Dual-band Absorption Peaks Research Articles

Perfect absorber with high sensitivity based on hexagonal star graphene surface

Graphene absorbers have attracted wide attention due to their high absorption rate and narrow bandwidth in the terahertz field. In this study, we proposed a dual-band terahertz tunable perfect absorber designed with a hexagonal star ring and a circular ring monolayer graphene metasurface, which exhibits tunable, polarization-insensitive, and high sensitivity characteristics. The graphene absorber was simulated by using the finite element method and validated by using the impedance matching method. Simulation results show that this structure has two perfect absorption peaks at 4.8 and 8.04 THz. The variation of the dielectric layer material was analyzed, and the parameters of the structure and the intrinsic graphene parameters were adjusted to control the absorption efficiency of the dual-band absorption peaks. Simulation results show that the high symmetry of the structure brings incident and polarization-insensitive properties, maintaining absorption higher than 98% over a wide range of incident and azimuth angles. The sensing performance of the device was investigated by varying the ambient refractive index, and the highest sensitivity parameter S of the absorber reached to 2.375 THz/RIU. These results demonstrate that this high-sensitivity sensor has great potential for terahertz imaging and microstructure detection.

Dual-Band X-Shaped Absorber Design for Sensor Applications

This study presents a compact absorber design with an X-shaped resonator (XSR) in the S-band region. The proposed design offers single or dual-band absorption peaks, depending on whether the arm lengths of the resonator are symmetrical or asymmetrical. Prototype fabrications of the absorber, whose numerical design was carried out using CST Microwave Studio, were also measured for verification. Based on the simulated and measured results, the proposed absorber exhibited over 93% absorption spectra with relatively narrow bandwidth characteristics desired, especially for sensor applications. It also provided cross-polarized reflections of less than 0.08 at the frequencies of interest. In addition, the absorption frequency changes depending on the dielectric constant and thickness variations of the sensing layer placed on the absorber were obtained numerically and experimentally to investigate the sensing performance of a dual-band configuration of the absorber. In addition, the same analyzes and measurements were carried out again for two separate single-band split-ring resonator (SRR)-based absorbers designed in this study, and their sensing performances were compared with the dual-band X-shaped absorber's performance. As a result, it was found that the proposed X-shape absorber was more sensitive than the SRR-based absorber, considering the comparison results.

Highly Sensitive Dual-Band Terahertz Metamaterial Absorber for Biomedical Applications: Simulation and Experiment.

In this paper, a terahertz (THz) metamaterial absorber (MTMA), incorporating surface Pythagorean tree fractal resonators, was designed and experimentally fabricated on the flexible substrate of polyethylene terephthalate. The design presented two peaks with strong absorption of more than 97% at 0.49 and 0.69 THz. The dual-band absorption peaks were seen to be shifted with the change in the refractive index of the surrounding medium, with a corresponding sensitivity of 0.0968 and 0.1182 THz/RIU. The spectral shift of the reflection resonance dip was utilized as an assessment index to evaluate the sensing performance of the new structure, and it was found to be 2.08 and 2.98 for the two resonance peaks, respectively. It was observed that the proposed structure acted as an epsilon negative material at the first resonance and as a mu negative material at the second resonance. Further investigations on the electric field, magnetic field, and surface current distributions were carried out to elaborate on the absorption characteristics at various resonance frequencies. The proposed sensor is a highly sensitive MTMA which can be used to investigate the interaction of matter with THz waves.

Perfect absorption and strong phonon polariton with a graphene-based silicon carbide grating and Tamm plasmonic structures

This study proposes a tunable dual-band mid-infrared graphene-based one-dimensional photonic crystal absorber with strong surface phonon polaritons and Tamm phonon polariton coupling. We use an LC circuit, transfer matrices, and coupled harmonic oscillator models to theoretically analyze the different modes, and the theoretical results are consistent with the simulation results. The resonance wavelengths and absorption intensities of the coupled mode can be adjusted by the Fermi level and structure parameters. Moreover, because the perfect dual-band absorption peaks of the designed structure are sensitive to the air layer’s refractive index, we demonstrate the possibility of its application in the field of refractive index sensors and analyze its potential in the field of biomolecular layer sensors. The designed structure also has broad applications in absorbers, photodetectors, and energy harvesting devices due to the excellent performance of the tunable perfect absorption peaks.

Tunable dual-band metamaterial absorber in the infrared range based on split-ring-groove array.

In this paper, we present a tunable dual-band perfect metamaterial absorber working in the infrared band by integrating a metallic split-ring-groove resonator array with a liquid crystal (LC) layer atop a metal substrate. By varying the height of the central nanodisks, the absorptivity of the dual-band absorption peaks can be simultaneously adjusted. The dual-band resonance frequencies of the proposed absorber exhibit continuous tunability by adjusting the refractive index of the LC, which can be controlled by applying external voltage. The mechanism of the perfect absorption is attributed to the gap plasmonic resonance coupling regime. The presented absorber exhibits good tolerance to incidence angles up to 60° and shows polarization dependent performance, which may offer promising applications in sensing, modulator, and optical absorption switching in the infrared regime.

Neural Network Topology-Based Terahertz Absorber Using Fractal Frequency Selective Surface

This work offers a new kind of polarization-insensitive, angular stable, tunable fractal frequency selective surface (FSS) based terahertz (THz) absorber. An equivalent circuit model (ECM) of the absorber is developed and impedance is obtained analytically. Further, an ECM-backed artificial neural network (ANN) approach is proposed and used to optimize the absorber to the desired frequency and bandwidth. The minimum mean square error between targeted and observed outputs is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.86\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> . The maximum absorption of 99% is achieved at a central frequency of 1.5 THz. The tunability is accomplished by varying the chemical potential ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{c}$ </tex-math></inline-formula> ) of the graphene layer introduced in the proposed absorbing structure. The resonance frequency shifts to 1.66 THz from 1.39 THz with a change in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{c}$ </tex-math></inline-formula> from 0.3eV to 0.6eV.The dual-band absorption peaks are noticed with fractal FSS based absorber within the operating frequency range of 0.1-4.0 THz. The maximum absorption of 0.99 and 0.98 at the resonant frequency of 1.0 THz and 3.1 THz with fractal FSS, respectively is achieved. Furthermore, the designed absorber works well for both perpendicular and parallel polarizations up to 60 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> angle of incidence. Moreover, the effect of structural parameters is also observed on the equivalent inductance and capacitance to understand the physics behind the structure. All the results obtained from ANN are verified with particle swarm optimization (PSO) and Whale optimization (WO) techniques. Good congruence among ANN, PSO, and WO results shows the effectiveness of the aforementioned technique. The possible applications of the proposed tunable absorber are THz imaging, sensing, detection, and stealth.

Tunable Terahertz Perfect-Absorbers With Dual Peak Based on Reverse Graphene Patch Metamaterials

In this paper, we proposed a tunable graphene-based metamaterial absorber (MA) at dual terahertz band to achieve perfect absorption. The electric field intensity distributions of demonstrated structure is illustrated to explain the origin of two absorption peaks. Simulation result shows the proposed MA owning polarization-insensitive property and wide incident angle tolerance. An inversion algorithm is used to extract the equivalent impedance and explore the physical mechanism of multiple-peak absorption. The equivalent impedance is explored through algorithm when the Fermi energy level alters, consequently the variation of resonant frequency of corresponding absorption peak is determined. Simultaneously, the resonant frequencies of absorption peaks can be adjusted by changing the geometric parameters of the graphene. Furthermore, we adapt the proposed structure into reversely designed pattern, achieving similar characteristic of dual-band absorption peaks and tunability. Thus, our work provides new insight and useful design guidance to various tunable multiple band terahertz metamaterial perfect-absorbers.

Dual-Band Plasmonic Perfect Absorber Based on the Hybrid Halide Perovskite in the Communication Regime

Due to the weak absorption of (CH3NH3)PbI3 in the communication regime, which restricts its optoelectronic applications, we design a adjustable dual-band perfect absorber based on the (CH3NH3)PbI3 to significantly enhance its absorption capability. Since the localized plasmon (LP) mode and surface plasmon (SP) mode are excited in the structure, which can both greatly enhance light absorption of the (CH3NH3)PbI3 layer, dual-band perfect absorption peaks are formed in the communication regime, and the absorption of (CH3NH3)PbI3 layer is increased to 43.1% and 64.2% at the dual-band absorption peaks by using finite-difference time-domain (FDTD) methods, respectively. By varying some key structural parameters, the dual-band absorption peaks of (CH3NH3)PbI3 can be separately shifted in a wide wavelength region. Moreover, the designed absorber can keep good performance under wide angles of incidence and manifested polarization correlation. Furthermore, not just for (CH3NH3)PbI3, the physical mechanism in this absorber can also be utilized to strengthen the absorption of other halide perovskites.

A dual-band metamaterial absorber for graphene surface plasmon resonance at terahertz frequency

Abstract In this paper, we present a dual-band metamaterial absorber for graphene surface plasmon resonance at terahertz frequency. We use the finite difference time domain (FDTD) method to study the absorption characteristics of the homocentric graphene ring and disk nanostructure. These simulation results show that the change of the geometrical parameters and the substrate thickness of the nanostructure can change the absorption characteristics and the emergence of dual-band absorption peaks. Moreover, we study the field distribution of nanodisks with different radius in detail. By changing the Fermi level of graphene, the wavelength of their absorption peaks can be adjusted flexibly. In addition, the proposed dual-band absorber also shows a good angle tolerance for both TE and TM polarizations. By calculation the surface-filled water (n = 1.332) and 25% aqueous glucose solution (n = 1.372) for the metamaterial absorber, the sensitivities of mode I and mode II are 5.0 μm/RIU and 15.0 μm/RIU. These research results will have broad application prospects for sensing and spatial light modulators.

Multiple magnetic resonance and microwave absorption of metamaterial absorbers composed of double split ring resonators on grounded carbonyl iron composites

This study investigates the triple-band absorption properties of metamaterial absorbers composed of a double split ring resonator (DSRR) on a grounded magnetic substrate of carbonyl iron powders. Computational tools are used to model the interaction between electromagnetic waves and the metamaterial structure. For perpendicular polarization with the electric field perpendicular to the SRR gap, triple-band absorption peaks are predicted in the simulation result of reflection loss. Magnetic resonance resulting from antiparallel currents between the upper DSRR and the lower ground plane is identified at the frequencies of the absorption peaks. The orientation of the two resonators influences the absorption characteristics, especially in the second and third peaks where the coupling between the inner SRR and outer SRR is strong. The current density distribution indicates that the two resonators oriented in the same direction achieve reduced coupling between them, which results in two absorption frequencies close to each other. For parallel polarization with the electric field parallel to the SRR gap, this study predicts dual-band absorption peaks corresponding to the magnetic resonance at the SRR wire.

Surface plasmon-enhanced dual-band infrared absorber for -based microbolometer application**Project supported by the One Hundred Talents Program of the Chinese Academy of Sciences, the National Natural Science Foundation of China (Grant Nos. 61376083 and 61307077), the China Postdoctoral Science Foundation (Grant Nos. 2013M530613 and 2015T80080), and the Guangxi Key Laboratory of Precision Navigation Technology and Application (Grant Nos. DH201505, DH201510, and

We propose a periodic structure as an extra absorption layer (i.e., absorber) based on surface plasmon resonance effects, enhancing dual-band absorption in both middle wavelength infrared (MWIR) and long wavelength infrared (LWIR) regions. Periodic gold disks are selectively patterned onto the top layer of suspended SiN/VO2/SiN sandwich-structure. We employ the finite element method to model this structure in COMSOL Multiphysics including a proposed method of modulating the absorption peak. Simulation results show that the absorber has two absorption peaks at wavelengths and with the absorption magnitudes more than 0.98 and 0.94 in MWIR and LWIR regions, respectively. In addition, the absorber achieves broad spectrum absorption in LWIR region, in the meanwhile, tunable dual-band absorption peaks can be achieved by variable heights of cavity as well as diameters and periodicity of disk. Thus, this designed absorber can be a good candidate for enhancing the performance of dual band uncooled infrared detector, furthermore, the manufacturing process of cavity can be easily simplified so that the reliability of such devices can be improved.

A wide-angle polarization-sensitive dual-band absorber in the infrared regime

We report a wide-angle polarization-sensitive dual-band absorber in the infrared regime with a three-layered structure. The unit cell in the top layer consists of two different strips. The simulation results show that the absorber has two distinctive absorption peaks at wavelengths λ=1.230μm and λ=2.275μm with the absorption magnitudes more than 0.98 and 0.97 for TM polarization (electric field perpendicular to the strips), respectively. The dual-band absorption peaks can be tuned by varying the widths of the strips, and the absorption magnitudes are more than 0.9 at the dual-band absorption peaks for angles up to 60°. At the same time, it reflects almost all light for TE polarization (electric field parallel to the strips). This absorber is a good candidate for potential applications such as polarization detectors and reflective polarizers.

Dual-band microwave absorption properties of metamaterial absorber composed of split ring resonator on carbonyl iron powder composites

This study investigated the dual-band absorption properties of metamaterial absorbers composed of a split ring resonator (SRR) on a grounded magnetic substrate. Polymer composites of carbonyl iron powders (CIP) of high permeability and magnetic loss were used as the substrate material. Computational tools were used to model the interaction between electromagnetic waves and materials with the SRR structure. For perpendicular polarization with an electric field (E) perpendicular to the SRR gap, dualband absorption peaks are predicted in the simulation result of reflection loss. Magnetic resonance resulting from antiparallel currents between the SRR and the ground plane is observed at the frequencies of two absorption peaks. The first strong absorption peak at the lower frequency (3.3 GHz) is due to magnetic resonance at the wire part of the SRR. The second absorption peak at the higher frequency (7.2 GHz) is due to magnetic resonance at the SRR split gap. The decreased capacitance with increased gap spacing moves the second absorption frequency to higher frequencies, while the first absorption peak is invariant with gap spacing. In the case of dual gaps at the opposite sides of the SRR, a single absorption peak is predicted due to the elimination of low-frequency resonance. For parallel polarization with the E-field parallel to the SRR gap, a single absorption peak is predicted, corresponding to magnetic resonance at the SRR wire. Open image in new window

A wide-angle dual-band polarization-sensitive absorber with a multilayer grating

In this paper, a wide-angle polarization-sensitive dual-band absorber at infrared wavelengths with a multilayer grating is reported. The simulation results show that the absorber has two absorption peaks at wavelengths λ = 1.365 μ m and λ = 3.035 μ m with the absorption magnitudes more than 0.97 and 0.99 for TM polarization (electric field perpendicular to the strips), respectively. And this absorber reflects almost all TE polarization (electric field parallel to the strips) light. The dual-band absorption peaks can be tuned by varying the width of the strips, and the absorption magnitudes are more than 0.9 for the dual-band absorption peaks for angles up to 70°.

Dual-band absorption of mid-infrared metamaterial absorber based on distinct dielectric spacing layers

We present the simulation, fabrication, and characterization of a dual-band metamaterial absorber in the mid-infrared regime. Two pairs of circular-patterned metal-dielectric stacks are employed to excite the dual-band absorption peaks. Dielectric characteristics of the dielectric spacing layer determine energy dissipation in each resonant stack, i.e., dielectric or ohmic loss. By controlling material parameters, both two mechanisms are introduced into our structure. Up to 98% absorption is obtained at 9.03 and 13.32 μm in the simulation, which is in reasonable agreement with experimental results. The proposed structure holds promise for various applications, e.g., thermal radiation modulators and multicolor infrared focal plane arrays.