3D Metamaterials Research Articles

Asymmetry spin-polarization Fermi arc and topological chiral beam splitter with the triply degenerate point in metamaterial.

Dirac points (DPs) and Weyl points (WPs) have received much attention in photonic crystals (PhCs) and three-dimensional (3D) metamaterials research due to the robust surface states and Fermi arcs. In this work, two pairs of triply degenerate points (TDPs) have been proposed in a 3D metamaterial by breaking the time reversal symmetry (T) with an external magnetic field. Based on these TDPs, two pairs of asymmetric surface states with spin-polarization are revealed, and a topological chiral beam splitter is demonstrated showing the different propagating directions of the right-handed polarization (RCP) and left-handed polarization (LCP) lights. Remarkably, we can achieve unidirectional propagation with RCP or LCP even excited by a linear source owing to the asymmetry surface state. Our work provides a new, to the best of our knowledge, platform to study spin-polarization surface states and the enhanced spin photonic Hall effect in the metamaterials.

Optical Anomalies due to Volume Collective Modes of Plasmonic Metamaterials

AbstractThe emergence of optical anomalies in 3D plasmonic metamaterials upon excitation of volume collective modes is studied. These modes engage a collective response of all the meta‐atoms across the volume of the structure and arise due to coupling of localized plasmonic modes with Bloch modes of the 3D lattice. Two types of volume collective modes are introduced; a reflective mode resilient to the plasmonic absorption, exhibiting reflection that approaches unity with extremely low loss, through a distinct high‐Q spectral locking of the response of all the constituent plasmonic resonators in the volume; in addition, a transmissive mode that supports the emergence of lattice matched scattered waves within the volume, leading to full transmission through a spectral transparency window. These attractive optical properties of the volume collective modes may lead to a breakthrough in the design of low‐loss and efficient 3D plasmonic metamaterials for novel linear and nonlinear photonic applications.

3D Chiral Metamaterials for Biosensing - INVITED

In this contribution we will discuss the experimental application of 3D chiral metamaterials as high sensitivity biosensors, exploiting circular dichroism in transmission. 3D metamaterials with chiral features can be realized by highly accurate and highly localized bottom-up nanofabrication approach. Large chiroptical effects can be engineered, originating from the single element optical resonances, but collective interactions in arrayed configurations can play a significant role, further enhancing these effects. Capability of biomarker detection in the femtomolar range is demonstrated even in complex biofluid matrix.

A graphene/h-BN MEMS varactor for sub-THz and THz applications.

Recent development of terahertz systems has created the need for new elements operating in this frequency band, i.e., fast tunable devices such as varactors. Here, we present the process flow and characterization of a novel electronic variable capacitor device that is made with the use of 2D metamaterials such as graphene (GR) or hexagonal boron nitride (h-BN). Comb-like structures are etched into a silicon/silicon nitride substrate and a metal electrode is deposited at the bottom. Next, a PMMA/GR/h-BN layer is placed on top of the sample. As voltage is applied between GR and metal, the PMMA/GR/h-BN layer bends towards the bottom electrode thus decreasing the distance between electrodes and changing the capacitance. The high tunability and complementary metal oxide semiconductor (CMOS)-compatible process flow of the platform for our device and its millimeter size make it promising for applications in future electronics and terahertz technologies. The goal of our research is to integrate our device with dielectric rod waveguides, thus making THz phase shifters.

Structural design and tunable mechanical properties of novel corrugated 3D lattice metamaterials by geometric tailoring

In this work, a novel corrugated 3D lattice metamaterial with stable mechanical response and deformation behavior was constructed by geometric tailoring. Through quasi-static compression experiments and finite element simulations, the effect of cell number, scaling factor and gradient design methods are systematically studied. Using specific energy absorption (SEA), plateau stress and densification strain as energy absorption indicators, the effects of various factors on the energy absorption performance of corrugated lattice metamaterials were evaluated. The results demonstrate that the proposed corrugated lattice has stable mechanical response and ideal energy absorption performance due to the stable deformation behavior. In addition, the scaling of the corrugated lattice unit cells can trim the lattice mechanical indicators. Furthermore, the continuous interface is effective for realizing controllable mechanical response and tunable energy absorption performance of gradient lattice metamaterials.

Lightweight 3D Graphene Metamaterials with Tunable Negative Thermal Expansion.

In this study, a 3D graphene metamaterial (GM) showing negative thermal expansion is prepared using a strategy of hyperbolically oriented freezing under a dual temperature gradient along orthogonal directions after the π-π stacking-derived assembly of 2D graphene sheets. As the fundamental construction element of the 3D GM, the graphene sheet displays anomalous shrinking deformation with a thermal expansion coefficient of (-6.12 ± 0.28) × 10-6 that is triggered by thermally induced out-of-plane vibrations of the CC bonds. A combination of numerical simulations and experimental investigations validates that anomalous negative thermal expansion (NTE) behavior can be effectively delivered to scalable 3D GM candidates at larger dimensions beyond the basic 2D graphene sheets at the microscale. The multiscale design and optimization of the structural characterization of the 3D GM further realize the desirable regulation of the NTE performance with the NTE coefficient ranging from negative ((-7.5± 0.65) × 10-6 K-1 ) to near-zero values ((-0.8 ± 0.25) × 10-6 K-1 ). This is attributed to the NTE-derived release regulation of the primary stress/strain of the microstructure, and the 3D GM exhibits high thermal stability while preserving the desirable structural robustness and fatigue resistance under thermo-mechanical coupling conditions. Therefore, this 3D GM offers promising potential for applications as protective skin, thermal actuator, smart switcher, and packing filler.

Large-area 1D selective emitter for thermophotovoltaic applications in the mid-infrared

Two- or three-dimensionally patterned subwavelength structures, also known as metamaterials, have the advantage of arbitrarily engineerable optical properties. In thermophotovoltaic (TPV) applications, metamaterials are commonly used to optimize the emitter’s radiation spectrum for various source temperatures. The output power of a TPV device is proportional to the photon flux, which is proportional to the emitter size. However, using 2D or 3D metamaterials imposes challenges to realizing large emitters since fabricating their subwavelength features typically involves complicated fabrication processes and is highly time-consuming. In this work, we demonstrate a large-area (78 cm2) thermal emitter. This emitter is simply fabricated with one-dimensional layers of silicon (Si) and chromium (Cr), and therefore, it can be easily scaled up to even larger sizes. The emissivity spectrum of the emitter is measured at 802 K, targeting an emission peak in the mid-infrared. The emissivity peak is ∼0.84 at the wavelength of 3.75 μm with a 1.2 μm bandwidth. Moreover, the emission spectrum of our emitter can be tailored for various source temperatures by changing the Si thickness. Therefore, the results of this work can lead to enabling TPV applications with higher output power and lower fabrication cost.

Surrogate model for a mechanical metamaterial undergoing microstructure instabilities and phase transformations

This paper addresses the modeling of periodic metamaterials with microstructure instabilities. Such instabilities are produced by bistable elastic mechanisms, i.e., snap-through deformation mechanisms, inducing phase transformations. Metamaterials with these features can be used for energy dissipation in elastic regimes between other applications.A new surrogate model of the bistable mechanism to replace High-Fidelity Finite Element simulations is developed in two sequential stages. In the first stage, a semi-analytical model of the bistable structural element is presented. Following an approach taken from the literature, the analysis of the bistable element is generalized to include load cases that had not been considered in the original study. These loading conditions naturally happen in functionally 2D and 3D metamaterials with complex microarchitectures. In a second stage, a frame element with linear kinematics and small deformations is described. The constitutive relations of the frame element, i.e., axial stress and moment in terms of axial strain and curvature, follow the same equations of the semi-analytical model derived in the first stage. A Variational Principle of Energetic Equivalence supplies the link between the semi-analytical model of the curved beam and the frame element. In this way, the response of this frame element, of only six degrees of freedom, reproduces the non-linear geometric behavior of the bistable element.The surrogate model is particularly efficient for simulating a large number of unit cells of the metamaterial and with the capacity to reproduce its behavior under general loading conditions. Thus, it is appropriate to assessing the metamaterial limit behavior, typically concerning phenomena such as energy dissipation and hysteresis under closed load cycles.

Inverse design of 3D reconfigurable curvilinear modular origami structures using geometric and topological reconstructions

The recent development of modular origami structures has ushered in an era for active metamaterials with multiple degrees of freedom (multi-DOF). Notably, no systematic inverse design approach for 3D curvilinear modular origami structures has been reported. Moreover, very few modular origami topologies have been studied to design active metamaterials with multi-DOF. Herein, we develop an inverse design method for constructing 3D reconfigurable architected structures — we synthesize modular origami structures whose unit cells can be volumetrically mapped into a prescribed 3D curvilinear shape followed by volumetric shrinkage to construct modules. After modification of the tubular geometry, we search through all the possible geometric and topological combinations of the modular origami structures to attain the target mobility using a topological reconstruction of modules. Our inverse design using geometric and topological reconstructions can provide an effective solution to construct 3D curvilinear reconfigurable structures with multi-DOF. Our work opens a path toward 3D reconfigurable systems based on volumetric inverse design, such as 3D active metamaterials and 3D morphing devices for automotive, aerospace, and biomedical engineering applications.

Energy dissipation in multistable auxetic mechanical metamaterials

Multistable mechanical metamaterials are periodic structures whose unit cells show bistable configurations. The snap-through behavior of the unit cell enhances the energy dissipation of the metamaterials. The materials are reusable and can dissipate energy multiple times since the deformation is within the elastic region. This paper presents two types of two-dimensional auxetic metamaterials: the shuriken-shaped motif with four axes of symmetry and the triangle motif with six axes of symmetry. The cylindrical and three-dimensional (3D) configurations are designed with the geometric topology method. We carry out experiments with 3D printed samples, finite element analysis (FEA), and theoretical investigation to reveal the various mechanisms of energy dissipation. The results demonstrate that the planar metamaterials exhibit different energy dissipation along various loading directions. Each type of metamaterial exhibits discrepant force-displacement characteristics. The triangle motif performs better than the shuriken-shaped motif in terms of energy dissipation along some loading directions. The proposed auxetic metamaterials perform better than the conventional multistable structures with zero Poisson’s ratio. Energy dissipation and auxetic behavior of the typically cylindrical and 3D metamaterials are verified numerically and experimentally.

3D Auxetic Metamaterials with Elastically-Stable Continuous Phase Transition.

In solid state physics, phase transitions can influence material functionality and alter their properties. In mechanical metamaterials, structural-phase transitions can be achieved through instability or buckling of certain structural elements. However, these fast transitions in one mechanical parameter typically affect significantly the remaining parameters, hence, limiting their applications. Here, this limitation is addressed by designing a novel 3D mechanical metamaterial that is capable of undergoing a phase transition from positive to negative Poisson's ratio under compression, without significant degradation of Young's modulus (i.e. the phase transition is elastically-stable). The metamaterial is fabricated by two-photon lithography at the micro-scale and its mechanical behavior is assessed experimentally. For another choice of structural parameters, it is then shown that the auxetic behavior of the considered 3D metamaterial class can be maintained over a wide range of applied compressivestrain.

Ultraviolet Sharp High-Order Magnetic Plasmon Based Fano Resonance of 3D Metamaterials

We theoretically study the ultraviolet sharp Fano resonances (FRs) produced through the optical diffraction coupling between the narrow collective surface mode supported by the array periodicity and the broad high-order magnetic plasmon (MP) mode in the three-dimensional (3D) metamaterials consist of aluminum vertical split-ring resonator (Al 3D-SRR) array. The linewidth of the second-order MP induced ultraviolet FR is as narrow as 7.3 nm due to the diffraction coupling feature of the magnetic fields. The intensity and position of the ultraviolet sharp FR are easily tuned by varying the array period as well as the base and arm length of the Al 3D-SRR structure. The conventionally defined performance index of optical sensors, sensitivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> ) and figure of merit ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FoM</i> ) of our designed 3D metamaterial in the ultraviolet range, possess quite large values of 88 nm/RIU and 12, respectively.

Sustainable 3D Printing of Recyclable Biocomposite Empowered by Flash Graphene.

Sustainability of 3D printing can be reflected in three main aspects: deployment of renewable inks, recycling of printed products, and applications for energy- and materials- savings. In this work, we demonstrated sustainable vat-photopolymerization (VPP)-based 3D printing in a whole life-cycle process by developing a renewable ink made of soybean oil and natural polyphenols and recycling the ink for reprinting or converting printed biocomposite to flash graphene (FG) as reinforcing nanofillers in the biocomposite. We also realized its applications in fabricating lightweight, materials-saving 3D structures, acoustic metamaterials, and disposable microreactors for time-saving and efficiency-improving synthesis of metal-organic framework nanostructures. In addition to enhancing the tensile strength and Young's modulus of the biopolymers by 42% and 232% with only 0.6 wt % FG nanofillers, respectively, FG improved the printability of the ink in forming 3D tubular structures, which are usually very hard to be achieved in transparent resin. Success of this work will inspire further development for sustainability in 3D printing.

3D radar stealth composite hierarchical grid structure with extremely broadband absorption performance and effective load bearing

Multifunctional structures with both excellent microwave absorption performance and mechanical properties have attracted great attentions recently due to wide applications in aircraft and ships. In this research, a novel absorption structure was designed and fabricated through molding and interlocking technology by perfectly combining the composite hierarchical grid structure with excellent mechanical properties and extremely broadband 3D absorption metamaterial. The mechanism of structural parameters affecting absorption and mechanical properties of the proposed 3D radar absorption composite hierarchical grid structure (3D-RACHGS) were investigated. The measured result of reflectivity showed that −10 dB absorption bandwidth of 3D-RACHGS achieves 34.8 GHz (2.6–4 GHz, 6.6–40 GHz) with an average reflectivity of −17.4 dB. Further simulation demonstrated that the broadband absorption is attributed to multiple stationary wave modes. The measurement result of out-of-plane compression showed that the specific strength of the 3D-RACHGS achieves 123.5 × 103 m2/s2, which proves its effective load bearing. Failure mechanism map was also constructed to predict the failure mode of the 3D-RACHGS with various structural parameters. The proposed 3D-RACHGS will contribute to the vigorous development of the novel structural absorption materials and have immense potential to be used in new generation multifunctional skin and inlet.

Topological materials for full-vector elastic waves.

Elastic wave manipulation is important in a wide variety of applications, including information processing in small elastic devices and noise control in large solid structures. The recent emergence of topological materials has opened new avenues for modulating elastic waves in solids. However, because of the full-vector feature and the complicated couplings of the longitudinal and transverse components of elastic waves, manipulating elastic waves is generally difficult compared with manipulating acoustic waves (scalar waves) and electromagnetic waves (vectorial waves but transverse only). To date, topological materials, including insulators and semimetals, have been used for acoustic and electromagnetic waves. Although topological materials with elastic waves have also been reported, the observed topological edge modes lie on the domain wall. A natural question arises: Is there an elastic metamaterial with topological edge modes on its own boundary? Here, we report a 3D metal-printed bilayer metamaterial that topologically insulates elastic waves. By introducing chiral interlayer couplings, the spin-orbit couplings for elastic waves are induced, which give rise to nontrivial topological properties. Helical edge states with vortex features were demonstrated on the boundary of the single topological phase. We further show a heterostructure of the metamaterial that exhibits tunable edge transport. Our findings could be used in devices based on elastic waves in solids.

How to see hidden patterns in metamaterials with interpretable machine learning

Machine learning models can assist with metamaterials design by approximating computationally expensive simulators or solving inverse design problems. However, past work has usually relied on black box deep neural networks, whose reasoning processes are opaque and require enormous datasets that are expensive to obtain. In this work, we develop two novel machine learning approaches to metamaterials discovery that have neither of these disadvantages. These approaches, called shape-frequency features and unit-cell templates, can discover 2D metamaterials with user-specified frequency band gaps. Our approaches provide logical rule-based conditions on metamaterial unit-cells that allow for interpretable reasoning processes, and generalize well across design spaces of different resolutions. The templates also provide design flexibility where users can almost freely design the fine resolution features of a unit-cell without affecting the user’s desired band gap.

A bio-inspired 3D metamaterials with chirality and anti-chirality topology fabricated by 4D printing

ABSTRACT Artificial architected metamaterials equipped with unique mechanical and physical properties that are naturally inaccessible can be obtained by rational design. In this work, the innovative three-dimensional (3D) chiral and anti-chiral metamaterials are developed referring to the face-rotating polyhedral (FRP) structure present in the virus. Through assembling planar triangular units into the regular octahedron cells, several typical forms of chiral and anti-chiral metamaterials can be obtained by different assembly methods. By changing the topology parameters, the Poisson’s ratio can be adjusted between [0, 2.8]. The metamaterials are fabricated by 3D printing utilizing shape memory polymer, and the mechanical properties are analyzed via Finite Element Analysis (FEA) and experiments, including Young’s modulus, Poisson’s ratio, and tension-twist coupling behavior. In addition, target metamaterial with specific local deformation behavior is obtained by programmatic calculations and distributions to meet special requirements or achieve unique applications. The shape memory property endows the mechanical metamaterials with more potential applications.

Synergistically program thermal expansional and mechanical performances in 3D metamaterials: Design-Architecture-Performance

Metamaterials, incorporating specific micro-architectures, could be purposely customized to export the programmability in both thermal expansional and mechanical performances, which are beneficial to obtain the thermal and structural stabilities in engineering devices. Here, by focusing on developing an original design strategy, multiple classes of metamaterials were devised and analyzed to integrate the programmable coefficient of thermal expansion (CTE) and mechanical performances (relative density, stiffness and strength). In detail, firstly, a series of the bi-material metaunits was devised, and a vector analysis method was proposed to analytically identify the CTE tensors. Then, an original design strategy, i.e., matrix transformation method, was developed to systematically devise multiple classes of 3D metamaterials with the unidirectional, transversal isotropic and isotropic CTEs. Besides, the mechanical performances, including the relative density, stiffness and strength, were theoretically established. It was identified that these metamaterials well balanced the directionality and programmability of the CTEs. Most importantly, by modulating the geometrical parameters, the desirable CTEs, light weight, high stiffness and strength could be synergistically achieved in these metamaterials. Eventually, a principle was established to guide the development of metamaterials. That was the original design strategy acted as the underlying foundation to map the specific architectures in metamaterials, correspondingly, to build the ability to synergistically program or customize the thermal expansional and mechanical performances.

Tunable multi-narrowband perfect absorber based on graphene and black phosphorus metamaterial

Black phosphorus (BP) and graphene are two-dimensional (2D) metamaterials that support surface plasmon resonance. We propose a tunable mid-infrared multi-narrowband perfect absorber based on graphene and BP metamaterial. Perfect absorption peaks can be explained by the interference of two excited states in the structure. The transfer characteristics of the system are calculated by the coupled mode theory (CMT), and the theoretical calculated results agree well with the finite-difference time-domain (FDTD) numerical simulated ones. The resonant positions of the absorption peaks are affected by the layer spacing. By changing BP carrier density and graphene Fermi level, the dynamic tunable function can be realized, and the absorption performance of the system is not affected within the adjustment range. Meanwhile, the absorption performance of the system is not insensitive to the polarization angle of the incident light, when the polarization angle is less than 30°. The designed system can be applied to a variety of optical devices, including plasma sensors, multi-frequency absorbers, reflectors, switching controllers and filters.

Graphene-integrated toroidal resonance metasurfaces used for picogram-level detection of chlorothalonil in the terahertz region.

Toroidal dipole resonance can significantly reduce radiation loss of materials, potentially improving sensor sensitivity. Generally, toroidal dipole response is suppressed by electric and magnetic dipoles in natural materials, making it difficult to observe experimentally. However, as 2D metamaterials, metasurfaces can weaken the electric and magnetic dipole, enhancing toroidal dipole response. Here, we propose a new graphene-integrated toroidal resonance metasurface as an ultra-sensitive chemical sensor, capable of qualitative detection of chlorothalonil in the terahertz region, down to a detection limit of 100 pg/mL. Our results demonstrate graphene-integrated toroidal resonance metasurfaces as a promising basis for ultra-sensitive, qualitative detection in chemical and biological sensing.