Wiregrid modelling scheme for curvature varying surface

A new wiregrid modelling scheme for a curvature varying scatterer is proposed. A conducting elliptic cylinder is modelled by wires with radii of different sizes depending on the radius of curvature on the surface. The size of each wire is generated from the model equation suggested in the study. Numerical results show that this new wiregrid model can be applied to enhance the accuracy of solutions for a curvature varying scatterer     

The matrix Riccati equation for scattering from stratified chiralspheres

Angular scattering from radially stratified spherical chiral objects is investigated. Based on the principles of invariant embedding, we formulate a matrix Riccati equation that can be used to examine basic scattering properties of spherical chiral structures with radial inhomogeneities in permittivity, permeability, and chirality. High- and low-frequency limits as well as weak reflection and constant impedance cases for this equation are examined. We show that in the limit of large radii of curvature, this formulation yields the planar result     

Modes in a maser interferometer with curved and tilted mirrors

Fabry-Perot interferometers have played an important role in the conception and realization of optical masers. The authors have previously made a study of the idealized interferometer. In this paper they present some results of a continued study of the effects of certain simple forms of aberration. The first is represented by tilted plane mirrors and the second by curved mirrors. Tilting the mirror causes the mode patterns to become asymmetric and the diffraction loss to become greater. It also tends to equalize the losses of the two lowest-order modes thus causing a beating phenomenon which has been observed experimentally. In the case of interferometers with mirrors of arbitrary radii of curvature, there exist regions of low loss and high loss as the mirror spacing is varied. The loss function can be represented by a contour map of a three-dimensional model which has certain symmetry properties. This model is useful in choosing proper mirror spacing for low loss operation of optical masers.     

Study and Design of Spiral Bent Waveguide Configuration

A new version of the scalar transverse electric（TE） wave equation in the bent waveguide is introduced. Then. TE polarized field in curved single-mode waveguides is analyzed by using the finite- difference beam propagation method（FD-BPM）. The bending loss in bent waveguides is gotten for the optical fields obtained from BPM and comparisons are made among losses of the waveguides with various curvature radiuses, refractive index differences and cross sections. Based on the results, the design of spiral bent waveguide configuration is proposed as follows： refractive index difference being of 0. 007, both width and thickness of waveguides being of 6 μm, the curvature radius in the spiral centre being of 4 mm, and the bending loss coefficient of the designed spiral bent waveguide being of 0. 302 3 dB/cm.     

Generalised Fresnel's law for loss due to curvature

Many rays, predicted by Fresnel's laws to be totally reflected from a curved interface between two dielectric media, are only partially reflected. We derive a generalised Fresnel transmission coefficient to account for this loss. Our transmission coefficient applies to an arbitrary surface; e.g. one defined by two arbitrary radii of curvature. It can be used to determine radiation loss from bent and straight circular optical fibres.     

In situ microwave characterization of nonplanar dielectric objects

In this paper, a novel experimental solution is presented for the nondestructive, noncontact, and in situ characterization of dielectric objects of curved shape using a spot-focused freespace measurement system. Measurements were made on Plexiglas and glass samples of cylindrical shape with different radii of curvature, and the complex permittivities were computed from the measured S₂₁ and S₁₂. Comparing the results with planar samples shows that the curvature does not significantly affect the accuracy of the measured permittivity of cylindrical surfaces if the radii of curvature are large compared to the size of the focusing spot. Results for a number of curved samples agree with the published data and this demonstrates the usefulness of a spot-focused free-space system for in situ characterization and evaluation of materials and complex structures during processing and fabrication. The other benefit of this approach is the noncontact nature of the method, which permits measurement of solids and liquids in high/low-temperature environments. The spot-focused beam permits characterization of small or large samples     

NRD波导中多种弯波导之间的耦合特性

针对ＮＲＤ波导中不同半径的弯波导之间的耦合特性,提出了一种新的通用的分析方法,当耦合结构分别简化为非对称结构（即直波导与弯波导耦合）和对称结构（即两个半径相同的弯波导的耦合）时,该方法也可相应简化,与已有的分析结果完全一致。本文还就不同半径的弯波导构成的耦合器的频率响应和带宽特笥,在６０ＧＨｚ时给出实验验证,证实了本文所提方法的通用性和有效性。     

Reflection at a Curved Dielectric Lnterface--- Electromagnetic Tunneling

The reflection of a locally plane wave from a curved interface between two nonabsorbing dielectric media is investigated. Our analysis is applicable to an interface of general shape, defined at each point by the two principal radii of curvature. When the wave is incident from the denser medium at angles greater than the critical angle it is only partially reflected, due to a form of electromagnetic tunneling. Generalized Fresnel transmission coefficients and an extension of Snell's law are derived to account for this transmission into the less dense medium. Ray tracing can then be applied to determine such phenomena as the bending losses in optical slab waveguides, and the curvature loss of skew rays within straight optical waveguides of circular cross section.     

A reflection ansatz for surfaces with electrically small radii of curvature

Uniform reflection coefficients are developed for two- and three-dimensional, edge-like, perfectly conducting surfaces in the deep lit region. The uniformity is with respect to the electrical size of the radii of curvature at the surface's specular point. This uniformity allows one to physically interpret the reflected field from a smooth surface as one of the radii of curvature approaches zero as a diffracted field. The coefficients are heuristically generated from the exact scattered field for a two dimensional parabolic cylinder with plane wave illumination. The significant variables in this solution are the radii of curvature at the specular point and the distance between the specular point and the incident shadow boundaries in the principal planes. The field prediction accuracy of these reflection coefficients are critically examined through comparisons with reflected fields extracted from scattered fields of canonical surfaces.     

Numerical calculations of radar scattering from sharply peakedocean waves

A numerical solution of the surface-current integral equation is used to calculate the radar backscatter for several wavelike surfaces. The surfaces used in this study represent solutions of the water wave equations for finite amplitude, irrotational gravity waves, with steepnesses selected so as to produce minimum radii of curvature ranging from zero to a value equal to the electromagnetic wavelength and with wave amplitudes ranging from about one-half to five times the electromagnetic wavelength. The results are used to evaluate the importance of edge diffraction effects on backscatter from sharply peaked ocean waves     

手征等离子体填充圆波导的传播特性

本文在柱坐标系中导出了手征等离子体波导内横向场量与纵向场量之间的关系,给出求解纵向场量的波动方程.利用波导壁上的电场边界条件,建立了手征等离子体介质填充的圆波导传播常数的特征方程,计算得到了几种低次模式的传播常数随归一化波导半径及材料参数的一系列变化曲线,分析得出了若干有意义的结论.     

Comparison of ? Obtained from the Conventional Definition with ? Appearing in the Radar Equation for Randomly Rough Surfaces

A comparison is made of the radar cross section of rough surfaces calculated in one case from the conventional definition and obtained in the second case directly from the radar equation. The objective of the analysis is to determine how well the conventional definition represents the cross section appearing in the radar equation. The analysis is executed in the special case of perfectly conducting, randomly corrugated surfaces in the physical optics limit. The radar equation is obtained by solving for the radiation scattered from an arbitrary source back to a colocated antenna. The signal out of the receiving antenna is computed from this solution and the result put into a form recognizeable as the radar equation. The conventional definition is obtained by solving a similar problem but for backscatter from an incident plane wave. It is shown that these two forms for ?' are the same if the observer is far enough from the surface; However, the usual far-field criteria are not sufficient. For the two cross sections to be the same, the observer must be far from the surface compared to the radii of curvature of the surface at the reflection (specular) points. Numerical comparison of the two cross sections has been made for normally distributed surfaces and the difference can be significant.     

Performance of a Cooperative Algorithm for power control in cellular systems with a time‐varying link gain matrix

A new version of the Cooperative Algorithm is proposed for distributed power control in time‐varying cellular environment. Unlike other approaches which assume a fixed link gain matrix, we consider a time‐varying model for shadow fading. We consider the performance of three schemes, namely, instantaneous SIR balancing, slow path loss compensation and the Cooperative Algorithm. Analytical results are obtained for the case where there are two cochannel users. We have shown that the sequence of signal‐to‐interference ratio (SIR) converges in distribution. The outage probability in steady state is obtained. It is shown that when the power control sampling period is small, the performance of the Cooperative Algorithm approaches that of instantaneous SIR balancing. For more than two users, a detailed simulation is performed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Time‐varying network link loss rate tracking from unicast end‐to‐end measurements

Time‐varying network link loss rate is a useful information for network managers to discover and locate the network link failures. This paper proposes a method to track time‐varying network link loss rates from unicast end‐to‐end measurements. The method first trains a state transition matrix to capture the spatio‐temporal characters of packet link transmission probabilities by sending end‐to‐end probe packets and then estimates the time‐varying link loss rates using the state transition matrix and the end‐to‐end measurements obtained from background traffic (the existed packets in network). We also introduce a validation step to check and retrain the state transition matrix in order to ensure the accuracy of the state transition matrix. Our method is capable of tracking the variation of link loss rates without incessantly sending probe packets, which is very feasible for many practical applications. The ns‐2 simulation results show the good performance of our method.     

Diffraction by a concave perfectly conducting circular cylinder

The determination of surface currents induced by a magnetic line source on a perfectly conducting concave cylindrical surface is dealt with in this paper. A "perfect" planar absorber is postulated along the cylinder diameter. The condition that the field be bounded at the origin requires the spectral representation of the characteristic Green's function to possess, in addition to a discrete spectrum comprising a finite number of whispering gallery (WG) modes, also a continuous spectrum. In the asymptotic high frequency limit the latter yields an "intrinsic" diffraction effect that together with the WG mode series correctly reproduces the singularity of the source. The connection between ray optics and the modal series is established by means of a representation comprising modes and rays. This composite representation provides insight into possible generalizations of the results to arbitrary concave cylinders with slowly varying radii of curvature. For circular cylinders with largeka, numerical results are presented for the magnitude of the surface magnetic field distribution.     

Bending losses of coated single-mode fibers: a simple approach

A new approach for the bending losses of coated optical single-mode fibers is developed based on a modified fiber geometry model, and the result is a simple formula. An improved condition for the peak locations is given, that allows for the wavefront curvature of the leaky mode in the bent fiber, since it is derived by wave optics. Simple explicit relations for both the peak spacings and the peak-to-trough ratio are given. Their asymptotic forms for small bend radii are independent of the fundamental-mode parameters. An interpretation of oscillations in the bend-loss curves in terms of a thin-film filter effect of the triple-layer structure on the lateral leaky-mode radiation fully explains the behavior, especially the loss increase in the peaks compared to the case of an infinite cladding. The agreement with numerical and experimental results of other authors is excellent     

Soft UV-nanoimprint lithography on non-planar surfaces

We report on a simple and effective process that allows direct UV-imprinting of micro- and nanostructures on non-planar surfaces, even at sharp edges such as step surfaces. The key for the process is the use of a thin flexible polymer stamp, which was fabricated by spin-coating poly(dimethylsiloxane) (PDMS) on a pre-patterned Si or poly(methyl methacrylate) (PMMA) master and releasing the thin PDMS layer after curing. The thin PDMS stamp was used to conformally mold a UV resist layer coated on various non-planar substrates with different radii of curvature. With this method, we have successfully demonstrated micro- and nanopatterns down to 63 nm on curved surfaces as well as sharp step-like structures. The process so developed will improve the versatility and applicability of molding technologies in many applications that require patterning non-planar substrates, considering that most molding technologies allow for patterning only on planar substrates or surfaces with large curvature radii.     

An Approximate Wave Equation for an Axially Symmetric Periodic Waveguide

The field problem of wave propagation in a waveguide of periodically varying section is investigated. An orthogonal curvi-linear coordinate system is developed leading to a separable wave equation. As a result, the problem is reduced to solving Hills Equation. The discussion is limited to the case of a waveguide with slowly varying radius but there is some expectation that useful results would be obtained, particularly for axial fields, without this restriction.     

Study of bending reliability and electrical properties of platinum lines on flexible polyimide substrates

We have experimentally studied the variation in electrical resistance of flexible platinum lines patterned on polyimide foil when they are subjected to circular bending constraints. The lines were patterned by means of standard photolithography and sputtering deposition. Two different photolithography masks were used for comparative evaluation: an un-expensive transparency mask and a standard chromium mask. Measurements of the temperature coefficient of resistance (TCR) and time stability of the resistance have been acquired for lines bent down to 1.25 mm radius of curvature on a customized bending setup, showing good reliability results. The robustness of the lines has been also assessed by registering their change in resistance while bending at different radii of curvature. The lines showed reliability issues for radii of curvature below 1.25 mm, presenting a resistance variation of 19% for transparency mask-fabricated lines and 9% for chromium mask-fabricated lines. The worse reliability performances of transparency mask lines, compared to the chromium mask ones, was found to be due to their imperfect edges, which promoted the formation and propagation of cracks during bending. The results of the experiments in this work permitted to compare the performances of flexible conductive lines with different geometry and fabricated with two different masks, establishing quantitative and qualitative bending limits for their appropriate operation in flexible electronics systems.     

Calculation of Mutual Coupling between Two RLTs in Millimeter Wave VCO Waveguide Cavities with Mode Matching Methods

In the design of millimeter wave voltage control oscillators (VCOs), mutual coupling effect is of great importance for it influences the tuning and power characteristics of VCOs significantly. In this paper, mutual coupling between two in-line radial line transformers (RLTs) in rectangular waveguide cavities of millimeter wave VCOs has been evaluated with mode matching methods. Mutual coupling characteristics varying with various parameters of resonate cavity such as the distance between two diodes, the position of sliding short, the radii of bias pins, the radii of RLTs, and the height of diodes are presented. Some useful conclusions concerning two RLTs configuration have been derived, which is helpful to design millimeter wave VCO of this structure.