A Design for Band Enhanced Dielectric Absorber Based on Fractal-Like Structure

A dielectric metamaterial absorber has been proposed, which consists of fractal-like structure and conductive sheet. The fractal-like structure is made by the high permittivity dielectric and also is covered by the conductive sheet. Absorptivity of such a dielectric metamaterial absorber is 99.1%, which can be found at 10.196 GHz; meanwhile, the absorber is polarization insensitive. To enhance the bandwidth of absorber, a novel absorber also is proposed, whose bandwidth is 0.566 GHz, which ranges from 9.752 to 10.318 GHz, and relative bandwidth is 5.64%. The maximum absorptivity can reach to 99.8%, and the proposed absorber also is polarization insensitive. In the meantime, the absorber shows excellent performance which is incident angle insensitive; when the incident angle is increased to 70°, the absorptivity is larger than 75%.

     

Metallic Photonic Crystal Absorber‐Emitter for Efficient Spectral Control in High‐Temperature Solar Thermophotovoltaics

A high‐temperature stable solar absorber based on a metallic 2D photonic crystal (PhC) with high and tunable spectral selectivity is demonstrated and optimized for a range of operating temperatures and irradiances. In particular, a PhC absorber with solar absorptance 0.86 and thermal emittance = 0.26 at 1000 K, using high‐temperature material properties, is achieved resulting in a thermal transfer efficiency more than 50% higher than that of a blackbody absorber. Furthermore, an integrated double‐sided 2D PhC absorber/emitter pair is demonstrated for a high‐performance solar thermophotovoltaic (STPV) system. The 2D PhC absorber/emitter is fabricated on a double‐side polished tantalum substrate, characterized, and tested in an experimental STPV setup along with a flat Ta absorber and a nearly blackbody absorber composed of an array of multiwalled carbon nanotubes (MWNTs). At an irradiance of 130 kW m^?2 the PhC absorber enables more than a two‐fold improvement in measured STPV system efficiency (3.74%) relative to the nearly blackbody absorber (1.60%) and higher efficiencies are expected with increasing operating temperature. These experimental results show unprecedented high efficiency, demonstrating the importance of the high selectivity of the 2D PhC absorber and emitter for high‐temperature energy conversion.     

A Compact Design of Multiband Terahertz Metamaterial Absorber with Frequency and Polarization Tunability

A new and simple design of quad-band metamaterial absorber for terahertz frequency has been proposed. The unit cell of the absorber is composed of a top metallic patch having H-shaped slot and a ground metallic plane, both separated by a dielectric layer. The proposed design is capable of providing four distinct absorption peaks over at 0.81, 1.98, 3.25, and 3.50 THz. Our design is a step ahead of the previously proposed terahertz absorbers for its simplistic design approach which removes the fabrication difficulty. Interestingly, rather placing multiple resonators in a single unit cell, we able to accommodate multiple orders of resonances in the proposed design using only a single metallic structure to achieve multiband absorbance. The sensing performance of the absorber in terms of surrounding index is also analyzed. Moreover, we have shown how the proposed structure can be easily converted into a frequency tunable absorber using a simple stub without changing the overall geometry of the absorber. This fast and easy frequency tunability feature is an additional advantage over the simple design of the structure. Also, we lead our work to its upgradation into a polarization tunable absorber where the absorption frequencies are controllable by the polarization of the incident light. The vibrant design of the proposed absorber is expected to find application in detection, imaging, radar cross-section (RCS) reduction, and sensing-related activities.     

Polarization-Controlled Metamaterial Absorber with Extremely Bandwidth and Wide Incidence Angle

Plasmonics - In this paper, a three-dimensional metamaterial structure absorber has been analyzed and discussed. The unit of the absorber is composed of nine different size resistive films which...     

Gold Nanowires-Based Hyperbolic Metamaterial Multiband Absorber Operating in the Visible and Near-Infrared Regimes

Plasmonics - Spectral feature of gold nanowires-based hyperbolic metamaterial (NWHMM) absorber was investigated. The absorber has NWHMM surface as the top layer, which is composed of periodically...     

Numerical Study of an Ultra-Broadband and Polarization Independence Metamaterial Cross-Shaped Fractal Absorber

A three-dimensional cross-shaped fractal metamaterial absorber with ultra-wide wavelength band, polarization-independence and wide-angle, is numerically investigated by the finite-difference time-domain method. In this absorber, the solar energy is trapped by the cross-shaped fractal of the upper layer, and the Si-ring filled with iron in the middle layer and the wavelength band can be broadened by the self-similarity of fractal structure. The absorber exhibits absorptivity higher than 91% for the wavelengths from 400 to 2000 nm and an absorption bandwidth of about 133%. Furthermore, the proposed absorber realizes polarization independence, and the maximum incident angle is 76°. However, as the iron material applied in the nano-metamaterial absorber (NMA) can be easily oxidized and rusted, it is replaced by nickel with characteristics such as corrosion resistance and high-temperature resistance; thus, an improved NMA is obtained. The improved absorber not only eliminates the corrosion-prone defects of the above proposed structure but also maintains polarization independence and high absorption and widens the angle of incidence up to 79° and thereby can be applied in many areas, such as solar energy harvesting.

     

Multiband Metamaterial Absorber Design Based on Plasmonic Resonances for Solar Energy Harvesting

A new metamaterial absorber is designed and characterized numerically for the harvesting of solar energy. The design is composed of three layers in which the interaction among them gives rise to the plasmonic resonances. The main operation frequency range of the proposed structure is chosen to be the visible regime. However, the design is also analyzed for the infrared and ultraviolet regimes. In order to characterize the absorber, some parametric studies with respect to the dimensions of the structure are carried out. According to the results, it is found that the proposed metamaterial absorber has 98.2 % absorption capability at 445.85 THz and 99.4 % absorption capability between 624 and 658.3 THz. Moreover, the polarization dependency of the structure is examined and it is found that the design operates well as a perfect absorber with polarization independency for the studied frequency range. As a result, the proposed metamaterial absorber can be used for solar energy harvesting as it provides multiple perfect absorption bands in the visible regime.     

High-Performance Tunable Multichannel Absorbers Coupled with Graphene-Based Grating and Dual-Tamm Plasmonic Structures

Plasmonics - We present a hybrid Tamm system targeting the tunable multichannel absorber. The proposed optical absorber is analyzed and investigated by using the transfer matrix method (TMM). The...     

A Band Enhanced Tunable Ultra-Broadband Absorber Based on Loading the Lumped Resistors and Cavity Resonance

Plasmonics - In this paper, we present and demonstrate a band enhanced tunable ultra-broadband absorber (TUA) based on loading the lump resistors (LRs) and cavity resonance. The absorber’s...     

Design of a Multi-functional Device Based on the Solid-state Plasma: Absorber and Splitter

Plasmonics - We propose a multi-functional device by using the solid-state plasma, which can be called a plasma metamaterial absorber (PMA). The absorber can get tunable absorption spectrum by...     

Wideband Graphene-Based Fractal Absorber and its Applications as Switch and Inverter

In this paper, the idea of square fractal geometry has been utilized to introduce a tunable wideband graphene-based perfect plasmonic absorber in the near-infrared region. It consists of a MgF₂ layer and an array of gold squares fractal loaded on a graphene layer. In the designed absorber a single layer of graphene has been used instead of multilayered graphene structures. The structure is polarization-insensitive under normal incidence due to the geometric symmetry. The absorption and bandwidth of the structure are almost insensitive to the incident angle up to 15° and 45° for TE and TM polarizations, respectively. Moreover, by choosing appropriate structural parameters, the resonance wavelength of the desired plasmonic absorber can be controlled. The absorption of the introduced structure can be tuned by changing the chemical potential of the graphene. Therefore, the proposed fractal absorber can act as switch and inverter at λ = 1995 nm. Furthermore, the equivalent circuit model of the absorber has been derived to confirm the validity of the simulation results. The superiorities of our fractal absorber are wide full-width at half-maximum of 406 nm, multi-applicant, perfect absorption, and fabrication feasibility due to the simple structure with the maximum absorption tolerance error of 5.12%.

     

Miniaturized Five-Band Perfect Metamaterial THz Absorber with Small Frequency Ratio

A five-band polarization-insensitive perfect metamaterial absorber (PMA) is reported in this paper for THz detection and sensing applications. The proposed absorber is constructed using interconnected circular ring elements enclosed by a square loop. The ring elements are interconnected using short strip lines which increases the electrical length to offer resonance at the lower frequencies of the THz regime without increasing the electrical length. The proposed absorber has a footprint of 0.12 λ_eff?×?0.12 λ_eff where λ_eff is the effective wavelength calculated at the lowest operating frequency. The absorber provides 92%, 84%, 90%, 100%, and 100% absorption at 0.24, 0.56, 0.65, 0.82, and 0.95 THz, respectively. The proposed structure offers structural symmetry, and hence, it is polarization-insensitive. The proposed five-band absorber has good angular stability consistent with many research works reported in the literature and has a small frequency ratio of 1:2.3:2.7:3.4:3.9. The proposed absorber can be used as a permittivity sensor and its sensitivity is estimated to vary from 5.8 GHz/permittivity unit (PU) to 23.56 GHz/PU.

     

High-Quality Plasmon Sensing with Excellent Intensity Contrast by Dual Narrow-Band Light Perfect absorbers

A new strategy for realizing ultra-narrowband plasmonic absorber has been theoretically demonstrated. Dual-band perfect light absorber with the bandwidth down to single digit level and the maximal absorption exceeding 99.2 % is achieved. Moreover, novel absorber-based sensor platform with high-quality factors (S?>?420 nm/RIU, FOM?>?84, and FOM*?>?5600) are obtained. These features hold the proposed absorber to be a feasible candidate for applications in the sensing detection and notch filtering.     

Tunable Salisbury Screen Absorber Using Square Lattice of Plasmonic Nanodisk

We propose a novel polarization independent Salisbury screen absorber to provide tunable resonant absorption at terahertz (THz) frequencies. The Salisbury screen absorber is designed by using a planar array of thin gold nanodisks arranged in a square lattice. Certain configurations of Salisbury screen have multiple distinctive absorption bands that support near-unity/FWHM absorption bandwidth reaching 36 THz/169 THz, respectively. Moreover, the absorption bandwidth depends upon the optical thickness of the dielectric spacer between the metasurface and the metallic ground plane. The proposed tunable Salisbury screen absorber can find practical applications in photonic detection, imaging, sensing, and solar cells at optical frequencies.     

Broadband Ultrathin Absorber and Sensing Application Based on Hybrid Materials in Infrared Region

A broadband and ultra-thin absorber in the infrared region is proposed. The structure is composed of three layers, and the most remarkable difference is that two hybrid materials (Sn and InSb) are used in the top layer. The numerical results show that a broadband perfect absorption from 85.2 to 114.3 THz can be achieved for either transverse electric or magnetic polarization waves due to the effect of using hybrid materials. Moreover, the power loss and surface current distribution in the absorber are investigated to explain the physical mechanism of high absorption. The metamaterial absorber is ultra-thin, having total thickness of 0.3 μm, i.e.,λ/10 with respect to the center frequency of the high absorption bands. The proposed hybrid materials which are used in the same layer provides a useful way to realize a broadband perfect absorber in the infrared region and it is important for a variety of applications, such as solar energy harvest, sensors, and integrated photodetectors .     

Ultrabroadband Mid-infrared Light Absorption Based on a Multi-cavity Plasmonic Metamaterial Array

We present a broadband plasmonic metamaterial absorber in the infrared region based on localized surface plasmon polaritons (LSPPs). The unit cell of the proposed metamaterial absorber consists of a multi-cavity structure, in which absorption resonances can be tuned independently through the modification of the width and shift of metallic walls. In order to avoid the degeneration between two contiguous resonances, which dramatically reduces the bandwidth, we introduce a zigzag design rule to arrange the cavities within a compact unit. Thus, the possible number of resonances is greatly increased, enabling an ultrabroadband absorption. A broadband absorber is demonstrated with only a few-layer structure and it also has an incident-angle-insensitive feature. Our results have potential applications in photovoltaic devices, emitters, sensors, and camouflage systems.     

Wide-Angle Near-Perfect Absorber Based on Sub-Wavelength Dielectric Grating Covered by Continuous Thin Aluminum Film

We design and numerically investigate an optical absorber consisting of the sub-wavelength dielectric grating covered by continuous thin aluminum film. In this absorber, the aluminum film act as an efficient absorbing material because of the enhanced electric field in the air nano-grooves, and the absorption spect+rum can be manipulated by Fabry-Perot cavity mode resonance. According to the spectrum manipulation mechanism, the wavelength of absorption peak can be tuned by changing the heights and widths of the air nano-grooves. More importantly, the high absorption is very robust to the incident angle around the designed wavelength. From the nanofabrication point of view, the light absorber can be fabricated more easily without the need for ion or electrochemical etching of metal and it is easy to be integrated into complex photonic devices.     

Design Meets Nature: Tetrahedrite Solar Absorbers

Computational inverse design and consequent experimental results allow for the identification of new tetrahedrite‐mineral compositions as promising absorber candidates in drift‐based thin‐film solar cells. In device simulations, cell efficiencies above 20% are modeled with absorber layers as thin as 250 nm. These new compositions thus open opportunities for realization of a new class of high‐efficiency thin‐film solar cell.     

A simplified physical model of pressure wave dynamics and acoustic wave generation induced by laser absorption in the retina

Shock waves have been proposed in the literature as a mechanism for retinal damage induced by ultra-short laser pulses. For a spherical absorber, we derive a set of linear equations describing the propagation of pressure waves. We show that the formation of shock fronts is due to the form of the absorber rather than the inclusion of nonlinear terms in the equations. The analytical technique used avoids the need for a Laplace transform approach and is easily applied to other absorber profiles. Our analysis suggests that the ’soft’ nature of the membrane surrounding retinal melanosomes precludes shock waves as a mechanism for the retinal damage induced by ultra-short pulse lasers. The quantitative estimates of the pressure gradients induced by laser absorption which are made possible by this work, together with detailed meso-scale or molecular modelling, will allow alternative damage mechanisms to be identified.     

Tunable Terahertz Plasmonic Perfect Absorber Based on T-Shaped InSb Array

High absorption efficiency is particularly desirable for various microtechnological applications. In this paper, a nearly perfect terahertz absorber for transverse magnetic (TM) polarization based on T-shaped InSb array is proposed and numerically investigated. Incident wave at the Fabry-Perot resonant frequency can be totally absorbed into the narrow grooves between the two adjacent T-shaped InSb arms. The absorption mechanism is theoretically and numerically studied by using the Fabry-Perot model and the finite element method (FEM), respectively. It is found that the proposed absorber has large angle tolerance. Moreover, the absorption peak can be controlled by varying the temperature. Furthermore, a new absorption peak will emerge while breaking the symmetry of the T-shaped InSb array. This tunable and angle-independent THz perfect absorber may find important applications in THz devices such as microbolometers, coherent thermal emitters, solar cells, photo detectors, and sensors.