基于聚酰亚胺基底的太赫兹滤波器

超材料是通过人工方式做成的具有特殊电磁特性的亚波长周期性金属结构,通过合理的设计样品结构,可以实现自然界中传统材料无法实现的电磁现象。超材料可以广泛用于电磁隐身、完美吸收、负折射率等研究领域,近些年,随着太赫兹技术的发展,太赫兹超材料器件被广泛研究。由于硅（Si）对于太赫兹波的透过率较高,通常选取Si作为基底材料。但Si硬度较高、不易弯曲且易碎等缺点限制了THz超材料的应用。聚合物材料聚酰亚胺具有柔性,作为基底,克服了传统硅基底的缺点,透过率可以与Si匹敌,而且其表面光滑,适合传统光刻技术加工。对聚酰亚胺在太赫兹波段光学性质的测试结果表明,此种材料的折射率在1.9左右,透过率达到80%以上。设计了一种双开口谐振环结构,研究了其太赫兹波透射性质以及随太赫兹波的入射角度和样品曲率的变化规律,发现透射峰强度和峰位均不发生改变。此结果展示了将平面滤波延伸到曲面滤波领域的可能性,若将聚酰亚胺基底做薄,为今后太赫兹频段隐身衣的研究提供基础。将不同结构的两种样品叠加在一起制成宽谱滤波器, 50%的带宽达到181 GHz。此种宽带滤波器制作简单,滤波效果显著,为太赫兹波段宽带滤波器的制作提供一种新思路。     

基于石墨烯编码超构材料的太赫兹波束多功能动态调控

提出了一种基于石墨烯带的太赫兹波段的1 bit编码超构材料,可以实现太赫兹波束的数目、频率、幅度等参数多功能动态调控.该结构由金属薄膜、聚酰亚胺、硅、二氧化硅、石墨烯带组成.通过对石墨烯带施加两种不同的电压,可以实现一定频率范围内相位差接近180?的"0"和"1"数字编码单元,进而构成1 bit动态可控的编码超构材料.全波仿真结果表明,不同序列的编码超构材料能够实现波束数目从单波束、双波束、多波束到宽波束的调控.相同序列的编码超构材料,通过施加石墨烯带的不同电压能够实现宽频段波束频率的偏移.对于000000或者111111周期序列的编码超构材料,通过施加石墨烯带的不同电压还能够实现波束幅度的调控.因此这种基于石墨烯带的编码超构材料为灵活调控太赫兹波提供了一种新的途径,将在雷达隐身、成像、宽带通信等方面具有重要的意义.     

基于编码超表面的太赫兹宽频段雷达散射截面缩减的研究

本文设计了一种柔性, 非定向低散射的1bit编码超表面, 实现了太赫兹宽频带雷达散射截面的缩减. 这种设计基于对“0”和“1”两种基本单元进行编码, 其反射相位差在很宽的频段范围内接近180°, 为一种非周期的排列方式, 该电磁超表面使入射的电磁波发生漫反射, 从而实现雷达散射截面的缩减. 全波仿真结果表明, 在垂直入射条件下, 编码超表面的镜像反射率低于-10 dB的带宽频段范围为1.0-1.4 THz, 该带宽内超表面相对同尺寸金属板可将雷达散射截面所减量达到10 dB以上, 最大缩减量达到19 dB. 把柔性编码表面弯曲在直径为4 mm的金属圆柱面上, 雷达散射截面的所减量高于10 dB以上的带宽频段范围为0.9-1.2 THz, 仍然可实现宽频带缩减特性. 总之, 编码超表面为调控太赫兹波提供一种新的途径, 将在雷达隐身、成像、宽带通信等方面具有重要的意义.     

High-birefringence hollow-core anti-resonant THz fiber

A novel high-birefringence hollow-core anti-resonant THz fiber is proposed in this paper. This fiber has a simple structure which consists of only ten Topas tubes. High birefringence is achieved by introducing two large tubes. The first two resonant frequencies are 1.44 and 2.88 THz by fixing tube thickness at 0.09 mm, which makes two low-loss transmission windows exist in the frequency range from 0.8 to 3.0 THz. The lowest loss is 2.10 dB/m occurring at 1.2 THz in the first transmission window and 1.68 dB/m at 2.34 THz in the second transmission window. By optimizing the structure parameters, high birefringence above 7 × 10^?4 in the frequency range from 1.0 to 1.24 THz are obtained. The highest birefringence is up to 8.7 × 10^?4 at 1.04 THz. Birefringence can be further increased to the order of 10^?3 by adjusting the structure parameters at the cost of loss increasing and the bandwidth decreasing. In addition, bent performance of this fiber is also discussed. In addition, this fiber can keep good performance when it is bent for x-direction. At the bend radius of 15 cm, the loss and birefringence has a more slightly change in the first transmission window than the second transmission window. The first transmission window own much better bent-insensitive characteristics.     

Optical properties of femtosecond laser-treated diamond

Coupling effect in spiral-shaped metamaterials composed of four half rings at different sizes is investigated to achieve tunability in THz range. This novel spiral-shaped structure was fabricated on flexible substrate with laser micro-lens array (MLA) lithography and measured by THz time domain spectroscopy (THz-TDS). The experimental results suggest that mutual capacitance and inductance coupling in the spiral-shaped structure would result in frequency shifts of the four resonances. The observed shifting trends of the four resonant frequencies are in good agreement with simulation and are further explained by the electric field distribution. By varying the gap sizes among the half rings, four resonant frequencies can be tuned flexibly. Such a spiral-shaped design has potential applications in multi-band tunable THz MEMS devices.     

太赫兹波段超材料的制作、设计及应用

本文从制作方法、结构设计和材料选择几方面综述了超材料在太赫兹波段的电磁响应特性和潜在应用。首先,介绍了获得不同维度、具有特异电磁响应以及结构可调超材料的各种微加工制作方法,进而分析和讨论了超材料的电磁响应特性。文中指出,结构设计可以控制超材料的电磁响应特性,如各向异性、双各向异性、偏振调制、多频响应、宽带响应、不对称透射、旋光性和超吸收等。超材料的电磁响应依赖于周围微环境的介电性质,因而可用于制作对环境敏感的传感器件。此外,电光、磁光、相变、温度敏感等功能材料的引入可以获得光场、电场、磁场、温度等主动控制的太赫兹功能器件。最后,简单介绍了超材料在太赫兹波段进一步发展所面临的机遇和挑战。     

Broadband visible reflectors using Au and Ag elliptic cylinder pattern

Broadband terahertz reflector is suggested based on the shape of circular- and elliptic-cylinder metamaterials. We periodically arrange the structural pattern with gold and silver thin films on the FR4 substrate and optimize to operate in the wavelength range of 300–750 THz. Comparing the spectral responses of metamaterials with changes in shape and material, the ellipse shape greatly increased the reflection, and the silver pattern led to induce a broadening of the reflection band. Also, we identify the underlying physics necessary to design broadband reflector at any wavelength band of interest. Our results show that we can obtain broad reflection with 126 THz bandwidth at normal incidence, these results have high potential in large area photonic applications and can serve as reflectors in thin active film.     

Dynamically tunable terahertz passband filter based on metamaterials integrated with a graphene middle layer

The dynamic tunability of a terahertz(THz) passband filter was realized by changing the Fermi energy(E_F) of graphene based on the sandwiched structure of metal-graphene-metal metamaterials(MGMs). By using plane wave simulation, we demonstrated that the central frequency( f_0) of the proposed filter can shift from 5.04 THz to 5.71 THz; this shift is accompanied by a 3 dB bandwidth(? f) decrease from 1.82 THz to 0.01 THz as the EFincreases from 0 to 0.75 eV.Additionally, in order to select a suitable control equation for the proposed filter, the curves of ? f and f_0 under different graphene EFwere fitted using five different mathematical models. The fitting results demonstrate that the Dose Resp model offers accurate predictions of the change in the 3 dB bandwidth, and the Quartic model can successfully describe the variation in the center frequency of the proposed filter. Moreover, the electric field and current density analyses show that the dynamic tuning property of the proposed filter is mainly caused by the competition of two coupling effects at different graphene EF, i.e., graphene-polyimide coupling and graphene-metal coupling. This study shows that the proposed structures are promising for realizing dynamically tunable filters in innovative THz communication systems.     

Analysis of graphene based optically transparent patch antenna for terahertz communications

With and without multi walled carbon nanotube (MWCNT) loaded graphene based optically transparent patch antennas are designed to resonate at 6 THz. Their radiation characteristics are analyzed in 5.66–6.43 THz band. The optically transparent graphene is deployed as the patch and ground plane of the antennas, which are separated by a 2.5 μm thick flexible polyimide substrate. By shorting the microstrip line and ground plane of the antenna with a MWCNT via, the return loss of the antenna is improved. The peak gain of 3.3dB at 6.2 THz and a gain greater than 3dB in 5.66–6.43 THz band is obtained for antenna loaded without MWCNT. Both the antennas achieved a −10dB impedance bandwidth of 12.83%. Gain, directivity and radiation efficiency of the proposed antennas are compared with conventional transparent patch antennas and graphene based non-transparent antennas. The antenna structures are simulated by using finite element method based electromagnetic simulator-Ansys HFSS.     

TERA-MIR radiation: materials,generation, detection and applications

This special edition is dedicated to original papers covering topics with the areas of interest of COST ACTION MP1204 whose main objective is to advance novel materials, concepts and device designs for generating and detecting THz (0.3–10 THz) and Mid Infrared (10–100 THz) radiation using semiconductor, superconductor, metamaterials and lasers and to beneficially exploit their common aspects within a synergetic approach. The results achieved benefit from the unique networking and capacity-building capabilities provided by the COST framework to unify these two spectral domains from their common aspects of sources, detectors, materials and applications. We are building a platform to investigate interdisciplinary topics in Physics, Electrical Engineering and Technology, Applied Chemistry, Materials Sciences and Biology and Radio Astronomy. In this sense THz and MIR are considered jointly, the driving force for both regimes being applications. The main emphasis of the research presented here is on new fundamental material properties, concepts and device designs that are likely to open the way to new products or to the exploitation of new technologies in the fields of sensing, healthcare, biology, and industrial applications. End users are: research centres, academic, well-established and start-up companies and hospitals. The strong coupling of THz radiation and material excitations has potential to improve the quantum efficiency of THz devices.     

激光诱导和化学镀铜制备太赫兹偏振器和滤波器

利用激光诱导与化学镀铜的方法在聚酰亚胺薄膜上制备了太赫兹线栅偏振器和带阻滤波器,用太赫兹时域光谱系统对所制备的器件进行了测试。测试结果表明,该方法制备的太赫兹线栅偏振器在0.2～1.5 THz范围内的消光比优于20 dB,耶路撒冷十字结构带阻滤波器的3个中心频率分别为0.41、1.07、1.47 THz。实验结果与时域有限差分法的仿真结果基本相符。研究表明激光诱导与化学镀铜是一种简单灵活且能有效地制备太赫兹器件的方法。     

Tunable dual-band infrared chiral metamaterials based on double-layered asymmetric U-shape split ring resonators

We have numerically demonstrated chiral metamaterials based on double-layered asymmetric U-shape split ring resonators. Dual-band circular dichroism is found in the whole frequency regime from 50 to 250 THz by studying the transmission properties. Huge optical activity and the induced negative refractive index are obtained at resonance by calculating the optical activity and ellipticity of the transmitted E-fields. Chirality parameter and effective refractive index are retrieved to illustrate the tunable optical properties of the metamaterials. The underlying mechanisms for the observed circular dichroism are analyzed. These metamaterials would offer flexible electromagnetic applications in the infrared regime.     

经典局域共振型水声超材料的吸隔声性能研究*

基于水声超材料吸声机理和多层平行介质平面波理论,建立局域共振型水声超材料结构,通过COMSOL进行建模计算,研究该结构的吸声性能机理,此外为了验证钢背衬的隔声性能,在该水声超材料结构基础上添加一层0.005m厚的钢背衬进行仿真对比。研究结果表明,在频段为200Hz-4000Hz时,水声超材料声学性能较好,吸声性能整体较优,且添加钢背衬的水声超材料隔声性能较优,甚至在某频率点达到15dB的隔声差值;此外通过位移场图进一步揭示水声超材料的吸声机理,发现水声超材料结构的位移场和钢背衬都对吸声性能会产生影响,钢背衬通过影响共振吸收来影响吸声性能,而位移场则通过位移幅度大小影响吸声性能。     

Efficacy of a wideband flexible antenna on a multilayer polymeric nanocomposites Fe3O4-PDMS substrate for wearable applications

The recently introduced polymeric nanocomposites substrate layer technology is used in the design of a flexible antenna array for wearable applications. This new technology allows a considerable widening of the bandwidth of classical microstrip topologies. This means that a relatively wide band can be combined with a full ground plane in a very simple structure, which is an ideal combination in wearable applications. The wideband and flexible features enabled the antenna to mitigate body-detuning effects. The proposed antenna prototype consists of a 2 × 2 array of rectangular patch elements with dimensions of 70 × 70 × 4.2 mm³. The measurements are performed in free space, and on-body under bent conditions. The antenna working within the frequency band of 5 GHz–8.2 GHz, with a fractional impedance (FBW) bandwidth of 50.34%. The antenna demonstrates a maximum radiation efficiency of 60%, and 9.8 dB of realized gain. Since this antenna is intended for on body-centric wireless communication application, the specific absorption rate is evaluated when the antenna is placed on the right arm of a realistic human phantom. The performances and features of the proposed antenna paved the way for off-body connections in a WBAN and wearable applications including WiFi, telemedicine and Vehicle-to-Everything (V2X).     

Wideband switchable dual-functional terahertz polarization converter based on vanadium dioxide-assisted metasurface

The terahertz technology has attracted considerable attention because of its potential applications in various fields.However,the research of functional devices,including polarization converters,remains a major demand for practical applications.In this work,a reflective dual-functional terahertz metadevice is presented,which combines two different polarization conversions through using a switchable metasurface.Different functions can be achieved because of the insulator-to-metal transition of vanadium dioxide(VO₂).At room temperature,the metadevice can be regarded as a linear-to-linear polarization convertor containing a gold circular split-ring resonator(CSRR),first polyimide(PI)spacer,continuous VO₂ film,second PI spacer,and gold substrate.The converter possesses a polarization conversion ratio higher than 0.9 and a bandwidth ratio of 81%in a range from 0.912 THz to 2.146 THz.When the temperature is above the insulator-to-metal transition temperature(approximately 68℃)and VO₂ becomes a metal,the metasurface transforms into a wideband linear-to-circular polarization converter composed of the gold CSRR,first PI layer,and continuous VO₂ film.The ellipticity is close to-1,while the axis ratio is lower than 3 dB in a range of 1.07 THz-1.67 THz.The metadevice also achieves a large angle tolerance and large manufacturing tolerance.     

Investigation of a nanostrip patch antenna in optical frequencies

This is the first report and investigation of a patch antenna in optical frequency range. Variety of plasmonic nanoantenna reported so far is good at enhancing the local field intensity of light by orders of magnitude. However, their far-field radiation efficiency is very poor. The proposed patch antenna emits a directional beam with high efficacy in addition to enhancing the intensity of near field. The nano-patch antenna (NPA) consists of a square patch of gold film of dimension 480 nm², placed on a substrate of dielectric constant \( \varepsilon_{\text{r}} \)  = 3.9 and thickness 150 nm with a ground plane of gold film of dimension 1,080 nm². The NPA resonates at 210 THz and has gain nearly 2 dB and radiation efficiency 45.18 %. The NPA might be useful in variety of applications such as optical communication, nano-photonics, biosensing, and spectroscopy.     

可调太赫兹与光学超材料

本文对可调太赫兹与光学超材料的研究进展进行了综述,并对其发展趋势和应用前景进行了展望。可以预见,可调超材料将继续成为超材料研究中的热点课题,并将成为引领光学器件和光学系统变革的潜在技术途径,对光学和太赫兹技术的发展将产生深远的影响。     

单方环结构左手材料微带天线

设计了一种简单的双面单方环结构左手材料,在4.8–5.25 GHz频率范围内该材料的等效介电常数和等效磁导率同时为负.将此单方环左手材料作为覆盖层,置于中心工作频率为5.0 GHz的微带天线之上. 仿真和实验研究表明:相对普通微带天线而言,覆层微带天线的性能得到了明显改善, E面和H面的半功率波束宽度分别收缩了25°和20°,定向性得到了提高, 5 GHz处的增益提高了3 dB, -10 dB带宽增加了600 MHz. 关键词： 单方环结构 左手材料 微带天线     

Mechanically tunable metamaterials terahertz dual-band bandstop filter

We experimentally demonstrate a mechanically tunable metamaterials terahertz(THz) dual-band bandstop filter. The unit cell of the filter contains an inner aluminum circle and an outside aluminum Ohm-ring on high resistance silicon substrate. The performance of the filter is simulated by finite-integration-time-domain(FITD) method. The sample is fabricated using a surface micromachining process and experimentally demonstrated using a THz time-domain-spectroscopy(TDS) system. The results show that, when the incident THz wave is polarized in y-axis, the filter has two intensive absorption peaks locating at 0.71 THz and 1.13 THz, respectively. The position of the high-frequency absorption peak and the amplitude of the low-frequency absorption peak can be simultaneously tuned by rotating the sample along its normal axis.The tunability of the high-frequency absorption peak is due to the shift of resonance frequency of two electrical dipoles,and that of the low-frequency absorption peak results from the effect of rotationally induced transparent. This tunable filter is very useful for switch, manipulation, and frequency selective detection of THz beam.     

Broadband terahertz light source pumped by a 1 μm picosecond laser

We obtained a frequency tunable, low-coherence, picosecond, terahertz (THz) output with a high repetition rate from a picosecond Nd:YVO₄ bounce laser in combination with tandem periodically poled stoichiometric lithium tantalate and 4′-dimethylamino-N-methyl-4-stilbazolium tosylate crystals. The frequency of the THz output was tunable in the range 2.1–7.1 THz with a linewidth of ~3.5 THz at 2.2 THz. The THz output had a maximum peak power of ~180 mW and an average power of ~0.65 μW at 3.9 THz. This system has the potential to realize ultra-high speed, THz coherence tomography.