Abstract-Graphene-Assisted Narrow Bandwidth Dual-Band Tunable Terahertz Metamaterial Absorber

Dexian Yan,  Miao Meng,  Jiusheng Li, Xiangjun Li
,

https://www.frontiersin.org/articles/10.3389/fphy.2020.00306/full

A tunable graphene terahertz metamaterial absorber is designed by treating a monolayer continuous dumbbell-shaped structure graphene layer, which can simultaneously realize the narrow bandwidth and dual-band absorption with transverse magnetic (TM) polarization and wide incident angle operation. Two pronounced absorption peaks are caused by the novel toroidal dipole phenomenon and magnetic plasmon polariton. By optimizing the geometry parameters, the relative narrow bandwidths of the two absorption peaks are 26.4 and 23.5 GHz at frequencies of 0.2242 THz and 0.5302 THz, respectively, with the absorption rate above 99.6%. Since the continuous dumbbell-shaped graphene structure is treated in the absorber, a more convenient way to realize the tuning ability by treating a bias voltage compared to the absorbers with discrete graphene structures. The designed device can work at a wide incident angles (up to 80°) under TM polarization with the absorption above 88% at low frequency. The simulation results are basically in good agreement with the results of the equivalent circuit model. This work offers huge potential applications in terahertz imaging, detecting and sensing, especially in the 6G communication systems.

Abstract-Tunable terahertz broadband absorber based on a composite structure of graphene multilayer and silicon strip array

Zhaocheng Zhai,  Le Zhang,  Xiangjun Li,  Sanshui Xiao,




https://www.sciencedirect.com/science/article/abs/pii/S0030401818307983

We propose a terahertz broadband absorber composed by silicon strips with continuous graphene on top of a metal mirror. The simulation results show that under the combined effect of the Fabry–Perot resonance and the dipole mode oscillation excited in the silicon strip array interacting with graphene, this structure can achieve an ultra-wide absorption band from 0.73 to 1.95 THz with absorbance of 90%. By changing the size of the silicon strips or the Fermi level of graphene, the working band of the absorber can be tuned.

Abstract-Integrated Terahertz Surface Plasmon Resonance on Polyvinylidene Fluoride Layer for the Profiling of Fluid Reflectance Spectra

• Xiangjun Li, 
• Jian Song
• , John X. J. Zhang
• 
  
• http://link.springer.com/article/10.1007/s11468-015-0147-4
• 
  
• We design terahertz (THz) surface-plasmon-resonance (SPR) sensors using a ferroelectric polyvinylidene fluoride (PVDF) thin layer for biological sensing. The reflectivity properties based on SPR are described using transfer matrix method (TMM) and numerically simulated using finite-difference time domain (FDTD) method. The sensing characteristics of the structure are systematically analyzed through the examination of the reflectivity spectrum. The results reveal that the pronounced SPR resonance peak has quasi-linear relationship with the refractive index variation of the material under investigation. Through analyzing and optimizing the structural parameters of the THz SPR sensor, we achieved the theoretical value of the refractive index detection sensitivity as high as 0.393 THz/unit change of refractive index (RIU) for a 20-μm-thick liquid sample with a 10-μm PVDF layer. This work shows great promise toward realizing a THz SPR sensor with high sensitivity for identifying the signatures of biological fluid sample.