加载异向介质非辐射介质波导中的慢波传输及应用

将开口谐振环作为加载单元,分析了含有开口谐振环结构非辐射介质波导的新型传输特性.由于异向介质的双各向异性效应,纵剖面磁波型和纵剖面电波型在此新型非辐射介质波导中的传输速度能够减慢,甚至达到零速度.对于波导中的能量关系也进行了分析,研究表明,在一定情况下,慢波传输将引起功率流动的增强.这些特性使得此新型非辐射介质波导更能满足小型化的设计要求. 关键词： 开口谐振环 异向介质 非辐射介质波导 慢波传输     

含有异向介质H形波导的特性研究

将开口谐振环作为加载单元,分析了含有异向介质H形波导的新型传输特性.由于异向介质的双各向异性效应,纵剖面磁波型和纵剖面电波型在此新型导波结构中的相速度能够减慢,并且会引起功率流动的增强.在一些情况下,纵剖面磁波型和纵剖面电波型将出现传播常量随频率增高而减小的异常高次模式.而在其它情况下,利用双各向异性效应可以有效减少纵剖面磁和纵剖面电波型的高次模漏波现象.尤其当异向介质取得单负参量时,此新型导波结构将能够完全抑制高次模漏波的出现.     

含有异向介质H形波导的特性研究

将开口谐振环作为加载单元,分析了含有异向介质H形波导的新型传输特性.由于异向介质的双各向异性效应,纵剖面磁波型和纵剖面电波型在此新型导波结构中的相速度能够减慢,并且会引起功率流动的增强.在一些情况下,纵剖面磁波型和纵剖面电波型将出现传播常量随频率增高而减小的异常高次模式.而在其它情况下,利用双各向异性效应可以有效减少纵剖面磁和纵剖面电波型的高次模漏波现象.尤其当异向介质取得单负参量时,此新型导波结构将能够完全抑制高次模漏波的出现.     

基于双Z形金属条的双入射型左手材料研究

提出了一种新型二维左手材料结构单元,该结构由介质板及其两侧放置的两个反向对称的Z形金属条组成.在电磁波垂直于介质板和平行于介质板入射两种情况下,这种结构单元于X波段均表现出左手通带特性.通过模拟仿真,提取等效电磁参数,建立等效磁谐振电路模型,分析验证了该结构的左手特性.并将双Z形结构与相似的工字形结构相比较,发现在电磁波垂直入射时两种结构均出现相似的左手通带,而在电磁波平行入射时,只有双Z形结构实现了双负特性.结果表明这种双Z形左手单元结构具有更优越的电磁波入射适应特性,即实现了双入射型左手结构单元. 关键词： 双Z形结构 二维 左手材料 双入射     

基于蘑菇型结构的双入射超宽带复合媒质材料设计与分析

通过设计一定的单元结构, 可以实现超宽带人工电磁材料. 基于蘑菇型金属结构, 提出了一种同时具有左右手通带无缝结合的超宽带双入射型复合媒质材料结构单元. 该结构由嵌入到介质板的两个反向对称的蘑菇型金属结构组成, 能够同时引发电谐振和磁谐振而得到左手通带. 通过利用CST软件仿真、等效电磁参数提取、折射率计算以及建立等效磁谐振电路模型等方法, 分析验证了该结构的双入射特性和左手特性. 仿真结果表明, 在电磁波垂直于介质板和平行于介质板入射两种情况下, 在X波段均表现出左手通带特性, 并具有1 GHz以上的左手带宽. 当电磁波垂直于介质板入射时, 在7.2 GHz-9.3 GHz频段为右手通带, 在9.3 GHz-11 GHz频段为左手通带; 当电磁波平行于介质板入射时, 在7.0 GHz-9.0 GHz频段为右手通带, 在9.0 GHz-10 GHz频段为左手通带. 在两种情况下分别于9.3 GHz与9.0 GHz处得到了零折射率, 从而构造了一种正-零-负复合媒质材料, 实现了具有3 GHz带宽的双入射超宽带平衡结构.     

异向介质填充非辐射介质波导和H波导中的高次模及漏波抑制

 通过对加载异向非辐射介质波导(NRD)和H波导的全波分析,研究了此新型导波结构的传输特性。由于开口谐振环所引起的双各向异性效应,在双负参数条件下,纵剖面磁(LSM)波型和纵剖面电(LSE)波型将可能出现传播常数随频率增高而减小的异常高次模式,从而引起漏波。而在其它情况下,利用双各向异性效应却可以有效减少LSM和LSE波型的高次模漏波现象。尤其当异向介质取得单负参数时,此新型导波结构将能够完全抑制高次模漏波的出现。     

基于介质与铁氧体的通阻捷变磁可调频率选择表面设计研究

提出了利用介质陶瓷和铁氧体材料构建可调型带通频率选择表面的设计思路.在C波段波导模式下通过仿真设计出高介电常数方形柱状结构,优化后使其产生宽频的负介电常数,基于等效媒质理论对该结构通阻特性进行分析研究,其传输禁带的产生途径在于介质中产生了具有类Drude谐振形式的电单极子.在相同的仿真环境下对铁氧体结构进行设计优化,调节外加偏置磁场,使铁磁谐振在相应的频点发生,产生负磁导率.利用负介电常数与负磁导率的"双负"特性规律,将两种结构进行组合,协同优化,使电磁谐振相互耦合,实现通带特性.C波段波导模式下的分析表明,两种结构在同一个频点电磁谐振耦合,可以实现"双负"通带的传输效果.在由于铁氧体的磁可调特性,通过改变外加偏置磁场,该通带可以在6—8 GHz范围内可调.对电磁场矢量分布状况和等效参数提取结果进行了数值分析研究,确定了电磁耦合的性质和形成机理,充分验证了这种方法的可行性.对该结构材料样品进行加工,并测试验证,最终实验结果与仿真结果基本一致,实现了"双负"通带的可调.该方法拓展了频率选择表面的设计思路,可用于设计多通带、可调谐频率选择表面.     

二维各向同性异向介质负折射特性仿真验证

提出了一种工作在C波段的二维各向同性异向介质，相比于以往的二维异向介质，它除了具有二维各向同性的优点外，还具有带宽更宽，单元结构的尺寸更小，构造也更简单的特点.通过分别仿真验证异向介质的双负特性和负折射特性最终肯定上述异向介质的存在. 关键词： 各向同性异向介质 宽频带 小单元 双负特性     

一种新型异向介质设计及实验验证

本文提出了工作在X波段的单面双S型异向介质结构,在仿真、实验两个方面对这种新型异向介质的异向特性进行了验证.实验和仿真结果均表明,这种新型的异向介质结构在这一工作频率下具有负折射特性.这种新型的异向介质具有两个优势:更加便于制造和便于添加可控器件使单面异向介质成为可控异向介质.     

1.7—2.7GHz宽频带小单元异向介质设计及其介质参数提取

提出一种单元电尺寸小、工作频带宽、损耗小、结构简单的异向介质设计方案，在1.7—2.7 GHz上所设计的异向介质结构单元电尺寸小于0.035，相对带宽达到45.5%，在整个工作频带上单个结构单元传输损耗小于0.75 dB.对由上述异向介质单元构成的半无限大异向介质平板的电磁波反射、透射特性进行了数值仿真分析，并提取出了电磁波在该异向介质平板中传播时的波数、相速、折射率以及该异向介质平板的有效介电常数和有效磁导率等一系列电磁特性参数，仿真与计算结果表明复波数的实部、相速以及折射率的实部在1.7—2.7 GHz的范围上为负值，并且在相同频带上，有效介电常数和有效磁导率的实部同时为负值，从而有效地验证了“后向行波效应”、“负折射效应”、“双负效应”等异向介质特有的电磁特性，对上述异向介质的存在性给予有力证明. 关键词： 异向介质 宽频带 小单元 介质参数     

包含左手材料的四层平板波导中的光导模

研究一个芯子层是左手材料,其他三层由传统材料构成的四层平板光波导系统,利用图解法对各种TE偏振的导波模式的解进行详细分析.研究表明,四层左手材料光波导既能支持振荡导模,也能支持表面导模,与三层左手材料光波导相比较,此四层波导的导波模式呈现一些新的特性.对于中间传统材料层存在振荡场的情形:芯子层支持振荡导模的光波导中存在基模,并且高阶振荡导模出现模式缺失的性质;芯子层支持表面导模的光波导可以支持基模和多个高阶模式,并且存在模式兼并的性质.对于中间传统材料层存在衰减场的情形,此四层波导结构可等效为三层左手材料光波导.这些新的光波导传输性质对各种光波导器件的制作有潜在的应用价值.     

A NEW FREQUENCY SELECTIVE SURFACE COMPOSED OF LEFT-HANDED MATERIALS

The frequency selective characteristics of a new dielectric periodic structure composed of left-handed materials (LHM) are carefully studied by a method which combines the multimode network theory with the rigorous mode matching method. The variations of the frequency selective characteristics with structure parameters and dielectric loss are presented and comparisons for the frequency selective properties between RHM and LHM gratings are also shown with some explanations. Guidelines for accurate design of the LHM dielectric frequency selective surface are given. Supported by the National Natural Science Foundation of China (No. 60171037) (No. 60371010) and (No. 63531020)     

Propagation of p-polarized waves in a linearly graded index film surrounded by negative index materials

The theory of step-index waveguides is well-established. Most practical slab waveguide structures have a graded-index profile. The basic properties of graded-index planar waveguide structures are similar to those of step-index waveguides with subtle differences. The most common types of graded-index slab waveguides are linearly and exponentially graded-index profiles. We here treat linearly graded-index slab waveguide. In this work, a three-layer waveguide structure with linearly graded-index film is considered. We assume three structures: the first structure comprises a left-handed material (LHM) cladding, the second structure contains a LHM substrate layer and the third has a LHM cladding and substrate. Closed-form expressions for electric and magnetic fields and the characteristic equation are derived. The three normalized parameters: the asymmetry coefficient (a), the normalized film thickness (V) and the normalized guide index (b) are used to study the dispersion properties of the proposed slab waveguide structure.     

左手介质矩形波导的吸收特性

采用微扰法研究了左手介质矩形波导的吸收特性。由于色散方程的限制,左手介质波导不能传输基模,它的吸收特性也与右手介质矩形波导明显不同。结果发现, 模式的衰减系数随长宽比(a/b)的增加而减小,而在右手介质波导中结果恰恰相反。除此之外,当不同模式的光波在同一左手介质矩形波导中传输时,每一模式都对应着相邻很近的吸收峰和吸收谷。同时高阶模的衰减系数较低阶模的大。但是,当不同模式的光波在同一右手介质矩形波导中传输时,它们的衰减曲线随着波导宽度的增加而振荡的变化,并且趋近于芯层衰减系数。另外一方面,在右手波导中,高阶模式的衰减系数较低阶模式小。     

Propagation of Gaussian beams family through a Kerr-type left-handed metamaterial

In this paper the propagation of elegant Hermite-cosh-Gaussian, elegant Laguerre Gaussian, and Bessel Gaussian beams through a Kerr left-handed metamaterial(LHM) slab have been studied. A split-step Fourier method is used to investigate the propagation of laser beams through this media. Numerical simulation shows that Gaussian beams have different focusing behaviors in a Kerr LHM slab with positive or negative nonlinearity. Beam focusing happens in slabs with positive nonlinearity and not in slabs with negative nonlinearity; however, negative nonlinearity is required for a Kerr LHM slab to act like a lens. Additionally, the focusing properties of beams can be controlled by controlling the thickness of the slab or the input power of the incident beam. A multilayer structure is also proposed to have beam focusing by thinner slabs and passing longer distances.     

Photon tunneling and transmittance resonance through a multi-layer structure with a left-handed materialvspace2pt

This paper investigates the photon tunneling and transmittance resonance through a multi-layer structure including a left-handed material(LHM). An analytical expression for the transmittance in a five-layer structure is given by the analytical transfer matrix method. The transmittance is studied as a function of the refractive index and the width of the LHM layer. The perfect photon tunneling results from the multi-layer structure, especially from the relation between the magnitude of the refractive index and the width of the LHM layer and those of the adjoining layers. Photons may tunnel through a much greater distance in this structure. Transmittance resonance happens, the peaks and valleys appear periodically at the resonance thickness. For an LHM with inherent losses, the perfect transmittance is suppressed.     

Negative refractive index in left-handed materials

The real part of the refractive index n(omega) of a nearly transparent and passive medium is usually taken to have only positive values. Through an analysis of a current source radiating into a 1D "left-handed" material (LHM)-where the permittivity and permeability are simultaneously less than zero-we determine the analytic structure of n(omega), demonstrating frequency regions where the sign of Re[n(omega)] must, in fact, be negative. The regime of negative index, made relevant by a recent demonstration of an effective LHM, leads to unusual electromagnetic wave propagation and merits further exploration.     

Structure for localizing electromagnetic waves with a left-handed-medium slab and a conducting plane

A new structure is proposed for localizing electromagnetic waves and energies with a left-handed-medium (LHM) slab and a perfectly electrically conducting (PEC) plane. When a current source is placed in front of a perfectly matched LHM slab with negative permittivity -epsilon0 and negative permeability -mu0 and a PEC plane is placed at the image point, we show rigorously that all the electromagnetic waves are confined in a region between the source and the PEC plane, and the fields outside the region are completely zero. Such an energy-localization system would be useful in medical treatments that use concentrated optical and microwave energies. However, a perfectly matched LHM is unphysical and does not exist in nature. Hence we further study the loss and retardation effects of LHM on the energy localization. Numerical results are presented for the lossy LHM structure to demonstrate the energy localization.     

关于左手性介质几何光学的研究(二)

利用几何光学方法研究了由左手性介质制成的简单透镜的光学特性.推理分析了左手性介质透镜处球形界面的负折射规律,并依此表明了常用光学公式仍适用于左手性介质.指出了左手性介质透镜相对于用传统介质制作的普通透镜所具备的固有优点,最后证实了利用单块左手性介质透镜即可完全消球差,并相应提供了零球差左手性介质透镜的设计实例.     

Negative refraction and imaging beyond the diffraction limit by a two-dimensional left-handed metamaterial

We report our experimental results on two-dimensional left-handed metamaterials (LHM) exhibiting negative refraction and subwavelength imaging. Transmission and reflection spectra of LHM are studied and a left-handed transmission band is observed at the frequencies where both dielectric permittivity and magnetic permeability are negative. Impedance matching is verified both with the experiments and simulations. The two-dimensional LHM structure is verified to have a negative refractive index. We employed three different methods to observe negative refraction; refraction through prism-shaped LHM, beam shifting method, and phase shift experiments. We further demonstrated subwavelength imaging and resolution using LHM superlenses. The effect of thickness on the resolving power is investigated experimentally.