一种介质-金属加载圆孔单元厚屏频率选择表面

厚屏频率选择表面能较好地改善FSS带宽性能,是实现隐身雷达天线罩的有效手段.为了全面掌握厚屏FSS的传输特性,给FSS的工程应用提供可靠依据,本文设计了一种介质-金属加载圆孔单元的厚屏频率选择表面.采用矩量法对此结构进行分析计算,主要研究了加载金属直径、加载介质厚度、电磁波入射角等几个参数对厚屏FSS传输特性的影响规律.仿真实验结果表明:带宽、中心频率及其透过率都对填充介质直径、加载金属直径、加载介质厚度、电磁波入射角和不同排列方式有不同程度的敏感性,可以通过合理调整加载金属直径及加载介质厚度来获得较宽的通带和较高的透过率.这为实现厚屏FSS在曲面隐身雷达天线罩上的应用提供了一种有价值的借鉴.     

Frequency selective surface structure optimized by genetic algorithm

Frequency selective surface (FSS) is a two-dimensional periodic structure which has prominent characteristics of bandpass or bandblock when interacting with electromagnetic waves. In this paper, the thickness, the dielectric constant, the element graph and the arrangement periodicity of an FSS medium are investigated by Genetic Algorithm (GA) when an electromagnetic wave is incident on the FSS at a wide angle, and an optimized FSS structure and transmission characteristics are obtained. The results show that the optimized structure has better stability in relation to incident angle of electromagnetic wave and preserves the stability of centre frequency even at an incident angle as large as 80°, thereby laying the foundation for the application of FSS to curved surfaces at wide angles.     

Frequency selective surface with a flat topped passband

Two frequency selective surface (FSS) configurations with flat topped passband are presented in this paper.One configuration is single layer FSS with λ/4 thickness dielectric loaded on both sides, and the other is double layers FSS. Based on the modal matching method, the frequency response properties including angle effect and polarization effect of both FSS configurations are analyzed, and the plots of the frequency versus transmission coefficient are obtained for different incident angles and polarizations. It is shown that the structure with the single layer FSS embedded centrally in the λ/2 thickness dielectric has a wider flat top bandwidth of 6.8 GHz than that of the double layers FSS of 3 GHz. In addition, the fabrication of single layer is relatively easier than the double layers FSS.     

一种圆孔单元厚屏频率选择表面结构的传输特性研究

设计了一种圆孔单元的厚屏频率选择表面(FSS)结构,采用矩量法对该结构的传输特性进行仿真研究.主要研究厚屏FSS在无介质加载条件下,其单元直径、排布周期、电磁波入射角等参数对厚屏FSS传输特性的影响规律.结果发现,厚屏FSS的单元直径、单元间距、入射角对带宽影响较大;而单元直径对中心频率影响不大.     

双屏频率选择表面结构的遗传算法优化

双屏频率选择表面能够更好地实现平顶效应和快速下降的边缘,是一种实现雷达舱对探测带外雷达波隐身的有效手段.本文针对双屏频率选择表面(FSS)在电磁波不同角度入射下的宽带通应用,采用遗传算法对FSS介质厚度、介电常数、单元图形、排列周期进行了整体优化,给出优化后的FSS结构和传输特性曲线;同时采用镀膜和光刻技术制备出相应的实验件,在微波暗室进行了测试.结果表明,优化后的结构在保证2 GHz的工作带宽下,对电磁波的入射角度有良好的传输稳定性,这为实现双屏FSS在曲面大角度下的应用奠定了基础. 关键词： 频率选择表面 遗传算法 优化     

Broadband dielectric film transflector for variable transmission optical filters

A broadband multilayer dielectric film transflector for applications in variable transmission optical filters is proposed. The dielectric film is composed of alternating TiO₂ and SiO₂ layers deposited on a substrate. The transmittance of the dielectric film transflector can be varied from 0 to 100% by adjusting the individual dielectric layer thickness and the number of layers. The conjugate gradient method is used to optimize the design of the transflectors. The obtained transflectors have good transmittance and reflectance within the whole visible range and the incident angle range 0-20°. The manufacturing tolerances on film thickness and refractive index are reasonably large.     

Improvement on the wave absorbing property of a lossy frequency selective surface absorber using a magnetic substrate

An equivalent-circuit model is used to analyse the improvement of the wave absorbing performance of the lossy frequency selective surface(FSS) absorber by using a magnetic substrate,showing that it is possible to widen the wave absorbing bandwidth.Three pieces of magnetic substrates are prepared.According to the complex permittivity and permeability,the reflectivity of the corresponding absorber is calculated by the finite difference time-domain(FDTD) method,and the bandwidth of the reflectivity below 10 dB is optimized by genetic algorithm.The calculated results indicate that the wave absorbing performance is significantly improved by increasing the complex permeability of the substrate;the reflectivity bandwidth below 10 dB of the single layer FSS absorber can reach 3.6-18 GHz with a thickness of 5 mm,which is wider than that with a dielectric substrate.The density of the FSS absorber is only 0.92 g/cm 3.Additionally,the absorption band can be further widened by inserting a second lossy FSS.Finally,a double layer lossy FSS absorber with a magnetic substrate is fabricated based on the design result.The experimental result is consistent with the design one.     

Research on asymmetric ＂Jerusalem＂ unit

An asymmetric Jerusalem unit and the frequency selective surface （FSS） structure composed of such units are designed. The transmittance of the designed FSS structure is calculated by mode-matching method and compared with the test results. The comparison results show that the FSS center frequency of the asymmetric structure unit drifts little with the variation of the incident angles of the electromagnetic waves and keeps relatively stable. The research offers a new choice for the application of FSS under the large scanning angle of electromagnetic waves.     

一维等离子体光子晶体的带隙研究

采用时域有限差分方法(FDTD),结合等离子体计算中的分段线性电流密度卷积技术(PLJERC)对一维等离子体光子晶体(1D-PPC)进行了数值模拟,给出了微分高斯脉冲在一维等离子体光子晶体中的传播过程。计算得到的带隙结构与K-P模型方法的结果一致。计算并分析了等离子体频率、介质介电常数、等离子体-介质层的厚度比以及周期厚度对一维等离子体光子晶体带隙结构的影响。     

Effects of manufacturing tolerances on the electrical performance of suspended and inverted microstrip lines

Effects of manufacturing tolerances in the dimensions and parameters of suspended and inverted microstrip lines on the electrical performance of these lines have been studied through sensitivity analysis. The closed-form expressions recently given by Pramanick and Bhartia for the analysis of these lines have been used to derive the mathematical expressions for various sensitivities and the dependence of sensitivities on the aspect ratios and on the substrate dielectric constant has been depicted graphically. Generally speaking, the effects of tolerances are seen to be reflected much more sharply in the sensitivities of the characteristic impedance than in those of the effective dielectric constant. Many other useful inferences are also drawn from the sensitivity graphs. The conclusions are presented in tabular form, so as to be of direct help to the user.     

电磁屏蔽用低频比小型化双频带频率选择表面

为满足敏感电子设备对频段密集相邻干扰信号的屏蔽需求,提出了一种低频比双频段带阻频率选择表面（FSS）结构。该结构由介质层和印刷在其两侧并谐振在不同频率的金属导带层构成。通过对两侧金属导带的互补型设计,削弱了两个谐振点间的耦合影响,使该FSS结构具有两个可以独立调节且紧密相邻的阻带,呈现出低频比特点。仿真结果表明,此结构可以实现低至1.16的谐振频率比。基于弯折结构的小型化设计使该FSS的单元尺寸仅为0.071λ,确保所提结构在TE和TM两种极化电磁波照射下,电磁屏蔽效能大于24 dB的入射角度稳定性高达60°。制作了实物并进行测试,实测结果与仿真结果吻合良好,验证了FSS结构设计的可靠性。     

Perfect-absorber metamaterial based on flower-shaped structure

We theoretically and experimetally investigated the narrow-band peak of perfect absorber (PA), which was realized with a metal–dielectric–metal scheme based on a flower-shaped structure (FSS). The PA slabs were designed and fabricated to work in the GHz range of electromagnetic radiation. The absorption is due to the magnetic influence and therefore, the resonance frequency can be easily controlled without affecting the efficiency of the absorption peak by changing the dimensional parameters of the FSS. In addition, the FSS also results in polarization independence of electromagnetic waves, as expected due to its geometry.     

一种性能稳定的新单元频率选择表面

通过对十字孔径单元的四个端点添加L形的孔径,给出了一种新单元的频率选择表面(FSS)设计,同时通过拆分,得到了相对应的拆分单元FSS.利用谱域法,对两种FSS结构从理论上进行了分析,在TE波入射时角度变化、大角度入射时极化变化对中心频率的影响以及通带带宽三个方面进行了研究,并采用镀膜和光刻技术制备了两种FSS结构的实验样件,在微波暗室中进行测试,得到的实验曲线与理论仿真曲线基本一致.结果表明：新单元的两种FSS结构的中心频率均能在TE波入射时实现角度稳定性和大角度入射时实现极化稳定性;拆分单元FSS的中心 关键词： 频率选择表面(FSS) 新单元 极化稳定性 角度稳定性     

Frequency Selective Surfaces with Anisotropic Dielectric Superstrates

A full wave analysis is developed for frequency selective surfaces composed of rectangular patches mounted on a dielectric anisotropic substrate and covered with a uniaxial anisotropic superstrate. The moment method is used in combination with the spectral domain immittance approach to determine the FSS structure reflection and transmission coefficients.     

利用等效电路模型快速分析加载集总元件的微型化频率选择表面

为了提高频率选择表面(FSS)设计优化速度, 利用等效电路方法对基于集总元件加载的微型化FSS结构进行了分析. 根据FSS物理结构建立了相应的等效电路模型, 通过ADS软件对全波分析曲线进行拟合提取了等效电路模型参数, 通过延长曲线范围增加极值点个数提高拟合参数精度. 利用所提取的等效电路参数计算了不同LC 参数下FSS的传输特性, 与全波分析精确结果相对比, 电路模型计算的透过率略高, 中心频点及-3 dB带宽与全波分析结果的相对误差均小于10%. 证明了利用等效电路模型分析复杂FSS结构的可行性, 为FSS设计和快速优化提供了参考. 关键词： 频率选择表面 等效电路 集总元件     

不同厚度衬底上矩形孔金属结构的太赫兹透射特性数值分析

利用时域有限差分法对不同材料和厚度衬底上矩形孔金属结构太赫兹（THz）波的透射特性进行了数值分析。研究表明：矩形孔金属阵列对THz光谱具有频率选择特性,这为太赫兹滤波功能器件的开发提供了基础。在实际应用中,这种金属微结构常常需要制备在某种衬底上,而衬底材料及厚度无疑会对其太赫兹透射特性带来影响。研究了不同衬底材料和衬底厚度的矩形孔金属结构太赫兹透射性质,通过数值模拟研究发现,对于同一种衬底材料,随着衬底厚度的增加,矩形孔金属结构的透射峰峰位向低频移动。比较高阻硅和聚四氟乙烯两种衬底材料发现,高介电常数的硅衬底引起的透射峰移动更为明显。     

脉冲形成线用CaO-TiO2-Al2O3基介质陶瓷介电性能

设计了一种脉冲形成线用新型CaO-TiO2-Al2O3基介质陶瓷体系,采用传统固相法通过优化组分和制备工艺,调控材料的微结构,获得了介电性能优异的介质陶瓷。其介电常数在15~35之间可调,介电损耗小于0.002,频率稳定性好。在厚度为1 mm时,介电强度高达50 kV/mm。研究了厚度对CaO-TiO2-Al2O3基介质陶瓷介电强度的影响规律,当厚度从1 mm减小到0.1 mm时,介电强度呈非线性增大,从50 kV/mm（1 mm厚样品）提高到92 kV/mm（0.1 mm厚样品）,可见,CaO-TiO2-Al2O3基介质陶瓷的电击穿与其机械损坏具有相似性。结合CaO-TiO2-Al2O3基介质陶瓷的化学组分和微观结构,CaO-TiO2-Al2O3基介质陶瓷优越的电击穿特性可以用弱点击穿理论解释。     

无机厚膜发光器件绝缘层的研究

采用丝网印刷技术,在Al2O3陶瓷基板上印刷、高温烧结内电极及绝缘层,制备出陶瓷厚膜基板,进而制备了新型厚膜电致发光显示器(TDEL)。整个器件结构为陶瓷基板/内电极/厚膜绝缘层/发光层/薄膜绝缘层/ITO透明电极。研究不同结构的无机厚膜发光器件对器件性能的影响,并对器件的亮度—电压、亮度—频率进行测量。结果显示绝缘层在无机发光器件中不是单纯的保护作用,它对器件的性能有十分重要的影响。主要是对注入电子的加速作用,从而提高发光亮度。绝缘层本身对无机厚膜发光器件的发光机理没有关系。     

Critical thicknesses of electrostatic powder coatings from inside

A simple electrostatic model is applied to the charge powder coating of a grounded conductor eventually covered by insulating layers. The electric field inside the powder coating and its evolution during the process are established with also the corresponding evolution in the dielectric layer and some practical consequences are also discussed. The thickness of the charged powder layer is limited by two types of process: a self-limiting process related to the vanishing field in the air gap and a field strength process occurring on one of the two sides of the coating–dielectric interface. Inside the powder coating, the electric field induces an increased electrostatic pressure on the powder grains at the substrate–coating interface and a vanishing pressure on the grains at the coating–air interface. This internal field is amplified into air bubbles and it may be responsible for the back ionisation process and of the formation of moon craters via the ionisation of the air molecules followed by the pressure exerted by the ions pushed in the direction of the free surface. For each of these limits, analytical expressions are established and they permit to identify the role of physical properties of the deposited powder (particle size and dielectric constant) as well as the role of thickness, structure, and dielectric constant of the insulating substrate. The present approach explains the difficulty in obtaining thick coatings on thick insulating substrates or thick coatings from the use of too fine powder grains. Finally, different behaviours as a function of the size of the deposited powder grains are deduced from the contribution of the electric field to the velocity of the particles sticking to the surface. Then and for the first time, the present contribution underlines the important role of the subsurface composition and the need to characterize the structure, dimension and dielectric constant of this subsurface for various applications concerning electrostatic spraying and powder painting of plastics and of insulating coatings on metallic work pieces.     

Numerical study on surface acoustic wave method for determining Young's modulus of low-k films involved in multi-layered structures

The surface acoustic waves (SAWs) technique is becoming an attractive tool for accurately and nondestructively characterizing the mechanical property of the brittle low dielectric constant (low-k) thin film. The theoretical equations for describing SAWs propagating on the multi-layered structure are derived in this study. The dispersion features of SAWs propagating on different structures of low-k/SiO₂/Si substrate, SiO₂/low-k/Si substrate, low-k/Si substrate, and low-k/Cu/Si substrate are investigated to instruct an accurate and facile fitting process for determining Young's modulus of low-k films. The dependence of dispersion relation on the film thickness, elastic modulus of low-k materials as well as frequency are provided and discussed in detail. The study shows an obvious influence of layered structure on the dispersion relation of SAWs. For a fixed structure, the dispersion curvature increases with the decrease of Young's modulus of low-k films.