Abstract-Tunable mantle cloaking utilizing graphene metasurface for terahertz sensing applications

Zahra Hamzavi-Zarghani, Alireza Yahaghi, Ladislau Matekovits,  Ali Farmani

 (a) Structure of graphene strips, (b) A dielectric cylinder coated by graphene strips.
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-24-34824

Design of sensors which are able to probe electromagnetic radiation with larger cross section and at the same time with having negligible perturbation in measurement has attracted significant attention. For this purpose, scattering-cancellation sensors or cloaking sensors are introduced. However, tunable cloaking sensors are very challenging. In this regards, here, a metasurface based on graphene strips is proposed to cloak a dielectric cylinder under illumination of TEz and TMz polarized incident waves in terahertz range. According to the in plane effective surface impedance tensor for the considered metasurface and the required surface impedance for achieving invisibility under TE and TM polarized impinging waves, the geometrical parameters of the covering structure and characteristics of graphene are obtained. Numerical simulations show radar cross section reduction for both TE and TM polarizations. Furthermore, the introduced metasurface is able to cloak the cylinder for incoming waves with circular polarization. In addition, it is shown that by properly adjusting the chemical potential of graphene, the required surface impedance to have cloaking for the two polarizations in other frequencies can also be achieved, which results in a tunable dual polarized cloaking. The proposed structure provides 2-11 dB reduction in scattering strength relative to the uncloaked configuration for 0.3eV variation of graphene chemical potential.

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

Abstract-Wideband circular polarization converter based on graphene metasurface at terahertz frequencies

Chongyun Wang,  Ming Chen,  Houquan Liu,  Chuanxin Teng, Hongchang Deng,  Libo Yuan

https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-58/issue-4/043106/Wideband-circular-polarization-converter-based-on-graphene-metasurface-at-terahertz/10.1117/1.OE.58.4.043106.short?SSO=1

Linear-to-circular polarization converters are widely used in optical and microwave systems, but the polarization devices of traditional materials are untunable, and devices made of graphene materials can overcome this disadvantage. A circular polarization converter based on graphene metasurface is designed, whose properties are tunable over a broad range at terahertz frequencies. With appropriate structural parameters, simulations show that the axial ratio of reflected electromagnetic wave of the proposed device is lower than 3 dB in the frequency band of 2.25 to 2.475 THz, which means the linearly incident polarization can be converted to the circular polarization wave. The proposed design can also work when the electromagnetic wave is oblique incidence up to 40 deg with a high polarization conversion ratio. Moreover, the operating frequency band can be arbitrarily adjusted by applying a bias voltage.

© 2019 Society of Photo-Optical Instrumentation Engineers (SPIE) 0091-3286/2019/$25.00 © 2019 SPIE

Abstract-Graphene aperture-based metalens for dynamic focusing of terahertz waves

Pei Ding, Yan Li, Li Shao, Ximin Tian, Junqiao Wang, and Chunzhen Fan

Fig. 3 (a) Phase distributions 𝑝(𝑥)$p(x)$of the metalens with a focal length of F = 150 um (p1) and 190 um (p2), respectively, at the incident frequency of f0 = 5 THz. The phase difference between the two lenses (𝑝2−𝑝1$p_2-p_1$) along the x axis is also illustrated. (b) E-field intensity distribution of the reflection field on the x-z plane for the metalens with a designed focal length F = 150 um at f0 = 5 THz for Ef = 1.0 eV. The simulated focal length is 140 um. (c) E-field intensity distribution of the reflected wave along the z-axis for different Ef. The simulated focal lengths remain unchanged. (d) The corresponding E-field intensity distributions of the reflected wave on the focal plane (z = 140 um) for different Ef.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-21-28038

We theoretically study a tunable reflective focusing lens, based on graphene metasurface, which consists of rectangle aperture array. Dynamic control of either the focal intensity or focal length for terahertz circular polarized waves can be achieved by uniformly tuning the graphene Fermi energy. We demonstrate the graphene apertures with the same geometry; however, spatially varying orientations can only control the focal intensity. To change the focal length, the spatially varying aperture lengths are also required. A comparative study between the metalenses, which generate only geometric or both gradient and geometric phase changes, has shown that the apertures’ spatially varying length distribution is the key factor for determining the modulation level, rather than the focal length’s modulation range. This kind of metalens provides tunable, high-efficiency, broadband, and wide-angle off-axis focusing, thereby offering great application potential in lightweight and integrated terahertz devices.

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