Array Of Thin Wires Research Articles

Effective-Medium Modeling of a Meanderline Metamaterial-Enhanced Resistive Wall Amplifier Circuit for Particle-in-Cell Simulations

Theory and simulations predict the metamaterial-enhanced resistive wall amplifier (MERWA) may offer improvements to megawatt-level high-power microwave (HPM) amplifiers in terms of combined bandwidth and gain rates. A low-power proof-of-concept test prototype has been designed using a metamaterial (MTM) consisting of a linear array of periodically spaced thin lossy meandered wires. Direct simulations of these arrays of thin meandering wires using typical 3-D particle-in-cell (PIC) solvers are inaccurate, creating significant challenges for obtaining trustworthy hot test simulations of the prototype device. This work enables predictive PIC simulations of the experimental MERWA prototype by replacing the thin lossy wire structure with an equivalent effective-medium model. We find that a finite-width rod having an anisotropic Drude–Lorentz permittivity is a suitable model to replace the lossy wire MTM structure. We detail our modeling process and assumptions, fitting procedures, and model fitting results. The model is validated by comparing PIC simulations to experimental results.

Strength of Superelastic NiTi Velcro-Like Fasteners

Velcro hook-and-loop fasteners invented more than 70 years ago are examples of the mechanism inspired by the tiny hooks found on the surface of burs of a plant commonly known as burdock. Several years ago, a novel Velcro-like fastener made of two arrays of hook-shaped thin NiTi wires was developed. Unique features of such fasteners, such as high thermally-tunable strength, fair force–stroke reproducibility, forceless contact or silent release, all derive from the superelasticity of the NiTi micro-wires. Recently, it was noticed that the presented fastener design allowed for a prediction of the number of active hooks. In this continuing study, the tension strength of the fastener was simulated as a function of hook density. Based on statistics, the model showed non-linear dependency of the number of interlocked hooks, N, on the hook density, m (N = round (0.21 m + 0.0035 m2 − 6.6)), for the simple hook pairs and the given hook geometry. The dependence of detachment force on stroke was simulated based on the Gaussian distribution of unhooking of individual hook connections along the stroke. The strength of the studied NiTi hook fasteners depended on hook density approximately linearly. The highest strength per cm2 reached at room temperature was 10.5 Ncm−2 for a density of m = 240 hooks/cm2.

Study of Interaction of Plasma Flows with Magnetic Field During Implosion of Cone-Cylindrical Nested Arrays

The results of the studies of the compression of the plasma of cone-cylindrical nested arrays of mixed composition at current flow through them of up to 3 MA at the Angara-5-1 facility are presented. The outer array of the nested array is a conical array of thin nylon fibers or tungsten wires, while the inner one is a cylindrical tungsten wire array. The implosion of current in this type of nested arrays is a unique opportunity for simulating the interaction of magnetized plasma flows with a strong magnetic field. In the space between the inner and outer arrays, the super-Alfven plasma flow from the outer array collides with the magnetic field of the discharge current through the inner array. As a result of this interaction in the space between arrays, different plasma flow modes are implemented: pre-Alfven (Vr VА), and a mode with the formation of the transition region—a shock wave (SW) between arrays, depending on the ratio of the plasma formation rates of arrays of nested array and on the ratio of their radii. The SW region formation in the space between arrays occurs near the inner array, where the kinetic pressure of the plasma flow from the outer array is balanced by the magnetic pressure of the discharge current of the inner array. New experimental data was obtained on the features of the SW region formation near the surface of the inner array and the nature of its change during the interaction. The use of an external conical array enabled us to obtain the SW position depending on the ratio of radii of the outer and inner arrays in one shot. It is shown that the interaction of plasma flows of the outer conical array with the magnetic field of the inner cylindrical array leads to a significant decrease in the zipper-effect at the final stage of plasma compression of the inner array and the pinch formation. The obtained experimental results are compared with the results of simulating the plasma motion between the arrays using the three-dimensional radiation-magnetohydrodynamic code MARPLE3D.

Design of Thin Wire Metamaterial-Based Interaction Structure for Backward Wave Generation

In this article, a thin wire (TW) metamaterial (MTM)-based interaction structure has been reported as a potential candidate for realizing a backward wave oscillator (BWO). The interaction structure has been designed by arranging an array of connected TWs periodically along the axis of a hollow rectangular waveguide. The TW array exhibits negative permittivity along the transverse dimensions and allows mode propagation below the transverse magnetic (TM) mode cutoff of the hollow waveguide. Two TW array variants, one with wires of square cross section (STW) and the other of circular cross section (CTW), have been considered. The frequency range (~12.3–13.3 GHz) of the fundamental backward TM mode has been verified using both the eigenmode and S-parameter simulations. For a stable operation, the operating point has been chosen at $\sim \pi $ /2 point on the fundamental backward mode at 12.8 GHz. The TW array has been designed in such a way so as to avoid the interception with the electron beam propagating down the interaction structure. A prototype of STW array inside a rectangular waveguide has also been fabricated. Preliminary beam–wave interaction simulation has also been carried out, and an output power of 12.98 kW has been observed with an electronic efficiency of 13.61%. This TW array is a simpler structure to realize and hence has the advantage of reduced fabrication complexity. This makes it a viable choice as a filling medium to realize an MTM-based BWO.

Analysis of Thin Truncated Cylinder Scatterers Using Incomplete Hankel Functions and Surface Impedance Boundary Conditions

The incomplete Hankel functions (IHFs) are employed to evaluate the scattered field from thin truncated cylinders excited by uniform plane waves or by arbitrarily oriented elemental current sources. Metallic and dielectric lossy structures are modeled by means of impedance boundary conditions (IBCs) including surface curvature effects. The scattering currents, expanded in triangular basis functions, are determined upon solving electrical field integral equations (EFIEs) by means of the point-matching method of moments (MoM). The scattered field is then expressed in closed analytical form in terms of IHFs, thus yielding highly accurate numerical results. Furthermore, accurate IHFs approximants are also derived to reduce the computational burden in the analysis of large electrical structures. The proposed approach is demonstrated in practical applications involving cylindrical dielectric structures used in planar lenses, lossy dielectric cylinders suitable to model cane-like vegetation, as well as polarization rotators featuring multiple stages composed of thin metallic wire arrays.

A new tungsten wire calorimeter for the negative ion source testbed BATMAN Upgrade

Within the framework of the ion source development for the ITER and DEMO Neutral Beam Injection (NBI) systems, IPP Garching has recently upgraded the radiofrequency-driven negative ion source testbed BATMAN. One of the requirements for the ITER NBI system is to produce a beam power density homogeneity above 90% over its large beam size extracted from an ion source of 1 × 2 m2. The beam uniformity is going to be investigated, on a smaller scale, in BATMAN Upgrade with the new ITER-like beam optics. The testbed is equipped with several beam diagnostic tools to measure beam power, uniformity and divergence. A new tungsten wire calorimeter (TWC) has recently been developed to characterize the beam quantitatively and with an improved spatial and temporal resolution. The TWC consists of an array of thin tungsten wires with a diameter of 0.3 mm, placed in the beam path. The wires are heated by the beam up to 3000 °C and emit visible light, which is observed by an optical camera. While the existing TWC provides a qualitative impression of beam power characteristics and is placed at a distance of almost 2 m from the beam extraction system, the new TWC is positioned only 19 cm downstream from the extraction system and allows observation of the single beamlets for the first time in this testbed. In order to determine the correlation between the pixel intensity measured by the camera and the power density impinging on the wires, one wire is equipped with an ohmic heating system which allows heating up the wire with a known power, thus enabling calibration of the diagnostic tool.In this paper the design, including FEM simulations of the wire thermal behavior, manufacturing and installation of the new TWC inside the BATMAN Upgrade testbed are described and the first, very promising, observations of beamlet intensities are presented.

Guided electromagnetic waves for periodic arrays of thin metallic wires near an interface between two dielectric media.

Guided localized electromagnetic waves propagating along one-dimensional (1D) arrays of thin metallic parallel wires, finite and infinite, are studied. The arrays are embedded into the upper dielectric half-space close to the interface separating it from the lower dielectric medium with different permittivity and the same permeability. Firstly, a dependence of resonance frequencies of excited wave modes for finite array with respect to the array height above the interface is studied. The array is excited by a normally incident plane wave. It is important that the order of the resonance modes changes if the distance between the array and the interface becomes small. An analysis, based on the Pocklington system of integral equations to evaluate resonance frequencies and compute the fields of excited modes above the array, was applied. This approach is based on the longwave approximation of thin wires. Secondly, the waves propagating along infinite 1D array of thin metallic wires that is close to the interface are studied. Dispersion curves are presented for the lowest case of half-wave resonance for different heights of the array over the interface. When the array approaches very close to the interface an anomalous dispersion is observed. The results of the numerical analysis were tested against computations obtained by means of other independent CST Studio Suite simulations.

Calculation of output power and X-ray spectrum of Z-pinches based on multiwire arrays

We present mathematical models and methods of the computational experiment using a three-dimensional RMHD model simulating the implosion of Z-pinches formed by an imploding cylindrical array of thin tungsten wires. The calculations take into account the discrete structure of the array and the extended plasma formation at the evaporation of the wire material and they yield the estimated values of the output power and X-ray spectrum. The data are presented on the spatio-temporal distribution in the parameters of the Z-pinch plasma, including the velocity, electron and ion temperatures, ionization degree, and the power output integrated over space. We have also calculated the characteristics of the Z- pinch X-ray spectrum depending on the photon energy at different times after the discharge current starts. It has been found that the trailing mass of tungsten on the periphery affects the emission intensity of the central part of the pinch in the radial direction, which can be explained by the emission absorption in the peripheral plasma layers of the trailing tungsten mass. A detailed model has been constructed of the central pinch formed by the electric current implosion of the material of multiwire tungsten arrays. This model enables one to calculate the intensity of the soft X-ray emission with a temporal, spatial, angular, and spectral resolution for specific experiments on the Angara-5-1 experimental complex intended to study the implosion of cylindrical multiwire arrays, for which there is sufficient information about the time profile of the absolute emission intensity in the low-energy range of the X-ray emission. The obtained numerical results can be directly compared with the experimental values. The RMHD model simulating the implosion of Z-pinches has been verified by comparing its results with the experimental implosion indicators.

Radiative power and x-ray spectrum numerical estimations for wire array Z-pinches

Magnetically driven plasma implosion is studied numerically with the use of a 3D radiative MHD model. We consider a Z-pinch formed by an array of thin tungsten wires. In our calculations we take into account a time-extended plasma production due to a material evaporation by an individual wire caused by the heating electric current. Using a detailed model of the pinch kernel, a soft x-ray radiation intensity is analyzed numerically with resolution of temporal, spatial, angular and spectral radiation characteristics. The results are represented for the conditions pertinent to experiments with cylindrical tungsten wire arrays at Angara-5-1 facility (TRINITI, RF).

Current Approach in Surface Plasmons for Thin Film and Wire Array Solar Cell Applications.

Surface plasmons, which exist along the interface of a metal and a dielectric, have been proposed as an efficient alternative method for light trapping in solar cells during the past ten years. With unique properties such as superior light scattering, optical trapping, guide mode coupling, near field concentration, and hot-electron generation, metallic nanoparticles or nanostructures can be tailored to a certain geometric design to enhance solar cell conversion efficiency and to reduce the material costs. In this article, we review current approaches on different kinds of solar cells, such as crystalline silicon (c-Si) and amorphous silicon (a-Si) thin film solar cells, organic solar cells, nanowire array solar cells, and single nanowire solar cells.

Analytical Study of Annular-Ring Microstrip Antennas Shorted With Thin Wires

A new theoretical analysis method is presented for annular-ring microstrip antennas with a short-circuited wall implemented as an array of thin cylindrical wires. Assuming wire spacing to be small compared to wavelength, the averaged boundary conditions are employed. An explicit characteristic equation, which determines resonant frequencies depending on wire spacing and radius is derived. A calculation technique for antenna input impedance is presented. Obtained results show good agreement between theoretical and experimental data. It is shown that the wire short-circuited wall can bring considerably different resonant properties compared to continuous metallic one.

Multiband meandered miniaturized patch antenna loaded with split ring resonator and thin wire arrays

ABSTRACTArtificial materials have attracted considerable attention as potential solutions to meet the demands of modern microwave technology for simultaneously achieving component minimization and higher performance in wireless communications, mobile communications, and satellite communication applications. So in this letter, we have investigated a multiband meandered miniaturized patch antenna with the use of split ring resonator (SRR) and thin wire arrays. SRR are promising building blocks for negative permeability metamaterials and thin wire arrays for negative permittivity. By combining SRR arrays and wire arrays together, we observed a transmission band where both permittivity and permeability are simultaneously negative. Simulated results for the S11 and electric field of an antenna are presented. The result shows multibands centered at 1.89, 2.04, 2.13, and 2.31 GHz. Design results are obtained by a high frequency structure simulator which is used for simulating microwave passive components. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:306–310, 2014

Accurate modeling of high order spatial dispersion of wire medium

The wire medium consisting of an array of parallel thin metallic wires was previously studied by using an effective medium with spatial dispersion. In this paper, the validity of conventional effective model was examined analytically and numerically by studying a canonical structure of the wire medium. It is noted that the conventional model fails for high transversal spatial harmonics, which consequently results in discrepancy in the scattering between the effective model and the physical structure. In this study, we propose a new effective model to include higher order spatial dispersions: instead of the second-order expansion, the proposed dispersion equation is based on the fourth-order expansion of the dispersion equation of the photonic states. Compared with the 3D full-wave simulation results of the wire medium, the proposed model has demonstrated significant improvement in numerical accuracy in characterizing the EM behavior in this type of metamaterials.

Measurement of the MTF of a Cone-Beam Breast Computed Tomography Laboratory Scanner

We measured the spatial resolution of the prototype scanner developed for laboratory investigations on Cone-Beam Breast Computed Tomography (CBBCT). The scanner has potential for high spatial resolution, since it employs a minifocus X-ray tube (0.04 mm nominal focal spot size) and a fine pitch (0.05 mm) flat panel detector. With the available maximum tube current (0.25 mA) and detector field of view (120 × 120 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), adequate sample volume coverage and exposure requirements as in a clinical scan are obtained via increasing the total acquisition time and by combining laterally translated projections at each angular position. The Modulation Transfer Function (MTF) of the system was evaluated in step-and-shoot acquisitions with the tilted wire method, by imaging a test pattern made by an array of vertical and horizontal thin metal wires. MTF measurements in each tomographic plane were performed. Spatial frequency values of 3-3.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">- 1</sup> at 10% MTF were measured. A lower spatial resolution performance is expected in continuous acquisitions, due to the gantry motion blur.

Excitation of oblique surface electromagnetic waves at an anisotropically conducting artificial interface by means of the attenuated-total-reflection method

In this paper, we present the theoretical analysis of excitation of well-bounded oblique surface electromagnetic waves propagating along an anisotropically conducting interface of two different dielectrics by means of the attenuated-total-reflection method. The flat surface of the interface contains a one-dimensional array of thin metal wires. It has been assumed that both the lattice constant of the array and the diameter of the wires are far less than the wavelengths of the surface waves. The surface electromagnetic waves may propagate along the interface at frequencies that are far lower than the plasma frequency of a metal, and the electric field of the waves is always perpendicular to the wires in any propagation directions. It has been shown that the oblique surface electromagnetic waves can be excited by the TM-polarized electromagnetic wave which becomes partially polarized during the excitation.

Surface electromagnetic waves at an anisotropically conducting artificial interface

Surface electromagnetic waves propagating along an anisotropically conducting interface of two different dielectrics have been theoretically investigated. The flat surface of the interface contains a one-dimensional array of thin metal wires. It was assumed that both the lattice constant of the array and the diameter of the wires are far less than the lengths of the surface waves. It has been shown that the surface electromagnetic waves may propagate along the interface at frequencies which are far lower than the plasma frequency of a metal, and the electric field of the waves is always perpendicular to the wires in any propagation directions. The existence conditions, dispersion relations, and energy fluxes of the surface waves have been derived. It has been demonstrated that the surface electromagnetic waves can be excited by means of the transition radiation and beam instability effects.

Electric detection of spin wave resonance using inverse spin-Hall effect

Spin wave resonance in Ni81Fe19/Pt thin wire arrays has been investigated using the inverse spin-Hall effect (ISHE). The spin wave in the Ni81Fe19 layer drives spin pumping, generation of spin currents from magnetization precession, and the pumped spin current is converted into a charge current by ISHE in the Pt layer. We found an electromotive force transverse to the spatial and the spin-polarization directions of the spin current. The experimental results indicate that the amplitude of the electromotive force is proportional to the spin wave resonance absorption intensity, enabling the electric measurement of spin wave resonance in nanostructured magnetic systems.

Convergence acceleration of the doubly periodic Green's function for the analysis of thin wire arrays

A method is proposed to accelerate the evaluation of the Green's function of an infinite double periodic array of thin wire antennas. The method is based on the expansion of the Green's function into series corresponding to the propagating and evanescent waves and the use of Poisson and Kummer transformations enhanced with the analytic summation of the slowly convergent asymptotic terms. Unlike existing techniques the procedure reported here provides uniform convergence regardless of the geometrical parameters of the problem or plane wave excitation wavelength. In addition, it is numerically stable and does not require numerical integration or internal tuning parameters, since all necessary series are directly calculated in terms of analytical functions. This means that for nonlinear problem scenarios that the algorithm can be deployed without run time intervention or recursive adjustment within a harmonic balance engine. Numerical examples are provided to illustrate the efficiency and accuracy of the developed approach as compared with the Ewald method for which these classes of problems requires run time splitting parameter adaptation.

Experimental and numerical study of omega type bianisotropic metamaterials combined with a negative permittivity medium

We report on the transmission properties of the omega (Ω) type metamaterials. Transmission through the periodic Ω-only and Ω-wire metamaterials are studied experimentally and numerically. A resonance band gap is observed for the periodic Ω medium around the resonance frequency of the single Ω unit cell. A transmission band is observed below the resonance band gap, when the periodic Ω structure is embedded in a negative permittivity medium composed of thin metallic wire arrays. We also studied the effect of periodicity on the transmission spectra of Ω type metamaterials.

Guiding, Focusing, and Sensing on the Subwavelength Scale Using Metallic Wire Arrays

We show that tapered arrays of thin metallic wires can manipulate electromagnetic fields on the subwavelength spatial scale. Two types of nanoscale imaging applications using terahertz and midinfrared waves are enabled: image magnification and radiation focusing. First, the tapered wire array acts as a multipixel TEM endoscope by capturing an electromagnetic field profile created by deeply subwavelength objects at the endoscope's tip and magnifying it for observation. Second, the image of a large mask at the endoscope's base is projected onto a much smaller image at the tip.