Polarization-insensitive Absorption Research Articles

Wideband close perfect meta surface absorber for solar photovoltaic and optical spectrum applications

The leading research challenge is to develop a meta-surface absorber design for optimal performance across ultraviolet, visible, and near-infrared wavelengths. In ongoing research, a meta-surface absorber is being introduced, designed to achieve near-perfect absorption of 99% across the 250–2500 nm UV–Vis-NIR spectrum for both Transverse electric (TE) and Transverse magnetic (TM) polarized waves. The aimed design features a symmetrical resonator pattern, resulting in a polarization-insensitive absorption response. Additionally, the absorption response demonstrates robustness when altering the geometric parameters of the meta-surface unit cell. Precise simulation and modelling of the proposed meta-surface absorber are achieved by Employing a Finite Difference Frequency Domain (FDFD) solver, coupled with the Finite Integration Technique (FIT) and a tetrahedral mesh component. Verification of absorption characteristics is conducted through three frameworks: impedance matching, interference, and an equivalent circuit model. The suggested meta-structure design exhibits a uniform absorption response, as determined through considerations of impedance matching, interference theory, and the equivalent circuit theory. The PCR value is significantly lower than recent studies, reinforcing that the proposed meta-surface primarily serves as an absorber, not a polarization converter. The absorption response of the suggested meta-structure design remains consistent across the range of electromagnetic wave polarization angles from 0 to 90 for both TE and TM waves. Furthermore, the absorption response of the proposed design demonstrates stability up to an incident angle of 70 for electromagnetic waves. The distribution of electric and magnetic fields, along with surface current density on the proposed design, validates the existence of localized, propagating, and cavity surface plasmon resonance. These collectively create anti-parallel current flow, leading to the absorption of incident EM waves. Furthermore, the suggested design achieves a solar energy thermal conversion efficiency of 99% across the operational spectrum at a working temperature of 573 K, substantiating its potential for use as a solar absorber. Thus, this study presents a meta-structure unit cell that addresses the challenge with near-perfect absorption, polarization independence, and angle robustness. Applications include photodetection, thermal mapping, solar harvesting, and photo-trapping.

A Lay-up-Oriented CFRP-Substrate Metamaterial Absorber with High Insensitivity to Polarization

Metamaterial absorbers with carbon fiber reinforced polymer (CFRP) substrates, which are called meta-CFRPs, have recently gained recognition for their excellent mechanical and electromagnetic performance. Different from traditional metamaterial absorbers with an isotropic substrate, meta-CFRPs with a highly anisotropic CFRP substrate are facing challenges in acquiring polarization-insensitive absorption. Here, a lay-up-oriented structure design method is proposed to solve this problem. Considering the lay-up configuration of CFRP laminates, metallic patterns are designed under corresponding polarization angles and then united together to form an integral structure. A meta-CFRP with a typical CFRP lay-up configuration([0°/45°/90°/−45°]3s ) is designed and tested. The experimental results exhibit over 99% microwave absorptivity at 2.44 GHz for all polarization angles. The maximum shift among the resonance peaks of the curves at all polarization angles is only 0.021 GHz. Further studies show that when there are cross-ply laminates in the first few layers of the CFRP substrate, the lay-up-oriented design method can be effectively simplified by ignoring the subsequent lay-up orientations after the first cross-ply layers. Our method can not only provide an effective way for acquiring polarization-insensitive microwave response on meta-CFRPs but also be expected to be promoted to metamaterial absorbers with other anisotropic materials.

Broadband long-wave infrared high-absorption of active materials through hybrid plasmonic resonance modes

Broadband high absorption of long-wavelength infrared light for rough submicron active material films is quite challenging to achieve. Unlike conventional infrared detection units, with over three-layer complex structures, a three-layer metamaterial with mercury cadmium telluride (MCT) film sandwiched between an Au cuboid array and Au mirror is studied through theory and simulations. The results show that propagated/localized surface plasmon resonance simultaneously contribute to broadband absorption under the TM wave of the absorber, while the Fabry–Perot (FP) cavity resonance causes absorption of the TE wave. As surface plasmon resonance concentrates most of the TM wave on the MCT film, 74% of the incident light energy is absorbed by the submicron thickness MCT film within the 8–12 μm waveband, which is approximately 10 times than that of the rough same thickness MCT film. In addition, by replacing the Au mirror with Au grating, the FP cavity along the y-axis direction was destroyed, and the absorber exhibited excellent polarization-sensitive and incident angle-insensitive properties. For the corresponding conceived metamaterial photodetector, as carrier transit time across the gap between Au cuboid is much less than that of other paths, the Au cuboids simultaneously act as microelectrodes to collect photocarriers generated in the gap. Thus the light absorption and photocarrier collection efficiency are hopefully improved simultaneously. Finally, the density of the Au cuboids is increased by adding the same arranged cuboids perpendicular to the original direction on the top surface or by replacing the cuboids with crisscross, which results in broadband polarization-insensitive high absorption by the absorber.

UWB Frequency-Selective Surface Absorber Based on Graphene Featuring Wide-Angle Stability

In this paper, an ultra-wideband and polarization-insensitive frequency-selective surface absorber is presented with oblique incident stable behavior. Different from conventional absorbers, the absorption behavior is much less deteriorated with the increase in the incidence angle. Two hybrid resonators, which are realized by symmetrical graphene patterns, are employed to obtain the desired broadband and polarization-insensitive absorption performance. The optimal impedance-matching behavior is designed at the oblique incidence of electromagnetic waves, and an equivalent circuit model is used to analyze and facilitate the mechanism of the proposed absorber. The results indicate that the absorber can maintain a stable absorption performance with a fractional bandwidth (FWB) of 136.4% up to 40°. With these performances, the proposed UWB absorber could be more competitive in aerospace applications.

High-Sensitivity Temperature Sensor Based on the Perfect Metamaterial Absorber in the Terahertz Band

In this study, a perfect metamaterial absorber (PMMA) based on an indium antimonide temperature-sensitive material is designed and investigated in the terahertz region. We demonstrate that it is an ideal perfect narrow-band absorber with polarization-insensitive and wide-angle absorption properties. Numerical simulation results show that the proposed PMMA can be operated as a temperature sensor with a sensitivity of 21.9 GHz/K. A graphene layer was added to the PMMA structure to improve the sensitivity, and the temperature sensitivity was increased to 24.4 GHz/K. Owing to its excellent performance, the proposed PMMA can be applied in thermal sensing, detection, and switching.

Nanoengineered nickel-based ultrathin metamaterial absorber for the visible and short-infrared spectrum

Nanostructured-based broadband perfect absorbers are of great interest in a wide range of applications, including spectroscopy, energy harvesting, and thermal photonics, etc. Here, a planar square meta-ring of nickel (Ni) is presented, which has the potential to absorb a large operational wavelength starting from 400 nm to 3000 nm. The proposed device model comprises a configuration of three layers with a top and bottom metal of Ni and a middle dielectric layer of aluminium nitride (AlN). The designed square ring metamaterial absorber (SRMMA) can attain an average absorption value of more than 90% over a large waveband from 400-3000 nm. Moreover, it can also maintain its absorption value up to 70% for oblique incident angles for both the wave polarization cases (TE and TM). Furthermore, it also exhibits the polarization-insensitive absorption response under the influence of different polarization angles, which is attributed to the four-fold symmetry in the geometry of the square meta-ring. Furthermore, our SRMMA also reduces fabrication complexity and cost due to its simplified design architecture. These promising features of the proposed SRMMA may have widespread applications in solar energy harvesting, thermal emission, and other optoelectronic devices.

A Simple Metamaterial for High-Performance Spectrum-Selective Absorption in the Visible Region

In this paper, we numerically demonstrated a simple metamaterial for wide-angle and polarization-insensitive absorption in the visible region, which simultaneously showed a strongly suppressed absorption in the near-infrared region. Numerical simulations demonstrated that under normal incidence the proposed absorber had a high absorptivity almost over 90% in the wavelength range from 340 nm to 770 nm, while a low absorptivity less than 10% from 1 μm to 2 μm. Because a small unit cell with four-fold symmetry was utilized, the selective absorption of this nanostructure was almost independent of the incident angle and polarization of the incident light. To understand the underlying physical mechanisms, the impedance and the electromagnetic field distributions in a unit cell were analyzed. Moreover, the influence of the structural geometry parameters on the absorption spectrum was systematically studied. Our results may provide a method for using a simple nanostructure to reduce the radiative heat loss for the visible light thermal conversion, or to depress the temperature rise induced by the absorption of below-bandgap photons for photovoltaic solar cells working in the visible region.

Dual-band tunable terahertz perfect absorber based on all-dielectric InSb resonator structure for sensing application

A dual-band terahertz (THz) perfect absorber (PA) based on the all-dielectric metamaterial (MM) composed of the vertical-square-split-ring (VSSR) structure InSb array was proposed and investigated numerically. Simulation results show that the absorbance of the proposed PA under room temperature T = 295 K is up to 99.9% and 99.8% at 1.265 THz and 1.436 THz, respectively, which is consistent well with the fitting results of coupling mode theory (CMT). According to the simulated electric field and power loss density distributions, the perfect absorption results from the excitation of the first- and second-order plasmonic resonance mode. Further results show that the designed PA is polarization-insensitive due to the high geometric rotational symmetry, and wide-angle absorption can be achieved for transverse magnetic (TM) waves. The geometric parameters of the VSSR structure InSb and the external environment temperature can be changed to adjust the resonance absorption properties of the designed dual-band PA. The dual-band PA can be functioned as a temperature sensor with a sensitivity of about 5.9 GHz/K and 6.4 GHz/K, respectively. Furthermore, the dual-band PA under T = 295 K also can be served as a refractive index sensor with a sensitivity of about 1.3 THz/RIU and 1.0 THz/RIU, respectively. Due to its excellent properties including simple design, easy fabrication, polarization-insensitive and perfect absorption, the proposed dual-band PA may find many potential applications in detecting, imaging, and sensing in the THz region.

Generating multiple resonances in ultrathin silicon for highly selective THz biosensing

A technique is implemented for achieving the multiband terahertz (THz) absorption with high-quality factor in an absorber containing an ultrathin silicon resonator. The symmetrical perturbation is done in the silicon layer for obtaining the multiple multi-order electric and magnetic resonances. The proposed absorber structure provides the polarization insensitive absorption spectrum with ten absorption peaks out of which seven remain with the level of more than 90%. The ultranarrow absorption spectrum can be utilized in THz biosensing applications specially for the detection of breast cancer, malaria in blood and glucose in water. It offers highest sensitivity as 0.416 THz/thickness unit (TU) and 1.02 THz/refractive index unit (RIU) during analyte thickness and refractive index sensing, respectively. The proposed absorber can provide the high value of quality factor along with all other improved parameters like sensitivity and figure of merit. Moreover, graphene nano-rings can also be utilized for obtaining the controllability in the frequency response of the absorber.

Broadband, wide-incident-angle, and polarization-insensitive high-efficiency absorption of monolayer graphene with nearly 100% modulation depth at communication wavelength

We theoretically study how to greatly improve the near-infrared light absorption of monolayer graphene through the excitation of magnetic resonance in metamaterials. The absorption maximum of monolayer graphene is able to reach up to about 77% at the communication wavelength of 1550 nm. The conventionally defined absorption bandwidth, i.e., the full width at half maximum (FWHM), is nearly 160 nm. Thanks to the localization nature of magnetic resonance, the broadband high-efficiency absorption of monolayer graphene is insensitive to the incident angle and the light polarization. The absorption maximum, the absorption bandwidth, and the resonance position all have almost no change, when the incident angle is increased to even 60 degrees for both p and s polarizations. By applying an external bias voltage to change Fermi energy, the absorption in graphene can be completely modulated, with a nearly 100% modulation depth. Furthermore, the graphene absorption has an abrupt and large change around the interband transition, which exhibits an electrical switching property. Our work may find potential applications in graphene-based optoelectronic devices such as photodetector and modulator.

Optically switchable ultra-broadband terahertz perfect absorption in doped superlattice photonic-crystal silicon

We propose an optically switchable ultra-broadband terahertz (THz) perfect absorber based on doped superlattice photonic-crystal silicon. The structure consists of a superlattice photonic crystal silicon slab capped by a SU-8 layer with no metal reflector. It achieves ultra-broadband perfect absorption due to the coupled cavity modes of superposed lattices with two different cavity radii and the enhanced diffraction assisted by the top SU-8 layer. Switchable absorption is realized by changing the carrier concentration of doped silicon controlled by pump beam. Simulation shows that proposed structure exhibits polarization-insensitive and wide-angle absorption with efficiency larger than 90% within 1.03 to 5 THz ultra-broadband, with modulation depth larger than 60% within bandwidth more than 1 THz. The all-dielectric structure uncommonly integrates optical switching, ultra-broadband absorption, polarization, and incident angle insensitivity, which may find potential applications in dynamic THz devices.

Design of an ultra-wideband solar energy absorber with wide-angle and polarization independent characteristics

An extremely effective solar energy absorber has been devised in the study. In order to achieve an almost-perfect ultra-wideband absorption spectrum under solar radiation, this structure is constructed with a silver metal-based phi-shaped resonator (PSR), SiO2 substrate, and silver metal ground layer. In the span of ultraviolet to the mid-infrared range, we attain an average absorption of 94.42%, achieving ultra-wideband properties. In addition, the absorption rate above 90% and 95% is observed for the bandwidth of 2680 nm and 1310 nm has an average absorption of 96.17% and 98.13%, respectively, according to our results eight near-perfect absorption peaks are also observed in this range. The optimized design is found by investigating how various design parameters affect the absorption spectrum. The polarization-insensitive and broad-angle absorption characteristics of the suggested solar absorber are 0°–60° wide, which makes it ideal for absorbing solar radiation that can be employed for solar energy conversion applications.

Broadband Metamaterial Solar Absorbers Based on the Earth First-rate Temperature-Insensitivity Metals for High Temperature Energy Harvesting

Artificially engineered solar absorbers, known as metamaterial solar absorbers (MSA), are yielding new opportunities for designing new photons management systems. Furthermore, the noble metals are indispensable in creating MSA owing to their plasmonic resonance in a desired spectral region. Nevertheless, in high temperature applications, the noble metals suffer from low melting points that make their uses largely impractical. In this work, the solution of using four of the Earth first-rate temperature-insensitivity metals in a proposed MSA is investigated. The proposed MSA structure is composed of high melting point metals (HMPM), deposited on a magnesium fluoride (MgF\(_2\)) dielectric spacer and a tungsten continuous plate. Meanwhile, owing to the dependence of MSA properties on structural parameters rather than band structure or chemistry, a geometrical optimization of the proposed absorbers is reported. Furthermore, the proposed MSA performance is investigated by computing the absorption spectrums. Results show relatively long bandwidths in the visible and near-infrared regimes. Besides, an underlying mechanism of the absorption enhancement with the corresponding electromagnetic field distributions is elucidated in detail. The calculated results indicate that the proposed MSA present wide bandwidths owing to the excitation of resonance modes of surface plasmons, dipolar interactions and cavity modes. Equally important, absorption measurements under wide polarization angles show polarization-insensitive high absorption at higher wavelengths, which is among the most important factors for an ideal solar absorber. The conclusion of this investigation is undoubtedly important, specifically that the proposed HMPM-based MSA would be the best choice for energy harvesting in high temperature applications.

Ultra-broadband terahertz absorber based on double truncated pyramid structure

Terahertz (THz) absorbers have attracted considerable attention due to their potential applications. However, the limited bandwidth of THz absorbers limits their further applications. To achieve ultra-broadband and high absorption characteristics in the THz band, a double truncated pyramid unit structure combining the hybrid planar structure and the few-layers vertical structure is proposed. The double truncated pyramid structure composed of five metal layers and five graphene layers has the advantages of ultra-broadband, tunability, polarization-insensitive and wide-angle absorption. The simulation results show that the absorption coefficient of the absorber is over 0.9 from 1.49 THz to 12.72 THz. The double truncated structure provides perfect ultra-broadband absorption, which can be attributed to the localized surface plasmon and surface plasmon. The mechanism of resonance can be further explained by surface current distribution. Meanwhile, the absorption mechanism of the absorber can also be explained by the impedance matching theory. The proposed THz absorbers have potential applications in sensing, stealth and other multispectral devices.

Chiral Absorber-Based Frequency Selective Rasorber With Identical Filtering Characteristics for Distinct Polarizations

In this article, we propose a new paradigm to design frequency-selective rasorber (FSR) with two-sided efficient absorptions and broadband transmission in a chiral structure. The proposed FSR is implemented via combining two chiral absorber layers with a bandpass frequency-selective surface (FSS). An absorptive split-ring resonator (ASRR) inserted with a resistive film is designed to provide efficient spin-sensitive absorption. Then, four ASRRs are arranged to form a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{4}$ </tex-math></inline-formula> symmetric split-ring absorber (SRA) with identical absorption for distinct polarized incident waves. The physical mechanisms of spin-selective absorption and polarization-insensitive absorption are discussed theoretically. The broadband bandpass FSS is introduced to provide a transparent window and ground plane for the absorbers. A prototype is fabricated and measured to verify the feasibility of the method. The simulation and experimental results manifest over 90% absorptive bands of 1.5–3.6 and 15.2–21.6 GHz and a transmission band of 8–12 GHz with insertion loss less than 2 dB. Compared with previous FSRs, the proposed FSR has a broadband transmission, efficient absorptions with high-frequency selectivity, and easy geometric structure.

Multi-functional tunable ultra-broadband water-based metasurface absorber with high reconfigurability

Promising microwave ultra-broadband water-based metasurface absorbers have attracted increasing attention due to their novel applications in EM radiation prevention, stealth technology, and energy harvesting. In this paper, the proposed water-based metasurface absorber, composed of mushroom-shaped and layer-shaped water with resin shell, can reach over 90% polarization-insensitive and wide-angle absorption from 7.2 to 100 GHz with a relative bandwidth of 173%. Moreover, the proposed absorber is reconfigurable to control the water content, salinity, and type of inside liquid for tunable absorption and infrared radiation with thermally tunable absorption. Since the experimental and simulated ultra-broadband absorption originates from multiple resonances concentrated on the top, the ground-free all-dielectric design is achieved. Furthermore, the proposed curved absorber is fabricated and demonstrated for omnidirectional absorption. The water-based metasurface absorber shows great potential in achieving both microwave and infrared radiation camouflage for practical shaped structures in both civil and military domains.

Multi-wavelength metamaterial absorber for retrieving complex refractive index of thin-film materials at infrared regimes

Multi-wavelength absorption in uncomplicated system is pursued continuously due to its advantage on measuring thin-film material dispersion. Here, we experimentally demonstrate a single-periodic metamaterial with polarization-insensitive multi-wavelength absorption for the infrared thin-film material measurement. The meta-atom of metamaterial absorber is constructed by holed cylindrical gold disk and gold ground separated by a ZnS substrate. Simulation shows that the multi-wavelength absorption is related to the multiple resonant eigenmodes. The metamaterial absorber is proposed through photolithography process and multi-wavelength absorptions occur at 3.95 μm, 4.27 μm and 10.90 μm, respectively, in the experiment. We show that the multi-wavelength absorption is very sensitive to the dielectric property of the coating thin-film material, which indicates the proposed absorber can be used to retrieve the complex refractive index of coating thin film at various wavelengths. Our work provides a convenient way to measure refractive indices at both mid-infrared and far-infrared regimes.

Wide-Oblique-Incident-Angle Stable Polarization-Insensitive Ultra-Wideband Metamaterial Perfect Absorber for Visible Optical Wavelength Applications.

Metamaterial absorbers are very attractive due to their significant absorption behavior at optical wavelengths, which can be implemented for energy harvesting, plasmonic sensors, imaging, optical modulators, photovoltaic detectors, etc. This paper presents a numerical study of an ultra-wide-band double square ring (DSR) metamaterial absorber (MMA) for the complete visible optical wavelength region, which is designed with a three-layer (tungsten-silicon dioxide-tungsten) substrate material. Due to the symmetricity, a polarization-insensitive absorption is obtained for both transverse electric (TE) and transverse magnetic (TM) modes by simulation. An absorption above 92.2% and an average absorption of 97% are achieved in the visible optical wavelength region. A peak absorption of 99.99% is achieved at 521.83 nm. A wide range of oblique incident angle stabilities is found for stable absorption properties. A similar absorption is found for different banding angles, which may occur due to external forces during the installation of the absorber. The absorption is calculated by the interference theory (IT) model, and the polarization conversion ratio (PCR) is also validated to verify the perfect MMA. The electric field and magnetic field of the structure analysis are performed to understand the absorption property of the MMA. The presented MMA may be used in various applications such as solar cells, light detection, the biomedical field, sensors, and imaging.

A low-profile consolidated metastructure for multispectral signature management

This work pertains to the design, numerical investigation, and experimental demonstration of an optically transparent, lightweight, and conformable metastructure that exhibits multispectral signature management capabilities despite its extremely low-profile configuration. In comparison to the existing hierarchical approaches of designing multispectral stealth solutions, attention has been paid to accommodate the conflicting requirements of radar and infrared (IR) stealth using a single metasurface layer configuration, which required a few constraints to be incorporated during the design stage to ensure compatibility. This methodology promulgates the desired multispectral response with minimal manufacturing footprint and facilitates an efficient integration with the other existing countermeasure platforms. The resulting design exhibits a polarization-insensitive and incident angle stable broadband microwave absorption with at least 90% absorption ranging from 8.2 to 18.4 GHz. Concomitantly it also exhibits an averaged IR emissivity of 0.46 in the 8–14 µm long-wave IR regime, along with high optical transparency (71% transmission at 632.8 nm). Notably, the total thickness of the metastructure stands at 0.10 ( corresponds to the wavelength at lowest frequency). The metastructure has been fabricated with indium tin oxide coated polyethylene terephthalate sheets, on which the frequency selective pattern is machined using Excimer laser micromachining, and the performances are verified experimentally. Furthermore, a hybrid theoretical model has been developed that not only provides crucial insights into the operation of metastructure but also presents a methodical semi-analytical approach to design.

An Active Metamaterial Absorber With Ultrawideband Continuous Tunability

In this paper, an active metamaterial (MM) absorber loaded with PIN diodes is proposed. By adjusting the bias currents of PIN diodes to change the value of the introduced equivalent resistance, the Q factors of multiple resonances of the whole structure are altered. Therefore, multiple broadband absorption states with moderate absorption performance at different frequencies are obtained. These states cover continuously tunable absorption frequencies in an ultrabroad frequency band. Bias circuits for PIN diodes are also specially designed to obtain polarization-insensitive absorption performance. Optimizing works were carried out by analyzing the operating mechanism based on the simulated field distribution and power loss distribution. The presented absorber covers an ultrawideband absorption bandwidth with a reflection coefficient below -10 dB from 0.78 GHz to 4.62 GHz (142.2% in relative bandwidth) by adjusting the PIN diodes. It is worth noting that the absorption bandwidth of the low-resistance state reaches 21.0% in the P band, which greatly improves performance in the low-frequency regime. The absorber shows good angular stability under oblique incident angles from 0° to 30°. In addition, the total thickness of the absorber is only 1/16 of the wavelength at the lowest operating frequency with an areal density of 2.06 kg/m2.