High-frequency surface currents induced on a perfectly conducting cylindrical reflector

An explicit expression for the surface current induced by sources on a perfectly conducting cylindrical reflector is obtained by taking into account the locality of the high-frequency diffraction phenomenon. The results show that the component previously conjectured by Ufimtsev involves several components having different propagation behaviors that can be separated into three main groups. When the reflector becomes infinitely large, the currents excited by edge diffraction are shown to reduce to those for the classical half-plane problem. The results are independent of the actual source configuration and may thus be useful in more complicated situations.     

Electromagnetic fields near a concave perfectly conducting cylindrical surface

Although no shadowing or diffraction effects occur, the surface fields excited by a high frequency source located on a perfectly conducting concave cylindrical boundary cannot be analyzed by geometrical optics since the caustics for rays, which have experienced many reflections, accumulate. In a previous study, alternative field representations in terms of whispering gallery (WG) modes, canonical integrals, and hybrid ray-mode combinations have been explored to compensate for the failure of geometrical optics. As the source and/or observation points move off the boundary, the number of relevant multiply reflected rays decreases, and the caustics eventually become separated sufficiently to be treated as isolated. Ray optics is then expected to apply provided that uniform corrections near caustics and their endpoints are included. This conjecture is confirmed in the present investigation, which tracks the field continuously from the "boundary layer" near the concave surface, where ray optics is invalid, to off-surface points where it applies, by generalizing the alternative field representations used previously. A rich variety of hybrid ray-mode combinations exists for off-surface source and observation points. Especially intriguing is the possibility of choosing a hybrid mix that completely avoids the need for the caustic (and endpoint) correction functions in a purely ray-optical formulation. The utility, accuracy, and range of validity of the various field representations is assessed by numerical comparison with a reference solution in terms of WG modes plus a continuous spectrum.     

Multiple microstrip lines on a multilayered cylindrical dielectricsubstrate on perfectly conducting wedge

The quasi-TEM characteristics of a class of cylindrical microstrip lines are rigorously determined. The class of microstrip lines considered consists of multiple infinitesimally thin strips on a multilayered dielectric substrate on a perfectly conducting wedge. Expressions for the potential distribution inside and outside the dielectric substrate, charge distribution on the strips, and capacitance matrix of the microstrip lines are derived. The problems of a microstrip line on a cylindrically capped wedge and on a cylindrical dielectric substrate on perfectly conducting core are also considered as special cases. Sample numerical results based on the derived expressions are given and discussed     

Two-dimensional pulsed propagation from extended planar aperture field distributions through a planar dielectric layer via quasi-ray Gaussian beams

A previously developed Gabor-based quasi-ray narrow-waisted (NW) Gaussian beam (GB) algorithm for time-harmonic propagation of aperture-excited two-dimensional (2-D) electromagnetic fields through a planar dielectric layer is extended here to the time domain (TD) to deal with short-pulse excitation. The dielectric layer is assumed to be nondispersive; however, slight Ohmic losses can be accommodated. The frequency domain (FD) algorithm is based on a self-consistent discretization of the aperture field distribution in terms of basis NW-GBs in conjunction with an efficient quasireal ray tracing scheme for tracking the individual basis beams. The TD results are obtained by analytic Fourier inversion from the FD in terms of pulsed beam wavepackets, following a procedure similar to that utilized by Galdi et al. (see IEEE Trans. Antennas Propagat., vol.49, p.1322-32, Sept. 2001) in connection with free-space aperture radiation. The proposed algorithm is validated and calibrated against a rigorous numerical reference solution via an extensive series of numerical experiments. A priori accuracy assessments in terms of critical nondimensional estimators, and computational costs, are also given attention.     

High-frequency fields excited by a line source located on a perfectly conducting concave cylindrical surface

Alternative representations are obtained for the high-frequency surface field excited on a perfectly conducting concave circular cylinder by an axial magnetic line current located on the surface. Included are ray-optical, canonical integral, whispering gallery mode, and near-field formulations, and various combinations of these. Asymptotic evaluations in different parameter ranges lead to results with varying accuracy and physical content. Their utility is assessed by extensive numerical calculations and comparisons. Most intriguing is a form of the asymptotic solution that involves only a number of geometric optical rays and a number of whispering gallery modes.     

Diffraction by a planar junction between a perfectly conducting anda periodically loaded impedance surface

By using a perturbative method, an integral representation for the field scattered by a planar junction between a perfectly conducting and a periodically loaded impedance surface is determined, when the junction is illuminated by a plane wave perpendicularly incident on its edge. Both a uniform, asymptotic expression and a series representation are presented for the first-order perturbative correction to the field scattered by the junction. The series representation is expressed in terms of Bessel functions of integer order and is suitable for field calculations at small distances from the edge. Several numerical results are presented to demonstrate the applicability of the proposed technique     

亚声速球/柱尾流对激光传输影响的数值模拟

采用大涡模拟方法计算了来流速度为0.4 Ma情况下球/柱形结构附近的流场,根据密度数据计算了光程差及气动相屏,并研究了尾流对激光传输的影响。结果表明:光程差空间均方根的时间平均值随发射角增大而增大,发射角从120增加到148时,其数值从0.11 m增加到0.28 m;光程差空间均方根随时间变化剧烈,发射角为148时,其时间均方根可达0.04 m;球/柱尾流对激光传输有很大影响,发射角为148情况下,Strehl比的时间平均值为0.33,并且Strehl比的时间平均值随发射角的增大而减小,发射角从120增加到148过程中,Strehl比的时间平均值减小了59%;Strehl比随时间变化剧烈,其时间均方根大于0.05。     

Design of a cylindrical LED substrate without radiator

To reduce the weight and production costs of light-emitting diode (LED) lamps,we applied the principle of the chimney effect to design a cylindrical LED substrate without a radiator.We built a 3D model by using Solidworks software and applied the flow simulation plug-in to conduct model simulation,thereby optimizing the heat source distribution and substrate thickness.The results indicate that the design achieved optimal cooling with a substrate with an upper extension length of 35 mm,a lower extension length of 8 mm,and a thickness of 1 mm.For a substrate of those dimensions,the highest LED chip temperature was 64.78 ℃,the weight of the substrate was 35.09 g,and Rjb =7.00 K/W.If the substrate is powered at 8,10,and 12 W,its temperature meets LED safety requirements.In physical tests,the highest temperature for a physical 8 W cylindrical LED substrate was 66 ℃,which differed by only 1.22 ℃ from the simulation results,verifying the validity of the simulation.The designed cylindrical LED substrate can be used in high-power LED lamps that do not require radiators.This design is not only excellent for heat dissipation,but also for its low weight,low cost,and simplicity of manufacture.     

High-frequency surface currents induced on a perfectly conducting cylindrical sheet by an obliquely incident plane wave

Explicit expressions for the surface currents of different kinds induced on a perfectly conducting cylindrical sheet by an obliquely incident high-frequency plane wave are derived. The results are in such forms that they can both be used directly in numerical applications and permit us to understand the structure of the induced surface current. It is shown that the components due to the surface and edge diffractions propagate along certain geodesic lines on which the transfer coefficients as well as the attenuation constants are dependent only on the curvature radius.     

Surface-acoustic-wave propagation on a piezoelectric substrate with a periodic metal grating

An analysis is presented for modes propagating via a periodic metal grating on the surface of a piezoelectric substrate. Assuming no loss in the structure, the numerical solution is exact in the limit, combining the effective permittivity function formulation with the least-squares residual applied at the surface.     

Planar monolithic integration of LED and FET devices on a conductive substrate

This paper describes results of a study on the monolithic integration of AlGaAs light-emitting diodes with GaAs field-effect transistors on a conductive p-GaAs substrate. Using a selective growth technique, a horizontal configuration is fabricated that allows separate optimization of the two types of devices and provides a quasi-planar surface. This approach is compatible with the standard GaAs integrated-circuit technology. By inserting an undoped layer and a p-n junction between the active layer of the FET and the substrate leakage currents below 500 µA for bias voltage up to 9 V are obtained for these insulation structures. The emitted light intensity of the LED, connected in series with the FET, exhibits a nearly linear dependence on the driving gate potential. Temperature or optical crosstalk effects were not observed. Fall and rise times around 20 ns were measured from the pulse response characteristics. This switching time is limited by the LED whereas the FET and isolation layers were found not to affect the switching behavior of the circuit in this time frame.     

亚声速横向球/柱流场对激光传输影响的数值模拟

采用大涡模拟的方法计算了来流速度为0.5~0.7 Ma情况下横向球/柱形结构附近的流场,给出了密度和光程差的统计结果,并采用相屏法研究了几种流场对激光传输的影响。结果表明:密度扰动均方根和光程差均方根随着来流速度和发射孔径的增加而增大;Ma从0.5增至0.7时,孔径为0.5 m情况下,密度扰动均方根增长了90%,孔径为0.25 m情况下,光程差均方根增长了90%;Ma=0.6情况下,孔径从0.25 m增加到0.75 m时,两个参数各增加了4倍。激光Strehl比随来流速度和发射孔径的增大而减小;发射孔径为0.25 m情况下,随着Ma从0.5增加至0.7,Strehl比从0.236下降至0.045;Ma=0.6情况下,发射孔径从0.25 m增加至0.75 m过程中,Strehl下降了90%。     

Millimeter-wave propagation through a terrestrial atmosphere

At millimeter-wave frequencies, the terrestrial atmosphere is absorptive, dispersive, and inhomogeneous. Because it is inhomogeneous, rays are bent by refraction, and because it is dispersive, the amount of bending depends on the frequency. Thus the path length between two terminals depends on frequency, which means that there is an additional frequency distortion to be accounted for. The author derives an `effective reactivity' to do such an accounting. He shows that the correction involved is rather small     

Radiation by a probe through a substrate

Radiation by a probe through a grounded substrate layer is considered. The reaction concept is adopted and the coaxial line aperture effects are taken into account. Image theory is invoked to simplify the evaluation of the involved Sommerfeld type integrals. These integrals are computed through a real axis integration which combines numerical and analytical techniques. An interpolation method is introduced which eliminates repetitive calculation of reaction quantities. The properties of the probe such as input, mutual impedance, radiation pattern and radiation efficiency are examined as functions of substrate parameters such as thickness and dielectric constant. The probe length may be chosen to be smaller than, equal to or greater than the substrate thickness. The effect of substrate transverse magnetic (TM) surface wave modes is analyzed and it is found that at each mode cutoff omnidirectional radiation is obtained in thebar{H}-plane with maximum radiation along the horizon. The effect of small substrate loss on the probe parameters is also considered.     

Design and fabrication of a planar patch-clamp substrate using a silicon-on-insulator wafer

noise.     

以绝缘体上硅为基底的平面膜片钳电极的设计和制作

The planar patch-clamp technique has been applied to high throughput screening in drug discovery. The key feature of this technique is the fabrication of a planar patch-clamp substrate using appropriate materials. In this study, a planar patch-clamp substrate was designed and fabricated using a silicon-on-insulator （SOI） wafer. The access resistance and capacitance of SOl-based planar patch-clamp substrates are smaller than those of bulk silicon-based planar substrates, which will reduce the distributed RC noise.     

Properties of a cylindrical antenna in an infinite planar or collinear array

A solution is given for the active impedance and current distribution on a cylindrical antenna in a uniform, infinite, planar, or collinear array. The analysis is applicable to the case in which the distance in the collinear direction between the ends of adjacent elements is small. The current distribution on the collinear array is found by relating the antenna current and electric-field variation on the cylindrical surface of infinite length which contains the array. This analysis is then extended to consider a planar array. Results obtained are applicable to any combination of element length and array phasing, for arrays with or without a ground plane. Comparisons with other investigations based upon sinusoidally distributed currents reveal substantial discrepancies for some configurations.     

Diffraction of a cylindrical wave by a perfectly conducting cylinder enclosed in a metamaterial shell with a negative refractive index

The problem of diffraction of a plane (cylindrical) wave by a perfectly conducting cylinder enclosed in a metamaterial shell is rigorously solved. The influence of the geometric dimensions of the shell, the value of the negative refractive index of the metamaterial medium, and the position of a cylindrical wave source on the field structure in the near zone of the scatterer is investigated. It is found that, in the quasi-optical range of the problem parameters, this structure does not exhibit ideal focusing. It is shown that, there are two types of caustics inside the shell. The first type is related with rays reflected by the surface of the interior cylinder and has one cusp point, and the second type is formed by the geometric-optics rays that are refracted by the outer boundary of the shell and do not fall on the surface of the interior perfectly conducting cylinder. The spatial distribution of the total field amplitude and of the equal-amplitude lines in the near zone of the scatterer is reported. The obtained numerical results are correctly interpreted from the physical viewpoint.     

Low temperature fabricated conductive lines on flexible substrate by inkjet printing

The optimal conditions of inkjet-printed nano-silver suspension and silver nitrate solution for fabricating continuous narrow conductive lines on a polyimide substrate are investigated by varying the driving pulse and droplet overlap. The dimensionless Weber number and Reynolds number are used to evaluate the droplet size after impact. It was found that the presence of a suspension of nanoparticles increases droplet diameter. With appropriate droplet overlap and driving pulse conditions, continuous lines of AgNO₃ with 24.3 μm in width and nano-silver suspension with 33 μm in width were fabricated. In addition, the effects of driving pulse voltage and droplet coverage on the bulging of as-printed conductive lines are also examined.     

Fabrication of large-area conductive patterns on ferrite substrate by laser micro-cladding

This paper investigates fabrication of large-area Ag-Pd conductive patterns on ferrite substrate using laser micro-cladding for microwave device application. The effects of the scan line spacing (i.e., beam overlapping factor) on the quality of the fabricated conductive film were studied in detail. Results showed that surface morphologies and electrical characteristics of laser-sintered conductive films were highly dependent on the value of the scan line spacing and the critical beam overlapping factor lay between 20% and 40%.