Investigation of anisotropic reinforcement patch corners

Corners at symmetrically attached reinforcement patches of in-plane loaded laminate plates constitute a source for stress localizations. The mechanical in-plane fields of such stress localizations are obtained by means of the boundary finite element method (BFEM). Corresponding in-plane investigations provide the singular in-plane force exponents and their displacement modes characterizing the corner situation. Due to the availability of the in-plane fields in a semi-analytical way their gradients are readily evaluated then. The interlaminar stresses inside the plate are retrieved by equilibrium considerations on a ply-by-ply basis.     

A composite medium with simultaneously negative permittivity and permeability

A new composite medium that possesses simultaneously negative permittivity and permeability in the microwave wavelength range is proposed. The medium is composed of evanescent waveguide structures responsible for the negative permittivity, with embedded cylindrical elements of a one-dimensional chiral medium accounting for the negative permeability. The evanescent waveguide structures exhibit blooming and antiresonances in the reflection coefficient.     

Artificial dielectric medium possessing simultaneously negative permittivity and magnetic permeability

An artificial dielectric medium comprising two sublattices of spherical particles made of a high-dielectric-constant (high-ε) material, which are embedded into a low-ε dielectric matrix, are considered. Particles belonging to different sublattices have different diameters. It is shown that the properties of this composite structure are equivalent to those of an isotropic medium possessing a negative refractive index (n < 0) in the vicinity of frequencies at which the H ₁₁₁ and E ₁₁₁ oscillation modes exhibit simultaneous resonance in particles of different diameters, which leads to the appearance of electric and magnetic dipole moments, respectively. Averaging of these dipole moments over the volumes of cells formed by the corresponding spherical particles determines their contributions to the permittivity and magnetic permeability of the composite medium. At frequencies above the resonance, both contributions become negative and, hence, the medium exhibits simultaneously negative values of the permittivity and magnetic permeability. The proposed composite structure consists only of dielectric components. Spherical particles with ε_d > 200 can be made of a ferroelectric material.     

Inkjet-printed patch antenna emitter for wireless communication application

This research focuses on exploring low-cost and rapid production solutions for fabricating emitters for patch antennas for wireless communication applications. Additive manufacturing technique is employed to fabricate two patch antennas using silver nanoparticle ink on FR4 substrate. Finite-element simulation software, HFSS is used to analyse and predict the theoretical performance of the antenna designs for 2.4?GHz MIMO and 6?GHz wireless data transmission. The fabricated antennas have resonant frequencies closely matching the design values. The work provides a viable solution for fabricating emitters and finally antennas commercially using inkjet printing platform, thus overall reducing the cost and simplifying the process.     

Radiation from a current sheet at the interface between a conventional medium and anisotropic negative refractive medium

In this paper we investigate the radiation from a current sheet at the interface between semiinfinite isotropic positive refractive medium and anisotropic negative refractive medium. The distribution of the electric and magnetic fields in two regions and Poynting vectors associated with propagating and evanescent waves are calculated. The reasons for the singularity of the electric or magnetic field are briefly provided if the waves are evanescent in two media.     

新型宽频带微带贴片天线的设计

提出了一种新颖的展宽三角形微带贴片天线工作频带的设计方法．通过在三角形微带贴片侧边附近加载与之平行的缝隙来实现双频工作,并添加一对平行于底边的缝隙使两个频点靠近,利用仿真软件进行优化,有效地展宽了贴片天线的频带．制作了实际的贴片天线,结果表明所设计天线的工作带宽(VSWR<2)是普通三角形微带天线的4.46倍,且天线尺寸与同频率的常规贴片天线相比缩小了9.3%．测量结果与仿真结果吻合,证明了所提方法的有效性．     

Wideband microstrip patch antenna design for breast cancer tumour detection

A patch antenna is presented which has been designed to radiate frequencies in the range 4-9.5 GHz into human breast tissue. The antenna is shown by means of previously unpublished simulation and practical measurements to possess a wide input bandwidth, radiation patterns that remain largely consistent over the band of interest and a good front-to-back ratio. Consideration is also given to the antenna's ability to radiate a pulse, and in this respect it is also found to be suitable for the proposed application     

Design of fractal patch antenna for size and radar cross-section reduction

This research study presents a novel design of star-shaped fractal patch antenna for miniaturisation and backscattering radar cross-section (RCS) reduction. The proposed fractal antenna gives 50% size reduction compared with a conventional circular microstrip patch (CCMP) antenna. The antenna is studied experimentally for return loss behaviour using vector network analyser R&S ZVA40. It can be useful for wireless application in 0.85-4 GHz frequency band. Further, the study focuses on backscattering RCS (both monostatic and bistatic) reduction by the proposed antenna compared with the CCMP antenna. It is found that increase in number of fractal iterations included in the conventional patch to design fractal antenna geometry reduces backscattering RCS at multiband compared to the conventional patch antenna. This reduction in backscattering RCS by the antenna is observed at multiband. The antenna can be tuned for low backscattering by variation in the substrate dielectric constant and thickness and the superstrate dielectric constant and thickness. For maximum RCS reduction by the antenna, optimisation of substrate thickness becomes necessary. The study also deals with effect of frequency and aspect angle variation on backscattering RCS reduction.     

Dual layer stacked rectangular microstrip patch antenna for ultra wideband applications

An antenna consisting of a U-slotted rectangular microstrip patch stacked with another patch of a different size on a separate layer is presented and its performance results are investigated. An equivalent circuit model of this stacked patch design structure is also presented based on an extended cavity model to predict the input impedance. The theoretical input impedance is evaluated from this circuit model and the experimental results support the validity of the model. In this case, stacking with a simple patch adds another resonance to the antenna thus providing a wider bandwidth. The dimension of the top patch is optimised to achieve ultra wide bandwidth. A maximum impedance bandwidth of 56.8% is achieved using this structure, and the return loss |S₁₁|of the antenna is less than -10 dB between 3.06 and 5.49 GHz and the radiation patterns are found to be relatively constant throughout the band. A coaxial feed with Gaussian modulated pulse is used for this antenna.     

中应变率加载下云杉各向异性力学行为研究

采用高速加载INSTRON设备对云杉开展10⁰ s^-1~10² s^-1中应变率压缩实验,研究了材料沿顺纹、横纹径向、弦向、以及径(弦)切面内与顺纹呈15°、30°、45°、60°和75°夹角方向的力学性能。实验表明随着加载方向由顺纹向横纹径(弦)向变化,材料屈服强度逐渐减小,应力-应变曲线塑性流动段由\     

Two-dimensional static deformation of an anisotropic medium

The problem of two-dimensional static deformation of a monoclinic elastic medium has been studied using the eigenvalue method, following a Fourier transform. We have obtained expressions for displacements and stresses for the medium in the transformed domain. As an application of the above theory, the particular case of a normal line-load acting inside an orthotropic elastic half-space has been considered in detail and closed form expressions for the displacements and stresses are obtained. Further, the results for the displacements for a transversely isotropic as well as for an isotropic medium have also been derived in the closed form. The use of matrix notation is straightforward and avoids unwieldy mathematical expressions. To examine the effect of anisotropy, variations of dimensionless displacements for an orthotropic, transversely isotropic and isotropic elastic medium have been compared numerically and it is found that anisotropy affects the deformation significantly.     

Hertz contact problems for an anisotropic physically nonlinear elastic medium

Conditions under which Hertz contact problems exhibit the property of self-similarity are determined. Qualitative conclusions concerning the character of selfsimilitude solutions from which, among other things, an equation similar to the familiar Mayer equation follows, are drawn. The problem of the collision between nonlinearly elastic bodies is also examined.Moscow Institute of Radio Engineering, Electronics, and-Automated Equipment. Translated from Problemy Prochnosti, No. 12, pp. 47–53, December, 1989.     

Scattering of radiation in an anisotropic turbulent medium

Scattering of laser radiation on density fluctuations in propagation of radiation through an anisotropic turbulent medium is analyzed. It is shown that the deviation angles in turbulent gas flows at atmospheric pressure equal ∼10⁻⁵–10⁻⁴ rad and can be detected by means of speckle photography. A statistical analysis of two-dimensional fields of deviation angles makes it possible to evaluate three-dimensional density correlation functions in a turbulent flow. It is shown that taking account of the turbulence anisotropy leads to distributions of the laser-radiation intensity over deviation angles that deviate substantially from the Gaussian distribution. Academic Scientific Complex “A. V. Luikov Institute of Heat and Mass Transfer of the National Academy of Sciences of Belarus,” Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 72, No. 1, pp. 96–101, January–February, 1999.     

Mechanical response of an anisotropic liquid-saturated porous medium

Summary.  An eigenvalue approach following Laplace transformation has been employed to study the mechanical response of an anisotropic liquid-saturated porous solid. Analytical solutions are obtained in the transformed domain. A numerical inversion technique is used for inverting the Laplace transforms and to get the results in the physical domain, numerically. The results are taken for two types of surface loadings: (i) Impulsive loading, (ii) continuous loading, for a particular model and are discussed graphically. Received July 30, 2001; revised December 9, 2002 Published online: May 20, 2003     

Investigation of hybrid elliptical antenna arrays

Novel types of antenna arrays constructed from combination of linear and elliptical antenna arrays are presented. These types are called elliptical, concentric elliptical, elliptical cylindrical and elliptical coaxial cylindrical arrays where only the array factors are considered. The effect of the element factor can be considered separately and combined to the array factor. The expression for the array factor of elliptical array has been obtained. Then, array factors of other three types are derived by the combination of linear and elliptical array properties. Their directivities and sidelobe levels are simulated in various current distributions. The effect of ellipse eccentricity, element spacing and number of elements are calculated and compared with those parameters.     

Design of square patch antenna with a notch on FR4 substrate

Simulation and measured results of a square patch antenna with a notch to search their possible application on modern communication systems including WiMax systems are presented. The antennas are designed on an FR4 substrate and the notch angle is varied under different conditions. It is found that on varying the notch angle from 180° to 164°, antennas resonate at a single frequency but on reducing the notch angle further, antennas start resonating at two frequencies with improved bandwidth. The optimum performance of an antenna is obtained when the notch angle is set to 151°. Different radiation parameters of the antennas under varying conditions are analysed and their possible applications in modern communication systems are investigated.     

Reversed Cherenkov transition radiation of charge entering anisotropic medium

The electromagnetic field of a charge crossing the interface between vacuum and an electrically anisotropic dispersive medium in which reversed Cherenkov transition radiation (RCTR) is generated has been theoretically studied. An algorithm for calculating the Fourier harmonics of the field based on exact formulas is developed and their asymptotics in the far field zone are determined. A special attention is devoted to the RCTR phenomenon, which was previously only studied for the so-called left-handed medium (LHM). Conditions for RCTR excitation are found and the effect of losses in the medium on the propagation of radiation is analyzed. The RCTR under the indicated conditions is compared to the analogous effect in LHM.     

Fundamental solutions for an anisotropic medium with a notch or an inclusion

Abstract

A fundamental solution for an anisotropic medium with a notch or a rigid inclusion of arbitrary shape is derived based on the complex potential formulation of anisotropic elasticity. The solutions for a crack, for a circular hole or inclusion, and for a half plane are obtained as special cases. The solution can be applied to the analysis of crack, notch and inclusion problems of anisotropic materials.     

Mechanics of layered anisotropic poroelastic media with applications to effective stress for fluid permeability

The mechanics of vertically layered porous media has some similarities to and some differences from the more typical layered analysis for purely elastic media. Assuming welded solid contact at the solid-solid interfaces implies the usual continuity conditions, which are continuity of the vertical (layering direction) stress components and the horizontal strain components. These conditions are valid for both elastic and poroelastic media. Differences arise through the conditions for the pore pressure and the increment of fluid content in the context of fluid-saturated porous media. The two distinct conditions most often considered between any pair of contiguous layers are: (1) an undrained fluid condition at the interface, meaning that the increment of fluid content is zero (i.e., δζ = 0), or (2) fluid pressure continuity at the interface, implying that the change in fluid pressure is zero across the interface (i.e., δp_f = 0). Depending on the types of measurements being made on the system and the pertinent boundary conditions for these measurements, either (or neither) of these two conditions might be directly pertinent. But these conditions are sufficient nevertheless to be used as thought experiments to determine the expected values of all the poroelastic coefficients. For quasi-static mechanical changes over long time periods, we expect drained conditions to hold, so the pressure must then be continuous. For high-frequency wave propagation, the pore-fluid typically acts as if it were undrained (or very nearly so), with vanishing of the fluid increment at the boundaries being appropriate. Poroelastic analysis of both these end-member cases is discussed, and the general equations for a variety of applications to heterogeneous porous media are developed. In particular, effective stress for the fluid permeability of such poroelastic systems is considered; fluid permeabilities characteristic of granular media or tubular pore shapes are treated in some detail, as are permeabilities of some of the simpler types of fractured materials.