Design of Linear-to-Circular Polarization Transformers Made of Long Densely Packed Metallic Helices

In this work, we study the realization of realistic polarization transformers formed by long metallic helices. To this end, we propose a new homogenization model to characterize the propagation of electromagnetic waves in a medium formed by infinitely long helices. We derive approximate analytical expressions for the effective permittivity, effective permeability and the magnetoelectric tensor of the composite material, taking into account the effects of spatial dispersion. We apply the new homogenization model to characterize novel linear-to-circular polarization transformers. Our results show that the metamaterial screen may be designed in such a way that an incoming linearly polarized wave may be transformed into a circularly polarized transmitted wave, and that the transmission efficiency of such polarization transformer may be as high as 95%.     

Investigation of a frequency-selective surface based on a planar mushroom-shaped metamaterial with an electronically tunable stopband

A design of a band-stop frequency-selective surface based on a planar mushroom-shaped metamaterial with an electronically tunable stopband has been proposed and investigated. The results of numerical simulation and experimental measurements of the parameters of a finite section of the metamaterial with mounted varicaps are presented. These results illustrate the shift of the structure stopband occurring simultaneously with a change in the capacitance of the lumped elements. Frequency dependences of the inherent dielectric parameters have been obtained. They indicate the presence of negative values of the effective permittivity and effective permeability of the proposed structure and the presence of the surface impedance that significantly exceeds the free-space characteristic impedance and is frequency-tunable.     

Propagation of electromagnetic waves in planar metamaterial waveguides and radiation of antennas based on such waveguides

Propagation of electromagnetic waves in planar waveguides made of metamaterials with negative values of the relative permittivity and relative permeability is analyzed. The specific features of radiation from antennas manufactured on the basis of planar metamaterial waveguides are studied. It is shown that radiation of such antennas is characterized by the backfire radiation effect, i.e., the maximum of the radiation pattern is formed at 180°. The causes of this effect and the conditions for its appearance are revealed. It is proved that this effect appears only in the antennas manufactured on the basis of metamaterial waveguides with negative values of the relative permittivity and relative permeability. A design version of a scanning two-mode antenna operating on the basis of this effect is proposed.     

2-D Isotropic Effective Negative Refractive Index Metamaterial in Planar Technology

We present a fully printable effective negative refractive index (NRI) metamaterial responsive to arbitrarily linearly polarized incident waves. The proposed metamaterial is composed of a periodic array of tightly coupled Jerusalem cross conductor pairs printed on the opposite sides of a dielectric substrate. Each pair supports both symmetric and antisymmetric resonance modes, whose superposition can lead to an effective NRI of the composite medium. A thorough characterization of the transmission properties of such metamaterial is performed, and conclusive evidences of the medium exhibiting effective NRI properties and impedance matching to free space are presented for a range of the structure parameters.      

Modes of a planar nonlinear-metamaterial waveguide

Modes of a planar dielectric waveguide are investigated. The waveguide is made from a nonlinear metamaterial with a negative permittivity and a negative permeability. The mode wavenumbers and field distributions are calculated for structures with parabolic permittivity and permeability profiles. It is shown that anomalously high field intensities can be observed in such a structure. The dependences of the mode propagation coefficients on the electric field are analyzed for the case of nonlinear media. The effect of nonlinearity saturation is considered.     

The dispersion characteristics of metamaterial waveguide modes

The eigenmodes and noneigenmodes of a planar metamaterial dielectric waveguide are investigated. The dispersion dependences and field distributions of the modes are calculated for structures with step and parabolic profiles of the permittivity and permeability. It is shown that the magnetic field can exhibit an anomalously large increase in a waveguide with variable permittivity and permeability profiles. The effect of the nonlinearities of media on the mode propagation coefficients is studied.     

具有宽带特性的超材料设计与分析*

分别提出具有宽带负磁导率特性的圆盘结构超材料和具有宽带双负特性的互联圆盘结构左手材料。对任意极化的垂直入射波,圆盘结构超材料可在8.71GHz到15.19GHz的频段上产生负的磁导率,而互联圆盘结构左手材料则可在6.04GHz到7.40GHz的频段上产生双负特性。通过有限元仿真、本构参数提取、表面电流分布计算、结构参数扫描等方法,对圆盘结构进行了详细分析。结果表明,该结构通过外加磁场激励起的电流环路构成磁谐振回路,进而获得负磁导率特性。利用无限划分的方法,分析了该结构实现宽带特性的原理,推导了等效的磁谐振频率和品质因数的计算公式,并给出其等效电路结构。通过参数扫描,分析了贴片半径、基板介电常数、损耗特性和入射角大小对负磁导率特性的影响规律。对互联圆盘结构左手材料,在提取其等效本构参数的基础上,着重分析了电响应特性,详细推导了等效电等离子体频率的计算公式。     

Novel Planar Metamaterial with a Negative Refractive Index

A new planar metamaterial (MTM) with simultaneous negative values of permittivity (ε) and permeability (μ) is proposed. Our MTM is composed of two identical copper patterns etched on both sides of dielectric laminate, which is very thin and easy to fabricate. Unlike conventional MTMs, the proposed structure shows a negative refractive index (NRI) behavior with respect to a normally incident wave. To explain the underlying principle of the NRI characteristics, an equivalent resonant circuit model based on surface current density distribution is investigated. An eigenmode analysis and a three‐dimensional wave simulation for the stacked MTM prism are also performed to verify the existence of negative refraction. The experimental results from the transmission and reflection measurement ensure the validity of our design approach and show good agreement with the theoretically predicted effective medium parameters.     

Design of Arbitrarily Controlled Multi-Beam Antennas via Optical Transformation

The design of arbitrarily controlled multi-beam antennas is investigated by using the technique of optical transformation. Based on the optical transformation, cylindrical waves emitted from a line source can be converted to plane waves through a metamaterial layer which has a circular shape in the inner outline and a polygon shape in the outer outline. Hence the line source together with the metamaterial layer constructs a high-performance multi-beam antenna. The number of sidelines and the shape of polygon are used to control the number and directions of beams. Analytical formulas of the permittivity and permeability tensors are presented for the metamaterial layer in the antenna. The designed multi-beam antennas are validated by full-wave simulations using the finite-element method. The proposed multi-beam antennas will be very useful in the intelligent traffic system.      

Q-Based Design Equations and Loss Limits for Resonant Metamaterials and Experimental Validation

Practical design parameters of resonant metamaterials, such as loss tangent, are derived in terms of the quality factor Q of the resonant effective medium permeability or permittivity. Through electromagnetic simulations of loop-based resonant particles, it is first shown that the Q of the effective medium response is essentially equal to the Q of an individual resonant particle. This implies that by measuring the Q of a single fabricated metamaterial particle, the effective permeability or permittivity of a meta-material can be estimated simply and accurately without complex simulations, fabrication, or measurements. Experimental validation shows that the frequency-dependent complex permeability analytically estimated from the measured Q of a single fabricated self-resonant loop agrees with the complex permeability extracted from S parameter measurements of a metamaterial slab to better than 20 %. This Q equivalence reduces the design of a metamaterial to meet a given loss constraint to the simpler problem of the design of a resonant particle to meet a specific Q constraint. The Q-based analysis also yields simple analytical expressions for estimating the loss tangent of a planar loop magnetic metamaterial due to ohmic losses. It is shown that tan delta ap 0.001 is a strong lower bound for magnetic loss tangents for frequencies not too far from 1 GHz. The ohmic loss of the metamaterial varies inversely with the electrical size of the metamaterial particle, indicating that there is a loss penalty for reducing the particle size at a fixed frequency.     

The effect of chirality on the existence of backward waves in metamaterials made from resonance planar chiral elements

Artificial media made from lattices of resonance planar chiral elements (RPCEs), such as planar double open rings and plane spirals, are considered. The effect of chirality on the electromagnetic properties of such media is investigated theoretically. It is shown that, when RPCEs are identically oriented, backward waves do not propagate in the medium, although there is a region where permittivity ? and permeability μ are negative simultaneously. However, such a metamaterial exhibits chirality and, hence, the refractive index turns out to be imaginary even when energy dissipation is disregarded. It is found that a medium with the opposite orientation of neighboring RPCEs is nonchiral; in such a medium, the resonance property of ? and μ is retained; the refractive index is real; and backward waves are present at frequencies at which both ? and μ are negative. For these media, it is found that there are regions where the directions of propagation of the wave energy and phase coincide (right-handed passbands), a region where these directions are opposite (left-handed passbands), and regions of evanescent waves.     

Diffraction at a thick screen including corrugations on the topface

A closed-form high-frequency solution is presented for the near-field scattering by a thick screen illuminated by a line source at a finite distance. This solution is applicable to a thick screen with perfectly conducting side walls and either perfectly conducting or artificially soft boundary conditions on the face joining the two wedges. This latter condition is obtained in practice by etching on that face quarter of a wavelength deep corrugations with a small periodicity with respect to the wavelength. It is shown that the artificially soft surface provides a strong shadowing for both polarizations; thus, it is suggested that such configurations may usefully be employed to obtain an effective shielding from undesired interferences. Several numerical calculations have been carried out and compared with those from a method of moments (MoM) solution for testing the accuracy of our formulation, as well as to demonstrate the effectiveness of the corrugations in shielding arbitrarily polarized incident field     

基于超材料的太赫兹幅度调制器设计

提出了一款基于超材料的太赫兹幅度调制器,其结构由开口"弓"形超材料结构、高电子迁移率晶体管、斜十字馈线和碳化硅衬底四部分构成."弓"形超材料结构开口处的连通和断开两种状态将对通过该结构的太赫兹波产生不同的响应.在开口处添加高电子迁移率晶体管可模拟开口连通和断开的效果.当对晶体管上的栅极不施加偏压时,超材料结构开口相当于导通,对太赫兹波透射系数高;当对晶体管上的栅极施加偏压时,超材料结构开口相当于断开,对太赫兹波透射系数低.仿真结果表明,在0.22 THz处,对晶体管栅极不施加偏压时,调制器的透射系数为0.579;对晶体管栅极施加偏压时,调制器的透射系数为0.040.通过公式计算得到其调制深度为93％,而且对x和y极化入射波具有不敏感的特性.同时,通过分析0.22 THz处的电场分布和表面电流分布研究了该太赫兹调制器的工作原理.所设计的太赫兹调制器具有调制深度高、结构简单和易于加工等特点,在太赫兹通信领域具有广阔的应用前景.     

Effects of Electromagnetic Radiation From Digital Wireless Telephone Frequencies on a Double Relaxation Oscillation SQUID

In this paper, the effects of electromagnetic fields from the frequency band of digital wireless telephones on a superconducting quantum interference device (SQUID) were experimentally investigated. A first-order planar gradiometer based on the double relaxation oscillation SQUID (DROS) was operated without low-frequency magnetic shielding, and was exposed to radiated electromagnetic fields in the frequency range of 300 MHz–2 GHz. The experiments have been performed in a fully anechoic chamber to minimize reflected waves in the chamber. The flux-to-voltage transfer and the field sensitivity of the gradiometer have been observed under the irradiation of fields. Results show that the performance of the gradiometer was significantly affected at a typical power level of the digital wireless telephones for both horizontally and vertically polarized electromagnetic waves. The noise level of the DROS output voltage also increases as the strength of the external fields becomes higher.      

基于磁束缚模式相消干涉的类EIT超材料

提出一种具有电磁诱导透明(EIT)效应的太赫兹超材料。该结构单元由非对称排布的2对双金属线(aCWs)组成。当入射电场为垂直极化时,所提结构在0.580 8 THz附近产生磁束缚模式的相消干涉,形成一个Q值较高的异常透明峰。在单元中加入开口谐振环(SRR),SRRs与非对称双金属线对之间产生干涉,形成新的透明峰。加入SRRs后,2对双金属线干涉产生的透明峰的传感特性得到改善。仿真表明,aCWs以及其与SRRs组合而成的结构(aCWs/SRRs)可用于太赫兹的单频带通滤波、双频滤波以及传感。     

Compact left-handed microstrip line based on multiple layered step impedance resonators

A novel compact left-handed (LH) microstrip transmission line is presented. To establish a negative permeability and permittivity, the transmission line is loaded with step impedance resonators (SIRs) and an array of thin wires on dual-layer architecture. Compared to existing LH structures, which incorporate conventional split ring resonators (SRRs), the proposed structure is three times smaller in size whilst achieving the same performance. To illustrate the electromagnetic properties of the metamaterial, both analytical and full wave analysis were performed and utilized to determine the effective electromagnetic parameters of the proposed structures. The experimental results show that a microstrip line periodically loaded with SIR only produces a rejection of ?6?dB at a resonant frequency of 5.50?GHz. The results also indicate a pass-band response for a left-handed microstrip line (LHML) constructed from SIR and thin wire arrays at the same resonant frequency.     

太赫兹超材料生物检测应用研究进展

超材料作为一种具备超常物理性质的人工复合材料,能够突破常规材料的限制,为设计先进功能材料开辟一种全新的思路。太赫兹波由于具有光子能量低、对生物物质无电离损害和分子指纹谱等特性,通过与超材料结合,可实现对生物物质高灵敏检测,越来越受到国内外学者的广泛关注。本文总结了近几年来太赫兹超材料传感器在生物分子和细胞检测领域上取得的进展,首先介绍了太赫兹超材料传感器的传感原理和性能指标,其次从超材料结构设计、衬底选择、以及与微流控和新材料结合等方面阐述了太赫兹超材料传感器在生物检测领域的发展。通过对超材料结构进行优化、采用低介电常数薄型衬底、结合微流控技术或在传感器上粘附新材料涂层,可进一步提高超材料传感器的灵敏度,并丰富其在生物医学检测上的功能。最后,对太赫兹超材料传感器的发展趋势和前景进行了展望。     

平面波在任意磁化方向旋磁媒质中传播时的极化特性

在铁氧体基片平面电路和发射天线中必须研究平面波在任意磁化方向旋磁媒质中的传播。这时平面波的特征波为ＴＥ波,其磁通密度、磁场、电通密度、电场的极化是不相同的,磁场的极化方向为左、右椭圆极化。     

Uniaxial IB-Medium Interface and Novel Boundary Conditions

The class of uniaxial electromagnetic IB media involving five medium parameters is defined as a special case of the previously defined class of general IB media (or skewon-axion media) involving 16 parameters. The problem of plane-wave reflection from and transmission through the interface of a uniaxial IB-medium half space is analyzed. It is shown that, for general values of the medium parameters, waves polarized TE and TM with respect to the normal direction are reflected as from the respective PEC and PMC boundaries. Unlike the anisotropic soft-and-hard surface which has a somewhat similar property, the uniaxial IB interface is isotropic in the plane of the interface. As a consequence, a novel class of electromagnetic boundaries can be defined for general fields requiring vanishing of the normal components of both D and B vectors at the boundary. Another realization of such a boundary in terms of an anisotropic metamaterial with zero axial permittivity and permeability is discussed.     

一种C波段压控超材料表面

提出了一种C波段透射率可调的压控超材料表面。该超材料表面由加载变容二极管的新型可调超材料单元构成,通过直流偏置电压控制变容二极管的电容值,调节超材料单元的电磁特性。通过仿真并计算超材料单元的散射系数、等效介电常数和等效磁导率,该单元的可调谐振频域为5.2~5.6 GHz。将压控超材料表面与微带天线相结合,超材料表面透射率可改变天线远场辐射方向图,通过其对远场辐射方向图的调节,验证了可调超材料表面的性能。对设计的压控超材料表面加0.5~10 V的直流偏置电压,该超材料表面工作频率为5.4 GHz,其透射率能有效调节20 dB。