in the IR atmospheric window (8–14 μ m ), with absorption reaching 90% and a bandwidth of 2.42 THz in 2–6 THz. Furthermore, the device is certainly tolerant to variations in the angle of incidence. It has a simple structure and a relatively easy preparation process. These advantages make it suitable for applications in the fields of anti-radar stealth in the THz band.

In plane mechanical properties of hexagonal V-chiral and Tri-chiral metamaterials

The reasonable design of man-made multifunctional metamaterials with advanced mechanical and physical properties that are not found in nature is both challenging and important. In this paper, novel chiral structures are designed by adding V- and Tri- chiral elements to the typical hexagonal honeycomb substrate, so as to realize the modulation of in plane mechanical properties. Finite element simulations show that the Poisson's ratio of the hexagonal V-chiral structure is negative when the strain is greater than 0.4, and that of the hexagonal Tri-chiral structure is always negative. Quasi-static compression tests show that the introduction of chiral properties results in a stronger load-bearing capacity, and the hexagonal Tri-chiral structure has a stronger energy absorption (EA) and specific energy absorption (SEA) capability. A parametric study is carried out by means of FEM, by adjusting the geometrical parameters of the proposed structures, the performance in terms of energy absorption and compressive stiffness can be improved. Subsequently, Bloch-Floquet theorem is employed for the dispersion relations of the chiral metamaterials and the results show that compared to conventional hexagonal honeycomb, chiral metamaterials are able to generate band gaps in a lower frequency range. Numerical simulation results show that the bandwidth of the proposed novel chiral metamaterials can be tuned through a reasonable selection of hexagonal edge length, wall thickness and radius. Experimental investigations are conducted to test the vibration transmission rate of Structure Ⅲ, and the results prove that the structure is capable of vibration suppression in the target frequency band range. Finally, by filling Structure Ⅲ with steel columns, the structure generates band gaps in the lower frequency range, hence the application of this chiral metamaterial is broadened.

Intelligently optimized arch-honeycomb metamaterial with superior bandgap and impact mitigation capacity

Engineering applications concurrently face challenges related to vibration, impact, load-bearing and energy absorption. Here, an arch-honeycomb metamaterial with split-ring resonators is proposed for wave attenuation and impact mitigation, with better energy absorption and lower initial peak stress. The split-ring resonators effectively induce bandgaps below 3 kHz, and the mechanisms of bandgap generation and polarization are studied through mode shapes, frequency contours and equivalent mass densities. Subsequently, a machine learning-based optimization framework is introduced to tailor the bandgaps, leading to a 155.59% increase in bandgap width. Furthermore, superior vibration isolation and impact mitigation are confirmed through experiments. Obvious attenuation peaks are observed in the bandgaps of the acceleration transmission spectrum in frequency domain. In time domain, the impact test demonstrates peak weakening and delay. The metamaterials offer advantages in wave attenuation, impact mitigation, load-bearing and energy absorption, providing valuable insights for the advancement of multifunctional metamaterials and their practical engineering applications.

Low frequency bandgap and high stiffness of innovative auxetic metamaterial with negative thermal expansion

Achieving multifunctional integration is crucial in mechanical metamaterials to meet the requirements of structures and equipment serving in complex environments across various engineering fields. In this study, we propose two novel bi-material and tri-material metamaterials based on the original edge-shared quadrangle (EQ/EQO) metamaterial, which exhibit negative thermal expansion (NTE), negative Poisson's ratio (NPR), and bandgap characteristics. The effective thermoelastic properties, including coefficient of thermal expansion (CTE), Poisson's ratio (PR), and Young's modulus, are compared and analyzed through theoretical formulation based on Timoshenko beam theory and numerical simulation using continuum elements with Abaqus. Additionally, finite element analysis is employed to calculate the energy band structures of these metamaterials based on Bloch's theorem, while the transmission characteristic curve verifies the validity of the obtained band structure. We systematically discuss the bandgap characteristics, coupling relationship between bandgaps and thermoelastic properties, as well as the influence of geometrical parameters on both bandgaps and thermoelastic properties. Our results demonstrate that the effective thermoelastic properties of these metamaterials are primarily determined by their frame structure's geometrical parameters, particularly the incline angle. Furthermore, for bi-material metamaterials, their specific stiffness closely relates to their bandgaps; however, for tri-material metamaterials, only the central local resonant unit determines their bandgap behavior. Notably, planar and 3D tri-material metamaterials can concurrently achieve a low-frequency bandgap along with high stiffness as well as NTE/NPR behavior. This work presents a new design strategy for optimizing multifunctional metamaterials' bandgaps while incorporating NTE behavior.

Lightweight cellular multifunctional metamaterials with superior low-frequency sound absorption, broadband energy harvesting and high load-bearing capacity

Multifunctional materials are highly desired for the design of compact engineering structures, such as aircraft where weight reduction, sound absorption, load carrying, and energy harvesting are key considerations. However, design challenge remains in the balance of multiple functionalities. Here, we combine the sandwich structure with the neck-embedded cavities to design a cellular metamaterial having sound-absorption, compression/impact resistance and energy harvesting functionalities. For sound absorption, an autoencoder-like neural network is constructed to generate an instant design, after which a probabilistic module is inserted to optimize it by searching solutions in a slightly expanded design space. This inverse design has been experimentally validated, showing broadband sound absorption from 400 to 650 Hz merely with nine ultra-thin resonators. Beyond serving as absorber, the resonant cavities, once installed with well-tuned piezoelectric membranes, can gather broadband acoustic energy at low frequencies. Additionally, the cellular metamaterial inherits the excellent mechanical properties of honeycomb cores, having a low density of 0.64 g/cm3 yet displaying a high yield strength (21.2 MPa) in out-of-plane compression test and a superior energy absorption capability (8.6 J/cm3) in low-velocity impact tests. This work presents an effective approach to design lightweight metamaterials of superior mechanical and acoustic functionalities highly sought-after in practical engineering.

Mountain-valley crease reconfiguration of 4-crease origami vertices and tessellations

Reconfigurable origami-inspired folding has recently gained significant attention due to its potential to achieve multi-shape changes through crease topological morphing, resulting in multi-functionality from a single original structure. However, it is one of the major challenges to determine all possible mountain-valley crease (MV) assignments that ensure rigid foldability and obtain duplicate configurations in large 2D origami tessellations or 3D cellular structures. In this study, we developed a straightforward algorithm that combines graphic representation and motion compatibility conditions to assess the reconfigurability of origami structures with 4-crease vertices including double corrugated, Miura-ori, and symmetric Eggbox vertices, as well as their 2D and even 3D cellular tessellations. Our analysis has revealed three types of oligo-modal origami tessellations characterised by a consistent number of MV assignments independent of tessellation size, and pluri-modal cellular origami structures that exhibit negative, zero, and positive Poisson's ratios which were verified through experiment. This work could serve as a stepping stone towards developing multifunctional metamaterials and devices based on reconfigurable origami through mountain-valley crease assignment.

Bi-directional extraordinary absorption, transmission multifunctional metamaterial based on circular metal-VO2 composites

Multifunctional metamaterials play a crucial role in advancing terahertz technology. In this paper, a multifunctional metamaterial composed solely of circular metal-vanadium dioxide (VO2) is designed and numerically demonstrated. The device comprises a top layer of circular VO2 ring, two polyimide dielectric layers, with two metal layers etched and filled with VO2, and a bottom embedded silver (Ag) circular ring dielectric layer. The metamaterial serves as a broadband and narrowband absorptive or transmissive substrate, utilizing the phase transition of VO2 between its metal and dielectric states. When VO2 is in its metal phase, the top circular VO2 ring periodic array functions as a broadband absorber, exhibiting a relative absorption bandwidth of approximately 93%. Meanwhile, the bottom circular Ag ring periodic array functions as a narrowband absorber and exhibits high sensitivity. In contrast, when VO2 is in the insulating phase, the metamaterial acts as a broadband transmittance substrate, exhibiting a maximum transmittance greater than 85%. This proposed metamaterial holds tremendous potential for utilization across various applications within the terahertz band, spanning from terahertz stealth radar to tunable biosensors and photodetectors.

Multifunctional metamaterial device based on VO2 and the equivalent diode.

This paper proposes a switchable multifunctional metamaterial device operating in the terahertz (THz) band. The device is loaded with an equivalent diode and utilizes vanadium dioxide (V O 2). The middle layer of the whole device, a metal layer, divides the device into the I side and the II side. When the diode is ON, the I side can achieve dual-band absorption at 1.975 and 4.345THz. When the diode is OFF, the I side can achieve single-band absorption at 4.28THz. In the case of V O 2 being insulating, the II side can achieve linear-to-linear (LTL) polarization conversion at 2.342-4.18THz. In the case of V O 2 being conductive, the II side can realize linear-to-circular (LTC) polarization conversion at 2.105-3.283THz. The device provides a new strategy for the subsequent combination of multiple functions. The device can be used in electromagnetic stealth, intelligent applications, radiometers, and sensors and has relatively large application potential in miniaturized multifunctional metamaterials and THz band research.

Additively manufactured multi-functional metamaterials: low coefficient of thermal expansion and programmable Poisson’s ratio

ABSTRACT By using Invar 36 alloy as the constituent material, a series of multi-functional metamaterials, integrating low coefficient of thermal expansion (CTE) and programmable Poisson’s ratio (PR), were originally designed and additively manufactured by laser powder bed fusion (PBF-LB). The densification, relative density, microstructures, CTE and PR were systematically characterised and analysed by experiments and numerical modelling. Specifically, the fabricated metamaterials demonstrate uniform microstructures, resulting in isotropic low CTEs ranging from 1.79 to 1.85 ppm/°C. Besides, the designed metamaterials achieve PR tuning in the range of −0.54∼+0.58, which is close to the theoretical predictions, confirming the PR programmability. The underlying mechanism is disclosed that the variable θ 1 dominates the transverse deformation behaviour of the metamaterial, achieving programmable PR. Summarily, these metamaterials achieve the integration of the low CTE and programmable PR, and provide a wider operating temperature range and superior mechanical performances than polymer-based multi-functional metamaterials, exhibiting a broader application prospect.

Laser additive manufacturing of hierarchical multifunctional chiral metamaterial with distinguished damage-resistance and low-frequency broadband sound-absorption capabilities

Traditional materials or advanced artificially engineered metamaterials are incapable of effectively addressing the simultaneous challenges of impact energy hazards and low-frequency noise. There is an urgent need for multifunctional materials that can address this multi-physics field coupling problem. Herein, a hierarchical multifunctional chiral metamaterial (HMCM) is proposed for damage-resistance and low-frequency broadband sound-absorption capabilities fabricated by means of laser powder bed fusion technology. Cavity resonators with internally extended tubes with hierarchical chiral configuration were selected as primary units. The damage-resistance performance of the HMCM was investigated systematically through experimental, numerical, and theoretical methods. Crashworthiness design and optimization on the multifunctional chiral metamaterial were implemented to explore the effect of geometrical parameters including distance ratio and wall thickness distribution on crushing resistance. It was determined that specific configurations in these parameters significantly enhance mechanism for dissipating energy of the HMCM. Furthermore, the designed metamaterial has been experimentally, numerically, and theoretically proven to possess quasi-perfect broadband sound absorption in the target range of 425 Hz to 553 Hz with an average sound absorption coefficient exceeding 0.9. Overall, this work not only offers a promising solution for designing multifunctional metamaterials but also highlights the potential of additive manufacturing techniques in the development of such sophisticated materials.

A magnetically actuated dynamic labyrinthine transmissive ultrasonic metamaterial

Currently, space-coiling acoustic metamaterials are static, requiring manual reconfiguration for sound-field modulation. Here, we introduce an approach to enable active reconfiguration, using standalone dynamic space-coiling unit cells called dynamic meta-bricks. Unlike their static counterparts, these meta-bricks, house an actuatable soft robotic-inspired magnetorheological elastomeric flap. This flap operates like a switch to directly control the transmitted ultrasound. For scalability, we present a hybrid stacking method, which vertically combines static and dynamic meta-bricks. This allows us to form a surface-integrated metasurface through concatenating variations of either fully static or hybrid stacks. By actuating dynamic metasurface sections, we experimentally demonstrate accurate modulation of λ/4 (≈2 mm) between two acoustic twin traps. We shift a levitated bead between the traps, validating that full-array operational dynamicity is achievable with partial, localised actuation. This work showcases the synergy between active and passive reconfigurability, opening possibilities to develop multifunctional metamaterials with additional degrees of freedom in design and control.

Origami Metamaterials Enable Low-Stress-Driven Giant Elastocaloric Effect.

Elastocaloric materials, capable of achieving reversible thermal changes in response to a uniaxial stress, have attracted considerable attention for applications in advanced thermal management technologies, owing to their environmental friendliness and economic benefits. However, most elastocaloric materials operating on the basis of first/second-order phase transition often exhibit a limited caloric response, field hysteresis, and restricted working temperature ranges. This study resorts to origami engineering for realizing multifunctional metamaterials with exceptional elastocaloric effects at both nano (exemplified by computational simulations for graphene) and meso (demonstrated by experimentation on thermoplastic polyurethane elastomers) scales. The findings uncover that the graphene origami exhibits low-stress-driven reversible and giant elastocaloric effects without a hysteresis loss and with a high elastocaloric strength. These effects are achieved across a wide working temperature range (100-600 K) and are tailorable by fine-tuning the topological parameters and configurational status of the origami metamaterials. We demonstrate the scalability of the origami design strategy for magnifying the elastocaloric effect by the 3D printing of a mesoscale origami-inspired thermoplastic polyurethane metastructure that showcases enhanced elastocaloric performance at room temperature. This study presents the potential for the realization of architected elastocaloric materials through surface functionalization and origami engineering. The findings impart exciting prospects of elastocaloric origami metamaterials as the next generation of multiscale and sustainable thermal management technologies.

Controllable Wrinkling Inspired Multifunctional Metamaterial for Near‐Field and Holographic Displays

AbstractTunable electromagnetic (EM) metamaterials have received significant attention due to their compelling advantages of integration and minimization compared with conventional bulky devices. Meanwhile, mechanically reconfigurable metamaterials have witnessed a striving period over recent years due to their simplified structural composition and confined modulation capabilities. Here, a controllable‐wrinkling‐based reconfiguration method is proposed to design split‐ring resonant units with dynamic transmittance spectra by switching between planar and wrinkling morphologies. For the linear polarized incidence, the geometries of planar and wrinkled units are optimized to achieve on‐demanded manipulation of the phases and amplitudes, respectively. By simultaneously implementing the amplitude design and the phase gradient, the mechanically inspired metamaterial is engineered to display a near‐field and a holographic image. For circularly polarized incidences, the spin‐decoupled phases and chiral effects demonstrated in the planar and wrinkled state assist in designing a metamaterial to possess spin‐multiplexed and strain‐modulated fourfold displays. These results demonstrate the practical feasibility of the wrinkling method in engineering tunable metamaterials, and the design flexibility, as well as the mechanical strategy, can extend the potential toward the application scenarios such as information processing, sensing, imaging, flexible meta‐devices, etc.

A Multifunctional Metamaterial Device with Tunable Broadband Absorption and Transmission Characteristics in the Terahertz Region

A Multifunctional Metamaterial Device with Tunable Broadband Absorption and Transmission Characteristics in the Terahertz Region

Terahertz multi-band absorber and dual-bandwidth polarization converter based on VO2 and graphene

A terahertz metamaterial with multiple functions is proposed based on patterned graphene, concentric gold rings and gold columns, and vanadium dioxide (VO2). By adjusting the temperature of VO2, it can be in metal state or insulator state, and correspondingly the metamaterial can work as a dual-bandwidth polarization converter or a multi-bandwidth absorber. When the metamaterial acts as a polarization converter, by adjusting the Fermi level of graphene, the converter can realize simultaneously x-polarized wave to y-polarized wave polarization conversion (CPC) and line-to-circular (LTC) polarization conversion (PC). In addition, by adjusting the Fermi level of graphene, the operating frequency and operating efficiency of the absorber and polarization converter can be dynamically tuned. By studying the electric field distribution and the surface current of the metamaterial, the physical mechanism of efficient absorption and dual-bandwidth polarization is explored. Moreover, the proposed multifunctional metamaterial is highly robust to incidence angle. It has potential applications in communication, spectroscopy, sensors, and physical detection.

Hydrodynamic metamaterials: Principles, experiments, and applications

AbstractHydrodynamic metamaterials, a nascent research field, possess immense potential for fluid flow manipulation. With engineered structure design, they offer unparalleled control over fluid behavior beyond the capabilities of conventional methods. In this review, we focus on hydrodynamic metamaterials and provide a comprehensive overview of the current state of this research field. We start by introducing basic theories and principles of hydrodynamic metamaterials and then illustrate the different functions of hydrodynamic metamaterials that have been realized in porous medium flow and Hele‐Shaw flow. Moreover, we also demonstrate the multifunctional metamaterials that have been developed in hydrodynamics. Some research progresses are highlighted due to their promising applications, including drag reduction, microfluidic manipulation, and biological tissue coculture. The review concludes by identifying major challenges and proposing research directions for the future.

A Bioinspired Bilevel Metamaterial for Multispectral Manipulation toward Visible, Multi-Wavelength Detection Lasers and Mid-Infrared Selective Radiation.

Manipulation of the electromagnetic signature in multiple wavebands is necessary and effective in civil and industrial applications. However, the integration of multispectral requirements, particularly for the bands with comparable wavelengths, challenges the design and fabrication of current compatible metamaterials. Here, a bioinspired bilevel metamaterial is proposed for multispectral manipulation involving visible, multi-wavelength detection lasers and mid-infrared (MIR), along with radiative cooling. The metamaterial, consisting of dual-deck Pt disks and a SiO2 intermediate layer, is inspired by the broadband reflection splitting effect found in butterfly scales and achieves ultralow specular reflectance (average of 0.013) over the entire 0.8-1.6µm with large scattering angles. Meanwhile, tunable visible reflection and selective dual absorption peaks in MIR can be simultaneously realized, providing structural color, effective radiative thermal dissipation at 5-8µm and 10.6µm laser absorption. The metamaterial is fabricated by a low-cost colloidal lithography method combined with two patterning processes. Multispectral manipulation performances are experimentally demonstrated and a significant apparent temperature drop (maximum of 15.7°C) compared to the reference is observed under a thermal imager. This work achieves optical response in multiple wavebands and provides a valuable way to effectively design multifunctional metamaterials inspired by nature.