Optically tunable metamaterial perfect absorber on highly flexible substrate

This paper reports our recent progress on a highly flexible dynamic perfect absorber at terahertz (THz) frequencies. Metamaterial unit cells were patterned on thin GaAs patches, which were fashioned in an array on a 5μm polyimide substrate via transfer printing technique, and the backside of the substrate was coated with gold film as ground plane. Optical-pump THz-probe reflection measurements show that the absorptivity at resonance frequency of 1.58THz can be tuned up to 57% through photo-excitation of free carriers in GaAs layers in presence of 800nm pump beam. Our flexible tunable MM perfect absorber exhibits potential applications in energy harvesting, imaging and stealth coating.

We present the design, characterization, theoretical and experimental verification of a tunable perfect metamaterial absorber (MA) based electromagnetic (EM) energy harvesting and sensor application. We have used the golden ratio while determining the dimensions allowing a simple configuration and an easy fabrication for the proposed structure. We have examined and analyzed the perfect absorption (both numerically and experimentally) and EM energy harvesting (numerically) behaviors of the proposed structure in order to verify and show the characteristics of the model. It is shown that 99.9 % maximum absorption rate is achieved at 6.78 GHz, and MA structure can be used as an EM energy collector. In order to support the numerical study, an experimental study is realized. We have then developed a sensor application of the proposed MA structure and observed the effects of the harvesting system. Perfect MA sensor based EM energy harvesting system is successfully achieved.

In this paper, we propose a frequency tunable metamaterial perfect absorber in the THz region based on graphene. The unit cell consists of a periodically patterned graphene cross-ring resonator and a gold film separated by a dielectric spacer. The simulation results demonstrate that the maximum value of absorption is 99.9% at 4.7 THz. By controlling the graphene conductivity, the frequency tunable characteristics can be achieved in this metamaterial absorber. When varying the diameter of the ring or the length of the cross, we find that resonance absorption frequency will significantly shifts. Moreover, the metamaterial absorber possesses the polarization-insensitive and a wide range of the incident angles up to 70° for both TE and TM polarization. Our absorber can be used in some practical applications due to its excellent absorption and simple structure.

Numerical investigation of a tunable metamaterial perfect absorber consisting of two-intersecting graphene nanoring arrays

The tunable narrow band perfect metamaterial absorber (PMA) based on guided-mode resonance (GMR) for the visible spectral region is proposed. The PMA is composed of a one-dimensional grating layer, two waveguide layers and an Ag substrate. Tunable narrow band PMAs are designed using rigorous coupled-wave analysis by comparing the GMR effects for the filters and absorbers. Afterwards, two tunable PMA samples are fabricated through thin-film deposition and ultraviolet lithographic patterning. Finally, the reflection spectra of the fabricated PMA samples are measured. The absorption spectra obtained by subtracting the measured reflection spectra from 1 are consistent with the theory.

In this paper, a dual-band perfect metamaterial absorber based on graphene is proposed in the terahertz region. The metamaterial absorber consists of two sizes of graphene disks and a gold film separated by a dielectric spacer in a unit cell. The numerical results demonstrate that the dual-band perfect absorption can be achieved by the superposition of the specific absorption peaks induced by different disks. The resonance frequency can be tuned via controlling the graphene conductivity and the sizes of the disks. The metamaterial absorber can achieve selectively frequency tunability and it can tune each resonance independently. And the dual-band absorption will not be changed when the small disks move along the diagonal within the range of our research. In addition, owing to the symmetry of the structure, the absorber is insensitive to polarization and can keep a high absorptivity with a wide angle. The flexible and simple design makes it possible for our proposed single-layer graphene absorber to be applied in many metamaterial fields, such as sensing, detecting, and cloaking objects.

Photoexcited broadband blueshift tunable perfect terahertz metamaterial absorber

High sensitivity dual-band perfect plasmon absorber based on graphene split-ring-resonator

In this paper, a tunable terahertz metamaterial absorber is proposed, and the resonant frequency can be controlled by the variation of temperature and the permittivity. For the top layer of the absorber, which consist of a split ring resonator (SRR), and substrate strontium titanate dielectric layer was filled into the two slits of the SRR. The simulated results show that the absorber has a distinct absorption peak at f = 1.26 THz for T = 300 K, which is close to the calculated resonant frequency fm ≈ 1.268 THz, and the absorptivity can achieve 99.93%. To explain the physical mechanism of the absorption, the relative impedance, the surface current and equivalent LC-circuit are analyzed, which could further demonstrate that the magnetic resonant play a major role for the absorption. Moreover, the resonant point will produce a blue-shift with the increase of the temperature, and a red-shift will be appeared with the varying of the permittivity, so that the tunable metamaterial absorber has an application in sensing.

Tunable perfect absorber and multifunctional logic device based on graphene metamaterial

Tunable quad-band perfect metamaterial absorber on the basis of monolayer graphene pattern and its sensing application

In this paper, we have shown that perfect absorption at terahertz frequencies can be achieved by using a composite structure where graphene is coated on one-dimensional photonic crystal (1DPC) separated by a dielectric. Due to the excitation of optical Tamm states (OTSs) at the interface between the graphene and 1DPC, a strong absorption phenomenon occurs induced by the coupling of the incident light and OTSs. Although the perfect absorption produced by a metal–distributed Bragg reflector structure has been researched extensively, it is generally at a fixed frequency and not tunable. Here, we show that the perfect absorption at terahertz frequency not only can be tuned to different frequencies but also exhibits a high absorption over a wide angle range. In addition, the absorption of the proposed structure is insensitive to the polarization, and multichannel absorption can be realized by controlling the thickness of the top layer.

A graphene-based tunable dual-band metamaterial absorber which is polarization insensitive is numerically proposed at mid-infrared frequencies. In numerical simulation the metamaterial absorber exhibits two absorption peaks at the resonance wavelengths of 6.246 μm and 6.837 μm when the Fermi level of graphene is fixed at 0.6 eV. Absorption spectra at different Fermi levels of graphene are displayed and tuning functions are discussed in detail. Both the resonance wavelengths of the absorber blue shift with the increase in Fermi level of graphene. Moreover, the surface current distributions on the gold resonator and ground plane at the two resonance wavelengths are simulated to deeply understand the physical mechanism of resonance absorption.

Recently, metamaterial absorber has attracted considerable attention because of a broad range potential application to electromagnetic stealth, electromagnetic detectors, and electromagnetic communication. And to solve the problem which traditional metamaterial absorbers can only operate at a fixed frequency or within a limited frequency range, the tunable metamaterial absorbers attract more and more attention. But the previous metamaterial absorber can only achieve adjustable absorption in a single frequency band, which has not met people’s increasingly higher requirements for practical applications. To solve this problem, a multispectral tunable metamaterial absorber was designed by combining VO2 and metamaterial absorbers using the phase transition characteristics. In this paper, the absorption rate curve in the terahertz band and infrared band had been simulated by CST Microwave Studio software. And the simulation results showed that the metamaterial exhibited meta-absorption in the terahertz band when the temperature was set to high temperature (80°C) and the VO2 behaved as a metal phase in this temperature. However, the simulation results showed that the metamaterial exhibited meta-absorption in the infrared band when the temperature was set to low temperature (40°C) and the VO2 behaved as an insulator phase. Furthermore, the absorptive properties of the metamaterial absorber had been simulated under different lengths of VO2-cross when the VO2 behaved as a metal phase and under different lengths of metal-cross when the VO2 behaved as an insulator phase. Finally, the mechanism of electromagnetic absorption and multispectral tunable were discussion by simulating and analyzing the surface current distribution and electric field of the metamaterial absorber. The results showed that the metamaterial absorber can realize meta-absorption in the terahertz band or infrared band by changing the temperature which have potential application values in the fields of multispectral stealth, multispectral detection and multispectral communication.

An tunable ultra-wideband metamaterial absorber (MMA) in the THz regions based on the phase transition of VO2 film was presented in this paper. Firstly, we simulated the absorption of MMA at different temperature, the results showed that the absorption was up to 90% from 5.464THz to 10THz with the bandwidth of 4.536THz when the temperature was 60°C and altering the designed MMA ’ s temperature can realize its amplitude tunable property. Secondly, its physical mechanism of electromagnetic absorption and amplitude adjustment were explored by monitoring the surface current and electric field. We proved that the MMA was insensitive to the polarization, incident angle and thickness of VO2 film at last.