Showing papers on "Metamaterial absorber published in 2011"

Ultra-broadband Microwave Metamaterial Absorber

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 7.8-14.7GHz, and the absorption is kept large when the incident angle is smaller than 60 degrees. The experimental results agree well with the numerical simulation.

Polarization-independent wide-angle triple-band metamaterial absorber.

Abstract: We report the design, fabrication, and measurement of a microwave triple-band absorber. The compact single unit cell consists of three nested electric closed-ring resonators and a metallic ground plane separated by a dielectric layer. Simulation and experimental results show that the absorber has three distinctive absorption peaks at frequencies 4.06GHz, 6.73GHz, and 9.22GHz with the absorption rates of 0.99, 0.93, and 0.95, respectively. The absorber is valid to a wide range of incident angles for both transverse electric (TE) and transverse magnetic (TM) polarizations. The triple-band absorber is a promising candidate as absorbing elements in scientific and technical applications because of its multiband absorption, polarization insensitivity, and wide-angle response.

Interference theory of metamaterial perfect absorbers

Abstract: The impedance matching in metamaterial perfect absorbers has been believed to involve and rely on magnetic resonant response, with a direct evidence from the anti-parallel directions of surface currents in the metal structures. Here we present a different theoretical interpretation based on interferences, which shows that the two layers of metal structure in metamaterial absorbers are linked only by multiple reflections with negligible near-field interactions or magnetic resonances. This is further supported by the out-of-phase surface currents derived at the interfaces of resonator array and ground plane through multiple reflections and superpositions. The theory developed here explains all features observed in narrowband metamaterial absorbers and therefore provides a profound understanding of the underlying physics.

A terahertz polarization insensitive dual band metamaterial absorber

Abstract: Metamaterial absorbers have attracted considerable attention for applications in the terahertz range. In this Letter, we report the design, fabrication, and characterization of a terahertz dual band metamaterial absorber that shows two distinct absorption peaks with high absorption. By manipulating the periodic patterned structures as well as the dielectric layer thickness of the metal–dielectric–metal structure, significantly high absorption can be obtained at specific resonance frequencies. Finite-difference time-domain modeling is used to design the structure of the absorber. The fabricated devices have been characterized using a Fourier transform IR spectrometer. The experimental results show two distinct absorption peaks at 2.7 and 5.2 THz, which are in good agreement with the simulation. The absorption magnitudes at 2.7 and 5.2 THz are 0.68 and 0.74, respectively.

Polarization insensitive, broadband terahertz metamaterial absorber

Abstract: We present the simulation, implementation, and measurement of a polarization insensitive broadband resonant terahertz metamaterial absorber. By stacking metal-insulator layers with differing structural dimensions, three closely positioned resonant peaks are merged into one broadband absorption spectrum. Greater than 60% absorption is obtained across a frequency range of 1.86 THz where the central resonance frequency is 5 THz. The FWHM of the device is 48%, which is two and half times greater than the FWHM of a single layer structure. Such metamaterials are promising candidates as absorbing elements for bolometric terahertz imaging.

Ultrathin multiband gigahertz metamaterial absorbers

Abstract: We propose ultrathin multiband metamaterial absorbers in the microwave frequencies in which the design, analysis, fabrication, and measurement of the absorbers working in multiple bands are presented. The metamaterial absorbers consist of a periodic arrangement of different scales of electric-field-coupled-LC (ELC) resonators and a metallic background plane, separated by only 1 mm dielectric spacer. By tuning the scale factor of the ELC unit cells, we achieve independently multiple absorptions at different customized frequencies. Experiments demonstrate excellent absorption rates in the designed frequency bands over wide angles of incident waves for both transverse electric and magnetic polarizations. The explanation to the physical mechanism of the multiband metamaterial absorber is presented and verified.

Experimental demonstration of terahertz metamaterial absorbers with a broad and flat high absorption band

Abstract: We present the design, numerical simulations and experimental measurements of THz metamaterial absorbers with a broad and flat absorption top both for transverse electric and transverse magnetic polarizations over a wide incidence angle range. 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.

An extremely broad band metamaterial absorber based on destructive interference.

Abstract: We propose a design of an extremely broad frequency band absorber based on destructive interference mechanism. Metamaterial of multilayered SRRs structure is used to realize a desirable refractive index dispersion spectrum, which can induce a successive anti-reflection in a wide frequency range. The corresponding high absorptance originates from the destructive interference of two reflection waves from the two surfaces of the metamaterial. A strongly absorptive bandwidth of almost 60GHz is demonstrated in the range of 0 to 70GHz numerically. This design provides an effective and feasible way to construct broad band absorber in stealth technology, as well as the enhanced transmittance devices.

Conformal dual-band near-perfectly absorbing mid-infrared metamaterial coating.

Abstract: Metamaterials offer a new approach to create surface coatings with highly customizable electromagnetic absorption from the microwave to the optical regimes. Thus far, efficient metamaterial absorbers have been demonstrated at microwave frequencies, with recent efforts aimed at much shorter terahertz and infrared wavelengths. The present infrared absorbers have been constructed from arrays of nanoscale metal resonators with simple circular or cross-shaped geometries, which provide a single band response. In this paper, we demonstrate a conformal metamaterial absorber with a narrow band, polarization-independent absorptivity of >90% over a wide ±50° angular range centered at mid-infrared wavelengths of 3.3 and 3.9 μm. The highly efficient dual-band metamaterial was realized by using a genetic algorithm to identify an array of H-shaped nanoresonators with an effective electric and magnetic response that maximizes absorption in each wavelength band when patterned on a flexible Kapton and Au thin film substrat...

Large-area wide-angle spectrally selective plasmonic absorber

Abstract: A simple metamaterial-based wide-angle plasmonic absorber is introduced, fabricated, and experimentally characterized using angle-resolved infrared spectroscopy. The metamaterials are prepared by nano-imprint lithography, an attractive low-cost technology for making large-area samples. The matching of the metamaterial's impedance to that of vacuum is responsible for the observed spectrally selective ``perfect'' absorption of infrared light. The impedance is theoretically calculated in the single-resonance approximation, and the responsible resonance is identified as a short-range surface plasmon. The spectral position of the absorption peak (which is as high as $95%$) is experimentally shown to be controlled by the metamaterial's dimensions. The persistence of ``perfect'' absorption with variable metamaterial parameters is theoretically explained. The wide-angle nature of the absorber can be utilized for subdiffraction-scale infrared pixels exhibiting spectrally selective absorption/emissivity.

Experiments on wireless power transfer with metamaterials

Abstract: In this letter, we propose the use of metamaterials to enhance the evanescent wave coupling and improve the transfer efficiency of a wireless power transfer system based on coupled resonators. A magnetic metamaterial is designed and built for a wireless power transfer system. We show with measurement results that the power transfer efficiency of the system can be improved significantly by the metamaterial. We also show that the fabricated system can be used to transfer power wirelessly to a 40 W light bulb.

Metamaterial-based integrated plasmonic absorber/emitter for solar thermo-photovoltaic systems

Abstract: We will present a concept of an integrated frequency selective absorber/emitter based on an ultra-thin plasmonic metamaterial for Solar Thermo-Photovoltaics (STPV) applications. By employing non-shiny metals (such as tungsten), the absorption spectrum of the metamaterial is designed to be broad-band in the visible range and narrow-band in the infrared range. A detailed balance calculation demonstrates the total STPV system e±ciency exceeding the Shockley-Queisser limit for emitter temperatures above Te = 1200K, and an e±ciency as high as 41% for Te = 2300K. Such emitter temperature is shown to be achievable under modest Sun concentration (less than 1000 Suns) because of the thermal insulation provided by the metamaterial. Experimental demonstration of the wide-angle frequency selective absorptivity will be presented, and its implications for developing broadband infrared absorbers/emitters will be discussed.

A wide-angle polarization-insensitive ultra-thin metamaterial absorber with three resonant modes

Abstract: In this paper, we report the design, fabrication, and measurement of a metamaterial absorber that is constructed of a periodic array of tetra-arrow resonators (TARs) printed on a dielectric material backed by a metal ground. The TAR absorber can operate at three different resonant modes. By adjusting geometry parameters of the structure, we can obtain a dual-band, polarization-insensitive, wide-angle thin absorber or a single band but ultra-miniature absorber that corresponds to three different resonant modes. Waveguide experiments are conducted to verify the proposed designs effectively. The measurement results show that all three absorptivity peaks come near to perfection.

Design principles for infrared wide-angle perfect absorber based on plasmonic structure.

Abstract: An approach for designing a wide-angle perfect absorber at infrared frequencies is proposed. The technique is based on a perfectly impedance-matched sheet (PIMS) formed by plasmonic nanostructure. It is shown that the effective impedance is more physical meaningful and beneficial than effective medium in describing the electromagnetic properties of metamaterial absorber. As a specific implementation of this technique, a wide-angle polarization-independent dual-band absorber is numerically demonstrated at frequencies of 100THz and 280THz with absorption close to 100% simultaneously. Circuit models are utilized to describe the impedance property of localized plasmon modes and the results show good agreement with that retrieved from reflection coefficient at normal incidence.

Multi-band and polarization insensitive metamaterial absorber

Abstract: The design and realization of a multi-band and polariza- tion insensitive metamaterial absorber is presented. The structure with thickness 1.1mm consists of six close rings which distribute in two metallic layers separated by FR4 flber glass PCB substrates. Ex- perimental results show that over 93.3% absorption can be achieved in this metamaterial absorber at multiple frequency bands (more than two). Due to the rotational symmetric pattern of the metamaterial, the performance of the absorber is insensitive to the polarization of the incident waves, indicating the superiority of the structure in the application.

Bandwidth-enhanced and polarisation-insensitive metamaterial absorber using double resonance

Abstract: A bandwidth-enhanced microwave absorber using a double resonant metamaterial is presented. Its bandwidth is increased compared with previous metamaterial absorbers. The proposed absorber has a thin configuration and its performance is constant for different polarisations. Numerical and experimental results support the proposed absorber's performance.

Perfect metamaterial absorber based on a split-ring-cross resonator

Abstract: In this paper, we present a polarization-insensitive metamaterial (MM) absorber which is composed of the dielectric substrate sandwiched with split-ring-cross resonator (SRCR) and continuous metal film. The MM absorber is not limited by the quarter-wavelength thickness and can achieve near-unity absorbance by properly assembling the sandwiched structure. Microwave experiments demonstrate the maximum absorptivity to be about 99% around 10.91 GHz for incident wave with different polarizations. The surface currents distributions of the resonance structure are discussed to look into the resonance mechanism. Importantly, our absorber is only 0.4 mm thick, and numerical simulations confirm that the MM absorber could achieve very high absorptivity at wide angles of incidence for both transverse electric (TE) wave and transverse magnetic (TM) wave. The sandwiched structure is also suitable for designing of a THz and even higher frequency MM absorber, and simulations demonstrate the absorption of 99% at 1.105 THz.

Polarization insensitive terahertz metamaterial absorber

Abstract: We present the simulation, implementation, and measurement of a polarization insensitive resonant metamaterial absorber in the terahertz region. The device consists of a metal/dielectric-spacer/metal structure allowing us to maximize absorption by varying the dielectric material and thickness and, hence, the effective electrical permittivity and magnetic permeability. Experimental absorption of 77% and 65% at 2.12 THz (in the operating frequency range of terahertz quantum cascade lasers) is observed for a spacer of polyimide or silicon dioxide respectively. These metamaterials are promising candidates as absorbing elements for thermally based terahertz imaging.

Polarization insensitive and omnidirectional broadband near perfect planar metamaterial absorber in the near infrared regime

Abstract: We present the design, characterization, and experimental demonstration of a polarization insensitive and omnidirectional broadband near perfect planar metamaterial absorber (MA) in the near infrared regime, which does not need to stack multilayer composite structures Experimental result shows that greater than 80% absorption is obtained across a wavelength range of 041 μm, which is in reasonable agreement with the simulation The electromagnetic response of the MA is theoretically investigated The broadband planar MA is polarization insensitive and the absorption remains high even at large incident angles

Single and dual band 77/95/110 GHz metamaterial absorbers on flexible polyimide substrate

Abstract: Ultra thin millimeter-wave absorbers on flexible polyimide substrate utilizing metamaterials are implemented for single and dual frequency bands in an emerging frequency spectrum of 77, 95, and 110 GHz. The dual band absorber is designed using a novel approach of imbedding high frequency resonator inside low frequency resonator capable of absorbing electromagnetic energy at both 77 and 110 GHz bands simultaneously. The total thickness of the absorber is just 126 μm (almost 1/20th of the wavelength). Measured peak absorptions for single frequency absorbers are 92, 94, and 99% at 77.2, 94.8, and 109.5 GHz, respectively, and for dual band absorber 92% at 77 GHz and 94% at 109.8 GHz.

An octave-bandwidth negligible-loss radiofrequency metamaterial

Abstract: Metamaterials provide an unprecedented ability to manipulate electromagnetic waves and are an enabling technology for new devices ranging from flat lenses that focus light beyond the diffraction limit to coatings capable of cloaking an object. Nevertheless, narrow bandwidths and high intrinsic losses arising from the resonant properties of metamaterials have raised doubts about their usefulness. New design approaches seek to turn the perceived disadvantages of dispersion into assets that enhance a device's performance. Here we employ dispersion engineering of metamaterial properties to enable specific device performance over usable bandwidths. In particular, we design metamaterials that considerably improve conventional horn antennas over greater than an octave bandwidth with negligible loss and advance the state of the art in the process. Fabrication and measurement of a metahorn confirm its broadband, low-loss performance. This example illustrates the power of clever implementation combined with dispersion engineering to bring metamaterials into their full potential for revolutionizing practical devices.

Dual-Band Terahertz Metamaterial Absorber with Polarization Insensitivity and Wide Incident Angle

Abstract: This paper presents the design, simulation and mea- surement of a dual-band terahertz metamaterial absorber with polarization-insensitivity and wide incident angle. The unit cell of the metamaterial consists of top resonator structures and low metal- lic ground plane, separated by an isolation material spacer to realize both electric and magnetic resonances. The physical mechanism of dual-band absorption and the sensitivity to the polarization direction and incident direction of the EM wave are theoretically investigated by simulating the x-component and normal component electric fleld distribution, current distribution on ERRs and metallic ground plane, and distribution of power ∞ow and loss at the resonance frequencies as well as difierent modes EM waves, based the FDTD calculated method, respectively. The results show that the absorber is not only correctly coupling to the incident electric fleld and magnetic fleld, but also can trap the input power into speciflc positions of the devices and ab- sorb it, besides insensitivity to the polarized angle and incident angle. Moreover, the experiment demonstrates that the absorber achieves two strong absorptions of 82.8% and 86.8% near 1.724 and 3.557THz.

Numerical study of metamaterial absorber and extending absorbance bandwidth based on multi-square patches

Abstract: A simple design of metamaterial absorber (MA) was proposed based on a periodic array of metal patch at microwave frequencies. Our design could exhibit absorption of 99.9% confirmed by numerical simulation. Such high narrowband absorption which mainly based on strong electric and magnetic resonances overlapping in a certain frequency range and perfect impedance-matched (z = 1) to the free space. Numerical simulations demonstrate that the MA could achieve very high absorptivity at wide angles of incidence for both transverse electric (TE) wave and transverse magnetic (TM) wave. The absorption band of our device is effectively extended by patterning multi-square patches of different dimension elements with appropriate geometrical parameters in a co-planar. Finally, the composite MA is only 0.4 mm thick, with a maximum absorption of 99.8% at 15.8 GHz, and a full width at half maximum (FWHM) bandwidth of 2 GHz by numerical simulation, which may have potential applications in the detection of explosives and stealth.

Optical metamaterial absorber based on leaf-shaped cells

Abstract: We present the model of an infrared metamaterial absorber composed of metallic leaf-shaped cells, dielectric substrate, and continuous metallic film. Numerical simulation confirms an absorptivity of 99.3% at the infrared frequency of 126.7 THz with this metamaterial model. The proposed metamaterial absorber could be fabricated with an electrochemical deposition technique. Our simulated results show the absorption feature of this metamaterial absorber could be well manipulated with different incident angles and radiation modes. The optical metamaterial absorber proposed in this paper has potential applications such as infrared imaging devices, thermal bolometers, wavelength-selective radiators, and optical bistable switches.

Equivalent circuit method analysis of the influence of frequency selective surface resistance on the frequency response of metamaterial absorbers

Abstract: A simple equivalent circuit method has been proposed to provide understanding of the absorption mechanism of a class of metamaterial absorbers. The absorbers are composed of lossy frequency selective surfaces (FSSs) over the grounded dielectric substrates. Based on the analytical method, the influence of FSS surface resistance on the frequency responses of metamaterial absorbers is discussed in detail. It is shown that wideband or narrowband absorbers can be obtained by changing the surface resistance of the FSS. The narrowband absorbers show a similar surface resistance dependence of the absorbing performance to Salisbury absorbers and the maximum bandwidth of metamaterial absorbers can be obtained with the proper surface resistance. This can serve as a guideline for the fast and efficient design of metamaterial absorbers. Finally, experimental results are presented for verifying the validity of the analytical method.

Optical properties of a fabricated self-assembled bottom-up bulk metamaterial.

Abstract: We investigate the optical properties of a true three-dimensional metamaterial that was fabricated using a self-assembly bottom-up technology. The metamaterial consists of closely packed spherical clusters being formed by a large number of non-touching gold nanoparticles. After presenting experimental results, we apply a generalized Mie theory to analyze its spectral response revealing that it is dominated by a magnetic dipole contribution. By using an effective medium theory we show that the fabricated metamaterial exhibits a dispersive effective permeability, i.e. artificial magnetism. Although this metamaterial is not yet left-handed it might serve as a starting point for achieving bulk metamaterials by using bottom-up approaches.

A wide-angle planar metamaterial absorber based on split ring resonator coupling

Abstract: A wide-angle planar metamaterial structure exhibiting strong absorption is presented. The structure functions as a near-perfect absorber with the incident electric field propagating not only across but also along the gaps of individual split ring resonator (SRR) elements. It is the coupling of adjacent SRRs that provides capacitance necessary to excite the LC resonance for absorption. Both simulations and experiments are shown in this paper. The experimental results indicate that when the electric field propagates along the gaps of individual SRR elements, the structure obtains 1.6-GHz-wide absorption with absorptivity larger than 90% at small incident angles. The proposed structure offers a potential way to create azimuth-independent broadband metamaterial absorber.

Tailored resonator coupling for modifying the terahertz metamaterial response

Abstract: We experimentally and numerically study the nature of coupling between laterally paired terahertz metamaterial split-ring resonators. Coupling is shown to modify the inductive–capacitive (LC) resonances resulting in either red or blue-shifting. Results indicate that tuning of the electric and magnetic coupling parameters may be accomplished not by changing the orientation or density of SRRs, but by a design modification at the unit cell level. These experiments illustrate additional degrees of freedom in tuning the electromagnetic response, which offers a path to more robust metamaterial designs.

Stacked-and-drawn metamaterials with magnetic resonances in the terahertz range

Abstract: We present a novel method for producing drawn metamaterials containing slotted metallic cylinder resonators, possessing strong magnetic resonances in the terahertz range. The resulting structures are either spooled to produce a 2-dimensional metamaterial monolayer, or stacked to produce three-dimensional multi-layered metamaterials. We experimentally investigate the effects of the resonator size and number of metamaterial layers on transmittance, observing magnetic resonances between 0.1 and 0.4 THz, in good agreement with simulations. Such fibers promise future applications in mass-produced stacked or woven metamaterials.

A planar polarization-insensitive metamaterial absorber

Abstract: The model of the polarization-insensitive metamaterial (MM) absorber composed of split cross-ring resonator (SCRR), cave-cross resonator (CCR) and dielectric substrate was proposed at microwave frequencies. Based on perfect impedance-matched ( z ˜ ( ω ) = 1 ) to the free space, the single unit cell could achieve near-unity absorbance by properly assembling the sandwich structure. We have simulated and measured the reflectivity and transmission properties of a planar MM absorber with the thickness of 0.6 mm. The absorptivity of a single layer MM absorber achieve greater than 96% around 10.07 GHz in experiments and 98% in simulations for incident electromagnetic (EM) wave with different polarizations.