Abstract-Reflective liquid crystal terahertz phase shifter with tuning range of over 360°

Jun Yang, Chenggang Cai,  Zhiping Yin, Tianyu Xia, Shuaicheng Jing,   Hongbo Lu, Guangsheng Deng

https://ieeexplore.ieee.org/document/8402281/

This study presents the design and experiment of a terahertz reflective phase shifter based on liquid crystal. The proposed voltage-tunable phase shifter takes advantage of the variable permittivity of the liquid crystal, adjusted by an external electric field, providing tunable reflective phase shift of terahertz (THz) waves. We analysed the performance of this phase shifter using a simple isotropic and homogeneous model considering the angle of incidence. The phase variation was achieved in a range greater than 360° and frequencies from 349 to 361 GHz. An array constituted of 900 patch elements was fabricated using the photolithographic process. It provided tunable phase range of 350° over the frequency range of 353.5-359.3 GHz at 40 V, where a maximum phase shift 362.6° was achieved at 357 GHz. The LC dielectric constant was obtained by fitting the computed reflectance spectrum to the measured result. We compared accurate model, considering both inhomogeneity and anisotropy of the liquid crystal, with the simplified model. In addition, the differences were analysed between the measurements, accurate and conventional model. The results show the liquid crystal phase shifter is great for beam scanning antenna array in THz.

Abstract-Antireflection self-reference method based on ultrathin metallic nanofilms for improving terahertz reflection spectroscopy

Weien Lai, Haibing Cao, Jun Yang, Guangsheng Deng, Zhiping Yin, Qian Zhang, Beatriz Pelaz, and Pablo del Pino

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-15-19470

We present the potential of an antireflection self-reference method based on ultra-thin tantalum nitride (TaN) nanofilms for improving terahertz (THz) reflection spectroscopy. The antireflection self-reference method is proposed to eliminate mutual interference caused by unwanted reflections, which significantly interferes with the important reflection from the actual sample in THz reflection measurement. The antireflection self-reference model was investigated using a wave-impedance matching approach, and the theoretical model was verified in experimental studies. We experimentally demonstrated this antireflection self-reference method can completely eliminate the effect of mutual interference, accurately recover the actual sample’s reflection and improve THz reflection spectroscopy. Our method paves the way to implement a straightforward, accurate and efficient approach to investigate THz properties of the liquids and biological samples.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-A Tunable Polarization-Dependent Terahertz Metamaterial Absorber Based on Liquid Crystal

Guangsheng Deng, Yujiao Lu, Zhiping Yin,  Weien Lai, Hongbo Lu,  Jun Yang, Aifeng Yang, Yang Ye, Dayong Liu, Baihong Chi,

http://www.mdpi.com/2079-9292/7/3/27

In this paper, a tunable polarization-dependent terahertz (THz) metamaterial absorber based on liquid crystal (LC) is presented. The measurement results show that absorption peak is at 239.5 GHz for a TE-polarized wave and 306.6 GHz for a TM-polarized wave, without exerting the bias voltage on the LC layer. An increase in bias voltage affects the orientation of LC molecules and causes redshifted resonant frequencies. By adjusting the bias voltage from 0 to 10 V, frequency tunabilities of 4.7% and 4.1% for TE- and TM-polarized waves, respectively, were experimentally demonstrated. Surface current and power loss distribution was analyzed to explain the physical mechanism of the absorber, while the absorption dependence on geometrical parameters and incident angles was also studied in detail. According to the obtained results, the proposed absorber is shown here to be capable of achieving tunable polarization-dependent absorption, and to have potential application in terahertz polarization imaging, terahertz sensing, and polarization multiplexing

Abstract-Electrically tunable terahertz dual-band metamaterial absorber based on a liquid crystal

Zhiping Yin,  Yujiao Lu,  Tianyu Xia,  Weien Lai,  Jun Yang,  Hongbo Lua,  Guangsheng Deng,

http://pubs.rsc.org/en/content/articlelanding/2018/ra/c7ra13047c#!divAbstract

In this paper, a liquid crystal (LC) based tunable metamaterial absorber with dual-band absorption is presented. The proposed absorber is analysed both numerically and experimentally. The analysis shows that the two absorption peaks, originating from the new resonant structure, are experimentally detected at 269.8 GHz and 301.4 GHz when no bias voltage is applied to the LC layer. In order to understand the absorption mechanisms, simulation results for the surface current and power loss distributions are presented. Since liquid crystals are used as the dielectric layer to realize the electrically tunable absorber, a frequency tunability of 2.45% and 3.65% for the two absorption peaks is experimentally demonstrated by changing the bias voltage of the LC layer from 0 V to 12 V. Furthermore, the absorber is polarization independent and a high absorption for a wide range of oblique incidence is achieved. The designed absorber provides a way forward for the realization of tunable metamaterial devices that can be applied in multi-band detection and imaging.

Abstract-Graphene-based tunable polarization sensitive terahertz metamaterial absorber

• Guangsheng Deng, 
• Ping Chen, 
• Jun Yang, 
• Zhiping Yin, 
• Longzhen Qiu

• Academy of Photoelectric Technology, Hefei University of Technology, Hefei 230009, China

Received 2 February 2016, Revised 4 May 2016, Accepted 27 May 2016, Available online 9 June 2016

http://www.sciencedirect.com/science/article/pii/S0030401816304680

A tunable metamaterial absorber composed of a metal ground plane, a SiO₂ dielectric spacer, a graphene layer and a metal pattern layer, which is polarization sensitive is numerically proposed at terahertz (THz) frequencies. Our calculated results show that when the Fermi level of graphene is fixed at 0.7 eV, the absorptivities for x-polarized wave are about 0.985 at 6.42 THz, and 0.991 at 8.37 THz, respectively, while the absorptivity for y-polarized wave is about 0.99 at 7.22 THz. Moreover, the calculated electric field and surface current distributions, along with power loss distributions enable us to deeply understand the physical mechanism of resonance absorption. More importantly, absorption spectra at different Fermi levels of graphene and different incident angles are displayed and tuning functions are discussed in detail. This work may provide a further step in the development of potential applications based on metamaterial absorber, such as THz polarization imaging, THz sensing and polarization multiplexing.