Continuous Wire Research Articles

Principles and applications of a controllable electromagnetic band gap material to a conformable spherical radome

This paper presents the principle of two types of conformable and controllable spherical radome based on Electromagnetic Band Gap (EBG) materials operating at around 10 GHz. The EBG structure is composed of a grid of metallic wires conformed on a hollow spherical object. Two switching control configurations are considered: (1) between an EBG structure made of electrically continuous wires and another one made of discontinuous wires, and (2) between two EBG structures made of discontinuous wires where each has a different period of discontinuities. Both switching configurations are simulated and experimentally characterized on passive prototypes. An excellent agreement is observed between simulations and measurements. The radiation patterns of two types of antennas, a horn antenna and a meteorological antenna, are also measured in the presence of the radome.

Experimental Studies on Friction Factor and Heat Transfer Characteristics Through Wire-Woven Bulk Kagome Structure

Periodic cellular metals with open, periodic cell topologies have received much attention owing to their potential for multi-functionality such as load bearing, thermal dissipation, and actuation. Recently, a new technique, known as wire-woven bulk Kagome, has been introduced, which is used for fabricating multi-layered Kagome with truss periodic cellular metal. The fabrication of the wire-woven bulk Kagome is based on a concept where continuous helical wires are systematically assembled in six directions. Besides its excellent load-bearing capability with light weight, the wire-woven bulk Kagome has potential for a heat dissipation media because of the high ratio of surface area to volume and low flow resistance. This article presents the experimental results of the fluid flow and heat transfer characteristics of the multi-layered wire-woven bulk Kagome composed of aluminum 1100 helix wires. Under forced-air convection conditions, the friction factor and heat transfer rate of the wire-woven bulk Kagome specimen were investigated for two specimen orientations. The results showed that the friction factor of the wire-woven bulk Kagome was mainly affected by the flow blockage area, and the heat transfer characteristics depended on the open-area ratio. In addition, the results were compared with other heat dissipation media (e.g., open-celled foams, woven screens, lattice-frame materials, and cast Kagome structures). The results showed that the heat transfer performance of the multi-layered aluminum wire-woven bulk Kagome competed favorably with the best heat dissipation media currently available.

An Experimental Approach to Continuous Dieless Wire Drawing (Variant A) Using ELI Ti–6Al–4V Alloy

This research paper describes a specifically constructed Variant A continuous dieless wire-drawing machine to experimentally determine the principal processing parameters for dieless wire drawing using extra low interstitial Ti–6Al–4V wire alloy. It was experimentally determined that the process was limited by the ratio of the ingoing and outgoing axial velocities, also known as the reduction ratio R and influenced by the primary drawing velocity V1. Reductions of up to 36% per pass wire in cross-sectional area (CSA) were achieved. However, a direct relationship between the wire diameter variation and an increase in overall achievable reduction in CSA was observed. The separation distance between the wire heating and cooling devices (S) was identified as one of the principal governing process parameters. It was found that processing in an inert gas environment led to an increased reduction on CSA of approximately 3% per pass when compared with processing in compressed air. This was attributed to a reduction in surface oxidation and stress cracking. The experimentally determined results showed excellent agreement with a proposed mathematical model. It was also determined that the calculated strain rate for the process fell within the boundaries of previously determined strain rates for this particular alloy. The successful operation of this experimental machine effectively illustrates the possible commercial validity of continuous dieless wire drawing.

Coupling Reduction Between Dipole Antenna Elements by Using a Planar Meta-Surface

The mutual coupling between dipole antenna array elements using a planar meta-surface as superstrate is experimentally investigated. The meta-surface is based on grids of short metal strips and continuous wires. A comparison between the mutual coupling when the dipoles are radiating in free space and in presence of the superstrate is presented. On average, between 3 to 14 dB reduction of the mutual coupling is achieved when the superstrate is used. The effect of the mutual coupling on the radiation performance of the array is studied by spherical near-field measurements of the radiation pattern when one driven dipole is fed and the others are matched with 50 Omega loads. The back-projected field on the aperture and on the E-plane is shown.

Fabrication of Ti-Zr Binary Metallic Wire by Arc-Melt-Type Melt-Extraction Method

Ti-Zr binary metallic wires without toxic elements were developed by an arc-melt-type melt-extraction method for potential application as biomedical materials. The Ti-Zr binary alloy showed high wire forming capability during the melt-extraction process, independent of the Ti concentration. Therefore, it was possible to form rapidly quenched wires using Ti 100-x Zr x (x = 10 at% to 80 at%) alloys. Continuous binary Ti-Zr alloy wires had good white luster, negligible surface roughness, high tensile strength, and high bending ductility.

MICROWAVE SCREEN WITH MAGNETICALLY CONTROLLED ATTENUATION

The efiect of magnetic bias on dielectric spectra of composite sheets fllled with Fe or Co-based microwires is studied experimentally and via simulation. The permittivity is measured using a free-space technique within the frequency band from 6 to 12GHz. The bias is applied either parallel or perpendicular to the microwave electric fleld; the bias strength varies from 0 to 2.5kOe. The composites with Fe-based wires reveal a single region of bias dependent permittivity under bias about 800{1000Oe. The composites with Co- based wires reveal two such regions: the high-fleld region is close to that of composites with Fe wires, and the low-fleld region corresponds to the coercive fleld of Co wires (2{3Oe). The high-fleld efiect is related to the dependence of ferromagnetic resonance (FMR) parameters on bias; the low-fleld efiect is related to the rearrangement of the domain structure of Co-based wires. The interference of magnetoimpedance and dipole resonance is analyzed, revealing the efiects ofi wire length, diameter, parameters of magnetic resonance and composite structure. The results are considered in view of application to the problem of controlled microwave attenuation. Simulation shows that the narrower is the FMR spectrum and the higher is the admissible loss of a sheet in a transparent state, the wider is the dynamic range of attenuation control. The attenuation range of a lattice of continuous wires is smaller than that of a screen with identical wire sections, where the magnetoimpedance efiect is amplifled resonantly. At 15GHz frequency the strength of the bias switching opaque sheet with Fe-based wires to the transparent state is about 2000Oe. For 3dB admissible loss, the range of attenuation control about 10dB is feasible in a composite with aligned wire sections. If the aligned sections are distributed regularly, the loss in a transparent state is about 1dB lower.

Processes and applications of electrostatic fiber formation

‘Electrospinning’ is an electrohydrodynamic jetting process that enables the production of continuous fibers, tubes and wires with diameters as small as 10 nm. The process itself is dependent upon electrostatic interactions such as charge-charge repulsion and charge-field interaction. The interplay of charge repulsion, viscoelasticity and surface tension gives rise to interesting electrohydrodynamic phenomena that challenge fundamental understanding as well as practical implementation and quality control in the final fibers. The morphology and diameter of these fibers can be understood and controlled through manipulation of fluid properties and operating parameters. The fibers thus produced are illustrative of nanotechnology in a 1-dimensional form, and have inspired considerable activity in the research community into their potential applications. Proposed uses range from high performance filtration media and membranes, to sensors and actuators, to medical devices and drug delivery vehicles. Two examples, tissue scaffold engineering and superhydrophobicity, are illustrated here.

Discrete versus Continuous Wires on Quantum Networks

Mesoscopic systems and large molecules are often modeled by graphs of one-dimensional wires connected at vertices. In this paper, we discuss the solutions of the Schrödinger equation on such graphs, which have been named "quantum networks". Such solutions are needed for finding the energy spectrum of single electrons on such finite systems or for finding the transmission of electrons between leads which connect such systems to reservoirs. Specifically, we compare two common approaches. In the "continuum" approach, one solves the one-dimensional Schrödinger equation on each continuous wire and then uses the Neumann-Kirchoff-de Gennes matching conditions at the vertices. Alternatively, one replaces each wire by a finite number of "atoms" and then uses the tight binding model for the solution. Here, we show that these approaches cannot generally give the same results, except for special energies, unless the lattice constant of the tight binding model tends to zero. Even in the limit of the vanishing lattice constant, the two approaches coincide only if the tight binding parameters obey very special relations. The different consequences of the two approaches are then demonstrated via the example of a T-shaped scatterer.

The bianisotropic medium model for left-handed metamaterials and numerical calculation of negative electromagnetic parameters

Abstract We introduce the bianisotropic medium model into left-handed metamaterials (LHMs). Based on the model, we propose a novel method, which differs from S-parameter retrieval method, to calculate the constitutive parameters of LHMs. Via the numerical calculation of permeability μ and permittivity e , the relation between resonance intensity and geometric parameters for arrays of hexagonal split-ring resonators (SRRs) is acquired. The dendritic structure allows for negative permeability μ in the frequency range of 7.6–9.4 GHz, which is in good agreement with experimental results. The permittivity spectra of arrays of continuous and cut wires reveal the plasmonic and ideal resonant responses, respectively. Moreover, the recovered permittivity e is free from antiresonance, which is consistent with physical laws.

Experimental Evidence for the Left-Handed Behavior of Combined Structures of a Cut-Wire Pair and a Continuous Wire

Experimental Evidence for the Left-Handed Behavior of Combined Structures of a Cut-Wire Pair and a Continuous Wire

Electromagnetic Behavior of Representative Metamaterial Structures

Electromagnetic Behavior of Representative Metamaterial Structures V. D. Lam Quantum Photonic Science Research Center and Department of Physics, Hanyang University, Seoul 133-791 and Institute of Materials Science, Vietnamese Academy of Science and Technology, Hanoi, Vietnam J. B. Kim, S. J. Lee and Y. P. Lee Quantum Photonic Science Research Center and Department of Physics, Hanyang University, Seoul 133-791 (Received 12 March 2008, in nal form 16 June 2008) We investigated systematically the electromagnetic behavior of di erent magnetic metamaterials, from the split-ring resonator to the cut-wire pair, for providing a negative magnetic permeability. The combination of a cut-wire pair and a continuous wire was also studied experimentally. We found that the combined structure exhibited both leftand right-handed transmission bands. Until the width of the cut-wire pair was increased to merge with the adjacent continuous wire to form the so-called shnet structure, the left-handed (LH) behavior continued to be observed. Finally, the e ect of the structural parameters on the LH behavior of the shnet structure was also investigated. These structures were designed, built and measured in the microwave frequency range. PACS numbers: 41.20.Jb, 42.25.Bs, 42.70.Qs

Radiationless Transitions of G4 Wires and dGMP

Steady-state and time-resolved emission techniques were employed to study the nonradiative process of deoxygunaosine monophosphate (dGMP) and novel uniform continuous G4 wires containing hundreds of stacked tetrads. We found that the time-resolved emissions of both dGMP and G4 wires decay nonexponentialy. At room temperature, the short-time decay of the G4 wires is about 10 ps. At low temperatures in ice, the fluorescence quantum yields of both dGMP and G4 wires increase as the temperature decreases. For the G4 wires, the fluorescence quantum yield increases from about 10−3 at room temperature to about 0.03 at liquid-nitrogen temperatures. The asymptotic long-time decay of the lifetime-corrected emission of the G4 wires obeys a power law. At all temperatures, the average fluorescence decay time of G4 wires is longer than that of dGMP. We successfully used an inhomogeneous nonradiative model to fit the experimental results.

The science of negative index materials

Metamaterials are designed to have structures that make available properties notfound in Nature. Their unique properties (such as negative index of refraction,n) can be extended from GHz all the way to optical frequencies. We review thescaling properties of metamaterials that have been fabricated and give negativen and negativepermeability, μ. It is found that most of the experimentally realized metamaterials haveλ/a between 2 (THz and optical region) and 12 (GHz region), whereλ is the operationwavelength and a is the size of the unit cell. The transmission losses for the experimental structures and the ratioλ/a for the simulated structures are presented. Finally, a comparison of the differentmetamaterial designs (fishnet, cut and/or continuous wires, and split-ring resonators andwires) is given.

Basal behavioral characterization of hsf1 deficient mice and its cellular and behavioral abnormalities underlying chronic unpredictable stressors

The heat shock factor 1 (HSF1) is a major transcriptional factor that controls the rapid induction of heat shock proteins in response to various environmental stressors. In this study, we globally investigated the effect of HSF1 deficiency on animal behaviors during postnatal growth, and abnormalities in hippocampal neurons and behavior in response to chronic unpredictable stressors (CUS). Mouse behaviors were measured in several behavioral paradigms, including elevated plus maze, open field, closed field, T-maze continuous alternation task (T-CAT), bridge-walking, and wire suspension tests. The hsf1-null mice exhibited reduction in basal anxiety levels and exploratory behavior, and working memory deficits, but normal motor coordination abilities. Chronic unpredictable stressors significantly increased apoptosis in hippocampal CA3 cells in both the hsf1-null and wild-type (WT) mice in the in situ TUNEL staining and induced more anxiety-like behavior in the hsf1-null mice than WT mice in the plus T-maze paradigm. We conclude that hsf1 gene deficiency results in significant abnormalities in mouse basal behaviors and sensitization to chronic unpredictable stressors.

Negative index short-slab pair and continuous wires metamaterials in the far infrared regime

Using transmission and reflection measurements under normal incidence in one and three layers of a mum-scale metamaterial consisting of pairs of short-slabs and continuous wires, fabricated by a photolithography procedure, we demonstrate the occurrence of a negative refractive index regime in the far infrared range, ~2.4-3 THz. The negative index behavior in that system at ~2.4-3 THz is further confirmed by associated simulations, which are in qualitative agreement with the experimental results.

Enhanced directed emission from metamaterial based radiation source

The enhanced directed emission from a metasurface which is illuminated at its resonance frequency by a dipole source is experimentally demonstrated. The metasurface consists of two cutwire layers and a continuous wire layer in between, which exhibits strong magnetic dipole resonance under excitation normal to the plane. The scanned near-field patterns show the confinement of the field in the presence of metasurface, which, in turn, provides an enhanced and directional radiation in the far field. The far-field patterns are obtained by direct measurement and by a far-field transformation of the scanned near field, which are found to be in good agreement.

Left-handed behavior of split-ring resonators: Optical measurements and numerical analysis

The periodic double-ring split-ring resonator (SRR) array was one of the first proposed magnetic metamaterials for the realization of a negative index of refraction. We experimentally and numerically study double-ring SRRs on silicon substrates in the midinfrared frequency regime. For light at normal incidence, we observe that an electric resonance in the outer ring and a magnetic resonance in the inner ring exist at similar frequencies in our sample, which suggests that the double-ring SRR array could simultaneously have a negative permittivity and a negative permeability, or a left-handed behavior. Our conjecture are confirmed by numerical simulations. We also propose a left-handed metamaterial composed of two single-ring SRRs in each unit cell. The left-handed behaviors in the two metamaterials studied here originate only from the SRR itself. Thus, there are no metallic continuous wires involved in the devices compared to conventional left-handed SRR metamaterials.

Preparation of Fe and Co based amorphous wires by in-water quenching process

The investigation addresses the effect of in-water quenching process parameters on the magnetic properties of Fe and Co based amorphous wires. The in-water quenching process parameters such as water drum speed, crucible nozzle orifice diameter, crucible nozzle to water level separation and gas pressure for melt ejection were found to be critically important to obtain continuous and ductile wires. The thinner wires with a diameter of ∼124 μm revealed superior soft magnetic properties with coercivities as low as ∼5˙63 A m–1 (70˙8 mOe) which was attributed to their high amorphous nature and consequent isotropy. This was also manifested from their surface morphology as observed by scanning electron microscopy. The Fe77˙5Si7˙5B15 and Co72˙5Si12˙5B15 (at.-%) wires in their as prepared state revealed high fracture strength, above 3000 MPa, and high microhardness ∼1200 HV (Vickers pyramid number).

Factors influencing efficiency of sliding mechanics to close extraction space: a systematic review

To review recent literature to determine strength of clinical evidence concerning the influence of various factors on the efficiency (rate of tooth movement) of closing extraction spaces using sliding mechanics. A comprehensive systematic review on prospective clinical trials. An electronic search (1966-2006) of several databases limiting the searches to English and using several keywords was performed. Also a hand search of five key journals specifically searching for prospective clinical trials relevant to orthodontic space closure using sliding mechanics was completed. Outcome Measure - Rate of tooth movement. Ten prospective clinical trials comparing rates of closure under different variables and focusing only on sliding mechanics were selected for review. Of these ten trials on rate of closure, two compared arch wire variables, seven compared material variables used to apply force, and one examined bracket variables. Other articles which were not prospective clinical trials on sliding mechanics, but containing relevant information were examined and included as background information. CONCLUSION - The results of clinical research support laboratory results that nickel-titanium coil springs produce a more consistent force and a faster rate of closure when compared with active ligatures as a method of force delivery to close extraction space along a continuous arch wire; however, elastomeric chain produces similar rates of closure when compared with nickel-titanium springs. Clinical and laboratory research suggest little advantage of 200 g nickel-titanium springs over 150 g springs. More clinical research is needed in this area.

Dependence of the distance between cut-wire-pair layers on resonance frequencies

We studied both experimentally and theoretically the influence of the distance between adjacent cut-wire-pair layers on the magnetic and the electric resonances in the microwave-frequency regime. Besides the dependence on the separation between cut-wire pairs, along the electric-field direction, the electric resonance strongly depends on the distance between cut-wire-pair layers, while the magnetic resonance is almost unchanged. This contrast can be understood by the difference in the distribution of induced-charge density and in the direction of the induced current between the electric and magnetic resonances. A simple model is proposed to simulate our experimental results and the simulation results are in good agreement with the experiment. This result provides important information in obtaining left-handed behavior when the cut-wire pairs are combined with the continuous wire.