Abstract-A dynamically tunable terahertz metamaterial absorber based on an electrostatic MEMS actuator and electrical dipole resonator array

Fangrong Hu, Ningning Xu, Weiming Wang, Yue'e Wang, Wentao Zhang,  Jiaguang Han, Weili Zhang

https://iopscience.iop.org/article/10.1088/0960-1317/26/2/025006/meta

We experimentally demonstrate a dynamically tunable terahertz (THz) metamaterial absorber based on an electrostatic microelectromechanical systems (MEMS) actuator and electrical dipole resonator array. The absorption of the THz wave is mainly a result of the electrical dipole resonance, which shows a tunable performance on demand. By preforming the finite integral technique, we discovered that the central absorption frequency and the amplitude can be simultaneously tuned by the applied voltage U. Characterized by a white light interferometer and a THz time domain spectroscopy system, our THz absorber is measured to show a modulation of the central frequency and the amplitude to about 10% and 20%, respectively. The experimental results show good agreement with the simulation. This dynamically tunable absorber has potential applications on THz filters, modulators and controllers.

Abstract-Broadband terahertz metamaterial absorber with two interlaced fishnet layers

AIP Advances

Siyu Tan, Fengping Yan,  Ningning Xu, Jingjing Zheng, Wei Wang, Weili Zhang,

Schematic of the proposed broadband metamaterial absorber: (a) the two interlaced square fishnet layers and the ground plane are separated by two identical polyimide spacers with the thickness h = 20 μm. (b) Microscopic graph of the fabricated sample. (c) and (d): The unit cell of the middle layer and the top layer with l = 150 μm, w1 = 35 μm and w2 = 15 μm.

https://aip.scitation.org/doi/10.1063/1.5017099

The realization of broadband absorption in the terahertz regime is of significant interest in high-sensitive signal detection and modulation. Previously, multi-layer metamaterials have been proposed and demonstrated to expand the absorption bandwidth by clustering multiple closely-positioned structures with different absorption peaks. Here, we proposed an alternative design for broadband metamaterial absorption by incorporating two interlaced fishnet layers, and achieved a broadband absorber with a full-width at half-maximum of about 0.99 THz. We also investigated the impact of the relative position of the two fishnet layers in the form of frequency tuning and expanding the absorption band.

Abstract-Active KTaO3 hybrid terahertz metamaterial

• Liang Wu, 
• Jinglong Liu, 
• Hui Li, 
• Chunfeng Ding, 
• Ningning Xu, 
• Xiaolei Zhao, 
• Zongcheng Xu, 
• Quan Sheng, 
• Jianquan Yao, 
• Jining Li, 
• Xin Ding & 
• Weili Zhang

https://www.nature.com/articles/s41598-017-05529-0

The dielectric properties of an active KTaO3 hybrid metamaterial structure and its tunability under external electric fields are investigated at room temperature by means of terahertz time-domain spectroscopy. Application of the electric field leads to an appreciable tuning of the dielectric loss, which is up to 17%. Meanwhile, the refractive index also changes appreciably. These findings are attributed to the internal space charge field in the crystal caused by the excited free carriers.

Abstract-Terahertz sensing of highly absorptive water-methanol mixtures with multiple resonances in metamaterials

Min Chen, Leena Singh, Ningning Xu, Ranjan Singh, Weili Zhang, and Lijuan Xie

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-13-14089

Terahertz sensing of highly absorptive aqueous solutions remains challenging due to strong absorption of water in the terahertz regime. Here, we experimentally demonstrate a cost-effective metamaterial-based sensor integrated with terahertz time-domain spectroscopy for highly absorptive water-methanol mixture sensing. This metamaterial has simple asymmetric wire structures that support multiple resonances including a fundamental Fano resonance and higher order dipolar resonance in the terahertz regime. Both the resonance modes have strong intensity in the transmission spectra which we exploit for detection of the highly absorptive water-methanol mixtures. The experimentally characterized sensitivities of the Fano and dipole resonances for the water-methanol mixtures are found to be 160 and 305 GHz/RIU, respectively. This method provides a robust route for metamaterial-assisted terahertz sensing of highly absorptive chemical and biochemical materials with multiple resonances and high accuracy.

© 2017 Optical Society of America

Abstract-Defect-Induced Fano Resonances in Corrugated Plasmonic Metamaterials

http://onlinelibrary.wiley.com/doi/10.1002/adom.201600960/abstract

A novel defect-induced planar meta-atom that supports multiple Fano resonances in a defective corrugated metallic disk (CMD) structure is proposed. Numerical and experimental results reveal that multiple Fano resonances can be excited at terahertz frequencies when the symmetry of the CMD is broken by introducing a small angular defect. These multiple Fano resonances result from mutual coupling between the bright dipolar mode evoked by the edge of the wedge-shaped slice and dark multipole spoof localized surface plasmon modes. Furthermore, the influence of the angle of defect on the Q-factor and the resonance intensity of the quadrupolar resonance peak is investigated. Large values of figure of merit are obtained due to higher Fano resonance intensity and Q-factor. Results from two defective slices in the CMD structure validate the mechanism of the observed phenomenon. The findings of this work would enable a defect-induced Fano resonance platform for biosensing, terahertz domain filtering, and strong light–matter interactions.

Abstract-Dual-Wavelength Terahertz Metasurfaces with Independent Phase and Amplitude Control at Each Wavelength

• Jun Ding
• , Ningning Xu
• , Han Ren
• , Yuankun Lin
• , Weili Zhang
•  & Hualiang Zhang

http://www.nature.com/articles/srep34020

We have designed, fabricated and characterized dual-wavelength metasurfaces that function at two assigned terahertz wavelengths with independent phase and amplitude control at each wavelength. Specifically, we have designed a dual-wavelength achromatic metasurface-based deflector deflecting the incident wave to the same direction at two selected wavelengths, which has circumvented the critical limitation of strong wavelength dependence in the planar metasurface-based devices caused by the resonant nature of the plasmonic structures. As a proof of concept demonstration, the designed dual-wavelength achromatic deflector has been fabricated, and characterized experimentally. The numerical simulations, theoretical predictions, and experimental results agree very well with each other, demonstrating the property of independently manipulating the phase profiles at two wavelengths. Furthermore, another unique feature of the designed metasurface is that it can independently tailor both the phase and amplitude profiles at two wavelengths. This property has been numerically validated by engineering a metasurface-based device to simultaneously generate two diffraction orders at two desired wavelengths.

Abstract-Sharp Toroidal Resonances in Planar Terahertz Metasurfaces

http://onlinelibrary.wiley.com/doi/10.1002/adma.201601611/abstract

A toroidal dipole in metasurfaces provides an alternate approach for the excitation of high-Qresonances. In contrast to conventional multipoles, toroidal dipole interaction strength depends on the time derivative of the surrounding electric field. A characteristic feature of a toroidal dipole is tightly confined loops of oscillating magnetic field that curl around the fictitious arrow of a toroidal dipole vector.