TE10矩形波导中填充金属线阵和铁氧体合成的新型左手媒质

在TE₁₀矩形波导中填充金属线阵和铁氧体合成了一种新型的左手媒质结构.分别使用了转移函数矩阵方法以及全波仿真工具Ansoft HFSS对所提出的结构进行了分析.结果表明,在横向磁化铁氧体等效磁导率实部为负的频段范围内,该合成结构呈现左手通带特性并伴随着后向波的传播现象.由于横向磁化铁氧体的等效磁导率为负的频段范围可调,故所提出的结构具有左手通带范围可调的特性. 关键词： 左手媒质 10矩形波导')" href="#">TE₁₀矩形波导 金属线阵 铁氧体     

Microwave left-handed composite material made of slim ferrite rods and metallic wires

This paper reports on experimental study of the microwave properties of a composite material consisting of ferrite and copper wires. It finds that the slim ferrite rods can modify the magnetic field distribution through their anisotropy, so that the ferrite's negative influence on the copper wires' plasma will be reduced. Left-handed properties are observed even in the specimen with close stuck ferrite rods and copper wires.     

Electronic structure and polarizability of quantum metallic wires

The electronic structure and the linear response to an external electric field of simple metal wires with a quantum-size cross-section have been studied within the density-functional theory and the “jellium” model. It is found that an increase in the wire radius leads to a nonmonotonic change in the work function and static polarizability of the wire. The photoabsorption spectra of Na wires with different cross-sections are obtained. The effect of a dielectric environment on the properties of metallic wires is investigated. An increase in the permittivity of a medium brings about a decrease in the static polarizability of metallic wires. It is demonstrated that the surface plasma resonance in the photoabsorption cross-section for Na wires placed in a dielectric matrix is shifted from the continuous spectrum toward the range somewhat below the ionization threshold.     

From the Anderson Model on a Strip to the DMPK Equation and Random Matrix Theory

We study weakly disordered quantum wires whose width is large compared to the Fermi wavelength. It is conjectured that such wires display universal metallic behavior as long as their length is shorter than the localization length (which increases with the width). The random matrix theory that accounts for this behavior—the DMPK theory—rests on assumptions that are in general not satisfied by realistic microscopic models. Starting from the Anderson model on a strip, we show that a twofold scaling limit nevertheless allows to recover rigorously the fundaments of DMPK theory, thus opening a way to settle some conjectures on universal metallic behavior.     

Anderson localization from the replica formalism

We study Anderson localization in quasi-one-dimensional disordered wires within the framework of the replica sigma model. Applying a semiclassical approach (geodesic action plus Gaussian fluctuations) recently introduced within the context of supersymmetry by Lamacraft, Simons, and Zirnbauer, we compute the exact density of transmission matrix eigenvalues of superconducting wires (of symmetry class CI.) For the unitary class of metallic systems (class A) we are able to obtain the density function, save for its large transmission tail.     

X-ray diffraction and Mössbauer spectroscopy studies of cementite dissolution in cold-drawn pearlitic steel

Cementite dissolution in cold-drawn pearlitic steel (0.8 wt.% carbon) wires has been studied by quantitative X-ray diffraction (XRD) and Mössbauer spectroscopy up to drawing strain 1.4. Quantification of cementite-phase fraction by Rietveld analysis has confirmed more than 50% dissolution of cementite phase at drawing strain 1.4. It is found that the lattice parameter of the ferrite phase determined by Rietveld refinement procedure remains nearly unchanged even after cementite dissolution. This confirms that the carbon atoms released after cementite dissolution do not dissolve in the ferrite lattice as Fe-C interstitial solid solution. Detailed analysis of broadening of XRD line profiles for the ferrite phase shows high density of dislocations (～10¹⁵/m²) in the ferrite matrix at drawing strain 1.4. The results suggest a dominant role of ?1?1?1? screw dislocations in the cementite dissolution process. Post-deformation heat treatment leads to partial annihilation of dislocations and restoration of cementite phase. Based on these experimental observations, further supplemented by TEM studies, we have suggested an alternative thermodynamic mechanism of the dissolution process.     

Absorption losses in periodic arrays of thin metallic wires

We analyze the transmission and reflection of electromagnetic waves calculated from transfer matrix simulations of periodic arrangements of thin metallic wires. The effective permittivity and the absorption of the arrangements of wires are determined. Their dependence on the wire thickness and the conductance of the metallic wires is studied. The cutoff frequency, or effective plasma frequency, is obtained and compared with analytical predictions. It is shown that the periodic arrangement of wires exhibits a frequency region in which the real part of the permittivity is negative while its imaginary part is very small. This behavior is seen for wires with thickness as small as 17 microm with a lattice constant of 3.33 mm.     

Tunable dual-band ferrite-based metamaterials with dual negative refractions

We report on three types of tunable dual-band metamaterial with dual negative refraction in this paper. The three types of metamaterial are composed of ferrite slabs and three different metallic resonators, including split-ring resonators (SRR), Ω-like resonators, and short wire pairs. The ferrite slabs under an applied magnetic bias provide one magnetic resonance frequency band and the three metallic resonators provide another magnetic resonance frequency band, respectively. The continuous wires within the metamaterials provide the negative permittivity in a wide frequency band covering the two magnetic resonance bands. We give the design, analysis and numerical demonstrations of three such types of metamaterial in detail. The effective electromagnetic parameters obtained from the simulated S-parameters indicate that the three types of metamaterial indeed exhibit two negative refraction passbands and the two passbands can also be shifted by changing the magnetic bias. Our results open the way to fabricate tunable dual-band metamaterial cloaks, absorbers, and antennas.     

Possible negative refraction in two dimensional ferromagnetic wire lattice

In this paper, we present theoretical and experimental results for the indication of negative refraction in ferromagnetic metallic wire lattice. We have studied microwave transmission through a two dimensional wire lattice made of ferromagnetic metallic wires under the applied static magnetic field. We have found that, the microwave transmission were significantly changed at ferromagnetic resonance frequency region. Thus the magnetic permeability can be tuned by external dc magnetic field. Since the dielectric permittivity of metallic wire lattice is negative and can take a value close to unity then the crystal exhibits negative index of refraction at microwave region under the external magnetic field.     

The use of controllable photonic band gap (CPBG) materials: An antenna application

In this paper, we theoretically and experimentally demonstrate the capability to realise controllable photonic band gap (CPBG) materials applied to the conformation of the radiation pattern of a planar antenna at 12 GHz. The CPBG materials studied are variable capacitance and conductance lattices fabricated with high frequency PIN diodes soldered along wires or metallic stripes on dielectric printed boards. Depending on the diode bias, the transmission factor of the lattice is controlled. Then, the emitted radiation of an antenna can be either transmitted or totally reflected by the material. In the transmission state, the antenna radiation is angular filtered by the CPBG material. In that case, it behaves like a controllable electromagnetic lens in the allowed frequency domain of the material.     

Atom probe microanalytical studies of some commercially important steels

The FIM atom probe has been used to study the atomic scale distribution of chemical elements in several important ferrous materials. Microanalysis of patented and drawn pearlitic steel wires reveals the partitioning of alloying elements between the carbide and ferrite phases. Studies of a similar material in the martensitic state show the progressive redistribution of carbon atoms during the martensite ageing process. Accurate phase analysis of a duplex stainless steel confirms and extends previous X-ray microanalytical studies, and reveals details of alloy element partititoning between austenite and ferrite.     

Measurement of surface defects on thin steel wires by atomic force microscopy

The characterisation of surface defects on thin metallic wires is very important for the industrial applications of these wires. The physical dimensions of the surface defects presented by several thin steel wires of different diameters have been measured using Atomic Force Microscopy (AFM). The measurements made show two main defects in thin steel wires: holes and scratches, but other defects like porosity or protuberances have also been observed. We have found an empirical relationship between the physical dimensions of the scratches and the wire diameter.     

Topological transition in coated wire medium

Employing nonlocal homogenization approach, we investigate the properties of a metamaterial consisting of parallel metallic wires with dielectric coating. We demonstrate that manipulation of dielectric contrast between wire dielectric shell and host material at fixed frequency results in dynamic switching of metamaterial dispersion regime from elliptic to the hyperbolic one, i.e. the topological transition takes place. It is proved that such transition can be induced by the variation of the metamaterial temperature. Our findings thus pave a way to the implementation of a tunable ‘elliptic‐hyperbolic’ metamaterial.     

Atomic-size oscillations in conductance histograms for gold nanowires and the influence of work hardening

Nanowires of different natures have been shown to self-assemble as a function of stress at the contact between two macroscopic metallic leads. Here we demonstrate for Au wires that the balance between various metastable nanowire configurations is influenced by the microstructure of the starting materials, and we discover a new set of periodic structures, which we interpret as due to the atomic discreteness of the contact size for the three principal crystal orientations.     

A plasma frequency modulation model for constructing structure material with arbitrary cross-section thin metallic wires

Considering the fact that just the electrons confined in the region of the skin depth will actually affect the plasma frequency due to the skin effect, a model for constructing epsilon-near-zero (ENZ) metamaterials through the arranged thin metallic wires with arbitrary cross-section is developed, utilizing the perimeter approximation. With our model, plasma frequency can be freely modulated just by the variance of the metallic wire perimeter, irrespective of the cross-section shape of wires. The finite element method (FEM) and S-parameters retrieval method were employed to numerically simulate the plasma frequencies, which have verified the validity of the theoretical model.     

Microwave magnetic properties of soft magnetic thin films

We review our works that focus on the microwave magnetic properties of metallic,ferrite and granular thin films.Soft magnetic material with large permeability and low energy loss in the GHz range is a challenge for the inforcom technologies.GHz magnetic properties of the soft magnetic thin films with in-plane anisotropy were investigated.It is found that several hundreds of permeability at the GHz frequency was achieved for Co100-xZrx and Co90Nb10 metallic thin films because of their high saturation magneti...     

Patterning thin metallic film via laser structured weakly bound template

A weakly bound buffer material is structured on a surface by interfering low power laser beams, as a template for patterning metallic thin films deposited on top. The excess buffer material and metal layer are subsequently removed by a second uniform laser pulse. This laser pre-structured buffer layer assisted patterning procedure is demonstrated for gold layer forming a grating on a single crystal Ru(1 0 0) under UHV conditions, using Xe as the buffer material. Millimeters long, submicron (0.65 μm) wide wires can be obtained using laser wavelength of 1.064 μm with sharp edges of less than 30 nm, as determined by AFM. This method provides an all-in-vacuum metallic film patterning procedure at the submicron range, with the potential to be developed down to the nanometer scale upon decreasing the patterning laser wavelength down to the UV range.     

Gapless excitations in strongly fluctuating superconducting wires

We study the low-temperature tunneling density of states of thin wires where superconductivity is destroyed through quantum phase-slip proliferation. Although this regime is believed to behave as an insulator, we show that for a large temperature range this phase is characterized by a conductivity falling off at most linearly with temperature, and has a gapless excitation spectrum. This novel conducting phase results from electron-electron interaction induced pair breaking. Also, it may help clarify the low-temperature metallic features found in films and wires whose bulk realization is superconducting.     

Morphological phases of crumpled wire

We find that in two dimensions wires can crumple into different morphologies and present the associated morphological phase diagram. Our results are based on experiments with different metallic wires and confirmed by numerical simulations using a discrete element model. We show that during crumpling, the number of loops increases according to a power law with different exponents in each morphology. Furthermore, we observe a power law divergence of the structure's bulk stiffness similar to what is observed in forced crumpling of membranes.