Abstract-Ultra-broadband terahertz bandpass filter with dynamically tunable attenuation based on a graphene–metal hybrid metasurface

 

Wenli Huang, Xiaoqing Luo, Yuanfu Lu, Fangrong Hu, and Guangyuan Li

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-60-22-6366

We propose an ultra-broadband terahertz bandpass filter with dynamically tunable attenuation based on a graphene–metal hybrid metasurface. The metasurface unit cell is composed of two metal stripes enclosed with a graphene rectangular ring. Results show that when the metasurface is normally illuminated by a terahertz wave polarized along the metal stripes, it can act as an ultra-broadband bandpass filter over the spectral range from 1.49 THz to 4.05 THz, corresponding to a fractional bandwidth of 92%. Remarkably, high transmittance above 90% covering the range from 1.98 THz to 3.95 THz can be achieved. By changing the Fermi level of graphene, we find that the attenuation within the passband can be dynamically tuned from 2% to 66%. We expect that the proposed ultra-broadband terahertz bandpass filter with tunable attenuation will find applications in terahertz communication and detection and sensing systems.

© 2021 Optical Society of America

Abstract-Broadband switchable terahertz half-/quarter-wave plate based on metal-VO2 metamaterials

 

Juan Luo, Xingzhe Shi, Xiaoqing Luo, Fangrong Hu, and Guangyuan Li

. Schematic of the proposed metamaterial composed of multi-layered metal-VO2${}_2$ hybrid structures. (a) When VO2${}_2$ is in the insulating state, it acts like dielectric, denoted by VO2${}_2$ (D) and indicated by the blue block, the metamaterial functions as an HWP converting linear 𝑦$y$ polarization into linear 𝑥$x$ polarization. (b) When VO2${}_2$ is in the conducting state, it acts like metal, denoted by VO2${}_2$ (M) and indicated by the red block, the metamaterial functions as a QWP converting linear 𝑦$y$ polarization into LCP. (c) Geometric parameters of the unit cell of the multi-layered metamaterial.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-21-30861&id=440195

We propose a metal-vanadium dioxide (VO2) metamaterial with broadband and functionality-switchable polarization conversion in the terahertz regime. Simulation results show that the function of the proposed metamaterial can be switched from a half-wave plate (HWP) to a quarter-wave plate (QWP) over a broad bandwidth of 0.66–1.40 THz, corresponding to a relative bandwidth of 71.8%. The HWP obtained when VO2 is in the insulating state has reflection of 90% and linear polarization conversion ratio exceeding 98% over the bandwidth of 0.58–1.40 THz. By transiting the phase of VO2 into the conducting state, the obtained QWP can convert the incident linearly-polarized wave to circularly-polarized wave with an ellipticity of 0.99 over 0.66–1.60 THz. Additionally, results show that the proposed broadband switchable HWP/QWP has a large angular tolerance. We expect that this broadband and switchable multi-functional wave plate will find applications in polarization-dependent terahertz systems including sensing, imaging, and telecommunications.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

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-Four resonators based high sensitive terahertz metamaterial biosensor used for measuring concentration of protein

Yuanyuan Li, Xieyu Chen, Fangrong Hu, Dongxia Li, Huan Teng, Qi Rong, Wentao zhang, Jiaguang Han,  Huasheng Liang

http://iopscience.iop.org/article/10.1088/1361-6463/aaf7e9

A terahertz (THz) metamaterial biosensor based on four identical resonators is experimentally demonstrated, and high sensitivity is achieved by exciting four synchronous LC oscillations in a unit cell. The effect of geometries on the resonance frequency of the sensor is investigated using finite integration time domain (FIDT) method, and the simulated sensitivity is 85 GHz per refractive index unit (RIU). The biosensor sample is fabricated using a surface micromachining process and characterized by a THz time domain spectroscopy (TDS) system combined with bovine serum albumin (BSA) solution as anelyte. The experimental results indicate that the resonance frequency shows distinct redshift when increases the concentration of BSA solution. When the concentration is high up to 765μmol/L, the frequency shift reaches 50 GHz, and the measurable minimum concentration is low to 1.5μmol/L. The biosensor is small in shape, wide in measurable range, convenient in operation and rapid in detection, which is of great significance for rapid concentration measurement, biomolecules detection and disease diagnosis.

Abstract-Experimental and theoretical investigations of tartaric acid isomers by terahertz spectroscopy and density functional theory

Tao Chen, Qin Zhang, Zhi Li, Xianhua Yin, Fangrong Hu,

https://www.sciencedirect.com/science/article/pii/S1386142518306334

The terahertz (THz) absorption spectra of l-, d-, and dl-tartaric acid have been measured in the frequency range from 0.2 to 2.0 THz by terahertz time-domain spectroscopy (THz-TDS). The characteristic absorption peaks of these three tartaric acid isomers were obtained, which showed remarkable difference between enantiomers (l- and d-tartaric acid) and the racemic compound (dl-tartaric acid) in their peak frequencies. In parallel with the experimental study, theoretical calculations on isolated-molecule and unit cell of tartaric acids using density functional theory (DFT) were also performed for simulating the experimental THz spectrum features, which were in good agreement with the experimental data. Results demonstrate that THz-TDS can distinguish the tiny diversity between tartaric acid chiral isomers and its racemic compound, and provided an effective method for molecular identification in biological and biomedical engineering.

Abstract-Highly Sensitive Detection of Carbendazim by Using Terahertz Time-Domain Spectroscopy Combined With Metamaterial

 Binyi Qin,  Zhi Li,  Fangrong Hu,  Cong Hu,  Tao Chen,  Huo Zhang,   Yonghong Zhao

http://ieeexplore.ieee.org/document/8252737/

The rapid and sensitive detection of pesticide residue is essential for ensuring the food safety of consumers. However, there are many disadvantages for current approaches to detect pesticide residue, such as complex pre-treatment and low sensitivity. In this paper, we demonstrate a highly sensitive carbendazim detection method by using terahertz time-domain spectroscopy (THz-TDS) combined with metamaterial. The metamaterial composed of metal ohm ring arrays, is applied in detecting different concentrations of carbendazim. Resonant peaks of metamaterial move to a lower frequency as the concentration increases. The results illustrate that metamaterial can detect trace amounts of carbendazim, as small as 5 mg/L, which is about 104 times enhancement compared to the squash method for THz-TDS detection. It also means that metamaterial combined with THz-TDS is a potential new approach for food quality and safety control.

Abstract-Intensity modulation of a terahertz bandpass filter: utilizing image currents induced on MEMS reconfigurable metamaterials

Fangrong Hu, Yixing Fan, Xiaowen Zhang, Wenying Jiang, Yuanzhi Chen, Peng Li, Xianhua Yin, and Wentao Zhang

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-1-17&origin=search

We experimentally demonstrated a tunable terahertz bandpass filter based on microelectromechanical systems (MEMS) reconfigurable metamaterials. The unit cell of the filter consists of two split-ring resonators (SRRs) and a movable bar. Initially, the movable bar situates at the center of the unit cell, and the filter has two passbands whose central frequencies locate at 0.65 and 0.96 THz. The intensity of the two passbands can be actively modulated by the movable bar, and a maximum modulation depth of 96% is achieved at 0.96 THz. The mechanism of tunability is investigated using the finite-integration time-domain method. The result shows that the image currents induced on the movable bar are opposite the resonance currents induced on the SRRs and, thus, weaken the oscillating intensity of the resonance currents. This scheme paves the way to dynamically control and switch the terahertz wave at some constant frequencies utilizing induced image currents.

© 2017 Optical Society of America

Abstract-Analog of Electromagnetically Induced Transparency at Terahertz Frequency Based on Bilayer-Double-H-Metamaterials

Yuee Wang, Zhi Li, Fangrong Hu, 

http://iopscience.iop.org/article/10.1088/1361-6463/aa9ba0/pdf

We design a bilayer-double-H-metamaterials (BDHM) composed of two layers of metallic and two layers of dielectric to analog a spectral response of electromagnetically induced transparency (EIT) at terahertz frequency. By changing the incident angle, the BDHM exhibits the EIT-like spectral response. The tunable spectral performances and modulation mechanism of transparent peak are theoretically investigated using a full-wave electromagnetic simulation software. The physical mechanism of the EIT-like effect is based on the constructive and destructive interference between the induced electrical dipoles. Our work provides a new way to realize the EIT-like effect only by changing the incident angles of metamaterials. The potential applications include tunable filter, sensor, attenuator, switches, and so on.

Abstract-Metamaterials-based terahertz sensor for quick diagnosis of early lung cancer

Xin Xu, Yan Wu, Tangyan He, Yuanyuan Li, Fangrong Hu, Huasheng Liang, Chunxia Yang, and Hong Zhong

https://www.osapublishing.org/col/abstract.cfm?uri=col-15-11-111703&origin=search

We experimentally demonstrate a metamaterials (MMs)-based terahertz (THz) sensor to quickly distinguish the cancer tissues from normal tissues. The MMs-based THz sensor has two strong resonance absorption peaks at about 0.706 and 1.14 THz, respectively. When the sensor is covered with cancer tissues, the redshifts at about 0.706 and 1.14 THz are 31 and 19 GHz, respectively. However, if normal tissue is attached to the surface of the sensor, the corresponding redshifts are only 15 and 12 GHz, respectively. This study proposes a new method for quick diagnosis of early lung cancer and other cancers.

© 2017 Chinese Laser Press

Abstract-Improving Terahertz Sheet Conductivity of Graphene Films Synthesized by Atmospheric Pressure Chemical Vapor Deposition with Acetylene

Mei Qi †, Yixuan Zhou †, Fangrong Hu ‡, Xinlong Xu *†, Weilong Li †, Anran Li †, Jintao Bai †, andZhaoyu Ren *†

† State Key Lab Incubation Base of Photoelectric Technology and Functional Materials, International Collaborative Center on Photoelectric Technology and Nano Functional Materials, Institute of Photonics & Photon-Technology, Northwest University, Xi’an 710069, China

‡ School of Electronic Engineering and Automation,Guilin University of Electronic Technology, Guilin 541004, China

J. Phys. Chem. C, Article ASAP

DOI: 10.1021/jp502260k

Publication Date (Web): June 17, 2014

Copyright © 2014 American Chemical Society

*Tel.: +86-29-88303336. Fax: +86-29-88303336. E-mail: xlxuphy@nwu.edu.cn., *Tel.: +86-29-88303336. Fax:+86-29-88303336. E-mail: rzy@nwu.edu.cn.

http://pubs.acs.org/doi/abs/10.1021/jp502260k

Graphene has shown great potential for terahertz (THz) applications in recent years. THz sheet conductivity of graphene is essential to assess the high performance of THz devices such as modulators based on graphene. In this work, THz sheet conductivity of graphene grown with different temperatures, along with the effects of chemical doping by HNO3, were studied in detail. Graphene films were synthesized on Cu surface by atmospheric pressure chemical vapor deposition with C2H2. Different samples with growth temperature from 850 to 1030 °C were characterized by Raman spectroscopy, transmission electron microscope, and UV–vis spectroscopy. THz time-domain spectroscopy was used to study the THz sheet conductivity of the samples before and after HNO3 doping. The results show that graphene grown at 1000 °C has the highest THz sheet conductivity. As compared to the sample grown at 850 °C, the value enhances 600%. In addition, after HNO3 doping, the THz sheet conductivity of the sample grown at 1000 °C becomes 2.42 mS, which enhances 44%. These indicate that both the optimization of the growth temperature and chemical doping can improve the THz sheet conductivity of graphene significantly. Combining with the characterization of the material, we have attributed the effect of the growth temperature to the influence of carrier momentum scattering time in graphene, and the chemical doping to the influence of the carrier concentration in graphene. This work advances the understanding of improving THz sheet conductivity by in situ growth and postgrowth and paves the way for efficient THz components with graphene.

Abstract-Improving Terahertz Sheet Conductivity of Graphene Films Synthesized by Atmospheric Pressure Chemical Vapor Deposition with Acetylene

Mei Qi , Yixuan Zhou , Fangrong Hu , Xin Long Xu ,Weilong Li , Anran Li , Jintao Bai , and Zhao Yu Ren

J. Phys. Chem. C, Just Accepted Manuscript

DOI: 10.1021/jp502260k

Publication Date (Web): June 17, 2014

Copyright © 2014 American Chemical Society
http://pubs.acs.org/doi/abs/10.1021/jp502260k

Graphene has shown great potential for terahertz (THz) applications in recent years. THz sheet conductivity of graphene is essential to assess the high performance of THz devices such as modulators based on graphene. In this work, THz sheet conductivity of graphene grown with different temperatures, along with the effects of chemical doping by HNO3, were studied in detail. Graphene films were synthesized on Cu surface by atmospheric pressure chemical vapor deposition with C2H2. Different samples with growth temperature from 850 to 1030 oC were characterized by Raman spectroscopy, transmission electron microscope, and UV-Vis spectroscopy. THz time-domain spectroscopy was used to study the THz sheet conductivity of the samples before and after HNO3 doping. The results show that graphene grown at 1000 oC has the highest THz sheet conductivity. Compared with the sample grown at 850 oC, the value enhances 600%. In addition, after HNO3 doping, the THz sheet conductivity of the sample grown at 1000 oC becomes 2.42 mS, which enhances 44%. These indicate that both the optimization of the growth temperature and chemical doping can improve the THz sheet conductivity of graphene significantly. Combining with the characterization of the material, we have attributed the effect of the growth temperature to the influence of carrier momentum scattering time in graphene, and the chemical doping to influence of the carrier concentration in graphene. This work advances the understanding of improving THz sheet conductivity by in-situ growth and post-growth and paves the way for efficient THz components with graphene.

Article & Abstract-Design of a polarization insensitive multiband terahertz metamaterial absorber

Fangrong Hu, Li Wang, Baogang Quan, Xinlong Xu, Zhi Li, Zhongan Wu,  Xuecong Pan
My Note: you can read the entire article here:
http://m.iopscience.iop.org/0022-3727/46/19/195103/

We design a terahertz (THz) metamaterial absorber having four narrowband high absorptivities of 98%, 97%, 98% and 97% at frequencies of 0.68 THz, 1.27 THz, 2.21 THz and 3.05 THz, respectively. The absorber consists of three metallic layers, which are separated by two dielectric spacers. The absorption performances are simulated using a commercialized full-wave electromagnetic simulation software, and the mechanism of absorption is theoretically investigated. The result shows that the absorber is insensitive to the polarization of THz wave and the position of every absorption peak can be effectively tuned by the geometries of the absorber. The potential applications of the absorber include spectrally selective detecting, THz sensing and thermal imaging.