基于空间能量分布调制增强和控制太赫兹信号

为了有效地对太赫兹波进行增强和连续控制,提出一种通过外部空间干扰调制太赫兹波的空间分布对太赫兹波进行增强和连续控制的方法。通过理论计算对比了未放置和放置空心金属波导的太赫兹波的空间分布,并研究了通过外部空间干扰改变太赫兹波传播路径对太赫兹波空间分布的影响。研究表明,采用改变空心金属波导和激光拉丝相对位置的方法,可以得到连续调控的太赫兹波的空间分布,并且太赫兹波空间分布的最强点能量强度增强了近5.9倍,可为宽带太赫兹波的连续调控提供参考。     

基于狭缝波导的太赫兹场限制能力及频带宽度的研究

狭缝波导由于具有将光场限制在中间空气狭缝区域中传输的特性,使其可用来提高太赫兹集成器件的性能。为了分析狭缝波导结构的太赫兹场的传输特性,利用二维有限时域差分法(COMSOL-光学模块)得到了硅材质的狭缝波导在波长为450μm时的太赫兹场的传输模式和频带宽度,并获得了狭缝波导结构参数与狭缝区域太赫兹场限制能力的关系以及与频带宽度的关系。研究结果为太赫兹狭缝波导的设计提供了参考。     

太赫兹介质波导与金属波导模式转换的设计

为实现太赫兹介质波导与金属波导之间模式的转换,设计了一种低损耗、高耦合效率的锥形波导耦合器。通过有限时域差分法（FDTD）对该结构的传输效率进行了仿真优化。仿真结果表明：锥形波导耦合器在170～220 GHz频段,其基模的传输损耗极低;在190～200 GHz频段,其TM基模的传输损耗接近无。该功能器件可以用于集成太赫兹芯片的耦合。     

变螺距卷弹簧的设计

1 引言一般普通螺距的卷簧,可在自动或半自动卷簧机上进行。但对变螺距、细而长的弹簧的卷制就很难实现了。现仅就机车内燃机上变螺距弹簧在普通车床上卷制的工作原理和方法作一介绍。该弹簧的簧丝直径d=1.6mm内径D_1=2.156mm,总长L=744mm。其中,中间部分长L_1=120mm,螺距t_2=4mm。在保持原设备工作性能的条件下,根据设计和工艺要求,考虑经济、效率等因素,在加长的C620车床上进行卷簧。2 卷簧的工作原理     

基于平行板波导的双槽谐振腔的特性研究

为使在太赫兹横电波模式下基于平行板波导的对称的双矩形谐振腔结构在滤波、传感等方面有更好的应用,在理论上使用有限元方法对该结构在太赫兹横电波模式下进行了理论上的模拟仿真,并使用时域太赫兹波谱系统在实验上对其理论仿真结果进行了验证。理论和实验均表明在太赫兹横电波模式下基于平行板波导的对称的双矩形谐振腔结构,对谐振频率的选择以及谐振频率Q值的大小均与两平行板的板间距有关,即随着板间距的增大,谐振频点均出现了红移,红移的速率为136GHz/mm,并且其Q值也随着板间距的增大而变大。此结果对太赫兹横电波模式下基于平行板波导的对称的双矩形谐振腔结构在滤波、传感等方面的应用提供了参数上的依据。     

电子密度对太赫兹波在均匀非磁化等离子体中的传输影响

针对地面与飞行器之间通信“黑障”问题,采用垂直极化的太赫兹波实现了地面与飞行器的通信。利用放电装置产生等离子体来模拟飞行器表面的等离子体鞘套,使用全光纤耦合式太赫兹时域光谱仪产生0～1 THz的太赫兹波,从实验的角度研究了垂直极化太赫兹波在不同电子密度的均匀非磁化等离子体中的传输特性。实验结果表明：电子密度越大,垂直极化太赫兹在等离子体中的传播速度越快;随着电子密度的增大,衰减会越小。所进行的研究为实现地面与飞行器之间的通信互联提供了重要的实验参考。     

一种太赫兹波导法兰定位销钉孔位置度的判定方法

在太赫兹系统中,波导传输线是最为常用的一种传输线形式。波导组件连接的装配精度,是影响波导组件电气性能和传输线传输功率损耗的关键因素。分析了现有方法应用于太赫兹波导法兰定位销钉孔位置度判定时,出现误差大、误判多等问题,提出了一种通过理想波导口与实际波导口的比对,进行太赫兹波导法兰定位销钉孔位置度判定的方法。     

太赫兹波纹喇叭制造工艺技术实验研究

传输太赫兹(Terahertz,THz)波的馈源结构的特征尺寸在亚毫米量级,且精度要求高.波纹喇叭馈源结构具有良好的电讯特性,但内腔结构复杂,制造难度大.针对太赫兹波纹喇叭的具体结构和技术要求,对微细加工和微电铸工艺技术进行了调研和分析,给出了一种利用这些技术的太赫兹波纹喇叭的精密成形工艺方案.开展了内腔筋宽为0.1 mm的波纹结构的工艺实验,为太赫兹波纹喇叭的精密成形提供了有益的工艺方法和工程经验.     

基于单层超表面的双频太赫兹波线偏振变圆偏振转换器

提出了一种基于单层超表面的双频太赫兹波线偏振变圆偏振转换器。该偏振转换器采用两个不同尺寸的十字型金属缝阵列结构形成两个线偏振变圆偏振转换频点,从而实现双频的太赫兹波线偏振变圆偏振转换。计算结果表明,设计的偏振转换器能在0.760THz和1.068THz将一束线偏振太赫兹波转换为圆偏振太赫兹波。该双频的线偏振变圆偏振转换器仅由单层的超表面组成,结构简单易于制备,因而为操控电磁波和设计新颖的太赫兹波器件提供了参照。     

太赫兹段慢波结构的微细加工技术研究新进展

太赫兹波兼具穿透性强、使用安全性高、定向性好、带宽高等技术特性,在国防、深空通信、远程成像、安全检查和医疗诊断等领域具有重大应用前景。基于慢波结构的电真空器件是在太赫兹频段产生瓦级功率输出,同时实现太赫兹辐射源小型化和经济化最具潜力的一种解决方式。慢波结构作为此类电真空器件的核心零件,其物理设计及制造水平将直接影响器件的带宽和增益,因此,从适合工作在太赫兹频段的慢波结构类型、加工精度与表面质量要求,以及制备工艺3个方面出发,对慢波结构的微细加工技术研究现状进行综述,重点分析太赫兹频段慢波结构的关键制造技术水平及应用现状,并探讨其在发展过程中需要面临的挑战和仍需注重解决的问题,希望能为后续高频器件研究工作的推进提供参考。     

A terahertz radiation spectrum analyzer

A spectrum analyzer of terahertz radiation pulses has been designed for spectroscopic studies of condensed media, gases, and plasmas. The operating frequency range is 0.05–6.00 THz, the frequency resolution is 0.5 cm⁻¹, and the aperture is 40 mm.     

一种基于SIW的阶梯式太赫兹宽带传输线

提出了一种适用于太赫兹频段、长距离传输的阶梯式宽带传输线.将2个基片集成波导(substrate integrated waveguide,SIW)分别置于一个矩形波导两端并分别呈直角转接,整个结构组成一级阶梯形状以实现波导口的空间位置平移.通过在矩形波导两端使用耦合窗的方法完成空气与基片介质之间无模式转换的转接.所提...     

Fresnel reflection in optical components and detectors for the terahertz frequency band

Plane-parallel dielectric and semiconductor windows, beam splitters and radiation absorbers, as well as reflecting metal surfaces, are important components used in experiments with monochromatic terahertz radiation. The wavelengths of this radiation are longer than the wavelengths of visible light; therefore, multibeam interference becomes important in relatively transparent components with a thickness of the order of 1 mm, which is typical for optical systems. This interference causes the characteristics of optical components and detectors to be dependent on the wavelength. It has been found that bolometric power meters with a crystal used as an absorber of terahertz radiation and pyroelectric detectors with a germanium entrance window demonstrate individual periodic variations in sensitivity under variations in the wavelength. Basic characteristics of the windows and beam splitters manufactured from germanium, polypropylene, and Dacron (the materials that are of the greatest interest for terahertz-band spectroscopy) are calculated in the wave band 30–300 μm. The phase shift of s- and p-polarized terahertz waves reflected from metal surfaces are calculated as functions of the wavelength and the angle of incidence. Using the Fresenel formulas for processing experimental data on the reflection coefficient of terahertz radiation incident onto a K8 glass specimen, it is shown that, in the terahertz frequency band, this coefficient is equal to 16% at normal incidence and the absorption coefficient is equal to 860 cm⁻¹. Original Russian Text ? V.V. Gerasimov, B.A. Knyazev, P.D. Rudych, V.S. Cherkassky, 2007, published in Pribory i Tekhnika Eksperimenta, 2007, No. 4, pp. 103–108.     

Compact terahertz time domain spectroscopy system with diffraction-limited spatial resolution

A compact and rigid terahertz time domain spectroscopy system is presented. The size of the device is 20 mm diameter times 61 mm length with four parabolic-shaped concave mirrors dug in it to effectively focus a terahertz beam on a sample. The device has no chromatic aberration over the whole bandwidth of the beam (0.3-2 THz), and an effective numerical aperture of about 0.45 is achieved, which has a capability to image the structure whose size is almost the same as the wavelength. Frequency resolved images clearly show this performance. We also show that quantitative retrieval of the complex refractive index of the structure as small as twice of the wavelength is possible.     

Principle and curve of planetary indexing cam mechanisms

A new type of planetary indexing cam mechanism called type IV is presented. The transmission principle of type IV is discussed. Based on the principle of formation of conjugate tooth contour, the equations of the cam’s pitch curve are derived. The continuity and symmetry of the cam’s pitch curve are also analyzed. It can be concluded that: 1) This type has no output institution so the output precision can be improved; 2) The asymmetrical two-ring structure is used to overcome dead point and its phase angle is equal to (π − 2π/n); 3) The continuous condition of the cam’s pitch curve is that the average transmission ratio is −n in an intermittent motion period. __________ Translated from Chinese Journal of Mechanical Engineering, 2006, 42(2) (in Chinese)     

Silicon diffractive optical elements for high-power monochromatic terahertz radiation

This paper presents a fabrication technique and results of studies of silicon binary diffractive optical elements (DOEs): a diffractive lens and a 1 : 2 diffractive beam splitter with an aperture diameter of 30 mm for the terahertz spectral range. The elements were fabricated in two versions: with and without an antireflection coating of parylene C. The DOE characteristics were investigated in the beam of the Novosibirsk free electron laser at a wavelength of 141 μm. The results are given of a study of the radiation resistance of the coating, which remained intact upon exposure to an average radiation power density of 4 kW/cm²; the peak power in a 100 ps pulse was almost 8 MW/cm². Experimental estimates of the diffraction efficiency of the elements coated with the antireflection coating are in good agreement with theoretical estimates.     

Impeller inlet geometry effect on performance improvement for centrifugal pumps

This research treats the effect of impeller inlet geometry on performance improvement for a boiler feed pump, who is a centrifugal pump having specific speed of 183 m·m³min⁻¹·min⁻¹ and close type impeller with exit diameter of 450 mm. The hydraulic performance and cavitation performance of the pump have been tested experimentally. In order to improve the pump, five impellers have been considered by extending the blade leading edge or applying much larger blade angle at impeller inlet compared with the original impeller. The 3-D turbulent flow inside those pumps has been analyzed basing on RNG k-ɛ turbulence model and VOF cavitation model. It is noted that the numerical results are fairly good compared with the experiments. Based on the experimental test and numerical simulation, the following conclusions can be drawn: (1) Impeller inlet geometry has important influence on performance improvement in the case of centrifugal pump. Favorite effects on performance improvement have been achieved by both extending the blade leading edge and applying much larger blade angle at impeller inlet; (2) It is suspected that the extended leading edge have favorite effect for improving hydraulic performance, and the much larger blade angle at impeller inlet have favorite effect for improving cavitation performance for the test pump; (3) Uniform flow upstream of impeller inlet is helpful for improving cavitation performance of the pump. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.