Showing papers on "Metamaterial absorber published in 2012"
TL;DR: The ability of the MPA to exhibit extreme performance flexibility will be discussed and the theory underlying their operation and limitations will be established and Insight is given into what the authors can expect from this rapidly expanding field and future challenges will be addressed.
Abstract: The advent of negative index materials has spawned extensive research into metamaterials over the past decade. Metamaterials are attractive not only for their exotic electromagnetic properties, but also their promise for applications. A particular branch–the metamaterial perfect absorber (MPA)–has garnered interest due to the fact that it can achieve unity absorptivity of electromagnetic waves. Since its first experimental demonstration in 2008, the MPA has progressed significantly with designs shown across the electromagnetic spectrum, from microwave to optical. In this Progress Report we give an overview of the field and discuss a selection of examples and related applications. The ability of the MPA to exhibit extreme performance flexibility will be discussed and the theory underlying their operation and limitations will be established. Insight is given into what we can expect from this rapidly expanding field and future challenges will be addressed.
1,419 citations
TL;DR: An ultrabroadband thin-film infrared absorber made of sawtoothed anisotropic metamaterial waveguide that can be applied in the field of designing photovoltaic devices and thermal emitters.
Abstract: We present an ultrabroadband thin-film infrared absorber made of sawtoothed anisotropic metamaterial. Absorptivity of higher than 95% at normal incidence is supported in a wide range of frequencies, where the full absorption width at half-maximum is about 86%. Such property is retained well at a very wide range of incident angles too. Light of shorter wavelengths are harvested at upper parts of the sawteeth of smaller widths, while light of longer wavelengths are trapped at lower parts of larger tooth widths. This phenomenon is explained by the slowlight modes in anisotropic metamaterial waveguide. Our study can be applied in the field of designing photovoltaic devices and thermal emitters.
826 citations
TL;DR: In this article, a microwave ultra-broadband polarization-independent metamaterial absorber is demonstrated, which is composed of a periodic array of metal-dielectric multilayered quadrangular frustum pyramids.
Abstract: A microwave ultra-broadband polarization-independent metamaterial absorber is demonstrated. It is composed of a periodic array of metal-dielectric multilayered quadrangular frustum pyramids. These pyramids possess resonant absorption modes at multi-frequencies, of which the overlapping leads to the total absorption of the incident wave over an ultra-wide spectral band. The experimental absorption at normal incidence is above 90% in the frequency range of 7.8–14.7 GHz, and the absorption is kept large when the incident angle is smaller than 60°. The experimental results agree well with the numerical simulation.
735 citations
TL;DR: It is shown that the film-coupled nanocubes provide a reflectance spectrum that can be tailored by varying the geometry (the size of the cubes and/or the thickness of the spacer) and can be controlled at scales out of reach of lithographic approaches that are otherwise required to manipulate matter on the nanoscale.
Abstract: Efficient and tunable absorption is essential for a variety of applications, such as designing controlled-emissivity surfaces for thermophotovoltaic devices, tailoring an infrared spectrum for controlled thermal dissipation and producing detector elements for imaging. Metamaterials based on metallic elements are particularly efficient as absorbing media, because both the electrical and the magnetic properties of a metamaterial can be tuned by structured design. So far, metamaterial absorbers in the infrared or visible range have been fabricated using lithographically patterned metallic structures, making them inherently difficult to produce over large areas and hence reducing their applicability. Here we demonstrate a simple method to create a metamaterial absorber by randomly adsorbing chemically synthesized silver nanocubes onto a nanoscale-thick polymer spacer layer on a gold film, making no effort to control the spatial arrangement of the cubes on the film. We show that the film-coupled nanocubes provide a reflectance spectrum that can be tailored by varying the geometry (the size of the cubes and/or the thickness of the spacer). Each nanocube is the optical analogue of a grounded patch antenna, with a nearly identical local field structure that is modified by the plasmonic response of the metal's dielectric function, and with an anomalously large absorption efficiency that can be partly attributed to an interferometric effect. The absorptivity of large surface areas can be controlled using this method, at scales out of reach of lithographic approaches (such as electron-beam lithography) that are otherwise required to manipulate matter on the nanoscale.
658 citations
TL;DR: In this article, the authors demonstrate the design, characterization, and interference-theory interpretation of a terahertz triple-band metamaterial absorber (MA) with three distinctive absorption peaks at 0.5, 1.03, and 1.71 THz with absorption rates of 96.4, 96.3, and 96.7%, respectively.
Abstract: We demonstrate the design, characterization, and interference-theory interpretation of a terahertz triple-band metamaterial absorber (MA). The experiments show that the fabricated MA has three distinctive absorption peaks at 0.5, 1.03, and 1.71 THz with absorption rates of 96.4%, 96.3%, and 96.7%, respectively. We use the multi-reflection interference theory to investigate the physical insight of the proposed triple-band terahertz MA, which provides a design guideline for MA of such type. The theoretical predictions of the interference model have excellent agreements with experimental results. The designed multiband absorber is easy to manufacture and insensitive to incident polarizations with high absorption, which is favorable for various applications.
378 citations
TL;DR: In this article, a solar thermo-photovoltaic (STPV) collection system based on a large-area, nano-print-patterned film of plasmonic structures acting as an integrated solar absorber/narrow-band thermal emitter (SANTE) is presented.
Abstract: We present the concept of a solar thermo-photovoltaic (STPV) collection system based on a large-area, nanoimprint-patterned film of plasmonic structures acting as an integrated solar absorber/narrow-band thermal emitter (SANTE). The SANTE film concept is based on integrating broad-band solar radiation absorption with selective narrow-band thermal IR radiation which can be efficiently coupled to a photovoltaic (PV) cell for power generation. By employing a low reflectivity refractory metal (e.g., tungsten) as a plasmonic material, we demonstrate that the absorption spectrum of the SANTE film can be designed to be broad-band in the visible range and narrow-band in the infrared range. A detailed balance calculation demonstrates that the total STPV system efficiency exceeds the Shockley–Queisser limit for emitter temperatures above Te = 1200 K, and achieves an efficiency as high as 41% for Te = 2300 K. Emitter temperatures in this range are shown to be achievable under modest sun concentrations (less than 1000 suns) due to the thermal insulation provided by the SANTE film. An experimental demonstration of the wide-angle, frequency-selective absorptivity is presented.
355 citations
TL;DR: A heat transfer model is constructed to investigate the temporal and spatial variation of temperature in plasmonic gold nanostructures and shows that the temperature of the gold nanoparticles can be raised from room temperature to >795 K in just a few nanoseconds with a low light luminance.
Abstract: Photothermal effects in plasmonic nanostructures have great potentials in applications for photothermal cancer therapy, optical storage, thermo-photovoltaics, etc. However, the transient temperature behavior of a nanoscale material system during an ultrafast photothermal process has rarely been accurately investigated. Here a heat transfer model is constructed to investigate the temporal and spatial variation of temperature in plasmonic gold nanostructures. First, as a benchmark scenario, we study the light-induced heating of a gold nanosphere in water and calculate the relaxation time of the nanosphere excited by a modulated light. Second, we investigate heating and reshaping of gold nanoparticles in a more complex metamaterial absorber structure induced by a nanosecond pulsed light. The model shows that the temperature of the gold nanoparticles can be raised from room temperature to >795 K in just a few nanoseconds with a low light luminance, owing to enhanced light absorption through strong plasmonic r...
336 citations
TL;DR: Multilayer, lithographically patterned, subwavelength, metal elements are demonstrated, whose distribution forms a computer-generated phase hologram in the infrared region (10.6 μm), leading to more compact, efficient and versatile optical components.
Abstract: As a result of advances in nanotechnology and the burgeoning capabilities for fabricating materials with controlled nanoscale geometries, the traditional notion of what constitutes an optical device continues to evolve. The fusion of maturing low-cost lithographic techniques with newer optical design strategies has enabled the introduction of artificially structured metamaterials in place of conventional materials for improving optical components as well as realizing new optical functionality. Here we demonstrate multilayer, lithographically patterned, subwavelength, metal elements, whose distribution forms a computer-generated phase hologram in the infrared region (10.6 μm). Metal inclusions exhibit extremely large scattering and can be implemented in metamaterials that exhibit a wide range of effective medium response, including anomalously large or negative refractive index; optical magnetism; and controlled anisotropy. This large palette of metamaterial responses can be leveraged to achieve greater control over the propagation of light, leading to more compact, efficient and versatile optical components.
333 citations
TL;DR: In this article, the feasibility of the realization of micromachined tunable metamaterials via structure reconfiguration and the current state of the art in the fabrication technologies of structurally reconfigurable metammaterial elements are reviewed.
Abstract: This paper reviews micromachined tunable metamaterials, whereby the tuning capabilities are based on the mechanical reconfiguration of the lattice and/or the metamaterial element geometry. The primary focus of this review is the feasibility of the realization of micromachined tunable metamaterials via structure reconfiguration and the current state of the art in the fabrication technologies of structurally reconfigurable metamaterial elements. The micromachined reconfigurable microstructures not only offer a new tuning method for metamaterials without being limited by the nonlinearity of constituent materials, but also enable a new paradigm of reconfigurable metamaterial-based devices with mechanical actuations. With recent development in nanomachining technology, it is possible to develop structurally reconfigurable metamaterials with faster tuning speed, higher density of integration and more flexible choice of the working frequencies.
284 citations
TL;DR: In this article, the design, numerical simulations and experimental measurements of terahertz metamaterial absorbers with a broad and flat absorption top over a wide incidence angle range for either transverse electric or transverse magnetic polarization depending on the incident direction are presented.
Abstract: We present the design, numerical simulations and experimental measurements of terahertz metamaterial absorbers with a broad and flat absorption top over a wide incidence angle range for either transverse electric or transverse magnetic polarization depending on the incident direction. The metamaterial absorber unit cell consists of two sets of structures resonating at different but close frequencies. The overall absorption spectrum is the superposition of individual components and becomes flat at the top over a significant bandwidth. The experimental results are in excellent agreement with numerical simulations.
260 citations
TL;DR: A broadband infrared absorber is proposed by engineering the frequency dispersion of metamaterial surface (metasurface) to mimic an ideal absorbing sheet by demonstrating a polarization-independent absorber with absorption larger than 97% and the concept of dispersion engineering may provide helpful guidance for the design of a broadband absorber.
Abstract: We propose a broadband infrared absorber by engineering the frequency dispersion of metamaterial surface (metasurface) to mimic an ideal absorbing sheet. With a thin layer of structured nichrome, a polarization-independent absorber with absorption larger than 97% is numerically demonstrated over a larger than one octave bandwidth. It is shown that the bandwidth enhancement is related with the transformation of the Drude model of free electron gas in metal film to the Lorentz oscillator model of a bound electron in the structured metallic surface. We believe that the concept of dispersion engineering may provide helpful guidance for the design of a broadband absorber.
TL;DR: Both qualitative analysis by equivalent circuit and accurate numeric calculation show that the coupling between the crisscross and the fractal square patch can enhance the bandwidth with the reflectivity below -10dB in the frequency range of 2-18GHz by producing a third absorption null.
Abstract: We report the design, fabrication, and measurement of a broadband metamaterial absorber, which consists of lossy frequency selective surface (FSS) and a metallic ground plane separated by a dielectric layer. The compact single unit cell of the FSS contains crisscross and fractal square patch which couple with each other. Both qualitative analysis by equivalent circuit and accurate numeric calculation show that the coupling between the crisscross and the fractal square patch can enhance the bandwidth with the reflectivity below −10dB in the frequency range of 2-18GHz by producing a third absorption null. In the end, the designed absorber was realized by experiment.
TL;DR: Smart metamaterial cloaking is demonstrated, wherein the meetamaterial device not only transforms electromagnetic fields to make an object invisible, but also acquires its properties automatically from its own elastic deformation, naturally from a boundary load.
Abstract: The ability to render objects invisible with a cloak that fits all objects and sizes is a long-standing goal for optical devices. Invisibility devices demonstrated so far typically comprise a rigid structure wrapped around an object to which it is fitted. Here we demonstrate smart metamaterial cloaking, wherein the metamaterial device not only transforms electromagnetic fields to make an object invisible, but also acquires its properties automatically from its own elastic deformation. The demonstrated device is a ground-plane microwave cloak composed of an elastic metamaterial with a broad operational band (10-12 GHz) and nearly lossless electromagnetic properties. The metamaterial is uniform, or perfectly periodic, in its undeformed state and acquires the necessary gradient-index profile, mimicking a quasi-conformal transformation, naturally from a boundary load. This easy-to-fabricate hybrid elasto-electromagnetic metamaterial opens the door to implementations of a variety of transformation optics devices based on quasi-conformal maps.
TL;DR: In this article, a broadband metamaterial absorber (MA) based on lumped elements is presented, which is composed of the dielectric substrate sandwiched with metal split-coin resonators welded with lumped element and continuous metal film, and the experiment results show that the bandwidth of absorption of 90% is about 1.5 GHz and the full width at half maximum (FWHM) can be up to 50%.
Abstract: A broadband metamaterial absorber (MA) based on lumped elements is presented, which is composed of the dielectric substrate sandwiched with metal split-coin resonators (SCR) welded with lumped elements and continuous metal film. We simulated, fabricated, and measured the lumped elements MA. Compared with the single SCR structure MA, the composite MA loaded with lumped elements has a wider absorptivity and works in a lower frequency. The experiment results show that the bandwidth of absorption of 90% is about 1.5 GHz and the full width at half maximum (FWHM) can be up to 50%, the absorptivity is also nearly unchanged for different polarizations. The further simulations of the absorptivity of composite MA with different lumped resistances and capacitances indicate that there exist optimal values for lumped resistances and capacitances, where the absorptivity is the highest and the bandwidth is the widest.
TL;DR: In this paper, a broadband metamaterial absorber consisting of circular metallic patches and a metallic ground plane separated by a dielectric layer was designed and measured. And the results show that the proposed absorber has high absorptivity, with a full width at half maximum absorption bandwidth of 2.8 GHz and the relative FWHM absorption ratio of 25.3%.
Abstract: The design, fabrication, and measurements of a broadband metamaterial absorber are reported. The proposed metamaterial absorber consists of circular metallic patches and a metallic ground plane separated by a dielectric layer. Increasing the number of metallic patches can broaden the frequency range when their resonances are closely packed together, thereby resulting in a broadband resonance. Experimental results show that the proposed absorber has high absorptivity, with a full width at half maximum absorption bandwidth of 2.8 GHz and the relative FWHM absorption bandwidth of 25.3 %. In addition, the absorber can operate at a wide range of incident angles under both transverse electric and transverse magnetic polarizations.
TL;DR: In this paper, a tunable hybrid metamaterial absorber (MA) in the microwave band was designed, fabricated and characterized by incorporating a VO2 film into the conventional resonant MA, and the impedance match condition was broken and a deep amplitude modulation of about 63.3% to the electromagnetic wave absorption was achieved.
Abstract: A tunable hybrid metamaterial absorber (MA) in the microwave band was designed, fabricated and characterized. The hybrid MA was realized by incorporating a VO2 film into the conventional resonant MA. By thermally triggering the insulator–metal phase transition of the VO2 film, the impedance match condition was broken and a deep amplitude modulation of about 63.3% to the electromagnetic wave absorption was achieved. A moderate blue-shift of the resonance frequency was observed which is promising for practical applications. This VO2-based MA exhibits many advantages such as strong tunability, frequency agility, simple fabrication and ease of scaling to the terahertz band.
TL;DR: A planar waveguide model and a mechanism based on standing wave resonances to interpret the unity absorptions of ultrathin planar metamaterial absorbers with multi-band absorptions at desired frequencies can be easily designed.
Abstract: We present a planar waveguide model and a mechanism based on standing wave resonances to interpret the unity absorptions of ultrathin planar metamaterial absorbers. The analytical model predicts that the available absorption peaks of the absorber are corresponding to the fundamental mode and only its odd harmonic modes of the standing wave. The model is in good agreement with numerical simulation and can explain the main features observed in typical ultrathin planar metamaterial absorbers. Based on this model, ultrathin planar metamaterial absorbers with multi-band absorptions at desired frequencies can be easily designed.
TL;DR: It is seen from simulation results that the synthesis method accurately predicts the center frequency of the multi- band metamaterial, which opens a door to a quick and accurate construction for multi-band slow light metamMaterial.
Abstract: In this paper, a multi-band slow light metamaterial is presented and investigated. The metamaterial unit cell is composed of three cut wires of different sizes and parallel to each other. Two transparency windows induced by two-two overlaps of absorption bands of three cut wires are observed. The multi-band transmission characteristics and the slow light properties of metamaterial are verified by numerical simulation, which is in a good agreement with theoretical predictions. The impacts of structure parameters on transparency windows are also investigated. Simulation results show the spectral properties can be tuned by adjusting structure parameters of metamaterial. The equivalent circuit model and the synthesis method of the multi-band slow light metamaterial are presented. It is seen from simulation results that the synthesis method accurately predicts the center frequency of the multi-band metamaterial, which opens a door to a quick and accurate construction for multi-band slow light metamaterial.
TL;DR: This letter proposes a new class of electrically-tunable terahertz metamaterial modulators employing metallic frequency-selective-surfaces (FSS) in conjunction with capacitively- tunable layers of electrons, promising near 100% modulation depth and < 15% attenuation.
Abstract: Switchable metamaterials offer unique solutions for efficiently manipulating electromagnetic waves, particularly for terahertz waves, which has been difficult since naturally occurring materials rarely respond to terahertz frequencies controllably However, few terahertz modulators demonstrated to date exhibit simultaneously low attenuation and high modulation depth In this letter we propose a new class of electrically-tunable terahertz metamaterial modulators employing metallic frequency-selective-surfaces (FSS) in conjunction with capacitively-tunable layers of electrons, promising near 100% modulation depth and < 15% attenuation The fundamental departure in our design from the prior art is tuning enabled by self-gated electron layers that is independent from the metallic FSS Our proposal is applicable to all possible electrically tunable elements including graphene, Si, MoS2, oxides etc, thus opening up myriad opportunities for realizing high performance switchable metamaterials over an ultra-wide terahertz frequency range
TL;DR: The design and characterization of a broadband terahertz absorber based on heavily Boron-doped silicon (0.7676 Ω cm) grating is presented and it is numerically demonstrated by utilizing both the zero and first order diffraction in the doped silicon wafer, relative absorption bandwidth larger than 100% can be achieved.
Abstract: Highly efficient absorber is of particular importance in terahertz regime as naturally occurring materials with frequency-selective absorption in this frequency band is difficult to find. Here we present the design and characterization of a broadband terahertz absorber based on heavily Boron-doped silicon (0.7676 Ω cm) grating. It is numerically demonstrated by utilizing both the zero- and first order diffraction in the doped silicon wafer, relative absorption bandwidth larger than 100% can be achieved. Furthermore, the design can be easily extended to higher frequencies as the optical property of doped silicon is tunable through changing the doping concentration.
TL;DR: This paper designs a microwave metamaterial absorber and experimentally demonstrates that its central frequency can be set anywhere in a 1.6 GHz frequency range, and shows that it is possible to create multiple absorption peaks by adjusting the size and/or shape of the dielectric slab, and to shift them by moving the slab relative to the meetamaterial.
Abstract: Metamaterials attain their behavior due to resonant interactions among their subwavelength components and thus show specific designer features only in a very narrow frequency band. There is no simple way to dynamically increase the operating bandwidth of a narrowband metamaterial, but it may be possible to change its central frequency, shifting the spectral response to a new frequency range. In this paper, we propose and experimentally demonstrate a metamaterial absorber that can shift its central operating frequency by using mechanical means. The shift is achieved by varying the gap between the metamaterial and an auxiliary dielectric slab parallel to its surface. We also show that it is possible to create multiple absorption peaks by adjusting the size and/or shape of the dielectric slab, and to shift them by moving the slab relative to the metamaterial. Specifically, using numerical simulations we design a microwave metamaterial absorber and experimentally demonstrate that its central frequency can be set anywhere in a 1.6 GHz frequency range. The proposed configuration is simple and easy to make, and may be readily extended to THz frequencies.
TL;DR: In this article, a multi-band metamaterial absorber comprising three multi-gap split-ring resonators (SRRs) with different radii and ring widths was designed in combinatorial approach.
Abstract: This paper presents a multi-band metamaterial absorber comprising three multi-gap split-ring resonators (SRRs) with different radii and ring widths, designed in combinatorial approach. Experiments demonstrate that it can perform absorption peaks at three resonant frequencies 7.10 GHz, 10.04 GHz, and 17.44 GHz with the absorption of 99.90%, 99.91%, and 99.68%, respectively. The physical mechanism of metamaterial absorber was explained through numerical calculation and simulation, which showed that three absorption peaks were caused respectively by the three four-gap SRRs. The absorber is insensitive to incident angles and polarization states, so it has broad prospect of application.
TL;DR: A new type of multi-layer metamaterial (MM) absorber is represented in this paper, which behave as a dielectric slab in transmission band and act as an absorber in another lower band.
Abstract: A new type of multi-layer metamaterial (MM) absorber is represented in this paper, which behave as a dielectric slab in transmission band and act as an absorber in another lower band. The equivalent circuit model of each layer in this MM absorber has been established. The transmission line (TL) model is introduced to analysis the mechanism of electromagnetic wave traveling through this MM absorber. Both theoretical and experimental results indicate this MM absorber has a transmission band at 21GHz and an absorptive band from 5GHz to 13GHz. A good match of TL model results and measurement results verified the validity of TL model in analyzing and optimizing the performances of this kind of absorber.
TL;DR: In this paper, the authors used plasmonic hybrid material in order to design and fabricate a broadband perfect PLASmonic metamaterial absorber in a stack of metal and copper-PTFE (Polytetrafluoroethylene) nanocomposite showing an average absorbance of 97.5% in the whole visible spectrum.
Abstract: Metamaterials and plasmonics as a new pioneering field in photonics joins the features of photonics and electronics by coupling photons to conduction electrons of a metal as surface plasmons (SP). This concept has been implemented for a variety of applications including negative index of refraction, magnetism at visible frequency, cloaking devices amongst others. In the present work, we used plasmonic hybrid material in order to design and fabricate a broad-band perfect plasmonic metamaterial absorber in a stack of metal and Copper-PTFE (Polytetrafluoroethylene) nanocomposite showing an average absorbance of 97.5 % in the whole visible spectrum. Our experimental results showed that the absorption peak of the stacks can be tuned upon varying the thickness and type of the spacer layer due to the sensitivity of plasmon resonance to its environment. To the best of our knowledge, this is the first report of a plasmonic metamaterial absorber based on copper with absorption around 100 % in the entire visible and near-Infrared (NIR).
TL;DR: This Letter describes the fabrication of a microelectromechanical systems (MEMS) bimaterial terahertz (THz) sensor operating at 3.8 THz, designed with a resonant frequency matching the quantum cascade laser illumination source while simultaneously providing structural support, desired thermomechanical properties and optical readout access.
Abstract: This Letter describes the fabrication of a microelectromechanical systems (MEMS) bimaterial terahertz (THz) sensor operating at 3.8 THz. The incident THz radiation is absorbed by a metamaterial structure integrated with the bimaterial. The absorber was designed with a resonant frequency matching the quantum cascade laser illumination source while simultaneously providing structural support, desired thermomechanical properties and optical readout access. Measurement showed that the fabricated absorber has nearly 90% absorption at 3.8 THz. A responsivity of 0.1°/μW and a time constant of 14 ms were observed. The use of metamaterial absorbers allows for tuning the sensor response to the desired frequency to achieve high sensitivity for potential THz imaging applications.
TL;DR: In this paper, an infrared dual-band metamaterial absorber composed of simple periodically patterned structures was designed and demonstrated, and two distinct absorption peaks of 74% and 96% were obtained, which were in reasonable agreement with the simulations.
Abstract: We report the design, characterization, and experimental demonstration of an infrared dual-band metamaterial absorber composed of simple periodically patterned structures. Experimental results show that two distinct absorption peaks of 74% and 96% are obtained, which are in reasonable agreement with the simulations. We demonstrate two absorption resonances that are derived from the mixture of magnetic and electric plasmon resonances. The dual-band absorber is polarization insensitive and the absorption peaks remain high with large angles of incidence for both transverse electric and transverse magnetic polarizations, which provide more efficient absorptions for nonpolarized or oblique incident beams.
TL;DR: A metamaterial absorber detector array that enables room-temperature, narrow-band detection of gigahertz radiation in the S band (2-4 GHz) is presented and the detector sensitivity and angular dependence are characterized.
Abstract: We present a metamaterial absorber detector array that enables room-temperature, narrow-band detection of gigahertz (GHz) radiation in the S band (2-4 GHz). The system is implemented in a commercial printed circuit board process and we characterize the detector sensitivity and angular dependence. A modified metamaterial absorber geometry allows for each unit cell to act as an isolated detector pixel and to collectively form a focal plane array . Each pixel can have a dedicated microwave receiver chain and functions together as a hybrid device tuned to maximize the efficiency of detected power. The demonstrated subwavelength pixel shows detected sensitivity of -77 dBm, corresponding to a radiation power density of 27 nW/m(2), with pixel to pixel coupling interference below -14 dB at 2.5 GHz.
TL;DR: A tunable dual-band perfect absorber based on extraordinary-optical-transmission (EOT) effect and Fabry-Perot cavity resonance that can be optimized to be insensitive to the polarization of the incident electromagnetic wave by slightly modifying the absorber structure.
Abstract: Magnetic resonance is considered to be a necessary condition for metamaterial perfect absorbers, and dual-band absorbers can be composed of a pair of metallic layers with anti-parallel surface currents. We designed and fabricated a tunable dual-band perfect absorber based on extraordinary-optical-transmission (EOT) effect and Fabry-Perot cavity resonance. The idea and the mechanism are completely different from the absorber based on the near-field interaction. The important advantage of our structure is that we can switch a single-band absorber to a dual-band absorber by changing the distance between two metallic layers and/or incident angle. The peak originating from the EOT effect becomes significantly narrower, resulting in an increase of the Q-factor from 16.88 to 49. The dual-band absorber can be optimized to be insensitive to the polarization of the incident electromagnetic wave by slightly modifying the absorber structure.
TL;DR: In this paper, an optically implemented absorption modulation and redshift switch of metamaterial absorber at terahertz frequencies was demonstrated, where the active structure of hybrid metal-semiconductor split ring resonators can be tuned by applying an external pump power.
Abstract: We demonstrate an optically implemented absorption modulation and redshift switch of metamaterial absorber at terahertz frequencies. Hybrid metal–semiconductor split ring resonators (SRRs) form the active structure, which can be tuned by applying an external pump power. This enables effective controls of the absorption strength and absorption peak frequency. As a function of incident pump power, the conductivity of silicon pads filled in the gap of SRRs is tuned efficiently, resulting in the modulation of absorption magnitude with a modulation depth of 60.5%, and a broadband switch of absorption peak frequencies varying from 1.11 to 0.87 THz. Multiple-reflection interference theory is used to analyze the reflection spectrum quantitatively under various silicon conductivities, and the results are in good agreement with full-wave simulations. The optical-tuned absorber demonstrates the viability to incorporate metamaterials to mature semiconductor technologies and has potential applications as an active terahertz modulator and switch.
TL;DR: It is shown that the weak optical response of graphene can be modified dramatically by coupling to the strong resonant fields in metallic structures.
Abstract: We have recently shown that graphene is unsuitable to replace metals in the current-carrying elements of metamaterials. At the other hand, experiments have demonstrated that a layer of graphene can modify the optical response of a metal-based metamaterial. Here we study this electromagnetic interaction between metamaterials and graphene. We show that the weak optical response of graphene can be modified dramatically by coupling to the strong resonant fields in metallic structures. A crucial element determining the interaction strength is the orientation of the resonant fields. If the resonant electric field is predominantly parallel to the graphene sheet (e.g., in a complementary split-ring metamaterial), the metamaterial's resonance can be strongly damped. If the resonant field is predominantly perpendicular to the graphene sheet (e.g., in a wire-pair metamaterial), no significant interaction exists.