Broadband Tunable Absorber Research Articles

Tunable Graphene‐Based Absorber Using Nanoscale Grooved Metal Film at Telecommunication Wavelengths

Graphene‐based absorbers have various modern applications across industries due to their exceptional properties. Some common applications include: thermal management and energy storage. Herein, the design and simulation of a broadband tunable absorber based on graphene with perfect absorption spectra in the near‐infrared region are reported. The proposed structure consists of an MgF2 layer and golden disc surrounded by L‐shaped golden arms placed on single layer of graphene. The structure guarantees polarization‐insensitive (PI) performance under normal incident due to the symmetrical design. The investigation of the PI of the structure reveals almost similar absorption for oblique incident angles up to 55° for TM and up to 60° for TE polarization. The desirable resonance wavelength is achievable by tuning the geometrical parameters. By changing the chemical potential of graphene, the absorption and bandwidth of absorber are controllable. A full width at half maximum of 330 nm is another superiority of this absorber. These considerable aspects of the proposed structure make it practical for varieties of applications such as cloaking, sensing, switching, and so on.

Dual controlled cross-shaped broadband terahertz absorber based on vanadium oxide—liquid crystal metamaterial

A low terahertz broadband tunable absorber was proposed, which composed of vanadium oxide (VO2) film and nematic liquid crystal layer. The simulation results show that the absorption is great than 90% in the frequency range of 0.458–1.1492 THz. The tuning absorber was realized by increasing the temperature to modulate the VO2 transited into metal state. Since the dielectric constant of the nematic liquid crystal can be adjusted by bias voltage, without changing the intensity of absorption, however, a shift in the bandwidth was observed. In addition, the designed structure is insensitive to incident light polarization and still remained high absorption at 60°. The tunable broadband metamaterial absorber can be used for attenuator and energy harvesting.

Dual-band and broadband tunable absorber based on Weyl semimetals

The density of the electric and the magnetic fields reveal the physical mechanisms of the absorption phenomenon. This paper presents perfect dual-band and broadband absorbers formed by Weyl semimetals (WSMs) and dielectric layers above the metallic ground plane. The tunability of absorption frequencies is achieved by changing the chemical potential of WSMs. The influence of structure parameters on dual-band absorption is also investigated. The dual-band absorbers shows absorptivity over 99% and are insensitive to the polarization angle of electromagnetic waves. The broadband absorbers show absorptivity over 80% in the wideband range of 2.49–4.96 THz. This proposed absorber has significant potential in terahertz detection, radar stealth, and biological monitoring.

A design strategy of wide angle, broadband tunable near-infrared absorber

Near infrared absorbers have many applications in the optoelectronic filed. In this study, we design and fabricate two near-infrared broadband tunable absorbers composed of V1-xWxO2/HfO2/Ag layers (the single-layer VO2 absorber) and V1-xWxO2/VO2/HfO2/Ag layer (the double-layer VO2 absorber). The absorption bands with above 90% of the single-layer VO2 absorber and the double-layer VO2 absorber can be tuned from 1366–1766 nm to 834–980 nm and 931–2000 nm to 845–1056 nm by thermally induced VO2 phase transition, respectively. And the two absorbers we fabricated maintained high absorption over a wide range of incident angles. Furthermore, this paper verified that the introduction of a double-layer absorption layer into the absorber structure can effectively broaden the absorption bandwidth of the absorber and increase the absorption strength.

Analyzing broadband tunable metamaterial absorbers by using the symmetry model

In this paper, a broadband tunable absorber based on bulk Dirac semimetal (BDS) in the far-infrared regime is studied. By optimizing the Femi energy and geometric size, the structure can achieve absorption levels greater than 90% in the 8.11-13.94 THz range, with a total thickness of 5.1 µm. Further, the bandwidth of this proposed absorber can be dynamically controlled by changing the Femi energy of the BDS instead of geometry. Meanwhile, the polarization and oblique incident angles in the TE and TM electromagnetic waves are also investigated. Finally, a new symmetry model is adopted to analyze the absorption mechanism, which is the innovation of this paper. This research result may provide potential applications for all types of optical photovoltaic devices and tunable biological chemistry sensors.

Broadband tunable perfect absorber with high absorptivity based on double layer graphene

Due to the problems of low absorptivity and the narrow bandwidth of existing broadband absorbers, a perfect broadband tunable absorber with high absorptivity based on double-layer graphene is proposed in this study with 99% high absorptivity as the reference standard, and its theoretical analysis is performed. The designed absorber consists of complete graphene, upper dielectric material, patterned graphene, lower dielectric material and the gold substrate. Through numerical calculation, the designed absorbing structure can achieve high absorption rate of more than 99% in the range of 2.54–3.70 THz, and has a continuous bandwidth of 1.16 THz. In addition, the absorption range is 52%–100% by changing the Fermi level of the graphene layer. The perfect absorber is symmetrical in rotation center and insensitive to incident angle and polarization. It can be widely used in terahertz switch, modulator design, power acquisition and other related fields.

Broadband tunable absorption based on phase change materials

Tunable absorbers have been the subject of many studies in recent years. However, broadband tunable absorbers, which are promising in many applications such as photovoltaic and daytime radiative cooling systems, have not been extensively explored. In this paper, we propose a 2D periodic circular truncated cones nanostructure based on Ge2Sb2Te5 (GST) for regulating broadband absorption. When the phase of GST changes between crystalline and amorphous, the absorption can be effectively tuned over a broad bandwidth. Numerical results show that the average absorption can reach 0.968 at the crystalline phase of GST, but only 0.020 at the amorphous phase of GST in the wavelength from 8 to 15 μm. In addition, the robustness of our proposed structure to the incident angles of the incident wave is also confirmed. The physical mechanism can be explained by the effective medium theory. The magnetic field at different wavelengths are presented for a more intuitive understanding. We believe the structure proposed in this work is promising in the applications of radiative cooling and thermal camouflage.

Graphene-embedded broadband tunable metamaterial absorber in terahertz band

Numerous studies have been conducted to design terahertz broadband metamaterial absorbers for various applications, such as electromagnetic stealth, photodetection, and broadband communications. It remains a hot research topic to design metamaterial absorbers (MAs) to achieve broadband absorption while maintaining a wide range of tunability. Here, we present a novel design of graphene-embedded metamaterial functioning as a broadband tunable absorber based on the field reinforcement effect and plasmon resonance of graphene. With a stacked configuration, the absorptivity of the MA proposed in this paper can be as high as 90% in a wide range of 1.2 THz. By comparative analysis, we exhibit that the MA shows a relatively wider absorption bandwidth than the one without the embedded graphene, which discloses the significance of integrating graphene layer in our design. The detailed numerical calculations of the surface currents and electric field distributions are presented in this paper to better uncover the physical mechanisms of the broadband and multi-band absorption. Moreover, further numerical calculations show that the designed MA also demonstrates several other excellent properties, such as tunability, polarization insensitivity, incident angle insensitivity and outstanding structural parameters tolerance. The proposed graphene-embedded MA can be used in various promising applications, like smart sensors, broadband absorber and imaging devices.

Terahertz Absorber With Reconfigurable Bandwidth Based on Isotropic Vanadium Dioxide Metasurfaces

The design of a broadband tunable absorber is proposed based on a thin vanadium dioxide metasurface, which is composed of a simple array of vanadium dioxide and a bottom gold film. When the conductivity of vanadium dioxide is equal to 2000 Ω -1 cm -1 , simulated absorptance exceeds 90% with 71% bandwidth from 0.47 to 0.99 THz and full width at half maximum is 98% from 0.354 to 1.036 THz with center frequency of 0.695 THz. Simulated results show that absorptance peak can be tuned from 5% to 100% when the conductivity changes continually from 10 Ω -1 cm -1 to 2000 Ω -1 cm -1 . The designed absorber may have useful applications in terahertz spectrum such as energy harvesting, thermal emitter, and sensing.

Broadband Tunable Metamaterial Absorber Based on U-shaped Ferrite Structure

A broadband tunable metematerial absorber is proposed and demonstrated. As demonstrated in waveguide, the absorber consists of eight U-shaped ferrite particles and a metallic ground plane. These U-shaped ferrites directly act as resonators, and when the incident electromagnetic wave and applied magnetic field are simultaneously acting on the U-shaped ferrite particles, U-shaped ferrites can produce ferromagnetic resonance (FMR). Absorption frequency of the all-ferrite absorber can be tuned by the applied magnetic field and the saturation magnetization. Simulation results show absorption above 70% in the frequency range from 8.55 GHz to 10 GHz under applied magnetic field with H 0 = 2700 Oe. By analysis, we find that the magnetic loss and dielectric loss lead to broadband absorption. The experiment test agrees well with the simulation results under different applied magnetic fields. This work provides an alternative route to realize tunable perfect absorbers with all-ferrite structures. With the artificial design of ferrite materials, the broadband tunable absorber can be designed and well serve in high power environment.

Tunable terahertz wave broadband absorber based on metamaterial

With the increasing scarcity of spectrum resources, terahertz wave technologies have attracted more and more attention in recent decades, and have made tremendous progress. Terahertz wave referring to electromagnetic waves with a frequency in a range of 0.1－10 THz has a wide range of applications in wireless communication, nondestructive imaging and remote sensing. Due to the advantages of high absorption, ultra-thin thickness, frequency selectivity and design flexibility, metamaterial absorbers have attracted more attention in terahertz band. In this paper, two terahertz metamaterial absorbers with different performances are designed which are named “T” terahertz multi-band absorber and “T” terahertz tunable broadband absorber, respectively. The absorbers are both comprised of three layers: metal substrate, matched dielectric layer and surface metamaterial layer. The main structures of these two absorbers are composed of four T-shape Au plates on the top of polyimide dielectric layer and an Au sheet acting as a bottom layer. The only difference between these two absorbers is that the terahertz broadband tunable absorber possesses a square photosensitive silicon in the metamaterial layer. The simulations results show that the terahertz multi-band absorber has six absorption peaks at 2.918, 3.7925, 4.986, 6.966, 7.2685, and 7.4665 THz, with the absorptivity peaks of 95.631%, 99.508%, 96.34%, 94.835%, 96.485%, 94.732%, respectively, and the average absorption rate is 96.26%. Terahertz tunable broadband absorber has the characteristics of broadband absorption. When the conductivity of silicon is 1600 S/m, the absorber reaches its absorption peak at 0.786 THz with the absorptivity of 99.998%, and the frequency bandwidth with the absorption rate exceeding 90% reaches 240 GHz. The more interesting thing is that by changing the conductivity of silicon, the terahertz tunable broadband absorber shows the ability to dynamically control the existence of absorption band and adjust the frequency position of absorption peak. For terahertz tunable broadband absorber, the frequency of absorption peak can be regulated in a bandwidth of about 30 GHz. The terahertz wave absorbers designed in this paper possess rather simple structures, therefore the proposed absorbers are easy to fabricate. Because of these excellent properties, the absorbers may have potential applications in optical switch, optical detection, optical imaging, band-stop devices, and other fields.

Broadband tunable absorber for terahertz waves based on isotropic silicon metasurfaces

A broadband tunable absorber is studied based on the silicon metasurface at terahertz frequencies. By tuning the conductivity of silicon, absorptance is more than 90% from 0.497 THz to 1.045 THz with central frequency of 0.771 THz when the conductivity is equal to 2500S/m. Simulated results show that absorptance peak can be modulated from 1% to 100% when the conductivity continuously changes from 0S/m to2500S/m. The central-symmetry structure leads to polarization independence. Our design may be used as optoelectronic modulator, tunable detector, and terahertz switch.

Polarization-sensitive tunable absorber in visible and near-infrared regimes

A broadband tunable absorber is designed and fabricated. The tunable absorber is comprised of a dielectric-metal-dielectric multilayer and plasmonic grating. A large size of tunable absorber device is fabricated by nano-imprinting method. The experimental results show that over 90% absorption can be achieved within visible and near-infrared regimes. Moreover, the high absorption can be controlled by changing the polarization of incident light. This polarization-sensitive tunable absorber can have practical applications such as high-efficiency polarization detectors and transmissive polarizer.

All-Dielectric Wet Sandy Soil Broadband Tunable Absorber Based on Interference Theory

A broadband tunable absorber based on the periodic structure array (PSA) of wet sandy soil (WSS) is investigated numerically, experimentally and theoretically at microwave frequencies. Simulated and measured results show that the simple PSA absorber with the water content of 30% reaches over 90% absorption in the 10.92-GHz wideband ranging from 6.24 GHz to 17.12 GHz. The absorption mechanism is illustrated by electric field (Ez), magnetic field and current distributions. The high absorption in the wide-frequency region originates from the mixtures of the electric and magnetic resonance. Further simulated results reveal that the absorption performance can be adjusted by changing widths, thicknesses and water contents of WSS. The high absorptivity can remain unchanged when the incident angle for both transverse electric and transverse magnetic modes goes up to 60°. The interference theory is used to analyze the physical mechanism of broadband absorption under different water contents. It provides a convenient and cheap path for designing a broadband absorber.

Broadband tunable graphene-based metamaterial absorber

This paper proposes a graphene-based broadband tunable absorber with over 90% absorption and is polarization insensitive at mid-infrared frequencies. The proposed absorber consists of a periodic array of a dual electric LC (ELC) metamaterial unit fabricated on a multilayer structure composed of Au/BaF2/graphene materials from the bottom to the top. In the proposed structure, interaction between the dual ELC unit and the graphene sheet generates three close resonant frequencies, thus leading to a broadband absorption from 25.08THz to 39.56THz. By varying graphene’s chemical potential, wide absorption bandwidth can be flexibly tuned. Due to the approximate symmetry of the structure, the proposed absorber demonstrates polarization-insensitive and wide-angle characteristics. Simulation results demonstrate that the absorption efficiency of the proposed structure can be as high as more than 90% from 25.08 THz to 44.81THz with variation of the graphene’s chemical potential from 0.2eV to 0.8eV.

Intensity tunable infrared broadband absorbers based on VO2 phase transition using planar layered thin films.

Plasmonic and metamaterial based nano/micro-structured materials enable spectrally selective resonant absorption, where the resonant bandwidth and absorption intensity can be engineered by controlling the size and geometry of nanostructures. Here, we demonstrate a simple, lithography-free approach for obtaining a resonant and dynamically tunable broadband absorber based on vanadium dioxide (VO2) phase transition. Using planar layered thin film structures, where top layer is chosen to be an ultrathin (20 nm) VO2 film, we demonstrate broadband IR light absorption tuning (from ~90% to ~30% in measured absorption) over the entire mid-wavelength infrared spectrum. Our numerical and experimental results indicate that the bandwidth of the absorption bands can be controlled by changing the dielectric spacer layer thickness. Broadband tunable absorbers can find applications in absorption filters, thermal emitters, thermophotovoltaics and sensing.

A Novel Absorber With Tunable Bandwidth Based on Graphene

A design of absorber using two-dimensional (2-D) periodic arrays of double-square split loops and resistive strips printed on grounded dielectric substrate is investigated in this letter. Unlike the traditional structure, graphene sheets are proposed for thin absorbing structures at microwave frequencies. The analysis of absorption properties is based on the dynamic model of graphene, which takes into account the surface impedance of graphene layer. Both narrowband and broadband tunable absorbers can be demonstrated with the same structure by tuning the conductivity of graphene. Furthermore, the equivalent circuit method (ECM) is used to introduce the working principles of the proposed absorber. In addition, the absorber shows relatively stable performance with different oblique incidence angles.

A novel structure for tunable terahertz absorber based on graphene

Graphene can be used as a platform for tunable absorbers for its tunability of conductivity. In this paper, we proposed an "uneven dielectric slab structure" for the terahertz (THz) tunable absorber based on graphene. The absorber consists of graphene-dielectric stacks and an electric conductor layer, which is easy to fabricate in the manufacturing technique. Fine tuning of the absorption resonances can be conveniently achieved by adjusting the bias voltage. Both narrowband and broadband tunable absorbers made of this structure are demonstrated without using a patterned graphene. In addition, this type of graphene-based absorber exhibits stable resonances with a wide range angles of obliquely incident electromagnetic waves.

Graphene metamaterials based tunable terahertz absorber: effective surface conductivity approach

In this paper we present the efficient design of functional thin-film metamaterial devices with the effective surface conductivity approach. As an example, we demonstrate a graphene based perfect absorber. After formulating the requirements to the perfect absorber in terms of surface conductivity we investigate the properties of graphene wire medium and graphene fishnet metamaterials and demonstrate both narrowband and broadband tunable absorbers.