矩量法计算烟幕粒子的红外消光特性

基于矩量法建立了旋转体烟幕粒子的红外消光模型,对圆片、等效球体和等效柱体等形状的石墨粒子进行了消光性能计算,研究了形状、尺寸、厚度等参数对粒子红外消光能力的影响.计算结果表明,小尺寸粒子以吸收消光为主,大尺寸粒子以散射消光为主;圆片形状的粒子具有最佳的红外消光能力,厚度变小时,圆片粒子对红外的消光能力显著升高;半径在1...     

Small Hemielliptic Dielectric Lens Antenna Analysis in 2-D: Boundary Integral Equations Versus Geometrical and Physical Optics

We assess the accuracy and relevance of the numerical algorithms based on the principles of geometrical optics (GO) and physical optics (PO) in the analysis of reduced-size homogeneous dielectric lenses prone to behave as open resonators. As a benchmark solution, we use the Muller boundary integral equations (MBIEs) discretized with trigonometric Galerkin scheme that has guaranteed and fast convergence as well as controllable accuracy. The lens cross-section is chosen typical for practical applications, namely an extended hemiellipse whose eccentricity satisfies the GO focusing condition. The analysis concerns homogeneous lenses made of rexolite, fused quartz, and silicon with the size varying between 3 and 20 wavelengths in free space. We consider the 2D case with both - and -polarized plane waves under normal and oblique incidence, and compare characteristics of the near fields.     

太赫兹3D打印透镜综述

太赫兹波由于其独特的电磁特性可应用于超高速率无线通信、生物化学物质检测以及高分辨率成像等领域。但由于太赫兹波的物理波长小,传统适用于低频的加工工艺难以满足其加工精度的要求;而微纳米加工工艺又具有加工复杂、成本高等缺点。3D打印技术的发展为太赫兹器件的加工提供了新的选择和更多的设计灵活度。文章介绍了香港城市大学太赫兹与毫米波国家重点实验室在3D打印太赫兹透镜方面的最新研究动态和实验研究新成果,包括基于3D打印的太赫兹高增益圆极化透镜、近场聚焦圆极化透镜、贝塞尔波束生成透镜的设计,高精度3D打印方法的探索以及太赫兹天线测试方法等。太赫兹3D打印透镜天线具有低成本、低损耗、能快速成型等特点,可应用于不同的太赫兹场景中。     

Double-slot antennas on extended hemispherical and elliptical quartz dielectric lenses

In this paper, the theoretical far-field patterns and Gaussianbeam coupling efficiencies are investigated for a double-slot antenna placed on quartz hemispherical lenses with varying extension lengths. The radiation patterns of the double-slot antenna are computed using ray-tracing inside the lens and electric and magnetic field integration on the spherical dielectric surface. The theoretical results are equally valid for double-dipole, log-periodic, and spiral antennas, and are presented in extension length/radius and radius/λ. Therefore, the results yield universal design curves for quartz lenses of different diameters and at different frequencies and using different antennas. The results indicate that forsingle units, there exists a wide range of extension lengths (ext. length/radius=0.61 to 0.76) which result in high Gaussian-coupling efficiencies to moderately highf/# systems. Forimaging array applications with high packing densities, an extension length/radius=0.82 to 0.93 (depending on frequency) will result in peak directivity and highest packing density but lower Gaussian-coupling efficiencies.     

Microwave Irradiation Design Using Dielectric Lenses (Short Papers)

Theoretical calculations and electric-field measurements were made to investigate the focusing effects of plane-wave-irradiated dielectric spheres (lenses). Spheres of different diameters and dielectric properties and plane wave sources of different frequencies were used in the calculations. The results indicate the feasibility of using dielectric lenses for selective partial-body irradiation in biological experiments.     

A polystyrene cap for matching a silicon lens at millimeter wavelengths

A polystyrene cap for a silicon lens has been fabricated by thermal molding. The cap is 0.5mm thick, and it acts as a quarter-wave matching layer at 94GHz. The measured performance from 75GHz to 170GHz agrees with theory. The reflection loss at 94GHz is reduced by 1.5dB. This is an economical way to make a millimeter-wave anti-reflection coating. This makes a monolithic circuit with a gallium-arsenide substrate and a silicon lens much more attractive than before. The total absorption and reflection loss for a linch diameter lens with the cap should be 1.1dB.     

利用单透镜结构实现自由空间激光进入单模光纤的耦合研究

自由空间激光与光纤的高效耦合可大幅降低激光 能量损耗。基于高斯光束通过透镜的传输规律,分 析经过单透镜变换后的激光光束特性,即像方激光光束特性。对自由空间激光与单模光纤的 优化耦合进行研究。通过分析匹配单透镜参数对像方光束的影响, 选择单透镜合适焦距参数,实现激光与光纤参数的高效匹配,满足激光光束的像方腰斑小于 10 μm且数值孔 径小于0.12。通过实例,分析采用焦距为5mm的单透镜对780 nm空间激光到单模光纤的耦合效 率,结果表明自由空间激光到单模光纤的耦合效率高达90%。该耦合 系统结构简单,可实现激光由自由空间到至光纤的高效率传输。     

一种高集成高空间分辨率220 GHz检波器

本文设计了一种高集成检波器,其包含贴片天线、匹配电路、肖特基二极管和透镜。在中芯国际130nm工艺下将天线、匹配电路、肖特基二极管集成到一个芯片上,检波器的集成度相比于分离式有了明显的提高。为增强片上天线的方向性,进行了带有空气腔的尼龙透镜的设计和优化。透镜上的空气腔不但提供了组装空间而且减小了透镜体积。通过测试,天线在220 GHz辐射增益为22 dB,其中透镜贡献约为20dB。检波器测试得到的响应率可达到130-150V/W,对应的等效噪声功率（NEP）估算为400-460 。     

Resolution of Near-Field Microwave Target Detection and Imaging by Using Flat LHM Lens

It is demonstrated in this paper that higher focusing resolution will be provided by flat left-handed metamaterial (LHM) lens if compared to convex dielectric lens and elliptical reflector focusing system. High-resolution near-field microwave target detection and imaging with flat LHM lens can be implemented by scanning the focal point of the flat LHM lens in the region under detection and screening directly the field intensity distribution of backscattered microwave refocused by the flat LHM lens. Numerical simulations demonstrate that sub-wavelength imaging resolution can be obtained by the proposed approach due to the sub-wavelength focusing resolution of flat LHM lens. Moreover, almost unique imaging resolution for the detection and imaging of target at different depths is also demonstrated. For practical LHM lenses, it is shown that the losses of LHM up to the order as reported in some LHM experiments will limit the sub-wavelength resolution of the proposed approach to an acceptable level.     

环烯烃共聚物太赫兹透镜的设计尧制备及特性分析

研究了一种新型光学聚合物,环烯烃共聚物在0.1～3 THz波段的折射率和透过率特性。借助Solid works软件设计了一款焦距为100 mm、有效孔径为1.75英寸的双凸球面透镜,并设计了制造透镜的模具。通过热压塑成型工艺制造了Topas COC太赫兹透镜,分析了温度和加热时间对透镜面型的影响。利用Zemax软件模拟分析了透镜在太赫兹波段150 m、300 m和600 m的波长、厚度、曲率半径和折射率对焦距的影响。研究表明:利用该技术制造的Topas COC透镜面型光滑、精度高、结构无缺陷、性能优良满足系统线性和紧凑的设计要求,在可见光区和太赫兹波段能够发挥准直和聚焦的作用。     

Microlens fabricated by the planar process

A novel microlens that can be integrated on a laser-diode substrate by the planar process is proposed. It consists of two microcylindrical lenses fabricated by the planar process, and all of their dimensions are less than 100 μm. One lens is a horizontal focusing lens whose curved shape determines focusing. The other is a vertical focusing lens whose gradient refractive index determines focusing. The relationship between fabrication errors and lens characteristics is quantitatively established by comparing lenses with various fabrication errors. Also a laser diode integrated with the horizontal focusing lens is successfully fabricated without damage     

Some Characteristics of Alternating Gradient Optical Transmission Lines

The effect of adding a negative lens between each pair of positive lenses of an optical transmission line is calculated. The negative lens reduces the ability of the transmission line to control the direction of the light beam. The changes in dominant mode spot size, allowed bending radius, critical bend periodicity, and sensitivity to random lateral lens displacements are computed for all ranges of lens spacings and focal lengths which are stable.     

A Multilayer Negative-Refractive-Index Transmission-Line (NRI-TL) Metamaterial Free-Space Lens at X-Band

A volumetric free-space negative-refractive-index (NRI) transmission-line (TL) metamaterial lens is described that employs fully printed interdigitated capacitors and meandered inductors designed to exhibit NRI properties at X-band (8-12 GHz). The volumetric topology is realized in a layer-by-layer fashion without any vias, which facilitates easy and rapid fabrication. The fabricated lens was tested for its transmission and dispersion properties using a free-space X-band measurement system consisting of an Agilent network analyzer, standard gain horn antennas, and Rexolite dielectric lenses fabricated in-house, and showed good correspondence with simulations. The focusing ability of the multilayer NRI-TL lens was also verified using a free-space field probing system based on small shielded-loop antennas affixed to a computer-controlled xyz-translator apparatus. Arguably, these results represent the first experimental evidence of coupling between TL-based metamaterials and sources in free space.     

硫系玻璃在民用红外车载成像系统中的应用

针对324256非制冷探测器,设计了一个工作波段为8~12 m,有效焦距为9 mm,F数为1.3,视场角为33.2626.28的红外车载镜头。镜头采用了硫系玻璃材料Ge28Sb12Se60制备的两片镜片,结合常规红外材料锗以及硫化锌材料制备其他两片镜片,通过合理分配各个镜片的光焦度达到系统整体无热化设计的效果。利用硫系玻璃易于精密模压制备非球面的特点,仅在一片硫系玻璃镜片上设计了一处非球面。设计结果表明该系统在-40~60 ℃的温度范围内具有良好的消色差/热差性能,且调制传递函数(MTF)接近衍射极限。     

Loss analysis of laser diode to single-mode fiber couplers withglass spheres or silicon plano-convex lenses

The single-mode laser diode to single-mode fiber coupling efficiency is analyzed for couplers with glass ball lenses and silicon plano-convex lenses, respectively. The contributions of the different origins of loss are given. It is found that in nearly all cases, most of the total loss is determined by the spherical aberration of the lends that collects the divergent laser diode (lens 1). This loss is calculated for a variety of glass ball lenses and silicon plano-convex lenses are shown to be dependent on the laser diode spot size (or divergence angle). The minimum loss of a coupling configuration is determined with good accuracy by the parameters of lens 1; a single additional parameter, the effective laser diode spot size (or effective divergence angle) for the laser diode; and the coupling arrangement. The calculated losses are compared with experimental values. In most cases, theory and measurement agree very well; differences are discussed     

Results on low-loss wideband ultrasonic transducers for non-invasive medical application

A new design for disc transducers with good efficiency and large bandwidth is presented here. The design method is based on the use of quarter-wave matching layers between the piezoelectric ceramic and the load, and the use of a quarter-wave unmatching layer between the same ceramic and its high acoustic impedance backing. Experimental and theoretical results are presented.     

Indoor signal focusing by means of Fresnel zone plate lens attached to building wall

A simple inexpensive on-wall Fresnel zone plate (FZP) lens for indoor focusing of microwave signals is studied. It consists of concentric metal rings mounted on the outside of an exterior building wall. In our theoretical and empirical work the on-wall FZP lens is illuminated normally by a plane or spherical wave, of vertical or horizontal polarization, but other, more general incidence situations can be treated by similar means. The scalar quasi-optical focusing theory of the free-space zone plate has been modified and used for design and analysis of one-, two-, and three-ring on-wall FZP lenses. It is found that the presence of the wall does not change the FZP lens focusing efficiency significantly, but it has a strong axial defocusing effect. A 2-GHz FZP lens assembly consisting of three metal rings made out of thin antimosquito mesh has a focusing efficiency of about 15 dB (measured) and 14 dB (calculated), and axial defocusing of about 0.22 m. Some variations of on-wall/on-roof FZP lenses and their feasible applications in the microwave/millimeter-wave communication links are also discussed.     

Beam scattering of the Luneberg lens by a complex source point

The complex source point method and vector mode function expansion are used to calculate the electromagnetic beam scattering by the Luneberg lens. A six-layered medium with different radii is considered as a model of the Luneberg lens. A comparison between the well-known numerical result in the Cartesian coordinate system and the new numerical one in the vector mode function is made for the incident Gaussian beam propagation in free space. The propagation properties are in good agreement with each other. The total electric field distributions along the transversal and longitudinal axes are examined for scattering by the Luneberg lens, whose dimension is assumed to be comparable with the beam width. The focusing effect of the Gaussian beam is much lower than that of the plane wave. The spot size focused by the Luneberg lens almost equals the wavelength for the various beam parameters including the plane wave.     

Méthode numérique utilisée dans le cadre ďapplications du principe ďéquivalence en électromagnétisme

Kottler’s formula is difficult to calculate when it is applied to regular surfaces of low curvature, that is when the main radius of curvature are small compared with the free wavelength. To correct the calculated field aberration we suggest the use of a correction normalized diffraction term which is applied to the differential surface. This term is the geometrical mean of the two soft and hard electromagnetic coefficients used in geometric theory of diffraction. The method has been tested with efficiency for spheres, cones and spheroids, and could be used to study the influence of a radome on the radioelectric behaviour of an antenna located inside it.