E型左手材料

由于E型结构具有产生负磁导率所需的等效电感和等效电容,据此提出一种新型左手材料,用E型SRR来实现负的磁导率,金属线结构来实现负的介电常数。等效模型分析证实这个结构确实能够实现稳定的左手特性。有限元法仿真并用S参数法提取等效介电常数、等效磁导率和折射率,得到样本在11.5～14GHz频段内具有明显的负折射率特性。棱镜折射实验也再次证明了该结构的负折射率特性。     

双频带电磁超材料单元设计及仿真

该文基于谐振型左手理论,提出一种将2种不同的多开口谐振环左手结构单元分别印刷在介质板的正、反面,这种复合结构实现了双频带左手特性。在微波频率范围内采用等效参数（NRW）提取算法,验证了该多开口谐振环的复合结构能实现负的介电常数和磁导率,同时采用LC谐振电路进行分析并解释其产生的机理。数值和仿真结果表明,存在2个介电常数、磁导率和折射率的实部都为负的频带。其负频带频率范围分别为16.5~18.96 GHz和22.8~24 GHz,负双频带带宽为3.66 GHz。由于其带宽性能良好的双负特性,可用于多频带或宽带微波器件的设计。     

左手材料理论及其应用

左手材料是一种介电常数和磁导率同时为负值的人工材料,这种材料具有负群速度、负折射率、逆多普勒效应和完美成像等多种奇特的物理性质.叙述了左手材料的概念和基本原理,简单回顾了左手材料研究的发展历程,介绍了左手材料的应用及其发展前景.     

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。     

浅析铁氧体-左手结构在微波领域中的应用

左手材料具有负介电常数和负磁导率的电磁特性,铁氧体具有负磁导率的电磁特性。因此,铁氧体-左手结构可以设计成负介电常数材料,近年来成为备受关注的研究课题,主要应用于隔离器、滤波器和移相器,在微波系统中具有很大的应用前景。文中介绍了铁氧体-左手结构的基本理论和性能特点,并对其在微波领域中的应用进行了试探性的分析。     

左手材料展望

左手材料（left—handed metamaterials;LHMs）是一种介电常数与磁导率同时为负值的电磁材料，因其中传播的电磁波的电场矢量、磁场矢量以及波矢方向满足左手定则而得名。左手材料概念最初由前苏联物理学家Veselago于1964年提出，他从Maxwell方程出发，分析了电磁波在介电常数和磁导率同时为负介质中传播的状况，从理论上指出这种介质的存在是不违反物理学定律的，并且具有负折射效应、逆多普勒效应、逆切仑科夫辐射、完美透镜。等奇异物理现象。但自然界不存在这种性质特异的物质，故在该理论提出的近30年内左手材料发展几乎处于停滞状态。20世纪90年代，随着人工周期性材料的发展，英国皇家学院院士Pendry教授重新开始了该领域研究。2001年Smith等根据Pendry的理论模型，首次制备出微波段具有负介电常数、负磁导率材料，并通过实验观察到了负折射现象。随后左手材料研究取得重大突破，并被Science杂志评为2003年度十大科技进展之一。     

基于复合左右手传输线的超宽带滤波器设计

本文基于复合左右手传输线理论提出了一种设计超宽带滤波器的新方法。该方法从传输的幅度和相位出发,利用微带线结构构建复合左右手传输线,通过控制复合传输线的左手响应频率和右手响应频率来构建微波带通结构。通过在微带线上采用缺陷地板结构物理上实现负等效介电常数,得到低通特性;采用微带线加载交指电容实现负等效磁导率,得到高通特性。最终通过将两种情况组合,构建具有较强左手特性和较弱右手特性的复合传输线,完成基于微带线结构的超宽带滤波器设计。文中给出的仿真结果和实测结果吻合良好,有利的证明了该方法的有效性和实用性。     

关于"负介电常数和负磁导率微波媒质的实验"的两点疑问

人为制造一种具有负介电常数ε和负磁导率μ的媒质,即所谓"负折射率"媒质(或称为"左手媒质"LHM)已成为目前研究的一个热点."中国科学"(G辑)2003年第33卷第5期"负介电常数和负磁导率微波媒质的实验"一文用实验方法验证了该类媒质的存在,在国内尚属首次.纵观全文有两点疑问,有必要提出来以推动该项研究.     

基于微带结构的新型混合左右手材料的研究

介绍了一种具有两个通带的新型混合左右手传输线,以及混合左右手材料传输线的传输特性和分析方法。该左手材料(Left-Handed Metamaterials,LHMs)在通带内呈现介电常数和磁导率同时为负的特性,两个通带分别出现在2.8 GHz和5.8 GHz处。通过仿真得到了色散曲线,折射率,等效介电常数和等效磁导率,从理论上验证了左手特性的存在。     

红外波段左手材料研制获新进展

据科学网报道,西北工业大学理学院应用物理系教授赵晓鹏研究组在红外波段左手材料制备方面的研究日前取得新进展,其研究成果发表于2008年6月出版的《先进材料》(Advanced Materials)上。左手材料是一种介电常数和磁导率同时为负的人工周期性结构材料,由于在其中传播的电磁波的相速度和群速     

低谐振频率电磁超材料单元设计与仿真

针对目前人工电磁超材料的谐振频率(吉赫兹(GHz)或太赫兹(THz))较大的问题,该文提出了一种新型尺寸较大的双面螺旋结构单元模型。通过HFSS仿真软件,建立了电磁超材料单元模型,分析了结构单元的S参数。采用Smith提取算法,得出了等效介电常数和等效磁导率的数学表达式。仿真结果表明,在2.0～2.1 MHz时,等效介电常数恒正,等效磁导率实部达到负极值,而等效磁导率的虚部也达到了最大值,即该频段为材料板的谐振频段,呈磁单负材料属性。     

Cobalt–Polymer Nanocomposite Dielectrics for Miniaturized Antennas

Cobalt–polymer magnetic nanocomposites have been synthesized and characterized for their microstructure and properties such as permeability, permittivity, dielectric and magnetic losses from 100 MHz to 2 GHz to study their suitability as antenna dielectrics. Oxide-passivated cobalt nanoparticles were dispersed in epoxies to form nanocomposite toroids and thin-film resonator structures on organic substrates. Permeabilities of 2.10 and 2.65 were measured up to 500 MHz, respectively, with 25-nm to 50-nm and 5-nm nanoparticles in the nanocomposites. The loss tangent ranged from 0.02 to 0.04 at these frequencies. A combination of stable permeability of ～2 at 1 GHz to 2 GHz and permittivity of ～7 was achieved with nanocomposites having 5-nm nanoparticles. The magnetic nanomaterials described in this paper can overcome the limitations from domain-wall and eddy-current losses in microscale metal–polymer composites, leading to enhanced frequency stability. The paper also demonstrates integration of metal–polymer nanocomposites as thin-film build-up layers with two-metal-layer structures on organic substrates.     

Enhanced Initial Permeability and Dielectric Constant in a Double- Percolating Ni0.3Zn0.7Fe1.95O4–Ni– Polymer Composite

A novel, three-phase, double-percolating composite with NiZn-ferrite particles and nickel particles embedded in a poly(vinylidene fluoride) matrix is prepared by a simple hot-pressing method. Large ferrite particles in the composite not only act as a magnetic phase, thus endowing the composite with a high initial permeability, but also present (in a high volume fraction) a discrete (non-percolating) phase, confining polymer and metallic particles into a continuous double-percolating structure of low volume fraction. In particular, a large enhancement in both the initial permeability and the dielectric constant of the three-phase composites is observed, which is due mainly to the addition of a small number of nickel particles that act as both magnetic and percolative metallic phases. The dielectric and magnetic behavior observed in the three-phase composites can be explained by effective-medium and percolation theories.     

基于微带贴片天线的微流控传感器研究

食用油经高温加热后,其相对介电常数和质量会发生改变,测量食用油的相对介电常数可以检测其 质量。文中提出了一种检测食用油质量的新型微带贴片天线传感器,通过测量输入反射系数的谐振频率的共振偏 移来测定不同介电常数的食用油,工作中心频点为1. 43 GHz 和2. 68 GHz。该设计基于谐振方法,采用基板集成波 导结构结合1~3. 2 GHz 工作频率的五角形缝隙天线,可提供最佳传感精度。该装置可以检测不同介电常数的油脂 类液体,测量的相对介电常数是复介电常数的真实部分,范围从2. 41 到2. 83。因此,所提出的贴片微流控传感器可 用于食用油质量的测定,具有良好的应用潜力。     

基于超介质的超宽带小型化天线设计

采用SRR 环和CLP 环两种不同谐振单元,构造了一种新型超介质结构单元。该单元的电谐振和磁谐振的谐振频点比较接近,易于频带融合,从而拓展超介质材料双负(介电常数和磁导率都为负)特性的频率带宽。利用加载的方法,在单极子天线上加载该种新型超介质结构单元,以改善天线的辐射特性。利用电磁仿真软件对其进行了仿真设计和优化。仿真结果表明,该天线实现了超宽带工作,在3. 8 ~ 14GHz 的频率范围内,驻波比小于2;同时,天线实现了高增益特性,在整个频率范围内,增益都高于7dB。最后,对天线进行了加工测试,实验测试结果与仿真结果基本吻合,进一步验证了该天线的工作性能。     

Propagation properties of ferromagnetic insulator guide

In order to realize new ferrite planar devices for applications at millimeter-wavelength frequencies, the authors have developed nonreciprocal ferrite devices schemes for incorporating ferromagnetic layers in dielectric insulator guide geometries. Their research program involves both the calculation and the measurement of device characteristics. For the calculation, a method of effective permeability, in which the permeability is a tensor, is introduced to characterize the ferrite material. The propagation properties of the insular guide are calculated by using a single-mode approach. The calculated results for dispersion, dielectric, and conductivity losses show resonant behavior with the application of a magnetic bias field for a guide configuration in which the ferrite replaces the insular dielectric. Ferrite phase shifters, filters, isolators, and circulators are potential applications of this guide configuration. For the experimental part of the study, wave dispersion and attenuation were measured in a purely dielectric insular guide from 26.5 to 40GHz. In addition to these experiments wave attenuation was measured as a function of magnetic bias field for the case where a hexagonal ferrite platelet was mounted on the ground plane near the insulator guide. General agreement is found between calculated and measured attenuation     

Material properties and RF applications of high k and ferrite LTCC ceramics

The continuous trend in modern electronic applications towards smaller size, higher integration density and enhanced functionality requires new materials, which allow embedding passive functions into the substrate. In this paper an LTCC material system with specialized dielectric and magnetic LTCC tapes cofireable in a low-shrinkage process for RF-passive integration is reported.An LTCC dielectric with a dielectric constant of up to 80 is presented. The material is successfully used in a cofired multi-material stack to realize a fully integrated band-pass filter for Bluetooth applications of 1.3 mm³ volume.A ferroelectric LTCC ceramic with a maximum dielectric constant of 3000 is presented and the reduction of the dielectric constant to a maximum value of 1100 under constrained-sintering is discussed.Magnetic permeabilities of 14 for a NiZnCo-ferrite and 3.5 for a Ba₃Co₂Fe₂₄O₄₁ (Co₂Z) ferrite have been realized under LTCC processing conditions, with gyromagnetic resonance frequencies above 1 GHz and 3 GHz respectively. The permeability of these materials is determined for constrained and unconstrained sintering conditions. A maximum absorption of 27 dB/cm and 30 dB/cm is measured for an embedded stripline in NiZnCo- and Co₂Z ferrite respectively. Two-winding planar RF-chokes in different multi-layer stacks are compared. A maximum of 14.3 nH inductance is realized for a 1.8 mm × 2 mm coil in an LTCC research pilot line.