Abstract-Metamaterial absorber with independently tunable amplitude and frequency in the terahertz regime

Xin Huang, Fan Yang, Bing Gao, Qi Yang, Jiamin Wu, and Wei He

 Independently tunable metamaterials absorber for amplitude and frequency with graphene and STO layer. (a) Top view of the unit cell. (b) Schematic representation and geometrical characters of the unit cell. (c) Schematic representation of the proposed absorber, which consist of a graphene sheet, two dielectric layers and one metallic background layer, with the terahertz wave along the z-axis. The geometrical parameters are given.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-18-25902

A tunable metamaterial absorber is proposed in the terahertz regime. The amplitude and center frequency of the absorber can be tuned independently. Owing to the effective combination of graphene and strontium titanate (STO) in one metamaterial structure, the tunable properties of the amplitude and center frequency are implemented. The amplitude can be tuned by adjusting the chemical potential of graphene sheet, and center frequency can get a shift through temperature changes in the STO material. In a full-wave numerical simulation, the amplitude of the absorber can be tuned from approximately 100% to 35% with a fixed center frequency when chemical potential varies from 0.7 eV to 0.0 eV. The center frequency of the absorber can shift from 0.43 THz to 0.3 THz when temperature changes from 400 K to 200 K. The complex surface impedance of the graphene and permittivity of STO material in this research range are thoroughly examined, and the independently tunable mechanism of the absorber is explored by elucidating the electric field distribution. The influence of the oblique incidence of electromagnetic wave to the absorber is studied. The absorber can be scalable to the infrared and visible frequencies and demonstrates promising application on tunable sensors, filters, and photovoltaic devices.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract- A Dual-Band Tunable Metamaterial Near-Unity Absorber Composed of Periodic Cross and Disk Graphene Arrays

Jianguo Zhang,  Jinping Tian,  Lu Li,

https://ieeexplore.ieee.org/document/8315442/

A three-dimensional dual-band perfect absorber in the THz range (3-10 THz) is theoretically investigated. The absorber is composed of periodically placed cross-and disk-shaped graphene arrays on the top of a gold layer separated by a thick SiO2 dielectric spacer. The simulated results show two absorption peaks with near-unity absorbance (99.923% and 99.601%) at wavelengths 43.747 μm and 69.94 μm, respectively. Also, the absorber is insensitive to the polarization of the incident light and has a good tolerance to the incident angle whether it is TE or TM waves. Moreover, the peak wavelengths of the absorber can be flexibly modulated by varying the Fermi level μC of graphene while no need to refabricate the structure. This paper provides a new perspective for the design of graphene-based tunable multiband perfect THz absorbers, but not limited to THz absorbers, and may also be used in other THz graphene-based photonic devices.

Abstract-Design of a size-efficient tunable metamaterial absorber based on leaf-shaped cell at near-infrared regions

Hailong Huang, Hu Xia, Wenke Xie,  Zhibo Guo, Hongjian Li,

https://www.sciencedirect.com/science/article/pii/S2211379718305692

A size-efficient tunable metamaterial absorber (MA) composed of metallic leaf-shaped cell, graphene layer, silicon substrate, and bottom metal film is investigated theoretically and numerically at near-infrared (NIR) regions. Simulation results reveal that the single-band high absorption of 91.9% is obtained at 1268.7 nm. Further results show that the single-band can be simply changed into dual-band high absorption by varying the geometric parameters of top metallic layer at same wavelength regions, yielding two high absorption coefficients of 96.6% and 95.3% at the wavelengths of 1158.7 nm and 1323.6 nm, respectively. And the effect of related geometric parameter on dual-band absorption intensities is also investigated to obtain the optimized one. The peak wavelength can be tuned via modifying the Fermi energy of the graphene layer through controlling the external gate voltage. The work shows that the proposed strategy can be applied to other design of the dual-band structure at infrared regions.

Abstract-Frequency tunable metamaterial absorber at deep-subwavelength scale

Ben-Xin Wang, Xiang Zhai, Gui-Zhen Wang, Wei-Qing Huang, and Ling-Ling Wang  »View Author Affiliations

http://www.opticsinfobase.org/ome/abstract.cfm?uri=ome-5-2-227

Optical Materials Express, Vol. 5, Issue 2, pp. 227-235 (2015)

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Metamaterial-based absorbers utilize the intrinsic loss, with the aid of appropriate structure design, to achieve near unity absorption at a certain frequency. The frequency of the reported absorbers is usually fixed and operates over a limited bandwidth, which greatly hampers their practical applications. Active or dynamic control over their resonance frequency is urgently necessary. Herein, we theoretically present a novel frequency tunable terahertz metamaterial absorber formed by a square metallic patch and a ground plane separated by a strontium titanate dielectric layer. Up to 80.2% frequency tuning is obtained by changing the temperature of the absorber, and there is very little variation in the strength of the absorption. The frequency shift is attributed to the temperature-dependent refractive index of the dielectric layer. Furthermore, the ratio between the lattice period and the resonance wavelength is close to 1/36 at 0.111 THz, which is smaller than the previously reported results. The proposed absorber has potential applications in detection, sensors, and selective thermal emitters.

© 2014 Optical Society of America