Showing papers on "Metamaterial absorber published in 2014"

Refractory plasmonics with titanium nitride: broadband metamaterial absorber.

Abstract: A high-temperature stable broadband plasmonic absorber is designed, fabricated, and optically characterized. A broadband absorber with an average high absorption of 95% and a total thickness of 240 nm is fabricated, using a refractory plasmonic material, titanium nitride. This absorber integrates both the plasmonic resonances and the dielectric-like loss. It opens a path for the interesting applications such as solar thermophotovoltaics and optical circuits.

Metamaterial Perfect Absorber Based Hot Electron Photodetection

Abstract: While the nonradiative decay of surface plasmons was once thought to be only a parasitic process that limits the performance of plasmonic devices, it has recently been shown that it can be harnessed in the form of hot electrons for use in photocatalysis, photovoltaics, and photodetectors. Unfortunately, the quantum efficiency of hot electron devices remains low due to poor electron injection and in some cases low optical absorption. Here, we demonstrate how metamaterial perfect absorbers can be used to achieve near-unity optical absorption using ultrathin plasmonic nanostructures with thicknesses of 15 nm, smaller than the hot electron diffusion length. By integrating the metamaterial with a silicon substrate, we experimentally demonstrate a broadband and omnidirectional hot electron photodetector with a photoresponsivity that is among the highest yet reported. We also show how the spectral bandwidth and polarization-sensitivity can be manipulated through engineering the geometry of the metamaterial unit ...

Plasmonic and metamaterial structures as electromagnetic absorbers

Abstract: Electromagnetic absorbers have drawn increasing attention in many areas. A series of plasmonic and metamaterial structures can work as efficient narrowband absorbers due to the excitation of plasmonic or photonic resonances, providing a great potential for applications in designing selective thermal emitters, biosensing, etc. In other applications such as solar-energy harvesting and photonic detection, the bandwidth of light absorbers is required to be quite broad. Under such a background, a variety of mechanisms of broadband/multiband absorption have been proposed, such as mixing multiple resonances together, exciting phase resonances, slowing down light by anisotropic metamaterials, employing high loss materials and so on.

Ultra-broadband terahertz metamaterial absorber

Abstract: We demonstrated an ultra-broadband, polarization-insensitive, and wide-angle metamaterial absorber for terahertz (THz) frequencies using arrays of truncated pyramid unit structure made of metal-dielectric multilayer composite. In our design, each sub-layer behaving as an effective waveguide is gradually modified in their lateral width to realize a wideband response by effectively stitching together the resonance bands of different waveguide modes. Experimentally, our five layer sample with a total thickness 21 μm is capable of producing a large absorptivity above 80% from 0.7 to 2.3 THz up to the maximum measurement angle 40°. The full absorption width at half maximum of our device is around 127%, greater than those previously reported for THz frequencies. Our absorber design has high practical feasibility and can be easily integrated with the semiconductor technology to make high efficient THz-oriented devices.

Liquid Crystal Metamaterial Absorber Spatial Light Modulator for THz Applications

Abstract: A terahertz (THz) spatial light modulator implemented with metamaterial absorbers (MMAs) functionalized with isothiocyanate-based liquid crystals (LCs) is experimentally demonstrated. The device is designed to work in refl ection mode and is arranged in a 6 × 6 pixel matrix where the response of each pixel is modulated by electronically controlling the orientation of liquid crystal dimers covering the entire metamaterial absorber landscape. Experiments show that each pixel can be controlled independently and that pixelated absorption patterns can be created at will. The SLM shows an overall modulation depth of 75%. Furthermore, computational results show that losses arising from LCs impose a severe limitation on the overall performance and that consequently the modulation depth of each pixel could be improved with liquid crystal mixtures designed primarily for THz frequencies. This work demonstrates the viability of liquid crystal-based reconfi gurable metamaterials and highlights their great potential use for future state-of-the-art THz devices.

Experimental demonstration of a broadband all-dielectric metamaterial perfect reflector

Abstract: All-dielectric metamaterials utilizing Mie resonances in high-permittivity dielectric resonators offer a low-loss alternative to plasmonic metamaterials. Here we present the demonstration of a single-negative all-dielectric metamaterial, comprised of a single layer of cylindrical silicon resonators on a silicon-on-insulator substrate, that possesses peak reflectance over 99% and an average reflectance over 98% across a 200 nm wide bandwidth in the short-wavelength infrared region. The study is also extended to disordered metamaterials, demonstrating a correlation between the degree of disorder and the reduction in reflectance. It is shown that near-unity reflection is preserved as long as resonator interaction is avoided. Realization of near-unity reflection from disordered metamaterials opens the door to large-area implementations using low-cost self-assembly based fabrication techniques.

Polarization-Independent and Ultrawideband Metamaterial Absorber Using a Hexagonal Artificial Impedance Surface and a Resistor-Capacitor Layer

Abstract: A polarization-independent ultrawideband metamaterial absorber is proposed for X-band applications. High absorptivity over an ultrawide spectrum is achieved by the combination of an artificial impedance surface (AIS) and a resistor-capacitor (RC) layer. In addition, the unique hexagonal shape of an AIS and RC layer enables polarization insensitivity. A circuit analysis is introduced based on a transmission-line model and shows good agreement with the full-wave analysis. Fabrication tolerance issues are considered with parametric studies in the electromagnetic simulation. The proposed absorber is fabricated on low-cost FR4 substrates, and its absorption performance is experimentally demonstrated at different angles and polarizations of incident electric fields.

Reconfigurable and Tunable Metamaterials: A Review of the Theory and Applications

Abstract: Metamaterials are being applied to the development and construction of many new devices throughout the electromagnetic spectrum. Limitations posed by the metamaterial operational bandwidth and losses can be effectively mitigated through the incorporation of tunable elements into the metamaterial devices. There are a wide range of approaches that have been advanced in the literature for adding reconfiguration to metamaterial devices all the way from the RF through the optical regimes, but some techniques are useful only for certain wavelength bands. A range of tuning techniques span from active circuit elements introduced into the resonant conductive metamaterial geometries to constituent materials that change electromagnetic properties under specific environmental stimuli. This paper presents a survey of the development of reconfigurable and tunable metamaterial technology as well as of the applications where such capabilities are valuable.

Near-Ideal Optical Metamaterial Absorbers with Super-Octave Bandwidth

Abstract: Nanostructured optical coatings with tailored spectral absorption properties are of interest for a wide range of applications such as spectroscopy, emissivity control, and solar energy harvesting. Optical metamaterial absorbers have been demonstrated with a variety of customized single band, multiple band, polarization, and angular configurations. However, metamaterials that provide near unity absorptivity with super-octave bandwidth over a specified optical wavelength range have not yet been demonstrated experimentally. Here, we show a broadband, polarization-insensitive metamaterial with greater than 98% measured average absorptivity that is maintained over a wide ±45° field-of-view for mid-infrared wavelengths between 1.77 and 4.81 μm. The nearly ideal absorption is realized by using a genetic algorithm to identify the geometry of a single-layer metal nanostructure array that excites multiple overlapping electric resonances with high optical loss across greater than an octave bandwidth. The response is...

Theoretical Investigation of Broadband and Wide-Angle Terahertz Metamaterial Absorber

Abstract: Broadband absorbers have attracted considerable attention due to their great prospect for practical applications. The mechanism is usually a superposition of several sets of structures with different geometrical dimensions. Herein, we numerically investigate an unconventional to existing metamaterial-based broadband terahertz absorber based on the multilayer same-sized square plate structure. Greater than 99% absorption across a frequency range of 300 GHz with the central frequency ~ 1.96 THz can be obtained. The FWHM of this device can be up to 42% (with respect to the central frequency), which is 2.6 times greater than that of the single layer structure. Such a property is retained well at a very wide range of incident angles. The mechanism of the broadband absorber is attributed to longitudinal coupling between layers. The results of the designed metamaterial absorber appear to be very promising for solar cell, detection, and imaging applications.

Triple band polarization-independent ultra-thin metamaterial absorber using electric field-driven LC resonator

Abstract: In this paper, a triple band polarization-independent metamaterial absorber using electric field-driven LC resonators is proposed over wide angle of incidence. The unit cell is designed by parametric optimization in such a way that triple band absorption occurs in C-band. The proposed structure exhibits triple band absorption property for any angle of polarization under normal incidence. It also shows high absorption for wide angle of incidence upto 60° for both TE and TM polarizations. The proposed structure is also fabricated and experimental results provide good agreement with the simulated responses. The constitutive electromagnetic parameters viz. effective permittivity and effective permeability are extracted from the simulated response, which support the absorption phenomena at all these three frequencies. The reflection from the structure is numerically computed and verified with simulated response, and it shows good agreement between them.

Review of Plasmonic Nanocomposite Metamaterial Absorber

Abstract: Plasmonic metamaterials are artificial materials typically composed of noble metals in which the features of photonics and electronics are linked by coupling photons to conduction electrons of metal (known as surface plasmon). These rationally designed structures have spurred interest noticeably since they demonstrate some fascinating properties which are unattainable with naturally occurring materials. Complete absorption of light is one of the recent exotic properties of plasmonic metamaterials which has broadened its application area considerably. This is realized by designing a medium whose impedance matches that of free space while being opaque. If such a medium is filled with some lossy medium, the resulting structure can absorb light totally in a sharp or broad frequency range. Although several types of metamaterials perfect absorber have been demonstrated so far, in the current paper we overview (and focus on) perfect absorbers based on nanocomposites where the total thickness is a few tens of nanometer and the absorption band is broad, tunable and insensitive to the angle of incidence. The nanocomposites consist of metal nanoparticles embedded in a dielectric matrix with a high filling factor close to the percolation threshold. The filling factor can be tailored by the vapor phase co-deposition of the metallic and dielectric components. In addition, novel wet chemical approaches are discussed which are bio-inspired or involve synthesis within levitating Leidenfrost drops, for instance. Moreover, theoretical considerations, optical properties, and potential application of perfect absorbers will be presented.

Bandwidth-enhanced polarization-insensitive microwave metamaterial absorber and its equivalent circuit model

Abstract: In this paper, a bandwidth-enhanced polarization-insensitive ultra-thin metamaterial absorber has been presented. A simple equivalent circuit model has been proposed describing the absorption phenomenon to estimate the frequency of absorption of the proposed microwave absorber. The basic structure consists of concentric rings embedded one inside another to enhance bandwidth by incorporating the scalability property of the metamaterials. Simulation results show that the structure has enhanced bandwidth response with full width at half maxima (FWHM) of 1.15 GHz (9.40–10.55 GHz) with two absorption peaks at 9.66 and 10.26 GHz (96% and 92.5% absorptivity, respectively). The structure is symmetric in design giving rise to polarization-insensitivity and can achieve high absorption for oblique incidence up to 40°. The proposed absorber has been fabricated and measured in anechoic chamber, showing that experimental results agree well with the simulated responses.

Wideband, thin, and polarization-insensitive perfect absorber based the double octagonal rings metamaterials and lumped resistances

Abstract: By loading the lumped resistances into the double octagonal rings metamaterials, a wideband, thin, and polarization-insensitive perfect absorber is investigated theoretically and experimentally. The perfect absorber is constructed of double octagonal rings loading the eight lumped resistances and the substrate with height of 3 mm. The effects of the double octagonal rings and eight lumped resistances are explored by absorption and the electric field distributions. The simulated results indicate that the structure obtains 9.25 GHz-wide absorption from 7.93 to 17.18 GHz with absorptivity larger than 90% at the incident angles from 0° to 20° and achieves above 12.2 GHz-wide absorption from 5.8 to 18 GHz with a full width at half maximum at wide incident angles from 0° to 70°. The fabricated metamaterial absorber device was measured and analyzed. A good agreement is observed between the simulation and the measurement.

Flexible and elastic metamaterial absorber for low frequency, based on small-size unit cell

Abstract: Using a planar and flexible metamaterial (MM), we obtained the low-frequency perfect absorption even with very small unit-cell size in snake-shape structure. These shrunken, deep-sub-wavelength and thin MM absorbers were numerically and experimentally investigated by increasing the inductance. The periodicity/thickness (the figure of merit for perfect absorption) is achieved to be 10 and 2 for single-snake-bar and 5-snake-bar structures, respectively. The ratio between periodicity and resonance wavelength (in mm) is close to 1/12 and 1/30 at 2 GHz and 400 MHz, respectively. The absorbers are specially designed for absorption peaks around 2 GHz and 400 MHz, which can be used for depressing the electromagnetic noise from everyday electronic devices and mobile phones.

Metamaterial-based perfect absorbers

Abstract: Metamaterials are artificially-engineered materials, possessing properties which are not readily observable in materials existing in nature. Since they show very novel properties such as left-handed behavior, negative refractive index, classical analog of electromagnetically-induced transparency, extraordinary transmission, negative Doppler effect, and so on, they can be used for perfect lens, invisibility cloaking, perfect absorption and transmission, etc. Metamaterial-based perfect absorbers (MMPAs) are promising candidates for the practical application of perfect absorbers. MMPA is usually composed of three layers. The first layer is periodically-arranged metallic patterns, whose structure and geometrical parameters should be carefully adjusted to fulfill the impedance-matching condition with the ambient, allowing no reflection of incident electromagnetic (EM) waves. The second layer is a dielectric layer, which allows a space for the EM waves to be dissipated, and sometimes plays a role of resonance c...

Experimental investigation of compact metamaterial for high efficiency mid-range wireless power transfer applications

Abstract: We investigate a compact metamaterial for enhanced magnetic coupling in a resonator coupled wireless power transfer system operating at around 6.5 MHz. The metamaterial is constructed by realizing an array of three-turn spiral resonators on a thin slab. Although the metamaterial has its own loss, the experimental results show that the proposed metamaterial slab enhances the power transmission capability. The number of unit cells in the array is an important parameter, because exceeding a certain number of unit cells does not enhance the efficiency due to the loss of the slab. Furthermore, strong surface mode resonance is observed when two slabs are assembled with proper gap spacing between them. By using the optimization approach, we achieve a significant efficiency improvement at a mid-range distance. The measured efficiencies are 71.1% and 54.3% at a 0.6 and 1.0 m distance, respectively. At a 1.0 m distance, this efficiency performance corresponds to a 270% improvement compared to a case with no metamaterial slab. In addition, we experimentally confirm the threshold distances above which the metamaterial shows enhanced performance.

Improving Power Transfer Efficiency of a Short-Range Telemetry System Using Compact Metamaterials

Abstract: Wireless power transfer using resonant inductive coupling has been employed in a number of applications, including wireless charging of electronic devices and powering of implanted biomedical devices. In these applications, power is transferred over short distances, which are much smaller (~ λ/100) than the wavelength of operation. In such systems, the power transfer efficiency of the link is inversely related to the range of operation. The power transfer efficiency is principally a function of the Q's of the individual coils and the coupling between them. In this paper, we demonstrate improvements in power transfer efficiencies using negative permeability metamaterials by increasing the mutual coupling between coils. A metamaterial slab is designed for operation at 27 MHz and is compact in size. The power transfer efficiency of the telemetry system in free space is compared to that in the presence of the metamaterial placed near one of the coils. The efficiency of the system increased in the presence of the metamaterial even as the free-space separation was held constant. This shows that compact negative permeability metamaterials can be used to increase power transfer efficiency of short-range telemetry systems used in various applications.

Switchable wavelength-selective and diffuse metamaterial absorber/emitter with a phase transition spacer layer

Abstract: We numerically demonstrate a switchable metamaterial absorber/emitter by thermally turning on or off the excitation of magnetic resonance upon the phase transition of vanadium dioxide (VO2). Perfect absorption peak exists around the wavelength of 5 μm when the excitation of magnetic resonance is supported with the insulating VO2 spacer layer. The wavelength-selective absorption is switched off when the magnetic resonance is disabled with metallic VO2 that shorts the top and bottom metallic structures. The resonance wavelength can be tuned with different geometry, and the switchable metamaterial exhibits diffuse behaviors at oblique angles. The results would facilitate the design of switchable metamaterials for active control in energy and sensing applications.

Integrating non-planar metamaterials with magnetic absorbing materials to yield ultra-broadband microwave hybrid absorbers

Abstract: Broadening the bandwidth of electromagnetic wave absorbers has greatly challenged material scientists. Here, we propose a two-layer hybrid absorber consisting of a non-planar metamaterial (MM) and a magnetic microwave absorbing material (MAM). The non-planar MM using magnetic MAMs instead of dielectric substrates shows good low frequency absorption and low reflection across a broad spectrum. Benefiting from this and the high frequency strong absorption of the MAM layer, the lightweight hybrid absorber exhibits 90% absorptivity over the whole 2–18 GHz range. Our result reveals a promising and flexible method to greatly extend or control the absorption bandwidth of absorbers.

Frequency Continuous Tunable Terahertz Metamaterial Absorber

Abstract: Metamaterial-based perfect absorbers utilize the intrinsic loss, with the aid of appropriate structural design (completely suppress transmission and reflection), to achieve near unity absorption at a certain frequency. The frequency of the reported absorbers is usually fixed and operates over a limited bandwidth, which greatly hampers their practical applications. Active or dynamic control over their resonance frequency is urgently necessary. Herein, we propose a novel approach for efficient tuning of the frequency of the absorber by shifting the movable part of the composite structure composed of the fixed and movable parts. The concept is rather general and applicable to various absorbers as long as the sandwich structure design is valid. The demonstrated continuous tuning of metamaterial absorber can find practical applications in detection, imaging, spectroscopy and selective thermal emitters.

A novel ultrathin and broadband microwave metamaterial absorber

Abstract: In this paper, the design, simulation, fabrication, and measurement of an ultrathin and broadband microwave metamaterial absorber (MMA) based on a double-layer structure are presented. Compared with the prior work, our structure is simple and polarization insensitive. The broadband MMA presents good absorption above 90% between 8.85 GHz and 14.17 GHz, with a full width at half maximum (FWHM) absorption bandwidth of 6.77 GHz and a relative FWHM absorption bandwidth of 57.3%. Moreover, the structure has a thickness of 1.60 mm (only λ/20 at the lowest frequencies). The experimental results show excellent absorption rates which are in good correspondence with the simulated results. The broadband absorber is promising candidates as absorbing elements in scientific and technical applications because of its broadband absorption and polarization insensitive.

Tunable terahertz left-handed metamaterial based on multi-layer graphene-dielectric composite

Abstract: A terahertz fishnet metamaterial, consisting of a gallium arsenide substrate sandwiched between multi-layer graphene-dielectric composites, is theoretically studied. Detailed analysis shows that this metamaterial has a left-handed transmission peak accompanied with an abnormal phase dispersion and a clear negative refractive index which originates from simultaneous magnetic and electric resonances. Our structure is unique because it has no metallic parts to achieve the left-handed properties. The most important utility of this metamaterial comes from the fact that its left-handed features can be dynamically controlled by applying external bias to shift the Fermi level in graphene.

Optically Modulated Multiband Terahertz Perfect Absorber

Abstract: Development of tunable, dynamic, and broad bandwidth metamaterial designs is a keystone objective for metamaterials research, necessary for the future viability of metamaterial optics and devices across the electromagnetic spectrum. Yet, overcoming the inherently localized, narrow bandwidth, and static response of resonant metamaterials continues to be a challenging endeavor. Resonant perfect absorbers have flourished as one of the most promising metamaterial devices with applications ranging from power harvesting to terahertz imaging. Here, an optically modulated resonant perfect absorber is presented. Utilizing photo-excited free carriers in silicon pads placed in the capacitive gaps of split ring resonators, a dynamically modulated perfect absorber is designed and fabricated to operate in reflection. Large modulation depth (38% and 91%) in two absorption bands (with 97% and 92% peak absorption) is demonstrated, which correspond to the LC (0.7 THz) and dipole (1.1 THz) modes of the split ring resonators.

Plasmonic tunable metamaterial absorber as ultraviolet protection film

Abstract: Plasmonic metamaterials designed for optical frequency have to be shrunk down to few 10th of nanometer which turns their manufacturing cumbersome. Here, we shift the performance of metamaterial down to ultraviolet (UV) by using ultrathin nanocomposite as a tunable plasmonic metamaterial fabricated with tandem co-deposition. It provides the possibility to realize a plasmonic metamaterial absorber for UV frequency with marginal angle sensitivity. Its resonance frequency and intensity can be adjusted by changing thickness and filling factor of the composite. Presented approach for tunable metamaterials for high frequency could pave the way for their application for thermo-photovoltaic, stealth technology, and UV-protective coating.

Bandwidth-enhancement of an ultrathin polarization insensitive metamaterial absorber

Abstract: An ultrathin polarization insensitive microwave metamaterial absorber is discussed, which consists of a periodic array of swastika-like structure printed on FR4 dielectric substrate backed by copper ground. The structure is simulated to give rise to nearly unity (99.64%) absorption at 10.10 GHz (X-band). The proposed structure is symmetric in nature and provides high absorption for any angle of polarization under normal incidence. It also shows high absorption (∼81%) for incident angle upto 60o. Further, a 2 × 2 array using two different variants of the same resonating structure has been studied and by optimizing its geometrical dimensions, the absorption peaks are brought closer to provide an enhanced bandwidth having full width at half maximum of 0.68 GHz (10.04–10.72 GHz). Both the single-band and bandwidth-enhanced structures are then fabricated and experimentally studied which shows good agreement with the simulated results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:350–355, 2014

Electrothermally actuated microelectromechanical systems based omega-ring terahertz metamaterial with polarization dependent characteristics

Abstract: We present the design, simulation, fabrication, and characterization of a continuously tunable Omega-ring terahertz metamaterial. The tunability of metamaterial is obtained by integrating microactuators into the metamaterial unit cell. Electrothermal actuation mechanism is used to provide higher tuning range, larger stroke, and enhanced repeatability. The maximum achieved tuning range for the resonant frequency is around 0.30 THz for the input power of 500 mW. This shows the potential of using electrothermally actuated microactuators based tunable metamaterial design for application such as filters, absorbers, sensors, and spectral imagers.

An ultra-thin chiral metamaterial absorber with high selectivity for LCP and RCP waves

Abstract: An ultra-thin chiral metamaterial absorber (CMMA) is constructed from twisted 'L-shaped' folded metallic wires. In particular, it has high selectivity for left-handed and right-handed circular polarized (LCP and RCP) incident waves, which is impossible in traditional metamaterial absorbers. The thickness of the CMMA is only 0.8 mm, with absorption of 93.2% for LCP and 8.4% for RCP waves, respectively. This superb performance can be applied in homogeneous circular polarizers for an arbitrarily polarized incident wave with high polarization conversion efficiency. Meanwhile, current distributions, retrieval results and multipole theory have been used in analyzing the absorption mechanism. Microwave experiments are performed to successfully realize these ideas, and measured results are in good agreement with the numerical results.

Micro-electro-mechanically switchable near infrared complementary metamaterial absorber

Abstract: We experimentally demonstrate a micro-electro-mechanically switchable near infrared complementary metamaterial absorber by integrating the metamaterial layer to be the out of plane movable microactuator. The metamaterial layer is electrostatically actuated by applying voltage across the suspended complementary metamaterial layer and the stationary bottom metallic reflector. Thus, the effective spacing between the metamaterial layer and bottom metal reflector is varied as a function of applied voltage. With the reduction of effective spacing between the metamaterial and reflector layers, a strong spectral blue shift in the peak absorption wavelength can be achieved. With spacing change of 300 nm, the spectral shift of 0.7 μm in peak absorption wavelength was obtained for near infrared spectral region. The electro-optic switching performance of the device was characterized, and a striking switching contrast of 1500% was achieved at 2.1 μm. The reported micro-electro-mechanically tunable complementary metamaterial absorber device can potentially enable a wide range of high performance electro-optical devices, such as continuously tunable filters, modulators, and electro-optic switches that form the key components to facilitate future photonic circuit applications.