Microstrip patch array antenna on photonic crystal substrate at terahertz frequency

Recent advancement in the fabrication and packaging technology has led to the micrometer and nanometer-scale device modeling. This technological development and subsequent reduction in the dimension of devices like modulators, detectors and antennas has brought a thought of increasing the operating frequency of the system to the extent of sub-millimeter wavelength. In the view of the technical breakthrough in the area of fabrication and packaging, we have explored a printed antenna array on the photonic crystal in the terahertz spectrum in this paper. An equivalent circuit model of the antenna has been proposed and a methodology to investigate various electrical parameters is discussed. Tunable parameters of the structure have been explored to optimize the electrical performance of the proposed antenna. The analysis is also compared by using two simulators: (a) CST Microwave Studio based on finite integral technique and (b) Ansoft HFSS based on finite element method. The effect of the photonic crystal as substrate to enhance the gain of this kind of the antenna has also been demonstrated. The gain, directivity, front-to-back ratio (F/B ratio), and the radiation efficiency of the proposed antenna at 600 GHz is 16.88 dBi, 17.19 dBi, 14.77 dB and 89.72%, respectively. Finally, the performance of the antenna has been compared with the reported literature.     

基于LT-GaAs外延片的THz片上系统

太赫兹（THz）波在物质检测方面发挥着巨大的作用,是一种非常有潜力的生化传感工具。但是传统的太赫兹时域光谱系统（TDS）结构复杂,系统的集成度低,占用空间较大。所以,如何对THz波进行有效引导、实现集成化传输并得到高质量光谱就成为太赫兹光谱系统的研究热点。太赫兹片上系统是将THz的产生、传输以及探测都集成到同一芯片上,然后通过相干探测的方法获得THz时域光谱。它可以实现对多种样品的检测,尤其在对难于取样的微量样品探测方面具有广泛的应用价值。它无需光路准直,操作简便,成品率高。两个研究工作都是基于低温砷化镓(LT-GaAs)外延片开展的。首先将一根直径为200 μm的铜线固定在LT-GaAs外延片的上方,通过真空蒸镀的方法制备出天线电极,同时得到天线间隙,研制出基于LT-GaAs外延片的THz天线。利用波长为800 nm的飞秒激光对其进行测试,得到了质量较高的THz信号,验证了天线的实用性。然后在另一外延片上利用光刻微加工工艺制作出传输线和微电极,得到了集成的THz片上系统。使用波长为1 550 nm的飞秒激光分别激发片上系统的太赫兹产生天线和探测天线,天线产生的太赫兹波在传输线上传播,在探测端同样得到了质量较高的THz时域信号,证实了THz片上系统的可行性。该方法省去了腐蚀牺牲层以及LT-GaAs薄膜的转移、键合等步骤,极大地提高了片上系统的成品率,避免了薄膜转移过程中易破碎及腐蚀液存在毒性的问题。最后,研究了外加电压对从片上系统中获得的THz波性能的影响,结果为电压越高,THz波的信号强度越强;另外,通过在传输线上方垂直放置铜箔的方法验证了THz波沿着传输线传播的事实。该研究中采用的基于LT-GaAs外延片的片上系统的制备方法简单,制作周期短,制作过程安全,应用领域广泛,这为将来与微流控芯片相结合实现对液体样品的探测打下了基础。     

Field enhancement and power distribution characteristics of subwavelength-diameter terahertz hollow optical fiber

Fields in subwavelength-diameter terahertz hollow optical fiber (STHOF) can be intensified by large discontinuity of the electric field at high index contrast interfaces. The influences of fiber geometry and refractive index of the dielectric region on the fiber characteristics, such as power distribution, enhancement factor, have been discussed in detail. By appropriate design, the intensity in the central region of STHOF may be enhanced by a factor of greater than 1.5 compared with subwavelength-diameter terahertz fiber without the central hole and the loss can be reduced. For its compact structure and simple fabrication process, the fiber may be very useful in many miniaturized high performance and novel terahertz photonic devices.     

新型半矩形环螺旋线慢波结构高频特性

针对行波管更高工作频率和更大输出功率的发展需要,提出了一种半矩形环螺旋线慢波结构。基于三维电磁仿真软件HFSS的模拟研究表明:调控慢波结构的尺寸可以获得合适的色散特性和互作用阻抗,与现有技术的半圆环螺旋线慢波结构相比较,半矩形环螺旋线慢波结构的色散变化很小,但是具有更高的互作用阻抗值。新结构具有平坦色散、高互作用阻抗、与微细加工技术相兼容以及方便与带状电子束互作用的综合优点。     

Microelectromechanical systems bimaterial terahertz sensor with integrated metamaterial absorber

This Letter describes the fabrication of a microelectromechanical systems (MEMS) bimaterial terahertz (THz) sensor operating at 3.8 THz. The incident THz radiation is absorbed by a metamaterial structure integrated with the bimaterial. The absorber was designed with a resonant frequency matching the quantum cascade laser illumination source while simultaneously providing structural support, desired thermomechanical properties and optical readout access. Measurement showed that the fabricated absorber has nearly 90% absorption at 3.8 THz. A responsivity of 0.1°/μW and a time constant of 14 ms were observed. The use of metamaterial absorbers allows for tuning the sensor response to the desired frequency to achieve high sensitivity for potential THz imaging applications.     

Radiation Properties of Carbon Nanotubes Antenna at Terahertz/Infrared Range

The geometric structure and the terahertz/infrared radiation characteristics of carbon nanotubes dipole antenna arrays have been investigated by CST MICROWAVE STUDIO based on finite integral methods. In terahertz and infrared frequency span, the antenna properties such as electrical field distributions, scattering parameters, standing wave ratio, gain, and two dimension directivity patterns are discussed. Our results show that N × N antenna arrays have higher radiation efficiency than single carbon nanotube dipole antenna. This work was supported by National Natural Science Foundation of China (60571026, 10396160).     

基于纳观域碳纳米管的太赫兹波天线研究

基于碳纳米管独特的结构特点建立了以其为基础的Pocklington积分方程,并设计了一种全新的碳纳米管太赫兹(THz)波天线.数值仿真和理论计算结果表明,碳纳米管能够产生高频THz电磁辐射,半波长为60μm、半径为2.712nm的单壁碳纳米管偶极天线在-10dB反射系数以下可以实现2.5THz与7.6THz的双频带工作,带宽分别为8.4%与2.7%,由其构成的纳米管天线阵可以获得10.3dB的高增益特性.所得结果有助于在纳观域开展高频THz波辐射源及天线的研究与设计. 关键词： 太赫兹波 碳纳米管 天线 辐射源     

基于2D微电子机械系统(MEMS)镜全向激光雷达光学系统设计

为了满足全向激光探测的需求,提出一种基于2DMEMS镜扫描的激光雷达结构。激光器通过1×6高速光开关分时地给6个扫描子系统提供光信号,6个扫描子系统探测视场叠加起来可实现360°激光探测。每个扫描子系统的扫描范围为60°×30°,其中包含一个扩展MEMS镜扫描角度的发射光学天线和一个大视场有增益的接收光学天线。发射光学天线将MEMS镜±10°的扫描角扩展到±30°,发散度小于0.2mrad;接收视场内的激光波经过接收天线在探测器上所成的半像高小于1mm,接收增益为3.65。通过计算修正后的激光雷达方程可得到发射功率20 W的激光束在工作距离100 m内的回波功率≥1 nW,结果表明该光学系统可适用于激光雷达系统。     

太赫兹综合孔径近场成像系统设计

根据太赫兹成像兼具微波穿透特性和红外线高分辨率成像的特点,在红外与毫米波成像系统的基础上,提出一种近场太赫兹波被动干涉合成孔径成像系统的设计方案,并对其实现方法进行了分析。系统采用二维波束扫描天线结构实现综合孔径成像,在保证高精度成像的同时降低了系统的复杂度。通过数值仿真对成像系统的成像性能进行分析,仿真结果表明系统具有较高的空间分辨率;并对系统的成像过程进行了模拟仿真,验证了系统的可行性。     

基于BS结构的太赫兹光谱数据库的设计与实现

随着太赫兹技术中关键科学与技术问题的解决和有关仪器发展,其在各个领域的应用也备受人们的关注。由于太赫兹光谱技术具有一些独特优势,在快速无损检测技术的发展方面具有重要的应用前景,该技术与其他方法互补,可以解决许多原来难以解决的检测问题。进一步开发太赫兹光谱技术实际检测方法的关键之一就是需要具有一套较为完整和可靠的太赫兹光谱数据库。介绍了近期开发的一个基于浏览器/服务器(Browser/Server)的太赫兹光谱数据库系统。根据实际需要设计了太赫兹光谱数据库的结构和主要功能。该数据库目前包括240多条太赫兹光谱信息,其数据来源包括三个部分：(1)收集了部分国外太赫兹光谱数据库的信息;(2)从文献中收集部分光谱数据;(3)国内部分实验室测量的太赫兹光谱数据。着重介绍了建立BS结构的太赫兹数据库的基本结构和项目,介绍了BS结构太赫兹光谱数据库的功能与检索方法。该数据库具有计算样品的光学参数功能,可以根据输入的太赫兹时域光谱数据计算出样品的吸收系数,折射率等其他光学参数,以便于样品特征研究和谱库检索。检索系统能方便的提供注册用户收集、查询、显示谱图及其实验数据和分子结构图、数据匹配等功能。该数据库可以登录http://www.teralibrary.com进行查询和使用。该数据库是根据目前的太赫兹光谱数据信息建立的,以后会逐渐完善。希望该太赫兹光谱数据库能够为用户提供强大、方便和高效的服务功能,进而推进太赫兹技术在更多领域的应用。     

A Terahertz Spectral Database Based on Browser/Server TechniqueSCIEI北大核心CSCD

With the solution of key scientific and technical problems and development of instrumentation, the application of terahertz technology in various fields has been paid more and more attention. Owing to the unique characteristic advantages, terahertz technology has been showing a broad future in the fields of fast, non-damaging detections, as well as many other fields. Terahertz technology combined with other complementary methods can be used to cope with many difficult practical problems which could not be solved before. One of the critical points for further development of practical terahertz detection methods depends on a good and reliable terahertz spectral database. We developed a BS (browser/server) -based terahertz spectral database recently. We designed the main structure and main functions to fulfill practical requirements. The terahertz spectral database now includes more than 240 items, and the spectral information was collected based on three sources: (1) collection and citation from some other abroad terahertz spectral databases; (2) collected from published literatures; and (3) spectral data measured in our laboratory. The present paper introduced the basic structure and fundament functions of the terahertz spectral database developed in our laboratory. One of the key functions of this THz database is calculation of optical parameters. Some optical parameters including absorption coefficient, refractive index, etc. can be calculated based on the input THz time domain spectra. The other main functions and searching methods of the browser/server-based terahertz spectral database have been discussed. The database search system can provide users convenient functions including user registration, inquiry, displaying spectral figures and molecular structures, spectral matching, etc. The THz database system provides an on-line searching function for registered users. Registered users can compare the input THz spectrum with the spectra of database, according to the obtained correlation coefficient one can perform the searching task very fast and conveniently. Our terahertz spectral database can be accessed at http://www.teralibrary.com. The proposed terahertz spectral database is based on spectral information so far, and will be improved in the future. We hope this terahertz spectral database can provide users powerful, convenient, and high efficient functions, and could promote the broader applications of terahertz technology.     

Terahertz radiation from armchair carbon nanotube dipole antenna

This paper investigates the electromagnetic radiation characteristics of a metallic, large aspect ratio single walled carbon nanotube antenna in the terahertz frequency region below 12.5 THz. The key features of terahertz pulse have been revealed on the carbon nanotube antenna in comparison with conventional photoconductive switching. The terahertz waveforms, radiation power and their field distributions have been evaluated and are analysed. The Fourier transformed spectra over the whole frequency range demonstrate that the carbon nanotube antenna can be used as radiation source for broadband terahertz applications.     

宽带高增益双层硅基MEMS微带天线阵列

针对传统微带天线带宽窄和增益低等问题,设计了一种易与射频（RF）前端集成的硅基微带天线。该天线设计结合MEMS工艺,将高阻硅和低阻硅通过键合工艺形成双层硅基底,来改善微带天线介质基板的等效介电常数,有效增大了天线的带宽。同时通过在地面引入缺陷地结构（DGS）,有效的抑制谐波的产生。在此基础上设计了中心频率为10 Hz,22天线辐射阵列。仿真结果表明,天线相对阻抗带宽达到15.9%,增益超过10.9 dB,比传统微带天线有明显提升,同时满足引信中天线抗干扰的要求。     

宽波束双馈源超宽带抛物面天线设计与仿真

 针对单馈源超宽带抛物面天线波束较窄的问题，设计了一种宽波束双馈源超宽带抛物面天线。该抛物面天线是由一个普通的抛物面从中间对称分式，并在中间以平板连接而成的。馈源采用改进型平面TEM喇叭天线，同轴垂直馈电方式。两个馈源分别置于抛物面的两个焦点上。并利用时域有限差分数值方法分析了该天线的辐射性能。通过改变抛物面的结构，调节双馈源与天线主轴的夹角等方法可以有效改善天线的辐射性能。结果表明，所设计的宽波束双馈源抛物面天线可以在远区更宽的空间上形成峰值功率比较均匀的电磁脉冲，在不降低峰值功率的前提下有效地增加了波束的宽度；在抛物面天线两边进行少量切割不会对辐射场产生明显影响，节省了空间。     

基于缺陷接地结构的太赫兹双频微带天线

提出了一种工作在太赫兹频段的双频微带天线。在普通矩形微带天线的基础上,在辐射贴片上加载45°和135°的矩形贴片增大辐射面积,增大高频谐振点处阻抗带宽。通过引入缺陷接地结构使得天线在接地板处的电流路径改变,并与辐射贴片相互耦合,从而实现双频特性。为提高天线增益,在辐射贴片边缘加载若干寄生矩形贴片,并增加了寄生贴片处的基板厚度。该款天线可以同时在520 GHz(508~532 GHz)和680 GHz(581~766 GHz)的频段下工作,其中高频段的相对带宽达到了27.5%,最大增益达到了3.54 dB和4.11 dB。该双频天线结构相对简单,各项性能指标稳定,对于工作在太赫兹频段上的通信系统和无线传输系统具有一定的应用价值。     

基于科赫曲线分形结构太赫兹带通滤波器

太赫兹滤波器是太赫兹通信、太赫兹成像和太赫兹检测等太赫兹应用系统中不可或缺的功能器件。按照不同的分类方式,滤波器有不同的种类,常见的按照选频功能可分为高通滤波器、低通滤波器、带阻滤波器和带通滤波器。为了实现在太赫兹波段的滤波效果,世界各地的研究人员利用不同的结构、材料和控制方式实现了功能各异的太赫兹滤波器,但是考虑到设计的器件要应用到太赫兹系统中,成本低廉、结构简单、性能优越的太赫兹滤波器一直是研究人员的追求。分形概念自提出以来在很多研究领域都有了快速发展,但是在太赫兹波段的应用还不是很常见,特别是应用于太赫兹功能器件的设计。引入分形中科赫曲线的概念设计并制备了一种新型的太赫兹带通滤波器,该滤波器是在金属薄膜上刻蚀出科赫曲线分形结构,当太赫兹波垂直入射到该滤波器时候实现了在太赫兹波段的窄带滤波。在滤波器的设计过程中,追求理论与实验相结合,首先在电磁仿真软件中建立科赫曲线分形结构滤波器模型进行计算,探究分形结构应用于太赫兹波段进行滤波的可行性,在进行多次计算之后得到优化后的尺寸和结构,然后根据优化后的尺寸加工出科赫曲线分形结构太赫兹滤波器样品,并且将样品放在太赫兹时域光谱系统中进行实验测量,得到实验数据后与仿真结果进行比较。在仿真中利用了时域有限差分法模拟科赫曲线分形结构太赫兹带通滤波器的传输特性,优化后的仿真结果表明:滤波器的谐振频率为0.715 THz,透射系数能够达到0.92,-3 dB带宽为21.9 GHz,将仿真得到的散射参数进行S参数反演得到了太赫兹滤波器样品的电磁参数,这在理论上分析了太赫兹波在谐振点处产生透射增强的原因。利用飞秒激光微加工系统制备了尺寸优化后的科赫曲线分形结构太赫兹带通滤波器样品,然后使用太赫兹时域光谱系统对样品的传输特性进行测试,对实验得到的时域数据进行快速傅里叶变换之后得到频域数据,再把频域数据进行归一化处理后与之前的电磁仿真结果进行对比,发现实验测得的结果与电磁软件仿真得到的结果较为吻合。     

Design of a multiband terahertz perfect absorber

A thin-flexible multiband terahertz metamaterial absorber(MA) has been investigated. Each unit cell of the MA consists of a simple metal structure, which includes the top metal resonator ring and the bottom metallic ground plane,separated by a thin-flexible dielectric spacer. Finite-difference time domain simulation indicates that this MA can achieve over 99% absorption at frequencies of 1.50 THz, 3.33 THz, and 5.40 THz by properly assembling the sandwiched structure.However, because of its asymmetric structure, the MA is polarization-sensitive and can tune the absorptivity of the second absorption peak by changing the incident polarization angle. The effect of the error of the structural parameters on the absorption efficiency is also carefully analyzed in detail to guide the fabrication. Moreover, the proposed MA exhibits high refractive-index sensing sensitivity, which has potential applications in multi-wavelength sensing in the terahertz region.     

Terahertz multi-metal-wire hybrid-cladding hollow waveguide for refractive index sensing

We propose a design of terahertz refractive index sensing based on the multi-metal-wire(MMW) hybrid-cladding hollow waveguide. The proposed terahertz hybrid-cladding hollow waveguide comprises one air core in the center surrounding MMW surrounded dielectric. The central air core is used for filling lossless measurands and transmitting terahertz light. In particular, the refractive index sensing is realized by measuring the mode field area(MFA) variation of radially polarized mode. The modal effective refractive index, mode field intensity distribution, and mode field area properties responding to the measurand refractive indexes for different operating frequencies and structure dimensions are investigated, respectively.Simulations show that the proposed terahertz refractive index sensor can realize easily the measurement of the measurand refractive index. Meanwhile, the effects of operating frequency and structure parameters on sensitivity and measurement accuracy are also studied. In view of the trade-off between sensitivity and measurement accuracy, the reasonable choice of the operating frequency and structure parameters can optimize appropriately the sensitivity and measurement accuracy, and the sensitivity can reach approximately 0.585 mm~2/RIU(RIU is short for refraction index units) with the proper frequency and structure parameter.     

Solid freeform fabrication of alumina using laser-assisted ESAVD

Electrostatic spray assisted vapour deposition (ESAVD) has been used successfully to produce films and coatings. A combination of laser-assisted (LA) deposition and ESAVD has been developed for the direct fabrication of alumina ceramics. This novel laser-assisted ESAVD technique involves spraying a liquid precursor onto a substrate whilst a laser beam is simultaneously used to heat the precursor and cause the decomposition and chemical reactions of the precursor in order to produce a solid deposit. A desired three-dimensional (3-D) object can be formed through layer-by-layer deposition using a computer-controlled platform. Dense or porous alumina ceramics can be deposited on the substrate by optimizing the processing parameters. This paper reports the fabrication of alumina parts by the laser-assisted ESAVD method. The effect of processing parameters including laser scanning speed, laser beam size and laser power on the microstructure will be presented. Scanning electron microscope (SEM) and X-ray diffraction (XRD) have been used to characterise the phase and structure of the deposited alumina parts.     

环状烯烃聚合物基底材料的太赫兹复介电常数和损耗特性研究

太赫兹时域光谱(THz-TDS)已被用于研究包括液体,半导体,爆炸物和气体等多种材料。然而自由空间太赫兹光谱系统存在着一些检测局限性,如微量物质难以被检测、系统尺寸难以实现微型化、空气中水的强烈吸收引起的信号衰减较大等问题。为了解决这些问题,研究人员设计了基于金属波导传输线结构的太赫兹芯片集成器件,通过飞秒红外激光激励传输线上的光电导材料实现太赫兹波的产生和检测。然而,在这些芯片上传输的太赫兹信号的频谱宽度很难达到自由空间太赫兹时域光谱系统的频带宽度,一个重要原因是由于传输信号受到随频率增加的传输线损耗所导致的衰减。通常这些损耗主要由三个部分组成：导体损耗,介电损耗和辐射损耗。研究表明：使用低介电常数材料作为共面传输线的衬底,将减少这种介电常数的失配,从而避免冲击波辐射损失;使用具有低损耗角正切的基底材料可以减少太赫兹传输线的损耗。环烯烃聚合物(COP)是一种具有环状烯烃结构的非晶性透明共聚物的材料,在太赫兹波段具有很高的透射率,为了探究这种材料是否能用于共面传输线的衬底,需要通过太赫兹时域光谱技术和介电函数理论分析它在太赫兹频段的光谱和介电特性,以及对这种材料作为基底时用在太赫兹传输线的传输特性进行仿真计算分析。使用透射式太赫兹时域光谱系统,对三种COP、熔融石英和PMMA进行了光谱测试,提取了它们的透射时域信号,采用Dorney和Duvillaret等提出的物理模型计算复介电函数。实验表明：与其他两种材料相比,COP材料在1 THz处的透过率更高,可以达到94.5%,同时介电损耗和介电常数更低,其中介电损耗在1 THz处达到4.31×10-4,因此将COP作为传输线基底材料时能有效减少基底的介电损耗。同时COP材料的介电常数在0.2～2.8 THz范围内维持在约2.3的水平,也有效减弱了辐射损耗。对实验材料基底组成的共面波导传输线进行了HFSS模拟,获得了它们的正向传输衰减系数(S₂₁ parameter),并对由基底引起的介电损耗和辐射损耗进行了计算分析。模拟和计算结果也表明在同一传输线结构下,与其他材料相比COP作为基底时的损耗更小。通过太赫兹时域光谱法与介电响应分析,表明了在太赫兹波段具有较低介电常数的COP材料更适合作为太赫兹传输线结构的基底材料,它可以有效的降低因基底引起的介电损耗和辐射损耗。这为太赫兹传输线的设计过程中衬底材料的选择与应用提供了实验和理论依据。