Hybrid Metamaterial Research Articles

Dynamically tunable single-layer VO2/metasurface based THz cross-polarization converter

We demonstrate a single-layer THz metadevice that exhibits cross polarization transmission, a key factor to achieve optical activity. The device is comprised of a two-dimensional array of split ring resonators, each with a vanadium oxide (VO2) pad, integrated into one of the two capacitive gaps of the unit cell. Through numerical investigations we find that as the conductivity of VO2 increases the amplitude of the cross-polarization intensity decreases but maintains a wider broadband range than previously reported for single layered hybrid metamaterial (MM) devices as the VO2 transforms from the insulator to metallic phase. Also the asymmetric transmission, optically modulated by the device, is higher than that of multi-layered MM devices. Due to the materials properties of VO2, our results introduce a promising method that allows for an active sub-cycle dynamic tunability for THz polarization conversion with multiple modalities using optical, electrical or thermal switching. The study is an important step forward in developing compact, integrated, passive and active metadevices for polarization and wavefront control application in the THz.

Heterointerface-Enhanced Ultrafast Optical Switching via Manipulating Metamaterial-Induced Transparency in a Hybrid Terahertz Graphene Metamaterial.

We have demonstrated the active manipulation of metamaterial-induced transparency (MIT) in a terahertz hybrid metamaterial with graphene overlayer under photoexcitation. It is found that the introduction of graphene can greatly modify the resonant dips and transparency window through the formed depolarization field around unequal-length double bars to weaken dipole resonances and their destructive interference. Transient control of MIT behaviors is determined by the photogenerated carrier dynamics, which influences the distributions of currents and electric fields in the resonant region to hinder the near-field coupling of two bright modes. Optical modulation depth is sensitive to bar spacing due to an anomalous increased double-bar coupling involving intracell and intercell interaction. Heterointerface formed by the added graphene with substrate could further enhance terahertz response via effective separation of the photoexcited carriers. Theoretical calculation based on the coupled Lorentz oscillator model reveals that the photoinduced terahertz response mainly originates from the coupling and damping in hybrid structures. Our findings could facilitate the development of graphene-based dynamical terahertz modulators and optoelectronic devices.

Self‐Assembled Metal–Dielectric Hybrid Metamaterials in Vertically Aligned Nanocomposite Form with Tailorable Optical Properties and Coupled Multifunctionalities

Metal–dielectric hybrid metamaterials have attracted increasing research interest in recent years because of their novel optical properties and promising applications in the fields of electronic and photonic devices. Dielectric permittivity is a key parameter that strongly influences the optical properties of materials. By self‐assembling the metallic and dielectric components in a pillar‐in‐matrix structure, a strong anisotropic structure forms and results in opposite signs of permittivity components (i.e., ε|| > 0 and ε⊥ < 0, or vice versa) and exotic optical responses including hyperbolic dispersion in the visible to near‐infrared region. Herein, the main approaches of tuning the permittivity in self‐assembled metal–dielectric vertically aligned nanocomposite (VAN) thin films are reviewed, including tuning the metal pillar density and geometry, film strain state and background pressure during growth, and seeking other metal‐free and complex structure designs. Future research directions are also proposed, including unique approaches to improve their thermal stability, integrate on flexible substrates toward wearable device fabrication, and explore real‐time tunable metamaterials.

Dynamic Manipulation of THz Waves Enabled by Phase-Transition VO2 Thin Film.

The reversible and multi-stimuli responsive insulator-metal transition of VO2, which enables dynamic modulation over the terahertz (THz) regime, has attracted plenty of attention for its potential applications in versatile active THz devices. Moreover, the investigation into the growth mechanism of VO2 films has led to improved film processing, more capable modulation and enhanced device compatibility into diverse THz applications. THz devices with VO2 as the key components exhibit remarkable response to external stimuli, which is not only applicable in THz modulators but also in rewritable optical memories by virtue of the intrinsic hysteresis behaviour of VO2. Depending on the predesigned device structure, the insulator-metal transition (IMT) of VO2 component can be controlled through thermal, electrical or optical methods. Recent research has paid special attention to the ultrafast modulation phenomenon observed in the photoinduced IMT, enabled by an intense femtosecond laser (fs laser) which supports “quasi-simultaneous” IMT within 1 ps. This progress report reviews the current state of the field, focusing on the material nature that gives rise to the modulation-allowed IMT for THz applications. An overview is presented of numerous IMT stimuli approaches with special emphasis on the underlying physical mechanisms. Subsequently, active manipulation of THz waves through pure VO2 film and VO2 hybrid metamaterials is surveyed, highlighting that VO2 can provide active modulation for a wide variety of applications. Finally, the common characteristics and future development directions of VO2-based tuneable THz devices are discussed.

Fano-Resonant Hybrid Metamaterial for Enhanced Nonlinear Tunability and Hysteresis Behavior.

Artificial resonant metamaterial with subwavelength localized filed is promising for advanced nonlinear photonic applications. In this article, we demonstrate enhanced nonlinear frequency-agile response and hysteresis tunability in a Fano-resonant hybrid metamaterial. A ceramic cuboid is electromagnetically coupled with metal cut-wire structure to excite the high-Q Fano-resonant mode in the dielectric/metal hybrid metamaterial. It is found that the significant nonlinear response of the ceramic cuboid can be employed for realization of tunable metamaterials by exciting its magnetic mode, and the trapped mode with an asymmetric Fano-like resonance is beneficial to achieve notable nonlinear modulation on the scattering spectrum. The nonlinear tunability of both the ceramic structure and the ceramic/metal hybrid metamaterial is promising to extend the operation band of metamaterials, providing possibility in practical applications with enhanced light-matter interactions.

All-optical tunable slow-light based on an analogue of electromagnetically induced transparency in a hybrid metamaterial.

We demonstrate and analyze the use of metamaterials featuring an analogue of electromagnetically induced transparency (EIT) in slow light technology. For most metamaterials, EIT-like effects suffer from intrinsic ohmic loss, and the metamaterial-based slow-light effect can only be tuned passively, which limits their application in slow light devices. We propose a hybrid metamaterial with a unit cell composed of a ring resonator formed from photoactive silicon (Si) and a rectangular bar formed from metallic silver (Ag). Based on an analogue of EIT in the designed hybrid metamaterial, we theoretically demonstrate an all-optical tunable slow-light effect in the telecommunication window. We successfully demonstrate the possibility of designing novel all-optical tunable chip-scale slow-light devices that could be used in optical buffering.

Nonlinear Modulation of Electromagnetically Induced Transparency Based on Graphene-Metal Hybrid Metamaterial Structure

Nonlinear Modulation of Electromagnetically Induced Transparency Based on Graphene-Metal Hybrid Metamaterial Structure

Graphene Multiple Fano Resonances Based on Asymmetric Hybrid Metamaterial.

We theoretically investigate multiple Fano resonances in an asymmetric hybrid graphene–metal metamaterial. The multiple Fano resonances emerge from the coupling of the plasmonic narrow bonding and antibonding modes supported by an in-plane graphene nanoribbon dimer with the broad magnetic resonance mode supported by a gold split-ring resonator. It is found that the Fano resonant mode with its corresponding dark mode of the antibonding mode in the in-plane graphene nanoribbon dimer is only achieved by structural symmetry breaking. The multiple Fano resonances can be tailored by tuning the structural parameters and Fermi levels. Active control of the multiple Fano resonances enables the proposed metamaterial to be widely applied in optoelectronic devices such as tunable sensors, switches, and filters.

Design of 3D Oxide–Metal Hybrid Metamaterial for Tailorable Light–Matter Interactions in Visible and Near‐Infrared Region

AbstractDielectric–metallic hybrid metamaterials exhibit extraordinary optical properties due to the light–matter interactions at the dielectric–metallic interfaces. The ability in precision control of the light–matter interactions in nanoscale is key to tailor the optical properties of hybrid metamaterials. In this work, a complex 3D framework of multilayered self‐assembled BaTiO3(BTO)‐Au hybrid thin films is demonstrated with such precision control of the light–matter interaction in nanoscale. Unique “bamboo‐like” Au nanostructures are formed via the bilayer and trilayer stacking of BTO‐Au hybrid layers with interlayers of SrTiO3, CeO2, or MgO. Different film strain states introduced by the three interlayers result in variable diameter and density of Au nanopillars. Both simulated and experimental optical data demonstrate the localized surface plasmon resonance change and hyperbolic dispersion wavelength shift in visible to near‐infrared because of the effective tuning of the Au nanopillar aspect ratio and free electron density. The highly tunable optical properties along with the ferroelectric behavior and thermal robustness of the 3D hybrid film enable it to be a great candidate for multifunctional applications. This study demonstrates a unique 3D approach for precision optical property tuning and combined functionalities in oxide–metal metamaterial systems toward future integrated photonic and electronic devices.

Hybrid Metamaterial Textiles for Passive Personal Cooling Indoors and Outdoors

Radiative cooling engineering generally utilizes thermal radiation and sunlight reflection to decrease the temperature of an object or space. In this work, a polymer-based nanophotonic textile (PBN...

In-plane mechanical behavior of novel auxetic hybrid metamaterials

We present in this paper two novel concepts of hybrid metamaterials that combine a core unit cell of re-entrant or cross-chiral shape and lateral missing ribs. The first topology is a hybrid between an anti-tetrachiral and a missing rib (cross-chiral) configuration; the second one has a variable cross-chiral layout compared to the classical missing rib square structure. Their in-plane mechanical properties have been investigated from a parametric point of view using finite element (FE) simulations. The two classes of metamaterials have been benchmarked to obtain optimized designs and specific effective properties. Nonlinear simulations and experimental tests of the new re-entrant missing rib metamaterials featuring optimized geometry parameters have been performed to understand the behavior of these architectures under large deformations.

Multipolar resonance and bandgap formation mechanism of star-shaped lattice structure

The star-shaped lattice structure is recognized as a typical auxetic metamaterial. Unlike the most research focused on the negative Poisson's ratio, in this paper the wave propagation behaviour and vibration attenuation mechanism of the periodic star-shaped lattice structure are studied based on the analytical 16 degrees of freedom (DOF) discrete mass-spring model. The dispersion relation and bandgaps of the 16 DOF mass-spring model are derived based on lattice dynamics. The dependence of the bandgap boundaries on the parameters of configuration angle, stiffness, and mass are studied accordingly. It is noteworthy that the eigenstate modes investigation reveals that the bandgaps attribute to the hybridization of the monopole, dipole, quadrupole, and rotational resonance, which is only noticed in multiphase hybrid metamaterials before. Most importantly, though examining the eigenstate modes of the degeneration points, the low-frequency bandgap between the acoustic and optical dispersion curves is opened by tuning the dominant parameters. The response of the finite periodic star-shaped lattice shows the frequency ranges with high attenuation agree well with complete bandgaps predicted by dispersion relation. The star-shaped lattice shows a very unique anisotropic solid when the slope of the dispersion curve is negative.

Multifunctional self-assembled BaTiO3-Au nanocomposite thin films on flexible mica substrates with tunable optical properties

Integration of multifunctional hybrid materials with hyperbolic, plasmonic and ferroelectric properties on flexible substrates is of great interest towards future flexible integrated electronic and photonic devices. In this work, the successful integration of BaTiO3-Au hybrid metamaterials on flexible mica substrates has been demonstrated using a one-step pulsed laser deposition (PLD) technique. Tunable optical properties have been achieved by controlling the geometries of the Au nanostructures between nanoparticles and nanopillars by varying the growth temperature. The overall structure and properties of the hybrid materials is stable upon cyclic bending test (more than 1000 bending cycles), evidenced by the robust physical properties and microstructural stability. Furthermore, room temperature ferroelectric property was confirmed by piezoresponse force microscopy mapping. This work demonstrates an effective approach for integrating multifunctional oxide-metal nanocomposites on flexible mica substrate, and paves a way towards future flexible integrated devices.

Analysis of the impact of a novel cool roof on cooling performance for a low-rise prefabricated building in China

The recently proposed scalable-manufactured randomized glass-polymer hybrid metamaterial (i.e. metamaterial film) exhibits good energy-saving potential for building applications. The most convenient way to employ this metamaterial film-based radiative cooling is to integrate it with buildings as cool roofs. However, metamaterial film-based radiative cooling is more suitable for buildings with higher roof area to floor area ratios, as this accounts for its relative lower cooling power of 110 W/m2 on a daily average. The prefabricated buildings in China are commonly less than two floors, which are preferable for the application of this metamaterial film-based radiative cooling. To clearly reveal the cooling performance of the metamaterial film-based cool roof (MFCR), a single-floor prefabricated building is modelled in this study, and the energy-saving potential and economic feasibility of the application of the MFCR on the prefabricated building are discussed in detail. When comparing the model in this study with buildings that have the more commonly used shingle roofs or typical white roofs, the annual cooling electricity consumption is reduced by 28.9%–43.0% and 7.8%–12.9%, respectively, for buildings with MFCRs located in five cities in China, each in a different climate zone. Furthermore, the simple payback period for the buildings with MFCRs located in all five climate zones is less than three years compared to the buildings with shingle roofs. Practical application: A recently proposed metamaterial film exhibits good energy-saving potential for building applications. This paper explores the application of this metamaterial film as a cool roof on a low-rise prefabricated building. The analysis of the cooling performance and economic value of this low-rise prefabricated building located in all five climate zones in China provides guiding significance for the application of MFCR.

Janus-Type Hybrid Metamaterial with Reversible Solar-Generated Heat Storage and Release for High-Efficiency Solar Desalination of Seawater

Interfacial solar seawater desalination, originating from the driving force of the conversion of sunlight into heat energy, is facing the negative influence of intermittent solar radiation alternat...

A dynamically adjustable broadband terahertz absorber based on a vanadium dioxide hybrid metamaterial

A dynamically adjustable terahertz (THz) broadband absorber based on a vanadium dioxide (VO2) hybrid metamaterial is theoretically designed. During the design, we first consider working frequency, bandwidth, excitation method and fabrication process. And then, a commercialized full wave electromagnetic (EM) calculation software CST microwave 2019 based on finite integration technology is used to simulate and optimize the performance of the device. Due to the device is excited by light, it consists of a top layer of VO2 oblique-split-ring-resonator (OSRR) array, a polyimide (PI) spacer and a bottom metal film. The simulation results show that, when the VO2 changes from insulating state to metal state under light stimulus, the absorption increases from 3% to over 90%. Meanwhile, when the VO2 is in metallic phase, the bandwidth of absorption greater than 90% reaches to 1.0 THz and the relative bandwidth is about 83%. The potential applications of the device are active EM stealth, THz wave detection and thermal imaging. This work paves a new way for simply constructing a low-cost dynamically adjustable THz broadband absorber.

Mechanical design and energy absorption performances of novel dual scale hybrid plate-lattice mechanical metamaterials

In this paper, novel dual scale hybrid mechanical metamaterials consisting of simple cubic structure (SC), body-centered cubic structure (BCC), face-centered cubic structure (FCC) unit cells at different scale levels were designed and proposed for impact energy absorption, where one large type A unit cell and eight (2 × 2 × 2) small periodicspatially architected type B unit cells with half size of type A unit cell along X, Y and Z directions were integrated together for harvesting final hybrid metamaterials. Comparisons of specific energy absorption performances between novel hybrid mechanical metamaterials and constituent simple single type of unit cell lattice during compression process were performed through experimental investigation, where the failure and energy absorption process were recorded using the digital camera. Afterwards, finite element analysis (FEA) was performed and compared with experimental results for investigating the mechanical benefits of novel hybrid Plate-lattice mechanical metamaterials, it was found that the novel hybrid plate-lattice mechanical metamaterials can generate enhanced specific strength, specific stiffness and elevated energy absorption performances indicators, demonstrated promising industrial application potentials as energy-absorbing materials and structures for aerospace, vehicles, transport industrial sections.

Hybrid metamaterials enable multifunctional manipulation of mechanical waves on solid-fluid interfaces

Mechanical waves exhibit complex propagations and waveform transitions on the interfaces of different media. By attaching an ultra-thin layer including local resonators on a solid panel, we demonstrate that this ultra-thin layer contains two control paths for solid and air, manipulating elastic and sound waves on the solid–air interface, respectively. Owing to simultaneously breaking the spatial symmetry of the solid panel and adjusting the boundary impedance of the solid–air interface, the proposed ultra-thin layer combines three operating states that are unique to each of the existing mechanical wave metamaterials. Specifically, we observe the “sound state” for intensely reflecting sound waves at the local anti-resonance, the “elastic state” for completely preventing elastic waves at the local resonance, and the “transition state” for totally converting elastic waves into sound waves at the entire monopole-type resonance. Hence, we denote such an ultra-thin layer as the “hybrid metamaterial.” Our work may broaden the way of designing multifunctional materials and devices for manipulating mechanical waves.

Thermally controlled electromagnetically induced transparency in hybrid metal-InSb metamaterials at THz frequencies

We demonstrate an active controlled electromagnetically induced transparency (EIT) device via thermal control in a hybrid metamaterial, which consists of two split-ring resonators (SRRs) with integrated InSb-metal and a cut wire (CW) in a unit cell. We can dynamically control the amplitude modulation of the EIT window, by varying the temperature of the InSb thereby changing the damping rate of the dark mode of SRRs. When the temperature of the InSb changes from 240K to 320K, the EIT window undergoes modulation from on to off, and the modulation depth reaches 86.8%. The results are not only promising in designing compact slow light devices in the terahertz regime but also leading some essential applications in terahertz communications.

Hybrid Metamaterial for the Secondary Radar Antenna System

This paper proposes the gain enhancement of dual-band and dual-polarized asymmetric horn antenna for the secondary radar system using hybrid metamaterial techniques. The hybrid metamaterial is comprised of the structures of woodpile electromagnetic bandgap (EBG) for gain enhancement of the primary main beam of the radar system at the operating frequency of 1,300 MHz with horizontal polarization; and the wire medium structure that is placed beside the EBG structure for gain improvement of the identification friend or foe (IFF) main beam, which is operated at the center frequency of 1,060 MHz with vertical polarization. Meanwhile, the cooperated structures have to function to control the directions of the primary and IFF main beams retaining at 0° and 6°, respectively, too. When the hybrid metamaterial structure is placed at the front of an asymmetric horn’s aperture, with suitable parameters and optimized spacing, it is found to increase the gains of the two beams compared to the single asymmetric horn around 3 dB and retain the directions of original main beams. The comparison of the results between simulation and measurement, such as the reflected power (S<sub>11</sub>), gain, and radiation patterns, are in good agreement.