We present a simple design of a broadband tunable metamaterial absorber (MMA) in the terahertz (THz) region, which consists of a single layer complementary gammadion-shaped (CGS) graphene sheet and a polydimethylsiloxane (PDMS) dielectric substrate placed on a continuous metal film. The Fermi energy level (E_f) of the graphene can be modulated dynamically by the applied DC bias voltage, which enables us to electrically control the absorption performance of the proposed MMA flexibly. When E_f = 0.8 eV, the relative bandwidth of the proposed MMA, which represents the frequency region of absorption beyond 90%, can reaches its maximal value of 72.1%. Simulated electric field distributions reveal that the broadband absorption mainly originates from the excitation of surface plasmon polaritons (SPPs) on the CGS graphene sheet. Furthermore, the proposed MMA is polarization-insensitive and has wide angles for both transverse-electric (TE) and transverse-magnetic (TM) waves in the broadband frequency range. The broadband absorption capacity of the designed MMA can be effectively adjusted by varying the Fermi energy level of graphene. Lastly, the absorbance of the MMA can be adjusted from 42% to 99.1% by changing the E_f from 0 eV to 0.8 eV, which is in agreement with the theoretical calculation by using the interference 41theory. Due to its simple structure and flexible tunability, the proposed MMA has potential application prospects in tunable filtering, modulators, sensing, and other multispectral devices.

A narrow-band metasurface absorber (MSA) based on InSb micro-cylinder arrays has been proposed and investigated numerically, which could be believed to be applicable for both temperature and refractive index (RI) sensing in terahertz (THz) region. Distinct from previous designs, the narrow-band MSA is only consisted of a sub-wavelength periodic micro-cylinder array based on InSb material possessing an extremely thermosensitive relative permittivity which varies with the external environment temperature, and a gold ground-plane deposited on a glass substrate. Numerical simulation results indicate that the proposed MSA can achieve an absorbance of 99.9% at 1.8985 THz and the corresponding Q-factor is about 120.9 at room temperature (300 K). It is inferred that the narrow-band perfect absorption of the MSA could be contributed to the surface plasmon polariton (SPP) resonance mode excitation. Furthermore, the absorption property of the designed MSA is found to be highly sensitive to the RI value variations of the surrounding mediums and fluctuations of external environment temperature. Thus, the proposed MSA can be not only operated as a temperature sensor with a sensitivity of 2.13 GHz/K, but also a RI sensor with a sensitivity of 960 GHz/RIU (refractive index unit). Due to its high sensing performance, it can be believed that the narrow-band MSA has great potential applications in chemical, biological or other optoelectronic related areas.

In this paper, a dual-band and high-efficiency circular polarization (CP) convertor based on anisotropic metamaterial (AMM) was proposed and investigated in microwave region. The proposed AMM based CP convertor is composed of a sub-wavelength metal grating sandwiched with bi-layered disk-split-ring (DSR) structure array, which can convert the normal incident CP wave to its orthogonal one around two adjacent frequency ranges. Based on the intrinsic anisotropic and Fabry-Perot-like cavity-enhanced effect, of, a high CP conversion efficiency can be achieved by applying the proposed AMM. Numerical simulation results indicate that the cross-polarization transmission coefficients can achieve maximum values of 0.84 at 4.5 GHz, and 0.92 at 7.9 GHz, respectively, which is in well agreement with experiment. In addition, the measured CP conversion efficiency is beyond 99 % at resonance frequencies. The mechanism of the CP conversion properties can be explained by the electromagnetic (EM) interference model and the simulated electrical field distribution. Due to its excellent polarization conversion properties, the proposed CP convertor based on AMM structure shows potential application in such as radar, remote sensing, and satellite communication.

A simple design of triple-band perfect light absorber (PLA) based on hybrid metasurface in visible region has been presented in this work, which turns out to be applicable for refractive index (RI) sensing. Distinct from previous designs, the proposed hybrid metasurface for visible PLA is only consisted of periodic silicon cross nanostructure arrays and gold substrate. The periodic silicon cross arrays deposited on the gold substrate contribute to excite the guided modes under the normal incident light illumination. According to the simulation results, it can be found that three perfect absorption peaks of 98.1%, 98.7%, and 99.6% which are located at 402.5 THz, 429.5 THz, and 471.5 THz, respectively, have been clearly observed in PLA. This triple-band perfect absorption effect could be attributed to the intrinsic loss of silicon material originated from the guided mode excitations caused by the standing waves of different orders. It has been confirmed that the perfect absorption properties of the PLA can be easily regulated by changing the geometric parameters of the unit-cell nanostructure. Furthermore, the designed PLA served as a RI sensor can achieve sensitivity of about 25.3, 41.3, and 31.9 THz /refractive index unit (RIU). It can be believed that the proposed design of PLA for RI sensing would provide great potential applications in sensing, detecting, the enhanced visible spectroscopy, etc.