基于介质谐振器原理的左手材料设计

本文通过对高介电常数介质基于介质谐振器理论进行分析,明确了利用高介电常数介质产生负介电常数或负磁导率的途径在于介质中产生具有Lorentz谐振形式的电磁响应的电偶极子或磁偶极子,指出了这种偶极子的产生来源于电磁波在介质中形成的驻波,而左手通带的形成正是由于电偶极子和磁偶极子之间的相互影响,破坏了驻波形成的条件所实现的. 模拟结果表明,通过将尺寸相同,介电常数不同的介质进行组合,使二者电谐振和磁谐振的频率点重合从而实现左手通带,最后利用高介电常数,低损耗的陶瓷进行样品制作并测试,测试结果证实了基于这一原理实 关键词： 全介质左手材料 介质谐振器 磁偶极子 电偶极子     

Low-loss negative-index metamaterial at telecommunication wavelengths

We fabricate and characterize a low-loss silver-based negative-index metamaterial based on the design of a recent theoretical proposal. Comparing the measured transmittance and reflectance spectra with theory reveals good agreement. We retrieve a real part of the refractive index of Re(n)= -2 around 1.5 microm wavelength. The maximum of the ratio of the real to the imaginary part of the refractive index is about three at a spectral position where Re(n)= -1. To the best of our knowledge, this is the best figure of merit reported for any negative-index photonic metamaterial to date.     

有耗异向介质层覆盖普通介质圆柱电磁特性的研究

研究了线电流源平行放置在有耗异向介质层覆盖的无限长介质圆柱附近模型的电磁特性.首先,提出电磁模型并给出此电磁模型的精确解.其次,利用精确解进行数值计算,得到不同电磁参数情况下该电磁模型的近场分布图形,并通过方向性系数和归一化辐射阻抗研究其远场特性.由于有耗异向介质的负折射特性和损耗的同时作用,相比于无耗异向介质层以及有耗普通介质层,得到了有耗异向介质层覆盖普通介质圆柱模型在近场和远场特性上极为不同的电磁特性. 关键词： 线电流源 异向介质 方向性系数 辐射阻抗     

Achieving a multi-band metamaterial perfect absorber via a hexagonal ring dielectric resonator

A multi-band absorber composed of high-permittivity hexagonal ring dielectric resonators and a metallic ground plate is designed in the microwave band.Near-unity absorptions around 9.785 GHz,11.525 GHz,and 12.37 GHz are observed for this metamaterial absorber.The dielectric hexagonal ring resonator is made of microwave ceramics with high permittivity and low loss.The mechanism for the near-unity absorption is investigated via the dielectric resonator theory.It is found that the absorption results from electric and magnetic resonances where enhanced electromagnetic fields are excited inside the dielectric resonator.In addition,the resonance modes of the hexagonal resonator are similar to those of standard rectangle resonators and can be used for analyzing hexagonal absorbers.Our work provides a new research method as well as a solid foundation for designing and analyzing dielectric metamaterial absorbers with complex shapes.     

Terahertz response of a microfabricated rod-split-ring-resonator electromagnetic metamaterial

The first electromagnetic metamaterials (EM3) produced by microfabrication are reported. They are based on the rod-split-ring-resonator design as proposed by Pendry et al. [IEEE Trans. Microwave Theory Tech. 47, 2075 (1999)] and experimentally confirmed by Smith et al. [Phys. Rev. Lett. 84, 4184 (2000)] in the GHz frequency range. Numerical simulation and experimental results from far infrared (FIR) transmission spectroscopy support the conclusion that the microfabricated composite material is EM3 in the range 1-2.7 THz. This extends the frequency range in which EM3 are available by about 3 orders of magnitude well into the FIR, thereby widely opening up opportunities to verify the unusual physical implications on electromagnetic theory as well as to build novel electromagnetic and optical devices.     

All-dielectric left-handed metamaterial based on dielectric resonator: design, simulation and experiment

Dipoles with Lorentz-type resonant electromagnetic responses can realise negative effective parameters in their negative resonant region. The electric dipole and magnetic dipole can realise, respectively, negative permittivity and negative permeability, so both the field distribution forms of electric and magnetic dipoles are fundamentals in designing left-handed metamaterial. Based on this principle, this paper studies the field distribution in high-permittivity dielectric materials. The field distributions at different resonant modes are analysed based on the dielectric resonator theory. The origination and influence factors of the electric and magnetic dipoles are confirmed. Numerical simulations indicate that by combining dielectric cubes with different sizes, the electric resonance frequency and magnetic resonance frequency can be superposed. Finally, experiments are carried out to verify the feasibility of all-dielectric left-handed metamaterial composed by this means.     

Probing solar system objects at infrared wavelengths

Two recent investigations of solar system objects are described as examples of the application of high spectral resolving power and of combined temporal-spatial power spectral analysis to planetary problems. The detection and characterization of water vapor in comets Halley and Wilson (19861) by airborne infrared observations is used to illustrate the extraction of physico-chemical information from doppler-limited spectra. Time series analysis of thermal emission from the atmosphere of Jupiter is used to illustrate the extraction of dynamical information from two dimensional photometric measurements.     

Low-loss multilayered metamaterial exhibiting a negative index of refraction at visible wavelengths

We experimentally demonstrate a low-loss multilayered metamaterial exhibiting a double-negative refractive index in the visible spectral range. To this end, we exploit a second-order magnetic resonance of the so-called fishnet structure. The low-loss nature of the employed magnetic resonance, together with the effect of the interacting adjacent layers, results in a figure of merit as high as 3.34. A wide spectral range of negative index is achieved, covering the wavelength region between 620 and 806 nm with only two different designs.     

树叶状红外频段完美吸收器的仿真设计

设计了一种由树叶状金属薄膜-介质层-金属薄膜构成的低剖面完美吸收器模型. 通过对金属介电性能采用Drude定理,仿真发现调节结构参数可在红外通讯频段几乎达到完美吸收 (吸收率为99.5%),并且在某些特定的结构参数下可以同时实现双频段的完美吸收 (其吸收率分别达到99.67%和97.13%),这在某种意义上展宽了吸收频带, 对红外吸收器的设计与应用极为有利.最后探索了叶颈宽度变化对双频吸收峰位置的影响, 以便对双峰吸收进行调频操作.这种红外频段的超材料吸收器具有结构简单、吸收效率极高、工作频段宽等优点.     

Radiation-induced transmission loss in optical materials at infrared wavelengths

Information concerning the effect of irradiation on the optical properties of materials in the infrared, sub-mm-and mm-wavelength regions is of increasing importance in fusion plasma diagnostics. The radiation induced transmission loss of a number of materials has therefore been investigated at wavelengths in the ranges 200 nm to 40 μm and 0.23 to 2.0 mm. The samples were irradiated with doses of up to 10¹⁰ rad in a nuclear reactor. While germanium shows considerable transmission loss at doses as low as 10⁶ rad, and the transmission of TPX decreases at 10⁹ rad, other materials, e.g. fused quartz and possibly ZnSe, exhibit sufficient radiation hardness for use in fusion plasma diagnostics.     

An open resonator technique for the measurement of atmospheric propagation characteristics at submillimetre wavelengths

A three-mirror open resonator technique is indicated for the measurement of absorption and refractive index of the atmosphere in the submillimetre wavelength region. The technique is illustrated at 337 μm wavelength for an atmosphere with a varying water vapour content.     

Negative refraction at infrared wavelengths in a two-dimensional photonic crystal

We report on the first experimental evidence of negative refraction at telecommunication wavelengths by a two-dimensional photonic crystal field. Samples were fabricated by chemically assisted ion beam etching in the InP-based low-index constrast system. Experiments of beam imaging and light collection show light focusing by the photonic crystal field. Finite-difference time-domain simulations confirm that the observed focusing is due to negative refraction in the photonic crystal area.     

Properties of optical resonator with a layered metamaterial

The properties of longitudinal and transverse modes of an open optical resonator containing layers of a metamaterial with negative refractive index are studied. Due to the presence of these layers, the metaresonator acquires unique properties compared to a conventional open resonator. Eigenmodes of the metaresonator are studied in which the properties depend on the average dispersion and the average diffraction, which may be either positive, negative, or zero. The conditions of the existence and profiles of the waveguiding modes are obtained. The resonator with zero average diffraction is of particular interest. It is shown that, in this case, the waveguiding mode may have an arbitrary amplitude profile. Under these conditions, the discrete set of the transverse modes becomes continuous, and the eigenfrequencies become independent of the transverse amplitude profile. The resonator’s stability conditions are derived based on the ray-matrix method and diffraction theory. It is shown that insertion of a metamaterial into the resonator substantially affects the region of stability and existence of the waveguiding modes. In particular, the unstable empty resonator can thus be rendered stable.     

Experimental demonstration of electromagnetic tunneling through an epsilon-near-zero metamaterial at microwave frequencies

Silveirinha and Engheta have recently proposed that electromagnetic waves can tunnel through a material with an electric permittivity (epsilon) near zero (ENZ). An ENZ material of arbitrary geometry can thus serve as a perfect coupler between incoming and outgoing waveguides with identical cross-sectional area, so long as one dimension of the ENZ is electrically small. In this Letter we present an experimental demonstration of microwave tunneling between two planar waveguides separated by a thin ENZ channel. The ENZ channel consists of a planar waveguide in which complementary split ring resonators are patterned on the lower surface. A tunneling passband is found in transmission measurements, while a two-dimensional spatial map of the electric field distribution reveals a uniform phase variation across the channel--both measurements in agreement with theory and numerical simulations.     

Surface electromagnetic waves at the interface between two dielectric superlattices

The electrodynamic properties of the interface between two periodic dielectric superlattices are studied. It is shown that the interface may serve as a guide for an electromagnetic wave whose field decays exponentially on both sides of the plane of the interface. The field and power flux distributions, as well as the frequency dependence of the field penetration depth, are studied.     

Dynamical electric and magnetic metamaterial response at terahertz frequencies

Utilizing terahertz time domain spectroscopy, we have characterized the electromagnetic response of a planar array of split ring resonators (SRRs) fabricated upon a high resistivity GaAs substrate. The measured frequency dependent magnetic and electric resonances are in excellent agreement with theory and simulation. For two polarizations, the SRRs yield a negative electric response (epsilon < 0). We demonstrate, for the first time, dynamical control of the electrical response of the SRRs through photoexcitation of free carriers in the substrate. An excited carrier density of approximately 4 x 10(16) cm(-3) is sufficient to short the gap of the SRRs, thereby turning off the electric resonance, demonstrating the potential of such structures as terahertz switches. Because of the universality of metamaterial response over many decades of frequency, these results have implications for other regions of the electromagnetic spectrum.     

微波超材料隐形结构及其新型快速实验方案

基于Maxwell方程组在坐标变换下的协变性,利用柱坐标变换以及开口谐振环周期排列而形成的超材料设计了一个工作于10.14GHz频率下的隐形结构.采用一种新型快速实验方案测量微波信号强度.实验结果表明在外围增加了隐形结构之后,圆柱金属的阴影和散射效应都被削弱,得到了预期的隐形效果.该实验系统降低了系统的结构复杂性并缩短了实验周期,为该领域的研究提供了一种新的简单有效的实验方案.