左右手材料光子晶体的双重光学滤波功能

为了设计高品质、高性能的光学滤波器件,采用传输矩阵法,研究左右手材料构成的光子晶体（HL）mDl（LH）m的窄带和宽带通道双重光学滤波功能,并进行了计算机仿真。介质层H是左手或右手材料时,随着排列周期数m增大,在频率ω/ω₀奇数倍处均出现单条窄透射峰;当m不等值变化时,ω/ω₀奇数倍处透射峰透射率均下降且下降速度相同,而ω/ω₀偶数倍处通带透射率不变;H为左手材料时,ω/ω₀偶数倍处还出现通带,且m越大透射峰或通带越窄,ω/ω₀奇数倍处及周围还出现多条窄透射峰。结果表明,光子晶体由左右手材料组成时将得到更好的宽、窄带双重光学滤波效果及调制方法。该研究对新型光学滤波器件的研究和设计具有指导作用。     

INVESTIGATION ON EFFECTS OF LEFT-HANDED MATERIALS ON FREQUENCY SELECTIVE CHARACTERISTICS OF DIELECTRIC PERIODIC STRUCTURES

The effects of left-handed materials (LHM) on frequency selective reflection and transmission characteristics of dielectric periodic structures are carefully investigated using a method which combines the multimode network theory with the rigorous mode matching method. In addition, the effects of LHM dielectric loss on the selective properties are also given. It has been shown that the selective behavior of periodic structures can be modified by adding LHM layers above and below the periodic layer.     

Efficient Design of Directive Patch Antennas in Mobile Communications Using Metamaterials

An efficient approach for designing directive patch antennas using metamaterials is presented. Based on the left-handed-material (LHM) transmission line model, circuit elements L and C of the LHM equivalent circuit model are computed in terms of the prescribed desirable characteristics of directive patch antennas. Formulae to calculate the LHM design parameters from the circuit elements L and C are developed. Design examples for the GSM900 and GSM1800 frequency bands in mobile communications are performed to illustrate validation and efficiency of this design approach.     

Design and analysis of quantized controllable doped left-handed materials

Two kinds of controllable doped left-handed materials (DLHMs) were designed by inserting inductors and capacitors into the traditional left-handed material (LHM) as heterogeneous elements respectively,which are DLHM with inductors (LDLHM) and DLHM with capacitors (CDLHM).The characteristics of transmission spectrum were studied by using finite-difference time-domain method (FDTD).Compared with the traditional LHM,the resonance strength of the LDLHM is weakened and the pass-band is narrowed,but with the increase of the value of the inserted inductors,the bandwidth is expanded.As capacitors inserted into the LHM,the pass-band of the CDLHM is expanded,but the pass-band is shifted to low frequency and the bandwidth is narrowed with the increase of the value of the capacitors,meanwhile,a new generated pass-band is also shifted to low frequency.Therefore,a quantized controllable doped left-handed material can be achieved.     

Imaging by LHM Slab Using Negative Refraction and Reflection

In this paper, we have shown a imaging system using negative refraction and reflection by Left-Handed materials (LHM) slab coated by a metal layerat one side. In this imaging system, one image is within the LHM by refraction, the other is at same side of source by reflection and refraction, which is different from the imaging only by refraction. If the LHM is slight loss and mismatch, the LHM slab can also be regarded as a perfect imaging system.      

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.     

Transmission Characteristics of Ridge Waveguide Loaded with Left-Handed Materials

This paper presents a numerical study of the electromagnetic wave propagation in a double ridge waveguide, loaded with left-handed materials (LHM). The LHM is defined phenomenologically by assigning to it a negative permittivity and negative permeability simultaneously. Transmission characteristics such as cutoff wavelength, single-mode bandwidth, dispersion and field patterns have been investigated by edge-based finite element method. The results are compared to those with air- and dielectric-loaded ridge waveguide. It was found that the LHM-loaded ridge waveguide can greatly increase the cutoff wavelength with the disadvantage of a dramatic reduction in the single-mode bandwidth. The behavior of the dispersion curve of LHM-loaded ridge waveguide is similar to the cases of waveguide loaded with air or dielectric, except for a significant improvement of the propagation constant. The boundary conditions at the interface between the air and the LHM have been well illustrated and the antiparallel wave vector in LHM were obtained by considering the field patterns. The unusual behaviors of the LHM-loaded ridge waveguide provides the potential opportunities to design novel microwave and millimeter devices.     

Transmission spectra of one-dimensional photonic crystals including negative-refractive-index media

We introduce a new model of one-dimensional （1D） photonic crystal composed of alternately arranged RHM and LHM layers with positive and negative refractive indices respectively, for which the transmission spectra of the model are calculated numerically with the transfer matrix method, and the bandgap structure and the polarization properties are analyzed. We found that the introduction of negative refractive index layers （i.e. LHM medium layers） gives rise to some peculiar band-gap structure and polarization properties as follows. Firstly, the forbidden bands are extremely wide and the transmission bands are very sharp without oscillation;and secondly, the change of incident angle has different influences on the forbidden bands of TE and TM modes. For the TM mode, the forbidden band width decreases substantially and finally vanishes, and for the TE mode with central wavelength, the total reflection happens at anv incident anale.     

基于左手介质的共面波导传输线特性研究

针对微带传输线型左手介质构造复杂且工艺要求高的缺陷,提出了一种新型共面波导型左手介质传输线。本文利用串联电容和并联电感来构造左手介质传输线,通过提取共面波导传输线的等效参数,并用全波仿真来模拟此左手介质后向波的传输特性,发现此左手介质的通带在6GHz 到14GHz 之间,其有效带宽为7.5GHz~12.7GHz,即相对带宽 约52%。     

有损耗左手材料模型的时域电磁分析

分析了电磁(EM)场在有损耗左手材料(LHM)模型中能量与损耗因子间的关系,推导了有耗LHM模型的时域有限差分法(FDTD)计算公式,数值模拟了EM场在该有耗LHM材料模型中的传播;对比无耗与有耗LHM模型的EM聚焦特性,分析EM场在不同损耗因子LHM材料中的传播.研究表明,数值结果与理论分析得到较好吻合.     

Broadband Microstrip Antenna With Left-Handed Metamaterials

A novel type of microstrip antenna is proposed for compact wideband wireless applications. The antenna is composed of six unit cells of left-handed metamaterial (LHM) and a dipole element. The dipole is directly connected to three of six LHM unit cells, which are arranged in a 2 $times$ 3 antenna array form. In this aspect, the proposed antenna is regarded as LHM loaded dipole antenna. The antenna is matched with a stepped impedance transformer and rectangular slot in the truncated ground plane. The coupled LH resonances and simultaneous excitation of different sections of unit cells and dipole result into broad bandwidth. The proposed antenna has a maximum gain of $-$1 dBi at 2.5 GHz. The measured return loss indicates 63% bandwidth for $vert{rm S}11vert≪-10 {rm dB}$ over the band of 1.3–2.5 GHz. The overall size of LHM loaded antenna is $lambda_{0}/2.87timeslambda_{0}/11.27timeslambda_{0}/315.80$ at the center frequency. The radiation of the electrically small LHM unit cells is also demonstrated by the simulated radiation pattern, which is an important concept for the antenna miniaturization.      

A compact wide band filter based on the left handed material theory

A novel micro CRLH (composite right/left-handed) wide band filter based on Left handed material (LHM) theory was designed and fabricated. As a promising design, the length of the main part is only 1/20 compared to the working wavelength. It can be used to eliminate the noise in RF interconnect and other area. The phase shift in LHM is negative. This characteristic can decrease the phase delay. And also, the absolute value of phase constant will increase when frequency decrease at the left handed band (LH-band), which contribute to minimize the design. The other advantage of the LHM is that the phase constant will changed to the opposite direction, when the wavelength changed with the working frequency. This provides a negative feedback to the electric length, so the left handed region has a wider band width. Measurements results show that relative bandwidth (3 dB) of 8 cells is 71.42%. The relative bandwidth (3 dB) of 4 cells is 58.46%.     

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.     

有损耗左手材料电波传播特性的FDTD分析

为研究电磁波在有损耗左手材料中的传播特性,采用时域有限差分（FDTD）法和色散媒质的Drude模型,推导出基于Drude模型的左手材料二维FDTD迭代方程。一维数值仿真结果验证了平面电磁波在穿过有耗左手材料时,其相速度大小与光速相同,方向与传播方向相反,且随着损耗因子的增大,左手材料内的电场强度幅值亦相应减小。此外,还利用多循环m-n-m脉冲作为激励源,对左手材料平板具有的完美透镜现象进行了二维数值仿真验证。结果表明,有耗平板左手材料具有明显的聚焦效果,在特定条件下能实现完美成像。     

Complex Envelope Crank-Nicolson Nearly PML Algorithm for the Left-handed Material FDTD Simulations

Unconditionally stable complex envelope (CE) absorbing boundary conditions (ABCs) are presented for truncating left handed material (LHM) domains. The proposed algorithm is based on incorporating the Crank Nicolson (CN) scheme into the CE finite difference time domain (FDTD) implementations of the nearly perfectly matched layer (NPML) formulations. The validity of the formulations is shown through numerical example carried out in one dimensional Lorentzian type LHM FDTD domain.     

Electromagnetic-field theory and numerically generated results for propagation in left-handed guided-wave single-microstrip structures

Dispersion diagrams and magnetic- and electric-field distributions are found for a microstrip structure containing a simple left-handed medium (LHM). The LHM material constituting the substrate has characteristics chosen to overlap with potentially realizable substances. Calculations are done using a fast solver anisotropic Green's function spectral-domain computer code. The theoretical-field method, valid for complex layered structures and anisotropies in the LHM, underlying the computational procedure, which is critical for finding the dispersion diagrams and field distributions, is presented. It is found that the dispersion diagrams and field distributions are very unusual and admit the possibility of completely new device realizations based on combining LHM with conventional materials in a multilayered configuration.     

左手介质在增强电偶极子辐射功率上的应用

基于严格的电磁场理论,给出了左手介质壳包围电偶极子后的辐射场本征函数级数解.应用该级数解求解出该情况下的辐射功率,并与自由空间中电偶极子辐射场进行了比较,指出了左手介质在增强电偶极子辐射功率上的应用,并运用微波电路理论对该特性进行了分析验证.     

左手结构及其在天线微波领域中的应用

左手材料因其具有介电常数和磁导率同时为负值的电磁特性,近年来得到科学界的广泛关注。基于微带线等传输线结构所构成的左手材料与传统右手材料相比传输相移特性亦有不同,因此在天线微波系统中具有很大的应用潜力。文中介绍了这类左手传输结构的基本设计理论和性能特点,并对其在未来天线微波领域中的应用进行了探讨。     

左手材料电磁散射特性的仿真研究

分别采用电磁场仿真软件CST MWS和CADFEK0仿真计算了不同电尺寸右手材料和左手材料介质球的电磁散射特性,并对电磁散射数值进行分析,同时与Mie理论计算结果相比较,可得出以下结论:无论在仿真电小尺寸还是电大尺寸的目标时,CADFEK0仿真效果部比CST MWS更佳.最后用CADFEKO软件仿真了金属球涂覆右手材料...     

Surface modes in slab waveguides with a left handed materials cover

The surface mode propagation along a dielectric slab waveguide which consists of the core and substrate of right handed materials (RHM) and the cover of left handed materials (LHM) is studied. The normalized frequency and normalized propagation constant are introduced to the left-handed material slab waveguides. The dispersion relations expressed by the normalized parameters are derived. Universal dispersion curves are obtained analytically. Based on that, the dispersion properties differ dramatically for d...