FDTD study of subwavelength imaging by a photonic crystal slab

The problem of subwavelength imaging via a photonic crystal slab lens made of two-dimensional (2D) square arrays of parallel dielectric cylinders in air is studied and discussed theoretically. The finite-difference time-domain method is employed to investigate the unique features of imaging by such lens. We confirm earlier findings that a photonic crystal slab lens can provide the imaging of a point source. By analysing the transmission properties of the proposed structure, we demonstrate that inside the all-angle negative refraction, there are some favourable directions for waves to travel. We show that the surface termination of the photonic crystal is a key parameter to obtain a good quality image. The super-resolution of two sources separated by a distance less than the wavelength is also considered. It is shown that the achievable resolution is limited by the slab length.     

基于SRR的二阶方环滤波器小型化设计

移动通信的飞速发展为微波元件的小型化提出了更高的要求,左手材料因为其负介电常数和负磁导率的特性而被广泛用于天线和滤波器的小型化设计中,SRR作为左手材料的基本构成,用于设计三种基于其原理的二阶微带带通滤波器。文中滤波器具有依次降低的中心频率,代表滤波器尺寸的缩减。其中具有串联叠层式谐振结构的滤波器尺寸为单层结构滤波器尺寸的11%,表现出较好的小型化效果。仿真与实测结果吻合较好,验证了文中结构的可行性。     

左手介质矩形波导导模和表面模的场分布

从麦克斯韦方程组出发,结合电磁场的边界条件,推导出介质矩形波导导模的一般色散方程.对普通介质矩形波导和左手介质矩形波导的导模场分布分别进行了数值模拟.通过对比两种介质矩形波导的导模场分布的模拟结果,发现左手介质矩形波导Ex22模的场分布比普通介质波导Ex00模的场更集中在波导中部.同时,根据处理普通介质矩形波导的Marcatili方法.类比得到左手介质矩形波导表面模的色散方程,并数值模拟了低阶模的场分布,结果表明,能量主要集中在波导的四个角区以及波导的边缘.     

Perturbation Analysis of Dielectric Grating Antenna with LHM Substrate

A dielectric grating leaky wave antenna with a substrate consisted of left handed material (LHM) is presented in this paper, the case where the n = −1 space harmonic of TM mode radiating into the space is carefully investigated through the improved perturbation analysis, which tremendously simplifies the analysis procedure with good calculation accuracy and brings considerable physical insight into the overall behavior of the dielectric grating antenna. It has been found that the new leaky wave antenna is of larger leakage constant than that of the traditional antenna with substrate of the right handed material (RHM). As a result the dimension of the antenna could be largely reduced, which is of practical significance for some applications. Extensive numerical results of the radiation characteristics are given to establish useful guidelines for the design of the new grating antenna.     

On the appropriateness of “molecules-in-molecule” models in describing of π-electronic states of composed aromatic systems

Configuration analysis (CA) allows the straightforward derivation of electronic state correlation diagrams and the critical examination of the appropriateness of simple molecules-in-molecule approaches. The formerly thoroughly investigated fluoranthene is taken as an example. The advantage of composite-molecule approach is demonstrated by the use of energy spectra of fluoranthene analogues.     

Investigation of gain effect of multi-band patch antenna based on composite rectangular SRRs

The paper focus on describing the important influence and physical law of the Split_Resonant_Rings (SRRs) based on Left Handed Material (LHM) on patch antennas. The FDTD method, together with FEM method is used to study the characteristics of patch antenna based on composite rectangular SRRs. A novel composite rectangular SRR system is formed by assembling the conventional patch antenna and SRRs, it is found that electromagnetic wave resonance occurs at several bands: GSM (880–960 MHz), DCS (1710–1881 MHz), and PCS (1850–1990 MHz). The electromagnetic wave's “tunnel effect” and evanescent waves’ enhancing effect are formed, which can improve the localization extent of electromagnetic wave's energy apparently, such effects can improve the antenna's radiation gain and its matching condition. The phenomenon indicates that such composite rectangular patch antennas are promising in wireless communications such as mobile phone, satellite communication and aviation.     

Transmission properties of asymmetric slab waveguides with left-handed materials

A new dielectric slab waveguide with a left-handed material (LHM) cover and substrate is proposed. The dispersion relations and normalized effective thickness of the asymmetric LHM slab waveguide are investigated, in view of the normalized parameters. A number of unusual properties are found, for example, the fundamental and first-order modes do not exist and higher-order modes have double degeneracy. The propagation modes are absent at the low normalized frequency, and the cutoff frequencies of some LHM slab waveguide modes decrease with increase in the asymmetry measure. Unlike traditional slab waveguides, the V –H curves of the LHM slab waveguides are in one-to-one correspondence. Both TE and TM modes are discussed; in addition, the dispersion relations and normalized effective thicknesses of the TM modes are discussed in detail, when the difference in refractive indices of the film and the substrate is small. The results show that the region of mode coexistence taking place near the cutoff frequency becomes narrower with increase in the difference in refractive indices of the film and the substrate. The influence of this difference on the normalized effective thickness curves is different, and becomes smaller and smaller with increase in the value of the asymmetry measure, if different values of the refractive indices are employed.     

Complete Polarization Conversion Characteristics of Dielectric Grating Composed of Left-Handed Materials

The TE/TM polarization conversion characteristics of dielectric grating composed of left-handed materials for the case of plane wave oblique incidence are carefully investigated by a method which combines the multimode network theory with the rigorous mode matching method. It is indicated that complete polarization conversion between TE and TM modes can be realized using left-handed gratings. This can hardly achieve in the conventional right-handed gratings. Comparisons of polarization conversion properties between right-handed gratings and left-handed gratings are given with physical explanations. This unique merit of left-handed periodic structure is of important significance for accurate design of new millimeter wave TE/TM polarization converters.     

左手材料全角度反射器的设计

利用传输矩阵理论,对左手材料(LHM)构成的一维 光子晶体(PC)反射器的反射带特性进行了分析。研究结果 表明,LHM反射器的全角度反射带(ODB)对入射角度是不敏感的,即具有全角度反射的功能。 而右手材料(RHM)反射器的 反射带对入射角度是非常敏感的,得到的是部分角度反射带。进一步分析发现,LHM PC反射 带 对周期数N不敏感,但会随着材料层厚度比k的增大,向高频方向移动,随晶 格常数h 的减小,向低频方 向移动。在此基础上,提出了设计左手材料全角度反射器的方法,并得到了3.1~ 3.9GHz频段之间、反射率高达100%的全 角度反射器。设计结果表明,本文思路可用于实现任意波段全角度反射器的设计。     

一种基于金属开口谐振环和杆阵列的左手材料宽带吸收器

用数值仿真在微波X波段研究了金属开口谐振环和杆阵列这一最基本的谐振结构.通过合理的参数调节,这种结构在10.91GHz附近可以表现出高达98%的吸收率,并且半高峰宽达到3.5GHz.用散射参量提取法计算其有效电磁参数,发现在谐振频率附近其介电常数、磁导率和折射率的实部均为负值.相比于传统的左手材料,这种结构的电磁参数在谐振区域均具有较大的虚部,是形成高吸收率的根本原因.本文的左手材料吸收器在电磁加热、电磁隐身等领域具有许多潜在的应用.