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A double-band perfect absorber is proposed based on M o S 2 metamaterial. The proposed absorber is composed of a monolayer molybdenum disulfide, a crystalline silicon layer, and a silver substrate. Utilizing the critical coupling principle of guided resonance, efficient optical absorption of molybdenum disulfide was achieved. Specifically, at the resonance wavelengths ( λ 1 = 610.431 nm , λ 2 = 654.484 nm ), two perfect absorption peaks of 99.42% and 99.31% were attained based on finite-difference time-domain (FDTD) simulations. Through detailed analysis of field distributions and spectral responses, the interactions between electromagnetic waves and this perfect absorber structure are examined. Based on the simulation results, the structure's geometric parameters wield control over the resonance wavelength range of M o S 2 , holding pivotal practical implications for bolstering its absorption potency and selectivity. Moreover, the innovative approach of employing critical coupling to amplify light-silica interactions holds promise for application across various atomic-scale thin materials. Additionally, the absorber's sensing capabilities are revealing many metrics. The highest quality factor, sensitivity, and figure of merit (FOM) of the sensors are recorded as 111.3, 178.4 nm/RIU, and 30.3 R I U - 1 , respectively. Hence, our findings potentially pave the way for enhancing light-matter interactions within monolayer transition-metal dichalcogenides, offering promise for applications in multiband absorbers and sensors. [ABSTRACT FROM AUTHOR]

In this paper, a polarization-insensitive magnetic tunable perfect metamaterial absorber is analyzed which shows its functionality as a refractive index (RI) sensor. The unit cell structure of reported absorber consists of a cross-shaped Indium Arsenide (InAs) array over aluminum ground plane and has dimensions less than λ c / 4 with thickness of 7.5 μ m and periodicity of 9 μ m making it an ultra-thin absorber. The proposed absorber provides an average absorption of 99.99% on the implementation of magnetic field (B) at 0.4 T. The resonance frequency and corresponding absorption rates can be controlled by varying the magnetic field from B = 0. 1 –0.4 T which provides high absorption as well as shift in the frequency spectrum by 0.3 THz/T. Additionally, parametric analysis has also been done to confirm the selection of the optimum value of the designed parameters of the structure. Furthermore, simulation results reveal that the proposed structure is very sensitive to the change of RI values in the surroundings thus, the proposed structure can be employed as a RI sensor high sensitivity of 1.083 THz/RIU over the range of 1–1.6 RI. In addition, the result shows that the sensor can detect different chemical compounds such as ethanol, gasoline, paraffin, sodium chloride, carbon disulfide with an average sensitivity of 0.925 THz/RIU. Thus, the proposed absorber with obtained sensitivity can be utilized as a biochemical sensor, making it one of the best contenders for chemical industry uses in diagnosis of different hazardous chemicals as well as finding its applicability in biomedical uses. [ABSTRACT FROM AUTHOR]

A tunable multiband terahertz metamaterial absorber, based on vanadium dioxide (VO2), is demonstrated. The absorber comprises a three-layer metal–insulator–metal (MIM) configuration with a split ring and slots of VO2 on the uppermost layer, a middle dielectric substrate based on silicon dioxide (SiO2), and a gold reflector on the back. The simulation results indicate that, when VO2 is in the metallic state, the proposed metamaterial exhibits nearly perfect absorption at six distinct frequencies. The design achieves an average absorption of 98.2%. The absorptivity of the metamaterial can be dynamically tuned from 4% to 100% by varying the temperature-controlled conductivity of VO2. The proposed metamaterial absorber exhibits the advantages of polarization insensitivity and maintains its absorption over 80% under different incident angle conditions. The underlying physical mechanism of absorption is explained through impedance matching theory, interference theory, and the distribution of electric fields. The ability to achieve multiband absorption with tunable characteristics makes the proposed absorber a promising candidate for applications in terahertz sensing, imaging, communication, and detection. The polarization insensitivity further enhances its practicality in various scenarios, allowing for versatile and reliable performance in terahertz systems. [ABSTRACT FROM AUTHOR]

The increasing demand for renewable energy has increased in the last decade due to climate change resulting from conventional energy and solar cells become popular. The perfect absorption in solar cells can be achieved with artificially engineered materials at low cost for solar absorbers with high efficiency. A perfect ultra-broadband solar absorber can be achieved by using metamaterial (MM) based on surface plasmon resonance phenomena. We design a near-ideal ultra-broadband plasmonic MM absorber for solar energy harvesting over an ultra-broadband wavelength range (0.4–4 μ m ). The structure is made up of periodic taper arrays consisting of a thin, multilayered titanium nitride–titanium dioxide MM. The proposed structure has an absorption greater than 96% between the visible to infrared (IR) regime. It is independent of both polarization and incident angle. The large operational bandwidth, high absorption percentage, and compact thin structure combined with the strong thermal stability of metal TiN make an advantageous choice for solar thermophotovoltaics. [ABSTRACT FROM AUTHOR]

Wideband perfect absorbers are widely demanded for various applications, including efficient photodetection, radiation cooling. However, achieving perfect absorption across an extensive range of wavelengths on engraved structured substrate remains a challenge due to the complex light responses. It presents a hierarchical conical metasurface that demonstrates distinct perfect absorption from visible to far‐infrared range (0.4–16 µm), which is composed of surface‐engraved high aspect ratio nanogratings on microcones. The perfect absorption in the typical reststrahlen band of 4H‐SiC primarily relies on a light‐trapping‐enhanced surface phonon polaritons (SPhPs) mechanism, where the microcones effectively confine and enhance the SPhPs excited by the nanogratings through light trapping. Outside the reststrahlen band, the dominant mechanism for light antireflection is the light trapping of microcones assisted by nanogratings, which act as an equivalent antireflection layer. The hierarchical cones exhibit exceptional broadband performance, achieving an average absorptance of 98% over the spectrum of 0.4–16 µm with wide‐angle feasibility, and are fabricated using one‐step ultrafast‐laser ablation with ring‐shaped vector beams. Notably, the hierarchical cones can be applied to various materials, showing significant potential for use in photodetectors. [ABSTRACT FROM AUTHOR]

In this article, we propose and numerically investigate a graphene-based electromechanically tunable perfect absorber design. The fundamental motivation is to demonstrate the electromechanically tunable feature in graphene metasurface at the mid-infrared regime, which otherwise exploited only the chemical potential feature in the literature. The structure consists of a gold grating on a gold substrate separated by an oxide spacer with an overlay of monolayer graphene with free-standing segments. By applying external DC voltages, the free-standing region of the graphene layer deflects, owing to the electrostatic force it experiences. This shifts the resonance absorption wavelength. In the mid-infrared region of 5–10 µm, a very low actuation voltage of 1.6 V displaces the graphene membrane by 1 nm, resulting in a wide shift of 60 nm in resonance wavelength. A continuous tunability with near-perfect absorption over a wavelength range of 200 nm for an applied voltage of only 7 V is demonstrated. At a voltage greater than 7 V, a mode hopping phenomenon is observed, hampering the perfect absorber operations with a shift in wavelengths. It is shown that the perfect absorption is again retained at some higher voltage. Such implementations hold promising applications in nanophotonics sensors, detectors, real-time beam steering, etc. [ABSTRACT FROM AUTHOR]

We consider the propagation of acoustic waves in a waveguide containing a penetrable dissipative inclusion. We prove that as soon as the dissipation, characterized by some coefficient η, is non zero, the scattering solutions are uniquely defined. Additionally, we give an asymptotic expansion of the corresponding scattering matrix when η → 0+ (small dissipation) and when η → +∞ (large dissipation). Surprisingly, at the limit η → +∞, we show that no energy is absorbed by the inclusion. This is due to the so-called skin-effect phenomenon and can be explained by the fact that the field no longer penetrates into the highly dissipative inclusion. These results guarantee that in monomode regime, the amplitude of the reflection coefficient has a global minimum with respect to η. The situation where this minimum is zero, that is when the device acts as a perfect absorber, is particularly interesting for certain applications. However it does not happen in general. In this work, we show how to perturb the geometry of the waveguide to create 2D perfect absorbers in monomode regime. Asymptotic expansions are justified by error estimates and theoretical results are supported by numerical illustrations. [ABSTRACT FROM AUTHOR]

Plasmonic nanostructures as narrowband perfect absorbers have garnered significant attention due to their potential applications in biosensing and environment detection. This study emphasizes the investigation of arrayed split ring nanostructures within the configuration of metal-insulator-metal (MIM) multilayers, resulting in a maximum light absorption of 99.94% in the near-infrared (NIR) spectral range. The exceptional absorption efficiency of the device is attributed to the strong resonance of electric and magnetic fields arising from the Fabry–Pérot cavity resonance. The resonant peak can be flexibly tuned by engineering the dielectric layer thickness, the period, and the geometric parameter of split rings. Remarkably, the device exhibits promising capabilities in sensing, demonstrating a sensitivity of 326 nm/RIU in visible wavelengths and 504 nm/RIU in NIR wavelengths when exposed to bio-analytes with varying refractive indices. This designed nanostructure can serve as a promising candidate for biosensors or environmental detection. [ABSTRACT FROM AUTHOR]

A plasmonic perfect absorber is proposed using a silver substrate in the visible near-infrared wavelength range. The unit cell of the periodic structure is designed and evaluated in this paper. The Ag layer is etched so that four trapezoidal trenches filled with Si3N4 couple plasmonic modes on the metal–insulator interfaces. Various optical modes are formed, from which, a surface and a bulk mode are thoroughly studied. The surface mode can be coupled to the graphene sheet surface through a thin dielectric layer. Moreover, the effect of the variation of the structure's geometrical parameters on these modes was discussed. The bulk mode changes by the volume of the trenches and the effective refractive index, whereas the surface mode shifts with the period of the unit cell, the trenches depth, and other parameters that change the coupling criteria. The variation of the surface mode of the proposed structure can be used in sensors and photodetectors. As an application instance, an optimized structure is proposed at the end of the paper for sensing applications, showing high sensitivity (560 to 600 nm/RIU) and a figure of merit (70 ~ 120 RIU−1) in a wide refractive index range. [ABSTRACT FROM AUTHOR]

In this work, we designed and theoretically investigated an adjustable perfect absorber metamaterial according to vanadium dioxide (VO 2 ). The VO 2 is a phase change material. By controlling its electrical conductivity from 2 × 10 2 to 2 × 10 5 S/m, the absorption continuously changed from 3.92 % to 100 % . The wider bandwidth and flexibility in selecting perfect absorption in the frequency range of 6.5 until 7.90 Thz are enhanced compared with other published VO 2 -based terahertz absorbers. We applied four common physical approaches to show the validation of results. These results are confirmed using the interference cancellation, modulation depth, electric field, surface current analysis, and impedance matching theory. Also, we investigate the influence output absorption spectrum by changing structure parameters. Therefore, the present THz perfect absorber has a vast capacity for profitable usages, such as photochemical energy absorption, modulating, sensing, cloaking, and stealth devices. [ABSTRACT FROM AUTHOR]

Ultrathin and broadband metamaterial absorber with loaded four lumped resistors is proposed and analyzed. The reported design is based on increasing the absorptivity by reducing the reflection and transmission coefficients simultaneously. Therefore, continuous metallic ground is used to achieve zero transmission while the reflection is reduced by matching the impedance of the proposed metamaterial absorber with the impedance of free space (Z = Z0 or μr = εr). Additionally, electric and magnetic resonances are achieved simultaneously with perfect absorptivity. The finite element method is used to simulate and analyze the reported absorber. The suggested absorber shows higher absorption than 90% over large frequency range (14.35–29.18 GHz) for both transverse electric and transverse magnetic polarizations. Further, the proposed design has high absorption through incident angle variation from 0° to 50°. Therefore, the reported perfect metamaterial absorber has good potential applications in communications, stealth and imaging fields. [ABSTRACT FROM AUTHOR]

In this paper, a dual-band ultra-narrow metamaterial absorber for sensing applications is presented. The unit cell of the structure consists of an Ag disk resonator located on a thin stack of graphene/SiO2/Au layers. The absorber shows high reflectivity in the whole of the incident light, ranging from 1.05 to 1.45 μm. Simulation results obtained by the finite-difference time-domain (FDTD) method indicate that the resonance behavior of the absorber depends on different factors including geometric parameters, the materials of the structure's components, the chemical potential of the graphene sheet as well as the shape of the resonators. For the optimal structure, the sensitivity, figure-of-merit (FOM) and quality-factor characteristics are as high as 760 nm/RIU, 109 RIU−1, and 193, respectively. Also, the absorption can reach 99.96% in the on-resonance wavelengths. As an optofluidic sensor, this structure can detect industrial analytes such as Methanol, Ethanol, Pentanol, Butanol, and Propanol with high accuracy. The proposed sensor has the advantages of high absorption, high sensitivity, and a fabrication-friendly structure, promising a great platform for the detection of industrial analytes. [ABSTRACT FROM AUTHOR]

This work reported a novel terahertz sensor based on metamaterial absorber. The proposed structure is composed of rectangular metallic resonator made of gold placed above on dielectric medium of a polyimide and a metallic board at the bottom. Due to high-intensity field energy confinement in the sensing regime, two resonance peaks occur at 1.355 THz and 2.785 THz with absorption nearly 100% is achieved. The proposed structure represents sharp resonances with a highest Q factor of 69.6 in the dual-band absorption spectra. The proposed structure is highly sensitive to the change of refractive index (RI) of the surrounding medium at fixed analyte. Furthermore, the proposed sensor exhibits high sensitivity of 0.735THz/RIU, and high FOM of 18.4 RIU−1 in the refractive index ranging from 1 to 2 with fixed analyte thickness of 35 μm. Moreover, the sensitivity and absorption strength influence of the sensor on the sample thickness covered by the sensor surface is also analyzed. Due to high Q factor and sensitivity, the design RI sensor is successfully employed in sensing and detection. [ABSTRACT FROM AUTHOR]

A triple-band metamaterial perfect absorber (MPA) is presented in monolayer graphene in the THz region, which is adjustable and polarization-independent. The first layer of the structure from the top is patterned graphene which contains a graphene ring at the center of the frame with four graphene wheel-shaped around it and four graphene triangles in the corner. This proposed structure has caused the absorber to achieve 98.64%, 99.97%, and 99.98% perfect absorption peaks at 8.17 THz, 9.74 THz, and 11.95 THz, respectively. We can vary the absorption peak frequencies to our desirable frequencies by changing graphene's Fermi level. This absorber has good tolerance for up to 60-degree change in the angle of incident waves. Moreover, a significant matter about the suggested absorber structure design is that it is polarization independent, so by tuning the polarization angle, the frequency peaks and absorption value remain unchanged. These aspects make the suggested absorber proper for imaging, detecting, filtering, and sensing applications. We have investigated the application of the MPA in refractive index sensing. The refractive index of unknown material can be measured by measuring the shift of the frequency peaks. The perfect metamaterial absorber is a good candidate for biosensor application based on the obtained results. [ABSTRACT FROM AUTHOR]

In this paper a perfect absorber with a photonic crystal cavity (PhC-cavity) is numerically investigated for carbon dioxide (CO2) gas sensing application. Metallic structures in the form of silver are introduced for harnessing plasmonic effects to achieve perfect absorption. The sensor comprises a PhC-cavity, silver (Ag) stripes, and a host functional material—Polyhexamethylene biguanide polymer—deposited on the surface of the sensor. The PhC-cavity is implemented within the middle of the cell, helping to penetrate the EM waves into the sublayers of the structure. Therefore, corresponding to the concentration of the CO2 gas, as it increases, the refractive index of the host material decreases, causing a blue shift in the resonant wavelength and vice versa of the device. The sensor is used for the detection of 0–524 parts per million (ppm) concentration of the CO2 gas, with a maximum sensitivity of 17.32 pm (pico meter)/ppm achieved for a concentration of 366 ppm with a figure of merit (FOM) of 2.9 RIU−1. The four-layer device presents a straightforward and compact design that can be adopted in various sensing applications by using suitable host functional materials. [ABSTRACT FROM AUTHOR]

Although many multi-band terahertz (THz)–metasurface perfect absorbers (MPAs) have been proposed, many efforts are still suffering from complex structure design and high fabrication cost, thus limited in practical application. Here, a simple design of the dual-band MPA was proposed in the THz region, which is composed of the complementary-star-shaped (CSS) structure all-dielectric GaAs array. Simulation results show that the designed MPA can achieve an absorbance of over 99.9% at 0.715 THz and 0.861 THz, respectively, which can be confirmed by the coupling mode theory (CMT). In addition, the high Q-factors of about 79.58 and 78.27 of the designed MPA can be achieved, respectively. The observed perfect absorption of the MPA is mainly contributed to the excitations of the surface plasmonic polaritons (SPPs) modes. The absorption properties of the MPA can be adjusted by varying the geometric parameters of the unit-cell structure. Due to its excellent properties, the designed dual-band MPA may find many potential THz applications in sensing, detecting, thermal emitting, and imaging. [ABSTRACT FROM AUTHOR]

A plasmonic perfect absorber (PA) utilizes high absorption of incident radiation and near-field enhancement which is so advantageous for many applications such as solar cell, infrared (IR) spectroscopy, and refractive index (RI) sensitivity. In this study, the numerically presented PA system has resonances from mid-infrared (MIR) to near-infrared (NIR) regions for different periodicities at 2.0, 2.4, and 2.8 µm. A fine-tuning mechanism is obtained to control the spectral response of PA through the geometrical parameters. Dual-band plasmonic resonances have nearly 98% absorption. Near-field intensity distributions are shown with the enhancement factor of 103 at the resonance frequencies. Refractive index sensitivity is also analyzed by embedding PA in different cladding mediums to show the sensing performance. Relationship between resonance wavelength and refractive index of the medium is observed for all resonant modes. The highest sensitivity value is 2382.48 nm/RIU and the figure of merit reaches as high as 28.29 RIU−1. [ABSTRACT FROM AUTHOR]

A kind of graphene-based perfect absorber which can generate low-threshold and high-extinction-ratio optical bistability in the near-IR band is proposed and simulated with numerical methods. The interaction between input light and monolayer graphene in the absorber can be greatly enhanced due to the perfect absorption. The large nonlinear coefficient of graphene and the strong light-graphene interaction contribute to the nonlinear response of the structure, leading to relatively low switching thresholds of less than 2.5 MW/cm2 for an absorber with a Q factor lower than 1000. Meanwhile, the extinction ratio of bistable states in the absorber reaches an ultrahigh value of 47.3 dB at 1545.3 nm. Moreover, the influence of changing the structural parameters on the bistable behaviors is discussed in detail, showing that the structure can tolerate structural parametric deviation to some extent. The proposed bistable structure with ultra-compact size, low thresholds, high extinction ratio, and ultrafast response time could be of great applications for fabricating high-performance all-optical-communication devices. [ABSTRACT FROM AUTHOR]

One of the fastest-expanding study areas in optics over the past decade has been metasurfaces (MSs). These subwavelength meta-atom-based ultrathin arrays have been developed for a broad range of functions, including lenses, polarization control, holography, coloring, spectroscopy, sensors, and many more. They allow exact control of the many properties of electromagnetic waves. The performance of MSs has dramatically improved because of recent developments in nanofabrication methods, and this concept has developed to the point that it may be used in commercial applications. In this review, a vital topic of sensing has been considered and an up-to-date study has been carried out. Three different kinds of MS absorber sensor formations, all-dielectric, all-metallic, and hybrid configurations, are presented for biochemical sensing applications. We believe that this review paper will provide current knowledge on state-of-the-art sensing devices based on MSs. [ABSTRACT FROM AUTHOR]

Solar energy is a clean and renewable energy source and solves today's energy and climate emergency. Near-perfect broadband solar absorbers can offer necessary technical assistance to follow this route and develop an effective solar energy-harvesting system. In this work, the metamaterial perfect absorber operating in the ultraviolet to the near-infrared spectral range was designed, consisting of a periodically aligned titanium (Ti) nanoarray coupled to an optical cavity. Through numerical simulations, the average absorption efficiency of the optimal parameter absorber can reach up to 99.84% in the 200–3000 nm broadband range. We show that the Ti pyramid's localized surface plasmon resonances, the intrinsic loss of the Ti material, and the coupling of resonance modes between two neighboring pyramids are highly responsible for this broadband perfect absorption effect. Additionally, we demonstrate that the absorber exhibits some excellent features desirable for the practical absorption and harvesting of solar energy, such as precision tolerance, polarization independence, and large angular acceptance. [ABSTRACT FROM AUTHOR]

A temperature‐tunable terahertz (THz) perfect absorber (PA) composed of a periodic array of deep subwavelength micro‐cross‐shaped (MCS) structures of the strontium titanate (STO) resonator is proposed and investigated theoretically, which can be applicable for the temperature sensing. Simulation results indicate that the absorbance of 99.8% at 0.221 THz can be achieved when the designed PA is under the room temperature of T = 300 K, which is in good agreement with the calculation done by the coupling mode theory (CMT). The simulated distributions of electric and magnetic fields in the unit‐cell structure of the designed PA reveal that the observed perfect absorption is mainly attributed to the Mie resonance of the all‐dielectric MCS structure STO. In addition, this designed PA is polarization‐insensitive and wide‐angle absorption for both transverse magnetic (TM) and transverse electric (TE) waves. The resonance absorption properties of the designed PA can be controlled by changing the geometrical parameters of STO resonator structure. The designed PA can be served as a temperature sensor, which has a sensitivity of about 0.37 GHz K−1 since the electrical property of the STO is dependent on the variation of surrounding temperature. Furthermore, the perfect absorption can also be achieved by the PAs using the square, circular, and ring STO structures. The proposed design concepts of the STO‐based tunable PAs can find potential THz applications in sensing, detecting, imaging, and so on. [ABSTRACT FROM AUTHOR]

Optical absorbers are widely utilized in plasmonic sensors, optical switch, and solar-cells due to their effectiveness in capturing electromagnetic radiation. Furthermore, these devices can be tailored to optimize absorption at particular wavelengths within the mid-infrared spectrum. In this study, a perfect optical absorber was designed which included a Silica substrate with di-electric nano rode which is doped in Silica, Gold grating, a phosphorene layer which is cover structure. The effects of coupling between the nanorod and gold grating were investigated using the finite element method. The results indicate that, within the designed structure, the placement of the nanorod in the substrate significantly enhances absorption to more than 98% and the independence of absorbance from the thickness of phosphorene (i.e. less than 0.1% variation in the absorption). This perfect absorber operates over a narrow absorption range of 4 to 16 nm which is a good candidate to optical filters. [ABSTRACT FROM AUTHOR]

• The absorber exhibits high absorption, the remarkable anisotropy and flexible tunability characteristics. • The absorption reach nearly 100 % thought bound states in the continuum even at electronic doping of n s = 0.1 × 1013 cm−2. • The quality factor can achieve a value of 611.2. Black phosphorus (BP) is a promising two-dimensional (2D) material with direct band gap and distinctive lattice structure. Control over its bandgap can be achieved through physical or chemical methods, enabling selective light absorption within specific wavelength ranges. This study designed a narrow-bandwidth perfect absorber with highly quality (Q) factor, anisotropy and flexible tunability based on BP. The proposed structure comprises a monolayer BP sheet on the square array of Si hollow nanodisks placed on a SiO 2 spacer with a gold substrate backing. We numerically demonstrate the narrowband perfect absorption, which is achieved through bound states in the continuum resonance supported by metasurfaces critically coupled to BP monolayer. Notably, simulation results show that the absorption magnitude can reach nearly 100 % even at low electronic doping of n s = 0.1 × 1013 cm−2, and the Q factor can achieve a value of 611.2. The absorption peak and the resonance wavelength can be flexibly tuned by adjusting the electron doping of BP, the geometrical parameters of the structure and the angles of incident. Additionally, due to the inherent in-plane anisotropic feature of BP, the proposed structure exhibits high polarization-dependence. These results make our design a promising candidate for polarization-selective and tunable high performance mid-infrared devices, including polarizers, modulators, and photodetectors. [ABSTRACT FROM AUTHOR]

I constructed two models for achieving a perfect absorption acoustic metamaterial using a hexagonal honeycomb structure in the air with a change in folding number. The purpose of these models was to construct a hexagonal honeycomb metamaterial derived from Polydimethylsiloxane (PDMS) polymer. I carried out finite element simulations using COMSOL Multiphysics software to take theoretical measurements for our honeycomb structure and to show the influence of structural parameters in our models. Our simulations revealed that, depending upon the theoretical analysis, an acoustic metamaterial that supports resonance at 210 Hz for folding number n = 6 can be developed to construct a low-frequency sound-absorbing technology. I demonstrate that the dissipative loss effect can be controlled by folding number and high space utilization through adjusting the hexagonal dimensions to achieve perfect absorption. I also demonstrate the important effects of folding number, rotation angle, and structural parameters on improving acoustic absorption performance for honeycomb structural design. The results are of extraordinary correspondence at low frequency for achieving an ideal sound absorbing material. [ABSTRACT FROM AUTHOR]

A new design of a triple band perfect metamaterial absorber based on Pythagorean fractal geometry is proposed and analyzed for terahertz sensing applications. The proposed design showed an enhanced sensing performance and achieved three intensive peaks at 33.93, 36.27, and 38.39 THz, corresponding to the absorptivity of 98.5%, 99.3%, and 99.6%, respectively. Due to the symmetrical nature of the recommended design, the structure exhibited the characteristics of independency on the incident wave angles. Furthermore, a parametric study was performed to show the effects of the change in substrate type, resonator material, and substrate thickness on the absorption spectrum. At a fixed analyte thickness (0.5 μm), the resonance frequency of the design was found to be sensitive to the refractive index of the surrounding medium. The proposed design presented three ultra-sensitive responses of 1730, 1590, and 2050 GHz/RIU with the figure of merit (FoM) of 3.20, 1.54, and 4.28, respectively, when the refractive index was changed from 1.0 to 1.4. Additionally, the metamaterial sensor showed a sensitivity of 1230, 2270, and 1580 GHz/μm at the three resonance frequencies, respectively, when it was utilized for the detection of thickness variation at a fixed analyte refractive index (RI) of 1.4. As long as the RI of the biomedical samples is between 1.3 and 1.4, the proposed sensor can be used for biomedical applications. [ABSTRACT FROM AUTHOR]

We propose and numerically investigate an angle-tuned polarization-independent multi-narrowband perfect absorber, which comprises a simple gold nanocube array on SiO2/oxidized aluminum mirror layers. The oxidized aluminum mirror is able to support the surface plasmon polariton mode on the SiO2/Al2O3 interface. The multi-narrowband absorption contributes to the simultaneously excited quasi-metalâ€"insulatorâ€"metal guided modes and standing wave cavity mode in the thick insulator layer by the incident light normal to the structure in the wavelength range 1400â€"2400 nm. Moreover, the absorption can be actively modulated by adjusting the incidence angle, and it is polarization independent. The perfect absorber is also suitable for sensing, with the figure of merit reaching 102 RIUâˆ'1 within the refractive index range from 1.3 to 1.36. [ABSTRACT FROM AUTHOR]

We present a metamaterial-based perfect absorber (PA) that strongly supports four resonances covering a wide spectral range from 1.8 µm to 10 µm of the electromagnetic spectrum. The designed perfect absorber has metal–dielectric–metal layers where a MgF2 spacer is sandwiched between an optically thick gold film and patterned gold nanoantennas. The spectral tuning of PA is achieved by calibrating the geometrical parameters numerically and experimentally. The manufactured quad-band plasmonic PA absorbs light close to the unity. Moreover, the biosensing capacity of the PA is tested using a 14 kDa S100A9 antibody, which is a clinically relevant biomarker for brain metastatic cancer cells. We utilize a UV-based photochemical immobilization technique for patterning of the antibody monolayer on a gold surface. Our results reveal that the presented PA is eligible for ultrasensitive detection of such small biomarkers in a point-of-care device to potentially personalize radiotherapy for patients with brain metastases. [ABSTRACT FROM AUTHOR]

Six band metamaterial perfect absorber at the terahertz region is made and designed of two rectangular bars and a metallic board separated by a dielectric spacer. The simulated results show that the absorber has six distinctive absorption modes at frequencies 1.80 THz, 3.35 THz, 4.5 THz, 5.25 THz, 5.95 THz, and 6.1 THz with absorption rates of 97%, 96.2%, 97.07%, 91.1%, 100%, and 83%, respectively. The absorption mechanism of the six-band absorber was investigated by near-field distribution. The frequencies of these absorption bands can be adjusted by controlling the structural parameters of the proposed design. Furthermore, the influence of the geometric parameters on the performance of six-band light absorption was also analyzed to further verify the underlying mechanism of these six bands. In addition, two conventional parameters, the sensitivity (S) and figure of merit (FOM) were used to investigate the sensing performance of the proposed design. FOM of the fifth absorption peak can reach up to 26.9 which is much higher than the previously reported values for the terahertz region. This type of six-band absorber finds many potential applications in sensing and detection, filters, solar energy, and stealth technology. [ABSTRACT FROM AUTHOR]

In this paper, we have presented a new design of a metamaterial perfect absorber (MPA) consisting of three layers of metal-dielectric-metal in which the top layer is considered of special kind square patches at different places in a unit cell. This MPA exhibits wideband, wide-angle, and polarization-independent absorption performance in the visible region. The proposed MPA structure is composed of a resonator of metal and spacer of a dielectric layer. The interactions between the resonator and the coupling of metal-dielectric create the plasmonics effects which are responsible for the perfect absorption. Under a specific condition, this simulated absorber structure exhibits an extremely high broadband absorption between 591.54 and 704.40 nm wavelength range with near-unity absorption, and a single peak observed at 385.33 nm with the absorption of 94.16%. We extracted the impedance of the absorber and matched it with free space, and also demonstrated the effective permittivity and permeability. Moreover, the parametric study of the resonators, dielectric layer, and multi-band topology has also been investigated. The polarization-insensitive-based metamaterial may be utilized to improve the efficiency of different devices in the visible range. Furthermore, we have calculated the absorption of the proposed MPA under solar radiation (AM1.5) for different structural parameters. The proposed absorber greatly enhances the conversion efficiency which is highly useful for solar cells. We also determined the short circuit current density of this absorber for different thicknesses of the GaAs layer. The meta-surface of Al metal provides a good performance in comparison to other costly metals and the proposed structure may be used for different devices. [ABSTRACT FROM AUTHOR]

Terahertz metamaterial absorbers (TMAs) can efficiently absorb electromagnetic wave in the range of 0.1–10 THz based on the tunable electromagnetic properties of artificially designed unit cells. TMAs can achieve perfect absorption, as well as broad band absorption. Specifically, TMAs can break the thickness limit of a device at a quarter wavelength, realizing ultra‐thin devices so as to facilitate integration with other systems. Accordingly, TMAs have high application value in communication, imaging, detection, security inspection, and other fields because of their characteristics of small size, perfect absorption, less restriction of natural materials, and tunable electromagnetic parameters. This review covers the fundamental principles and recent advances of TMAs, from the essential structural features of TMAs and working principle of various types of TMAs to the design and applications of corresponding structures, especially the TMAs that can be tuned by various approaches. The development trend and challenges of TMAs are briefly discussed too. It is envisioned that this review can help R&D of the future TMAs for real applications. [ABSTRACT FROM AUTHOR]

This paper demonstrated a sensor device based on metamaterial in the terahertz region for sensing and detection of toxic gases in pollution air environment. The suggested design comprised of H-typed metallic resonator atop on layer of dielectric and a layer of metallic at the bottom. The simulation results display dual frequencies found at 3.495 THz and 3.945 THz with absorption rate closed to 99%. The suggested sensor is extremely sensitive to the surrounding medium of the RI variation with sensor sensitivity that increases up to 1.41THz/RIU (refractive index unit) while figure of merit (FOM) reaches up to 12.81 RIU−1 lies between 1 and 1.032 RI range. The novelty of the work lies in its novel design, a low cost and highly accurate sensor device, and impressive ability to surpass in gas sensing with extremely high sensitivity. Additionally, the sensor device has the ability of detection of several harmful gases with extremely high sensitivity (S) of 6.47 THz/RIU observed for chlorine (Cl2) gas that was not previously reported in the literature. The suggested work can be footing for designing highly sensitive gas sensors for environmental pollution monitor. The proposed research work can also be significant in other optical sensing applications such as chemical and bio sensing industry applications. [ABSTRACT FROM AUTHOR]

Optically anisotropic materials show important advantages in constructing polarization-dependent optical devices. Very recently, a new type of two-dimensional van der Waals (vdW) material, known as α-phase molybdenum trioxide (α-MoO3), has sparked considerable interest owing to its highly anisotropic characteristics. In this work, we theoretically present an anisotropic metamaterial absorber composed of α-MoO3 rings and dielectric layer stacking on a metallic mirror. The designed absorber can exhibit ultra-narrowband perfect absorption for polarizations along [100] and [001] crystalline directions in the visible light region. Plus, the influences of some geometric parameters on the optical absorption spectra are discussed. Meanwhile, the proposed ultra-narrowband anisotropic perfect absorber has an excellent angular tolerance for the case of oblique incidence. Interestingly, the single-band perfect absorption in our proposed metamaterials can be arbitrarily extended to multi-band perfect absorption by adjusting the thickness of dielectric layer. The physical mechanism can be explained by the interference theory in Fabry–Pérot cavity, which is consistent with the numerical simulation. Our research results have some potential applications in designs of anisotropic optical devices with tunable spectrum and selective polarization in the visible light region. [ABSTRACT FROM AUTHOR]

In this paper, we propose a highly selective and efficient gas detection system based on a narrow-band IR metasurface emitter integrated with a resistive heater. In order to develop the sensor for the detection of specific gases, both the microheater and metasurface structures have been optimized in terms of geometry and materials. Devices with different metamaterial structures and geometries for the heater have been tested. Our prototype showed that the modification of the spectral response of metasurface-based structures is easily achieved by adapting the geometrical parameters of the plasmonic micro-/nanostructures in the metasurface. The advantage of this system is the on-chip integration of a thermal source with broad IR radiation with the metasurface structure, obtaining a compact selective radiation source. From the experimental data, narrow emission peaks (FWHM as low as 0.15 μm), corresponding to the CO2, CH4, and CO absorption bands, with a radiant power of a few mW were obtained. It has been shown that, by changing the bias voltage, a shift of a few tens of nm around the central emission wavelength can be obtained, allowing fine optimization for gas detection applications. [ABSTRACT FROM AUTHOR]

Metamaterial perfect absorbers (MPAs) with dynamic thermal tuning features are able to control the absorption performance of the resonances, providing diverse applications spanning from optical switches and filters to modulators. In this paper, we propose an MPA with diverse functionalities enabled by vanadium dioxide (VO2) embedded in a metal-dielectric plasmonic structure. For the initial design purpose, a silicon (Si) nanograting on a silver (Ag) mirror is proposed to have multiple resonant responses in the near infrared (NIR) region. Then, the insertion of a thin VO2 layer at the right position enables the design to act as an on/off switch and resonance tuner. In the insulator phase of VO2, in which the permittivity data of VO2 is similar to that of Si, a double strong resonant behavior is achieved within the NIR region. By increasing the temperature, the state of VO2 transforms from insulator to metallic so that the absorption bands turn into three distinct resonant peaks with close spectral positions. Upon this transformation, a new resonance emerges and the existing resonance features experience blue/red shifts in the spectral domain. The superposition of these peaks makes the overall absorption bandwidth broad. Although Si has a small thermo-optic coefficient, owing to strong light confinement in the ultrasmall gaps, a substantial tuning can be achieved within the Si nanogratings. Therefore, the proposed hybrid design can provide multi-resonance tunable features to cover a broad range and can be a promising strategy for the design of linearly thermal-tunable and broadband MPAs. Owing to the proposed double tuning feature, the resonance wavelengths exhibits great sensitivity to temperature, covering a broad wavelength range. Overall, the proposed design strategy demonstrates diverse functionalities enabled by the integration of a thin VO2 layer with plasmonic absorbers. [ABSTRACT FROM AUTHOR]

We report the design and simple spray coating fabrication process of a perfect absorber based on carbon nanotubes (CNTs) and carbon black particles with omnidirectional high absorption efficiency beyond 99.9% over the broad wavelength range from 400 nm to 20 μm. The carbon black particles are introduced into the CNT solution to form multi-scale all-carbon-based nanomaterials, effectively modifying the morphology of the sprayed layer to improve the light absorption. The promising absorption characteristics of the CNT–carbon black layer are attributed to not only the intrinsic optical properties of the carbon nanomaterials but also the unique surface nanostructures that efficiently trap light. In addition to serving as absorbers in the coating layer, the CNTs, more importantly, act as connectors between carbon black particles for absorber preparation at a large scale, which is the key to modifying the surface morphology. The all-carbon-based coating layer is also shown to be effective for solar thermal harvesting and self-cleaning function. The developed mixing method for CNTs and carbon black particles in solutions opens a new path for the realization of multi-functional sprayed layers based on CNTs and advances the technology of CNT coatings for scale-up to industry applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, we designed a dual band metamaterial perfect absorber (MPA) for Ku band applications. The overall ultrathin layer of proposed absorber consists of square patch with 450 diagonal slot structure within a copper square patch which loaded on both sides of dielectric thickness 1.6 mm FR-4 substrate. The results show that designed MPA gives two absorption bands at 12.45 and 14.18 GHz and absorption rates are 99.73% and 99.87% respectively. The proposed dual-band absorber has a polarization sensitive characteristic, the absorption performance is almost changing with different polarization angles. Furthermore, resonance centres of two absorption bands can be adjusted by changing related parameters. The novelties of proposed structure are simple, easy fabricate, low cost, durable, suitable for real-time applications and long-term stability considering the fabrication technique and non-destructive measurement method. The dualband absorber can be used in practical applications such as bolometer, EM wave spatial filter and satellite communications. [ABSTRACT FROM AUTHOR]

In this work, silicon dioxide based four-fold swastika shaped metamaterial nano structure absorber for solar radiation absorption in the near infrared (NIR) regime is proposed. The dimension of the unit cell is 648.50 × 648.50 nm2 which is designed on dielectric silicon dioxide and metallic conductor aluminum. The proposed structure is investigated by the finite-deference time domain (FDTD) method based software CST microwave studio. The metamaterial absorber (MMA) unit cell is simulated within the frequency range (200–398) THz that yielded dual resonance peaks at 260 THz and 378.0 THz with 95.50 % and 97.32 % of absorbance of solar energy, respectively. Additionally, the proposed nano design structure of unit cell was boosted up to attain the dual absorption band by engineering the design parameters. The electromagnetic response of the MMA was theoretically inspected and the excellent properties of the proposed designed absorber have promising applications in plasma-enhanced photovoltaic, optical absorption switching and infrared modulator optical communication. [Display omitted] • Silicon dioxide based four-fold swastika shaped metamaterial nano structure absorber developed for solar radiation absorption in the near infrared (NIR) regime. • The proposed nano design structure of unit cell was boosted up to attain the dual absorption band such as 260 THz and 378.0 THz with 95.50 % and 97.32 % absorbance respectively. • The dimension of the unit cell is 648.50 × 648.50 nm2 which is designed on dielectric silicon dioxide and metallic conductor aluminum. • The designed absorber has promising applications in plasma-enhanced photovoltaic, optical absorption switching and infrared modulator optical communication. [ABSTRACT FROM AUTHOR]

This study proposes using double-layer wire-grid structures to create narrow-band, perfect plasmonic absorbers, which depend on polarization, for the short-wavelength visible and near-ultraviolet regions of the electromagnetic spectrum. A rigorous coupled-wave analysis reveals that the maximum absorption attained using Ag and Al is ~ 90% at 450 and 375 nm. Experiments using Ag yielded results similar to those predicted by simulations. These results demonstrate that narrow-band perfect plasmonic absorbers, which depend on the polarization, can be realized at 450 and 375 nm using Ag or Al. [ABSTRACT FROM AUTHOR]

Nowadays, graphene is one of the most used materials in the manufacturing of optical instruments, such as sensors, photovoltaic cells, and especially absorbers. The unrivaled ability of graphene in the formation of high-quality surface plasmons creates extraordinary features for absorber devices. Here, by exploiting the nanoplasmonic structure consisting of one-dimensional nanophotonic crystal made of graphene-silver half-ellipse grating next to the dielectric layer, the aim of this research is to achieve broadband absorption and perfect absorber in addition to increasing single-layer and multi-layer graphene absorption by creating surface plasmons and study the absorption spectrum in the near-infrared region. For this purpose, the studied nanostructure is optimized under different incident angles, geometric parameters of the structure, and also the dielectric refractive index. The proposed structure increases the absorption of graphene up to 85% along with wondrous absorption bandwidth over the entire near-infrared region from 770 to 3000 nm. In addition to achieving broadband plasmonic perfect absorber, an ultra-broadband, nearly perfect absorber, with the absorption of more than 80% in the whole near-infrared spectral zone has been introduced whose wide range of 1497 nm has an absorption above 90%. This range is far beyond the bandwidth of less than 1200 nm of conventional absorbers. In addition to high strength and low angular sensitivity, this absorber has the wonderful ability to effective absorb the solar radiation and can display abundant applications in solar cells, thermal emitters, and infrared detectors. [ABSTRACT FROM AUTHOR]

In this paper, a refractive index plasmonic nano-sensor based on a tunable perfect absorber has been proposed in the near-infrared region. The proposed sensor consists of a truncated cone resonator with more than 99% absorption and ultra-narrow bandwidth. Liquid crystal has been used in the designed nano-structure to tune the structure by variation of the incident angle and applying the external bias field to obtain the near perfect and ultra-narrow absorption peak. The proposed nano-sensor has a high sensitivity of 1363.63 nm/RIU and a high figure of merit of 1136.36 RIU−1 at the telecommunication wavelength of 1550 nm. Furthermore, after obtaining appropriate conditions for the liquid crystal layer, we have suggested a new resonator to boost the interaction of surface plasmons and the test medium. Therefore, the sensitivity and figure of merit are increased to the values of 1509 nm/RIU and 1257.5 RIU−1, respectively. This excellent performance of the sensor has huge potential for precision applications such as biomedical science and biosensor. Hence, the capability of the proposed nano-sensor in the field of histopathology for cancerous tissue diagnosis and detection of toxic and flammable gases to prevent endangering human health has been studied. In this case, the high sensitivity of 1368.06 nm/RIU and high figure of merit of 1179.36 RIU−1 have been obtained. [ABSTRACT FROM AUTHOR]

In this paper, a new model of multi-layer metamaterial perfect absorber (MPA) in the terahertz region has been introduced. This model is similar to the classic absorber model, ie the three traditional layers of metal-dielectric-metal. The difference is that the middle layer has changed in height and consists of 3 separate layers with the same material. Therefore, the middle layer of the proposed structure is metamaterial. Numerical results of the simulation show that the absorption rate of the perfect absorber at 6.86 THz is 99.99%. Also, by changing the width of the two middle layer columns w, a dual-band perfect absorber with an average absorption rate of 97.18% is obtained at frequencies of 4.24 THz and 6.86 THz. A significant advantage of this paper over other works is that this absorber is adjustable, in addition to obtaining a nearly perfect dual-band absorber with a narrow-band peak by adjusting the parameters and also a nearly broad-band absorber can also be obtained by changing the parameters without re-manufacturing the structure. We believe that the proposed absorber has potential in filtering, detection and imaging. [ABSTRACT FROM AUTHOR]

A very large dynamic optical reflection modulation from a simple unpatterned layered stack of phase‐change material ultra‐thin films is experimentally demonstrated. Specifically, this work demonstrates that properly designed systems comprising deeply subwavelength GeSbTe (GST) films, a dielectric spacer, and a metallic mirror produce a dynamic modulation of light in the near‐infrared from very strong reflection (up to R≈80%) to perfect absorption (A>99.995%) by simply controlling the crystalline state of the phase‐change material. While the amplitude of modulation experimentally reaches an optical contrast higher than 104, intermediate levels of reflection in between extreme values can also be actively encoded, corresponding to partial crystallization of the GST layer. Several layered system designs are further explored and guidelines are provided to tailor the efficient wavelength range, the angle of operation, and the degree of crystallization leading to perfect absorption. [ABSTRACT FROM AUTHOR]

Metasurfaces allow for the spatiotemporal variation of amplitude, phase, and polarization of optical wavefronts. Implementation of active tunability of metasurfaces promises compact flat optics capable of reconfigurable wavefront shaping. Phase‐change materials (PCMs) are a prominent material class enabling reconfigurable metasurfaces due to their large refractive index change upon structural transition. However, commonly employed laser‐induced switching of PCMs limits the achievable feature sizes and restricts device miniaturization. Thermal scanning‐probe‐induced local switching of the PCM germanium telluride is proposed to realize near‐infrared metasurfaces with feature sizes far below what is achievable with diffraction‐limited optical switching. The design is based on a planar multilayer and does not require fabrication of protruding resonators as commonly applied in the literature. Instead, it is numerically demonstrated that a broad‐band tuning of perfect absorption can be realized by the localized tip‐induced crystallization of the PCM. The spectral response of the metasurface is explained using resonance mode analysis and numerical simulations. To facilitate experimental realization, a theoretical description of the tip‐induced crystallization employing multiphysics simulations is provided to demonstrate the great potential for fabricating compact reconfigurable metasurfaces. The concept can be applied not only for plasmonic sensing and spatial frequency filtering, but also be transferred to all‐dielectric metasurfaces. [ABSTRACT FROM AUTHOR]

We design and simulate a tunable dual-band perfect absorber. This absorber is composed of a circular graphene layer with an ellipse cut out in the centre, separated by a dielectric layer in the middle and a gold mirror at the bottom. Results reveal that there exist two perfect absorption peaks in the terahertz band. The position of the absorption peak can be changed by adjusting the Fermi level and geometric parameters of the graphene pattern. Furthermore, the absorber is insensitive to the polarized incident light with a wide incident angle. Functionalities are achieved based on a simple and symmetrical single-layer graphene pattern, which can greatly reduce the manufacturing costs. The proposed absorber can be applied in the field of graphene-based photonic devices, such as detectors, sensors, and filters. [ABSTRACT FROM AUTHOR]

Multiple-band metamaterial absorbers as an important branch of metamaterial-based resonant devices have shown considerable application prospects in real life. However, current designs have many shortcomings in the realization of multiple-band absorption, including complex pattern structure, time-consuming fabrication steps, and strong interaction between sub-elements. Herein, a simple design of multiple-band metamaterial absorber based on single metallic resonator is presented. Basic cell of the multiple-band absorption is formed by a square metallic patch (cut by a concentric air gap) placed on a metallic mirror separated by an insulating medium material. The metamaterial structure can interact strongly with the incident beam to produce the fundamental mode resonance, third-order resonance, and two other resonances resulted from the concentric air gap introduction. The combining effect of the four discrete resonance modes provides the ability to achieve quad-band absorption. The quad-band absorption shows great dependence on the structure dimensions. Based on this, we further design a kind of multiple-band absorption having the adjustable number of absorption peaks by introducing photosensitive silicon material in the initial area of the air gap. The number of resonance peaks can be tuned flexibly from quad-band absorption to dual-band absorption by changing the conductivity (i.e., material property) of photosensitive silicon material. [ABSTRACT FROM AUTHOR]

Broadband perfect absorbers are of great importance for various applications such as stealth technologies, thermal photovoltaic cells, optical communication, photodetection, and photovoltaic devices. However, they are often made by lithographic techniques with high cost and complexity, which hinders their practical applications. The design of broadband and ultrahigh absorber at low cost and ease in fabrication is still a big challenge in the field of optics. Here, an all‐solution‐processed plasmonic perfect absorber is proposed and demonstrated by incorporating Mxene Ti3C2Tx (Tx = F, O or OH) and gold nanoparticles (NPs) in metal–insulator–metal configuration. The absorption of the designed plasmonic absorber can reach up to 99% with polarization‐ and angle‐independence in a broad range of wavelengths from ultraviolet to near‐infrared region. This ultrahigh and broadband absorbance is attributed to the synergy of plasmon resonance, magnetic resonance, and cavity effect between gold NPs layer and Mxene film, which is further corroborated by simulations of the finite element method for both random and patterned orientation of the gold nanoparticles. The excellent optical property together with the easy fabrication method paves the way for preparing photon‐absorbing nanostructures in photocatalysis and solar photovoltaics. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a highly efficient light trapping design that is made of a metal-oxide-semiconductor-semiconductor (nanograting/nanopatch) (MOSSg/p) four-layer design to absorb light in a broad wavelength regime in dimensions smaller than the hole diffusion length of the active layer. For this aim, we first adopt a modeling approach based on the transfer matrix method (TMM) to find out the absorption bandwidth (BW) limits of a simple hematite (α-Fe2O3)-based metal-oxide-semiconductor (MOS) cavity design. Our modeling findings show that this design architecture can provide near-perfect absorption in shorter wavelengths. To extend the absorption toward longer wavelengths, a nanostructured semiconductor is placed on top of this MOS design. This nanostructure supports the Mie resonance and adds a new resonance in longer wavelengths without disrupting the lower wavelength absorption capability of MOS cavity. By this way, a polarization-insensitive absorption above 0.8 can be acquired up to λ=565 nm. Moreover, to have a better qualitative comparison, the water-splitting photocurrent of this design has been estimated. Our calculations show that a photocurrent as high as 10.6 mA cm−2 can be achieved with this design that is quite close to the theoretical limit of 12.5 mA cm−2 for hematite-based water-splitting photoanode. This paper proposes a design approach in which the superposition of cavity modes and Mie resonances can lead to a broadband, polarization-insensitive, and omnidirectional near-perfect light absorption in dimensions smaller than the carrier's diffusion length. This can be considered as a winning strategy to design highly efficient and ultrathin optoelectronic designs in a variety of applications including photoelectrochemical water splitting and photovoltaics. [ABSTRACT FROM AUTHOR]

Solar radiation is mainly concentrated in visible light region (50%), to achieve the perfect absorption of this spectral band is significant for many energy-related fields include solar cells, hot-electron devices, and perfect cloaking. In this paper, we theoretically designed and numerically demonstrated a broadband perfect absorber that works in visible light (400–800 nm). The perfect absorber consists of silica-titanium nitride-silica-titanium nitride four-layer structure, which has an ultra-thin thickness of 325 nm. This broadband absorber can continuously achieve light absorption from 400 to 800 nm, with an average absorption rate as 99.52% under normal incidence. This absorber obtained 99.98% maximum absorption rate at wavelength 620 nm and 97.18% minimum absorption rate at 400 nm. The multiple integration of propagating surface plasmon resonance, localized surface plasmon resonance, and Fabry-Perot resonance generates the perfect absorption function for this device. The high refractory, polarization independence, large incident angle insensitivity, and simple manufacturing method make this absorber more suitable for solar energy collection and thermal photovoltaics application. [ABSTRACT FROM AUTHOR]

A thin screen exhibiting dynamically switchable transmission/absorption functionalities is highly desired in practice. However, a trilayer transmissive metasurface with active elements controlled in a uniform manner cannot exhibit independently controlled transmission and absorption properties due to intriguing interplays between the scattering and absorbing properties in systems exhibiting inversion symmetries. This motivates to employ the coupled‐mode theory to establish a generic phase diagram for such transmissive metasurfaces with active elements loaded in different layers tuned independently and to guide researchers design tunable metadevices with completely decoupled transmission/absorption responses. Based on such a phase diagram, a microwave metasurface is designed/fabricated with PIN diodes incorporated, and it is experimentally demonstrated that its functionality can switch from perfect transparency to perfect absorption, controlled by external voltages applied across the diodes. In addition to finding immediate applications in practice (e.g., smart radomes), the results of this study also provide a new type of tunable meta‐atom for building metasurfaces with flexible wave‐front control abilities. [ABSTRACT FROM AUTHOR]