Electromagnetic Performance Analysis of Novel Multi-band Metamaterial FSS for Millimeter Wave Radome Applications

The electromagnetic design and performance analysis of dual/ multi-band metamaterial frequency selective surface (FSS) structures have been carried out for radome applications in microwave and millimeter wave frequency regimes. The proposed metamaterial FSS structure, consisting of cascaded MNG (mu-nega -tive) and DPS (double positive) layers, exhibits dual-band transmission responses at V-band and W-band. Excellent transmission efficiency (more than 95%) has been obtained over the frequency range 45.8-53.1 GHz at first resonance, and from 93.0-97.1 GHz at second resonance. The incorporation of additional DPS layer to the proposed metamaterial-FSS structure facilitates multiband bandpass characteristics at 30 GHz (in Ka-band), 64 GHz (in V-band), and 93.6 GHz (in W-band). The reflection and insertion phase delay characteristics are also analyzed at high incidence angles in view of streamlined airborne nosecone radome applications.     

EM Analysis of Metamaterial Based Radar Absorbing Structure (RAS) for MillimeterWave Applications

The EM performance analysis of a multilayered metamaterial based radar absorbing structure (RAS) has been presented in this paper based on transmission line transfer matrix (TLTM) method for millimeter wave applications. The proposed metamaterial-RAS consists of cascaded DPS and MNG layers of identical configurations. It exhibits extremely low reflection (< 42 dB) at 95 GHz and absorbs more than 95% power of incident wave over the frequency range of 90.4- 100 GHz without metal backing for both TE and TM polarizations. In view of aerospace applications, the reflection, transmission, and absorption characteristics of the proposed metamaterial-RAS are also studied at different incident angles (0°, 30°, and 45°) for both polarizations.     

Polarization Independent Dual-band Metamaterial Based Radar Absorbing Structure (RAS) for MillimeterWave Applications

The EM analysis of multi-layered metamaterial based radar absorbing structure (RAS) with dual-band characteristics in millimeter wave frequency regime has been carried out in this paper using transmission line transfer matrix (TLTM) method for TE and TM polarizations. The proposed metamaterial-based RAS exhibits dual-band characteristics at centre frequencies 120 GHz and 175 GHz with very low power reflection. It absorbs more than 90% power of incidence wave over the frequency range from 111-131 GHz at first resonance and from 164.5-185 GHz at second resonance without metal backing plate, which is desirable for stealth applications. It also showed very low (< 1.6%) transmission over the frequency of interest for both TE and TM polarizations. The proposed metamaterial-RAS has potential applications in the design of multi-band sensor systems and RCS reduction in millimeter wave frequency regime.     

Inkjet Printed Metamaterial Loaded Antenna for WLAN/WiMAX Applications

In this paper, the design and performance analysis of an Inkjet-printed metamaterial loaded monopole antenna is presented for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications. The proposed metamaterial structure consists of two layers, one is rectangular tuning fork-shaped antenna, and another layer is an inkjet-printed metamaterial superstate. The metamaterial layer is designed using four split-ring resonators (SRR) with an H-shaped inner structure to achieve negative-index metamaterial properties. The metamaterial structure is fabricated on low-cost photo paper substrate material using a conductive ink-based inkjet printing technique, which achieved dual negative refractive index bands of 2.25–4.25 GHz and 4.3–4.6 GHz. The antenna is designed using a rectangular tuning fork structure to operate at WLAN and WiMAX bands. The antenna is printed on 30 × 39 × 1.27 mm3 Rogers RO3010 substrate, which shows wide impedance bandwidth of 0.75 GHz (2.2 to 2.95 GHz) with 2 dB realized gain at 2.4 GHz. After integrating metamaterial structure, the impedance bandwidth becomes 1.25 GHz (2.33 to 3.58 GHz) with 2.6 dB realized gain at 2.4 GHz. The antenna bandwidth and gain have been increased using developed quad SRR based metasurface by 500 MHz and 0.6 dBi respectively. Moreover, the proposed quad SRR loaded antenna can be used for 2.4 GHz WLAN bands and 2.5 GHz WiMAX applications. The contribution of this work is to develop a cost-effective inject printed metamaterial to enhance the impedance bandwidth and realized the gain of a WLAN/WiMAX antenna.     

Graded Dielectric Inhomogeneous Planar Layer Radome for Aerospace Applications

Controllable artificial dielectrics are used in the design of radomes to enhance their electromagnetic (EM) performance. The fabrication of such radome wall structures with controllable dielectric parameters seems to be an arduous task. Further even minor fluctuations of dielectric properties of radome wall due to fabrication uncertainties tend to result in drastic degradation of radome performance parameters. In the present work, a novel inhomogeneous radome with graded variation of dielectric parameters is proposed which limits the constraints on fabrication and facilitates excellent EM performance characteristics. This radome wall consists of five dielectric layers cascaded such that the middle layer has maximum dielectric constant and electric loss tangent. The dielectric parameters of the layers on both sides of the middle layer decrease in a graded (or step-wise) manner. The EM performance characteristics of the IPL radome with graded dielectric parameters are superior to that of conventional monolithic half-wave radome.     

Soft Computing for Terahertz Metamaterial Absorber Design for Biomedical Application

The terahertz region of the electromagnetic spectrum plays a vital role in biomedical imaging because of its sensitivity to vibrational modes of biomolecules. Advances in broadband terahertz imaging have been emerging in the field of biomedical spectroscopy. Biomedical imaging is used to distinguish between the infected (cancer) and the non-infected tissue, which requires broad band and highly efficient radar absorbing material (RAM) designs (to obtain high resolution image of the tissue). In this paper, a metamaterial broadband RAM design is proposed towards biomedical spectroscopy applications in the THz region. The particle swarm optimization (PSO) algorithm is used for the design and optimization of the RAM, which enhances the absorption to nearly 99.32% at the required operational frequency.     

Gain-Enhanced Metamaterial Based Antenna for 5G Communication Standards

Metamaterial surfaces play a vital role to achieve the surface waves suppression and in-phase reflection, in order to improve the antenna performance. In this paper, the performance comparison of a fifth generation (5G) antenna design is analyzed and compared with a metamaterial-based antenna for 5G communication system applications. Metamaterial surface is utilized as a reflector due to its in-phase reflection characteristic and high-impedance nature to improve the gain of an antenna. As conventional conducting ground plane does not give enough surface waves suppression which affects the antenna performance in terms of efficiency and gain etc. These factors are well considered in this work and improved by using the metamaterial surface. The radiating element of the proposed metamaterial based antenna is made up of copper material which is backed by the substrate, i.e., Rogers-4003 with a standard thickness, loss tangent and a relative permittivity of 1.524 mm, 0.0027 and 3.55, correspondingly. The proposed antenna with and without metamaterial surface operates at the central frequency of 3.32 GHz and 3.60 GHz, correspondingly. The traditional antenna yields a boresight gain of 2.76 dB which is further improved to 6.26 dB, using the metamaterial surface. The radiation efficiency of the proposed metamaterial-based 5G antenna is above 85% at the desired central frequency.     

基于传递矩阵法的不确定链式结构固有频率区间分析

基于传递矩阵法，将链式结构中的不确定性参数用区间数来表示，导出关于系统固有频率的非线性区间方程，并针对该方程的求解，提出了一种区间逐步离散算法。此方法通过不确定性参数取区间离散值，将区间方程转化为相应的确定性方程，再搜索方程解中的最大最小值来确定系统各阶固有频率的边界。文中给出两个具有不确定性参数的链式结构算例，计算结果表明该算法是可行和有效的。     

转动态薄辐齿轮振动分析的传递矩阵法

本文用截锥壳模拟薄辐齿轮，由截锥薄壳理论导出了计算转动态截锥壳振动特性及瞬态响应的传递矩阵公式。文末给出了算例。     

薄壁结构弯扭耦合振动分析

本文考虑转动惯量、剪切变形和翘曲,讨论了用迁移矩阵法分析薄壁结构的弯扭耦合振动问题。文中讨论了断面突变处的协调条件及端部封板对振动特性的影响。算例表明,本文的理论和方法是可靠的。     

一种多体系统冲击响应谱分析法

提出一种多体系统冲击响应谱分析法,以一个基础受加速度冲击刚柔系统为例,详细阐述了该方法的理论基础,主要为:首先利用传递矩阵法求得系统任意点的状态矢量和系统振型;建立系统相对基础运动微分方程.进而建立系统的多体动力学方程;利用系统增广特征矢量的正交性求得广义坐标,结合速度冲击谱的定义获得各模态最大响应,最后经各模态响应合成得到系统的冲击响应时间历程.用一个具体工程实例,通过与一般力学解析方法、有限元冲击响应谱分析法结果的对比,验证了所提方法的有效性.     

传递矩阵法在高频振动分析中的应用

本文分析了传统传递矩阵法不能进行高频振动特性分析的原因，并提出了一种有效的解决方法，以供参考。     

A Novel Primal-mixed Finite Element Approach for Heat Transfer in Solids

A new reliable primal–mixed finite element approach for the heat transfer analysis in solids, is examined in detail. The essential contribution is that both variables of interest, temperature and heat flux, are calculated simultaneously from the same system of finite element equations. In addition, as a novelty, continuity of the trial and test heat flux functions is enforced, to avoid the need for some a posteriori heat flux smoothing technique. In order to minimize the accuracy error and enable introduction of the flux constraints, tensorial character of the present finite element equations is fully respected. The proposed finite element is subjected to low and high order convergence and efficiency tests in steady state and transient heat transfer analysis, which enlighten its solvability, stability, accuracy and effectiveness, i.e. its reliability.     

涡轮分子泵入口结构改进的计算研究

针对涡轮分子泵的入口管道束流效应和涡轮端盖反射效应对传输几率的不利影响、以及大口径涡轮分子泵与小型仪器相连接的难题, 本文提出分子泵入口结构的改进方案:将涡轮转子的平板端盖改成锥形反射屏结构, 把过渡连接件做成圆弧过渡段结构。文中根据实际结构参数, 建立了不同结构类型的计算模型, 采用试验粒子蒙特卡洛方法, 基于自由分子流态基本假设, 利用Molflow+软件, 计算了各个结构模型的传输几率。计算结果表明:当倾角α的取值范围在60°~70°、圆锥底角β的取值范围在25°~45°之间时, 理论上可将涡轮分子泵的抽气速率提升5%左右。     

某弹用涡轮喷气发动机动力特性分析

应用传递矩阵法计算了某弹用涡轮喷气发动机的临界转速和振动响应,分析了转子支承刚度对临界转速的影响,以及不同支承条件和不同油膜间隙下转子的稳态不平衡响应。研究表明,当转子系统的前支承刚度不高于1×107N/m,挤压油膜阻尼器的油膜间隙不小于7.0×10-5m时,发动机的动力特性能得到有效的改善。     

微穿孔板传递矩阵计算方法的改进及实验

传统的声电类比法对双层微穿孔板吸声结构进行计算时,忽略了空腔声质量的影响,对于空腔距离比较短,频率比较低时是适用的,但是当空腔距离比较大或频率比较高时,则存在误差。用传递矩阵法对微穿孔板吸声结构进行分析：解决了空腔声阻抗的近似计算带来的误差;对于微孔部分传递矩阵中的声阻抗计算仍然采用马大猷教授的理论,不需要引入修正参数δx。通过上述工作,进行了微穿孔板吸声结构的吸声系数的计算和相应的实验验证,理论计算结果与实验数据吻合良好。     

A Subspace-Projected Approximate Matrix Method for Systems of Linear Equations

Given two $n×n$ matrices $A$ and $A_0$ and a sequence of subspaces$\{0\}=\mathscr{V}_0⊂···⊂\mathscr{V}_n=\mathbb{R}^n$with dim$(\mathscr{V}_k)=\mathscr{k}$, the $k$-th subspace-projected approximated matrix $A_k$ is defined as $A_k=A+Π_k(A_0−A)Π_k$, where $Π_k$ is the orthogonal projection on $\mathscr{V}_{k}^⊥$. Consequently, $A_{k}v=Av$ and $v^{∗}A_{k}=v^{∗}A$ for all $v∈\mathscr{V}_{k}$. Thus $(A_{k})^{n}_{k≥0}$ is a sequence of matrices that gradually changes from $A_0$ into $A_n=A$. In principle, the definition of $\mathscr{V}_{k+1}$may depend on properties of $A_k$,which can be exploited to try to force $A_{k+1}$ to be closer to $A$ in some specific sense. By choosing $A_0$ as a simple approximation of $A$, this turns the subspace-approximated matrices into interesting preconditioners for linear algebra problems involving $A$. In the context of eigenvalue problems, they appeared in this role in Shepard et al. (2001), resulting in their Subspace Projected Approximate Matrix method. In this article, we investigate their use in solving linear systems of equations $Ax=b$. In particular, we seek conditions under which the solutions $x_k$ of the approximate systems $A_kx_k=b$ are computable at low computational cost, so the efficiency of the corresponding method is competitive with existing methods such as the Conjugate Gradient and the Minimal Residual methods. We also consider how well the sequence $(x_k)_{k≥0}$ approximates $x$, by performing some illustrative numerical tests.     

流体管道横向振动的频域传递矩阵法

通过Fourier变换,把经典的时域描述的流体管道横向振动4方程模型变换到频域,求解此模型,可以得到单管的频域解析解.在此基础上,结合管段节点的平衡条件,推导出多管段的传递矩阵法,把单管的频域分析扩展到多管段组成的管路,传递矩阵法可以求解多管段的任意管段和任何坐标位置的值.最后,利用Dundee大学实验管道对结果进行验证分析,并通过算例来说明本方法的应用.     

近邻软磁层偏置磁阻磁头结构参数设计的数学模型

概述了软磁层偏置磁阻磁头的工作原理和特点 ,采用传输线模型对其工作点的选取和结构参数进行了初步设计 ,与实验结果符合较好