Query: metamaterial absorbers

title: Dual band visible metamaterial absorbers based on four identical ring patches
abstract: This paper proposes a dual frequency tunable ideal visible light metamaterial absorber based on the sub wavelength range, which achieves perfect absorption in the visible light band. The absorber consists of an Au reflector and a nodal (SiO2) layer, and a top Au absorber layer. The absorption structure on the top of the absorber adopts the style of ancient Chinese coins and forms a square arrays structure. As a result, the absorber's two absorption peaks are perfect absorption peaks, and the absorption rate can reach 99.9% In addition, we also researched the influence of adjusting the absorber's geometric parameters on the absorber, and analyzed the absorption mechanism under different circumstances. Through research, it can be known that the absorber has near perfect dual band absorption characteristics that do not depend on polarization angle and incident angle insensitivity. Therefore, the absorber designed by us will have a broad application prospect in the filter, solar cell, and so on.

title: Broadband microwave coding metamaterial absorbers
abstract: In this paper, a broadband metamaterial microwave absorber is designed, simulated and measured. Differently from the traditional method which is only based on unit cell boundary conditions, we carried out full wave finite integration simulations using full sized configurations. Starting from an elementary unit cell structure, four kinds of coding metamaterial blocks, 2 x 2, 3 x 3, 4 x 4 and 6 x 6 blocks were optimized and then used as building blocks (meta block) for the construction of numerous 12 x 12 topologies with a realistic size scale. We found the broadband absorption response in the frequency range 16 GHz to 33 GHz, in good agreement with the equivalent medium theory prediction and experimental observation. Considering various applications of metamaterials or metamaterial absorbers in the electromagnetic wave processing, including the radars or satellite communications, requires the frequency in the range up to 40 GHz. Our study could be useful to guide experimental work. Furthermore, compared to the straightforward approach that represents the metamaterials configurations as 12 x 12 matrices of random binary bits (0 and 1) our new approach achieves significant gains in the broadband absorption. Our method also may be applied to the full sized structures with arbitrary dimensions, and thus provide a useful tool in the design of metamaterials with specific desired frequency ranges.

title: Structured graphene metamaterial selective absorbers for high efficiency and omnidirectional solar thermal energy conversion
abstract: An ideal solar thermal absorber requires efficient selective absorption with a tunable bandwidth, excellent thermal conductivity and stability, and a simple structure for effective solar thermal energy conversion. Despite various solar absorbers having been demonstrated, these conditions are challenging to achieve simultaneously using conventional materials and structures. Here, we propose and demonstrate three dimensional structured graphene metamaterial (SGM) that takes advantages of wavelength selectivity from metallic trench like structures and broadband dispersionless nature and excellent thermal conductivity from the ultrathin graphene metamaterial film. The SGM absorbers exhibit superior solar selective and omnidirectional absorption, flexible tunability of wavelength selective absorption, excellent photothermal performance, and high thermal stability. Impressive solar to thermal conversion efficiency of 90.1% and solar to vapor efficiency of 96.2% have been achieved. These superior properties of the SGM absorber suggest it has a great potential for practical applications of solar thermal energy harvesting and manipulation. Here, the authors demonstrate a selective solar thermal absorber with wavelength selectivity, arising from metallic trench like structures, using broadband dispersionless ultrathin graphene metamaterial film, with excellent thermal conductivity.

title: Broadband Metamaterial Absorbers
abstract: Artificially engineered materials, so called metamaterials (MMs) demonstrate interesting electrodynamic properties, including negative refractive index,[1] electromagnetic (EM) wave cloaking,[2] and inverse Doppler effect[3] that are not The recent rise of metamaterials opens new opportunities for absorbers due to their designed electrodynamic properties and effects, allowing the creation of materials with effective values of permittivity and permeability that are not available in naturally occurring materials. Since their first experimental demon stration in 2008, recent literature has offered great advances in metamaterial perfect absorbers (MMPAs) operating at frequencies from radio to optical. Broadband absorbers are indispensable in thermophotovoltaics, photodetec tion, bolometry, and manipulation of mechanical resonances. Although it is easy to obtain MMPAs with single band or multiband, achieving broadband MMPA (BMMPA) remains a challenge due to the intrinsically narrow band width of surface plasmon polaritons, localized surface plasmon resonances generated on metallic surfaces at nanoscale or high Qfactor in GHz region. To guide future development of BMMPA, recent progress is reviewed here: the methods to create broadband absorption and their potential applications. The four mainstream methods to achieve BMMPAs are introduced, including planar and vertical element arrangements, their welding with lumped elements and the use of plasmonic nanocomposites, accompanied by the description of other, less common approaches. Following this, applications of BMMPA in solar photovoltaics, photodetection, bolometry, and manipulation of mechan ical resonances are reviewed. Finally, challenges and prospects are discussed. Hall of Fame Article

title: Design of Narrow Discrete Distances of Dual /Triple Band Terahertz Metamaterial Absorbers
abstract: Various kinds of structure designs have been proposed to achieve the multiple band metamaterial absorbers. However, the discrete distance of adjacent frequencies of multiple absorbers is considerably large, which will inevitably overlook a large amount of information hidden in the off resonance absorption areas. Herein, a narrow discrete distance of dual band terahertz absorber based on two pairs of an Au strip/dielectric layer backed by Au film is designed. Two nearly 100% absorptivities of resonance peaks having the discrete distance of only 0.30 THz are realized. The relative discrete distance of the device is 13.33% and this value can be adjusted via the length change of an Au strip. Furthermore, we present two narrow discrete distances of a triple band absorber through stacking one more pair of an Au strip and dielectric layer. Results prove that two discrete distances of only 0.14 THz and 0.17 THz in adjacent absorption modes of the first two and the last two are achieved, respectively; the relative discrete distances of them are respectively 6.57% and 7.22% which are far from previous reports. Narrow discrete distances (or low values of relative discrete distance) of the multiple band absorbers have a large number of applications in the investigation of some hidden information in very near frequencies.

title: Photonic Metamaterial Absorbers: Morphology Engineering and Interdisciplinary Applications.
abstract: Recent advances in nanofabrication technologies have spurred many breakthroughs in the field of photonic metamaterials that provide efficient ways of manipulating light matter interaction at subwavelength scales. As one of the most important applications, photonic metamaterials can be used to implement novel optical absorbers. First the morphology engineering of various photonic metamaterial absorbers is discussed, which is highly associated with impendence matching conditions and resonance modes of the absorbers, thus directly determines their absorption efficiency, operational bandwidth, incident angle, and polarization dependence. Then, the recent achievements of various interdisciplinary applications based on photonic metamaterial absorbers, including structural color generation, ultrasensitive optical sensing, solar steam generation, and highly responsive photodetection, are reviewed. This report is expected to provide an overview and vision for the future development of photonic metamaterial absorbers and their applications in novel nanophotonic systems.

title: Broadband multilayer graphene metamaterial absorbers
abstract: Two types of broadband and polarization independent graphene metamaterial absorbers are designed. One is a composite four ring structure with azimuthally symmetry, the other is a nested multi ring structure. The nested structure is more compact and has a broader band of absorption. The bandwidth with over 90% absorption is 7.1 THz for the composite four ring structure. The bandwidth increases to 8.7 THz and 11.9 THz for the nested dual ring and three ring absorber, respectively. The wide bandwidth and polarization independent absorption owe to the combination of symmetric multi resonators with different sizes in unit cell. Physical mechanisms of the broadband absorbers are given by the impedance matching theory as well as the surface current distributions. Instead of one single layer graphene as papers reported before, multilayers of graphene are coated on the dielectric surface to form the metal resonant multilayer graphene dielectric metal ground structure. It is found that both the absorbing width and magnitude increase greatly as the graphene layers increase while a large dip appears when the number of graphene layers is large enough. Moreover, by investigating the absorptions under different graphene permittivities, we find that the reduced graphene permittivity is better to simplify the calculation.

title: A survey of theoretical models for terahertz electromagnetic metamaterial absorbers
abstract: In the past few decades, electromagnetic metamaterial absorbers have attracted tremendous attention due to near unity absorption of incident electromagnetic waves over a desired frequency range determined by the metamaterial inclusions as opposed to the constituent material properties. Importantly, metamaterial absorbers enable numerous potential applications which include wave manipulation, terahertz and infrared imaging, energy harvesting, radiative cooling, and chemical detection. To understand the underlying physics of metamaterial absorbers, various theoretical models have been developed. However, these models are seemingly conceptually unrelated, each yielding a distinct set of equations and conclusions. This paper reviews four prevalent theoretical approaches which include effective medium theory, transmission line modelling, coupled mode theory, and interference theory. We show that each of the four theoretical approaches provides an understanding of metamaterial absorbers from different points of view, each with distinct advantages and limitations. Moreover, the four theoretical models are interconnected and we discuss that, quite generally, impedance matching is the crucial condition for perfect absorption.

title: Vanadium dioxide based broadband THz metamaterial absorbers with high tunability: simulation study.
abstract: With their unprecedented flexibility in manipulating electromagnetic waves, metamaterials provide a pathway to structural materials that can fill the so called "THz gap" It has been reported that vanadium dioxide (VO2) experiences a three orders of magnitude increase in THz electrical conductivity when it undergoes an insulator to metal transition. Here, we propose a VO2 based THz metamaterial absorber exhibiting broadband absorptivity that arises from the multiple resonances supported by a delicately balanced doubly periodic array of VO2 structures and numerically demonstrate that the corresponding absorption behavior is highly dependent on the VO2's THz electrical properties. Considering the phase transition induced dramatic change in VO2's material property, the proposed metamaterial absorbers have the potential for strong modulation and switching of broadband THz radiation.

title: Terahertz biosensing based on bi layer metamaterial absorbers toward ultra high sensitivity and simple fabrication
abstract: Metamaterial absorbers have proven their ability to sense in the terahertz domain. However, the sensitivity is always limited by the poor spatial overlap between the analyte and the localized enhanced electromagnetic field. Here, we try to tackle this challenge by utilizing an absorber with a bilayer cross shaped plate hole structure to ingeniously excite hot spots covering the analyte. As a result, the sensitivity is significantly improved, theoretically about 7 and 18 times higher than that of the conventional cross shaped absorber and its complementary cross shaped absorber, respectively. We then experimentally demonstrate its ability to quantitatively detect biotin with a sensitivity of 153 GHz/mM, higher than that of previously reported biotin sensors. Additionally, the polarization independent nanostructure decreases the design and fabrication complexity and maintains high reflection at a wide range of incident angles over 50deg. These findings open up opportunities for metamaterial absorbers to realize ultrasensitive biosensing in the fingerprint region of the terahertz regime.