A finite difference-time-domain technique for modeling narrow apertures in conducting scatterers

The finite difference-time domain (FDTD) technique has proven to be a valuable tool for the calculation of the transient and steady state scattering characteristics of relatively complex scatterer and source configurations. In spite of its usefulness, it exhibits serious deficiencies when used to analyze geometries that contain fine detail. An FDTD technique is described that utilizes Babinet's principle to decouple the regions on both sides of the aperture. The result is an FDTD technique that is capable of modeling apertures that are much smaller than the spatial grid used in the analysis and yet is not perturbed by numerical noise when used in the "scattered field" mode. Numerical results are presented that show the field penetration through cavity-backed apertures that are much smaller than the spatial grid used during the solution.     

A hybrid FD-MoM technique for predicting shielding effectiveness of metallic enclosures with apertures

In this paper, a hybrid technique combining the finite-difference (FD) method and the method of moments (MoM) in the frequency domain is proposed to predict the shielding effectiveness of rectangular conducting enclosures with apertures under external illumination. The interior and exterior regions of the enclosure are analyzed separately by employing the field equivalence principle. Internal electromagnetic fields are discretized using the (FD) method, while external fields are formulated by the MoM. Enforcement of continuity of the tangential magnetic field over the aperture surface gives the desired equation to solve for electromagnetic fields everywhere. Numerical results for the shielding effectiveness of a rectangular cavity with apertures calculated by the new hybrid technique are presented and validated by comparing with experimental data.     

A new excitation technique for wide-band short backfire antennas

A new excitation technique is developed to improve the impedance bandwidth and to lower the manufacturing cost of a short backfire antenna (SBA). The new excitation structure consists of a planar monopole and a microstrip feed line, both of which are printed on the same dielectric substrate. By splitting the printed monopole with a slot, a wide-band performance can be achieved. The new split-monopole-excited SBA achieves an impedance bandwidth of about 15% [voltage standing wave ratio (VSWR <2)] while maintaining good radiation performance. As an example, an SBA configuration with the new excitation topology was designed and measured at the 5 GHz UNII band, and good agreement was observed between the simulation and experiment. The effects of the geometric parameters of the excitation structure on the impedance performance are investigated and the operating mechanism of the split-monopole-excited SBA is discussed. Being a low-cost, high-gain, and wide-band directional antenna, the new SBA can find applications in various wireless systems, such as LMDS, WLAN, and the emerging WiMAX networks.     

双孔散斑照相用于物体通过漫射介质成象

物体通过大雾等漫射介质的成象问题一直吸引众多研究者的注意。光学全息技术、光栅干涉仪技术已经显示出在实验室条件下的有效性。但由于所使用的设备比较复杂，很容易受外界震动的干扰，使其应用场所受到很大制约。本文提出了使用双孔散斑照相技术使物体通过漫射介质成象。用这种技术得到的实验结果显示这项技术在象的对比度方面比直接得到的象有很大提高。同时所使用的设备简单，受外界震动的影响小，因而具有很大的实用价值。     

A new technique of cancelation of the MOSFET leakage currents and parasitic capacitances

The paper presents a new topological technique to be used with MOSFET's to appreciably minimize their channel and drain leakage currents (by a factor of 4) and parasitic capacitances (about 10 times smaller). It also enhances the channel inversion rate due to the channel potential distribution and leads consequently to greater device-switching speeds (10 times greater). This technique will allow a smaller device to device separation without fearing from any proximity effects. It is based on the creation of a transverse lateral field which is oriented so as to keep the channel electrons within its potential-well and to reduce the channel to substrate depletion layer width. A detailed study and characterization of the new technique is comprised.     

A nerve cuff technique for selective excitation of peripheral nervetrunk regions

Numerical modeling and experimental testing of a nerve cuff technique for selective stimulation of superficial peripheral nerve trunk regions is presented. Two basic electrode configurations ("snug" cuff monopolar and tripolar longitudinally aligned dots) have been considered. In addition, the feasibility of "steering" excitation into superficial nerve trunk regions using subthreshold levels of current flow from an electrode dot located on the opposite side of the nerve has been tested. Modeling objectives were to solve for the electric field that would be generated within a representative nerve trunk by each electrode configuration; and to use a simple nerve cable model to predict the effectiveness of each configuration in producing localized excitation. In three acute experiments on cat sciatic nerve the objective was to characterize the effectiveness of each electrode configuration in selectively activating only the medial gastrocnemius muscle. Modeling and experimentation both suggest that longitudinally aligned tripolar dot electrodes on the surface of a nerve trunk, and bounded by a layer of insulation (such as a nerve cuff), will restrict excitation to superficial nerve trunk regions more successfully than will monopolar dot electrodes. Excitation "steering" will improve the spatial selectivity of both monopolar and tripolar electrode configurations.     

A synthesis method for bidimensional apertures

A generalization of the Woodward-Lawson synthesis method is introduced for a wide class of apertures (including as particular cases the rectangular, the rhombic, and the hexagonal). By resorting to a rather general type of bidimensional Fourier series expansion, the aperture distribution is obtained as a superposition of orthogonal constant amplitude linearly phased components, whose complex amplitude coefficients are the values of the radiation pattern in a regular lattice of "cardinal points" on which the desired pattern function is exactly matched As a numerical application of the method, two examples of pattern synthesis with a hexagonal aperture are treated in detail.     

A new technique to accurately determine latch-up holding conditions using light excitation

A simple and accurate method to determine the true CMOS latch-up holding current and voltage by avoiding the "quasi-stable" negative resistance region is reported. A combination of microscope light excitation and a low-output impedance programmable power supply permits millivolt resolution, eliminates the need for a series current limiting resistor, and allows automatic testing. Results from test structures fabricated with n-well CMOS process are used to illustrate the method. With the terminal voltage during the excitation only 20-100 mV above the holding voltage, the method is practically nondestructive and therefore especially suitable for characterization of structures with high latch-up currents.     

Investigation of barium laser excitation processes usinglaser-induced-perturbation technique

We report experiments in which the active medium of a pulsed discharge-excited barium laser is illuminated by dye laser radiation, tuned to produce significant changes in the populations of selected states of neutral barium which are the upper and lower levels of barium laser transitions. The resulting perturbations to the discharge-excited laser output have enabled excitation processes relating to laser emission at 1.13, 1.50, 2.55, 2.92, and 4.72 μm from barium vapor to be identified     

New technique for measuring small MOS gate currents

A new technique is presented for the measurement of small gate currents on MOSFET devices in noisy environments. Hybrid technology is used to build the equivalent of a double-gate FAMOS-type device using two conventional MOSFET devices. Measurements of substrate hot-electron currents are given as an example.     

A comparison between two kinds of equivalent currents to analyze conducting bodies with apertures using moment methods: Application to horns with symmetry of revolution

A system of integral equations (SIE) based on the unique-hess theorem that uses only electric equivalent currents (EEC) is formulated to analyze conducting bodies with apertures. This SIE is compared with an SIE that uses both electric and magnetic equivalent currents (EMEC). In general, to solve both SIE's numerically difficult computations of Cauchy principal-value integrals with highly singular kernels are required. These integrals appear when computing electric (magnetic) fields created by magnetic (electric) currents. Their evaluation can be avoided using the EEC approach in many practical cases when the main interest is in the radiation patterns of aperture antennas. The two SIE's are compared by carrying out an analysis of rotationally symmetric horns using the moment method (MM) in its formulation for bodies of revolution. Numerical results of electric currents and radiation patterns are presented for small horns of various geometries. These results compare quite well with measurements for both SIE's. However, the central processing unit (CPU) time for the EEC formulation is an order of magnitude smaller than for the EMEC formulation.     

硬边光阑、超高斯光阑和锯齿光阑的比较研究

以复宗量拉盖尔—高斯(ELG)光束为例,对ELG光束经硬边光阑、超高斯光阑和锯齿光阑的衍射特性作了详细的比较研究。数值计算结果表明,超高斯光阑和锯齿光阑的优点是能有效抑制菲涅尔衍射调制并有较大的填充因子。     

On the amplitude center of radiating apertures

An explicit formula is derived for locating the amplitude center of planar apertures radiating scalar fields. Numerical examples are given which shows the validity of the formula for scalar conical and pyramidal horns.     

Measurement of ultralow gate tunneling currents using floating-gate integrator technique

We report for the first time that a gate tunneling current measurement sensitivity better than 3/spl times/10/sup -22/ A has been achieved by using a floating-gate integrator technique. The technique involves monitoring the charge change in the floating-gate integrated with an on-chip op-amp and an on-chip feedback capacitor. We used this technique to study the stress-induced leakage current (SILC) and its cycling dependence of 70 /spl Aring/ oxides in the direct tunneling region at oxide voltage as low as 1.9 V. The technique has been validated through correlation to direct measurement on MOSFET arrays and theoretical calculations. The measured SILC current is modeled with an Inelastic trap-assisted tunneling model.     

A fast circuit model description of the shielding effectiveness of a box with imperfect gaskets or apertures covered by thin resistive sheet coatings

This paper presents an intermediate level circuit model (ILCM) for the prediction of the shielding effectiveness (SE) of a rectangular box containing one or more rectangular gaskets of known transfer impedance or constitutive parameters. The box may also possess a rectangular aperture covered by a thin resistive sheet. The ILCM takes into account multiple waveguide modes and is thus suitable for use at high frequencies and with relatively large boxes. The gaskets may be positioned anywhere in the irradiated front face of the box, and the SE at any point within the box may be found when irradiated by a plane wave. Solution times using the ILCM technique are three orders of magnitude less than those required by traditional numerical methods such as finite difference time domain (FDTD), transmission line matrix (TLM), or method of moments (MoM), even when using a relatively slow interpreted language such as MATLAB. Accuracy, however, is not significantly compromised. Comparing the circuit model with TLM over eight data sets from 4 MHz to 3 GHz resulted in an rms difference of 3.90 dB and a mean absolute difference of 2.35 dB in the predicted SE values. The ILCM accurately reproduces the detailed structure of the SE curves as a function of frequency and observation point.     

Comparison of vertical-cavity surface-emitting lasers with half-wave cavity spacers confined by single- or double-oxide apertures

Data are presented on vertical-cavity surface-emitting lasers (VCSEL's) laterally confined with either single- or double-oxide apertures in a half-wave cavity spacer. Despite a higher nonradiative recombination rate, double aperture as compared to single-aperture devices show lower threshold current density and higher differential quantum efficiency for smaller optical modes. The advantage of double apertures is attributed to the better optical confinement that results in a reduced lateral diffraction loss.     

包含光阑的激光谐振腔模式

用光线矩阵方法研究了两类带有光阑的谐振腔。对包含软边光阑的腔,从衍射积分方程出发,求出了本征模式的普遍解析解。对包含硬边光阑的腔,用适当孔径的高斯光阑代替实际小孔,得到模式的近似解。用于分析常见的小孔选模腔、自孔径选模腔及包含光阑的热稳腔等,所得结果和实验测量值良好地相符。     

A method for analysing and synthesizing line-drawings

Line-drawings can be advantageously described by means of ordered lists of point coordinates. High data reduction ratios can be obtained by allowing only relevant points to be entered in the coordinate lists. In the method described here, original line-drawings are thinned in a preprocessing stage. The thinned image is then analysed and the line points are marked according to their relevance. By means of a line-following processing pass the coordinates of the marked points are entered in an ordered list. Performing the image synthesis, the listed points are succesively connected by polygon segments. Further, the coordinate list can be processed, in order to trade off image reconstruction quality for data reduction ratio.     

Polarizability of some small apertures

The basic integral equations for the electrostatic and magnestostatic problems are reviewed. These equations are solved with a digital computer for four typical aperture shapes. The results of the calculations are compared with Cohn's experimental values. Some data are given concerning the corresponding acoustic problems.     

Electromagnetic transmission through mesh covered apertures and arrays of apertures in a conducting screen

The problem of electromagnetic transmission through wire mesh covered arbitrarily shaped aperture or arrays of apertures (possibly covered by a thin lossy dielectric sheet) in a perfectly conducting ground plane is considered. The equivalence principle and image theory are used to derive an integral equation for the equivalent magnetic currents. The method of moments is utilized to solve the integral equation, with the aperture modeled by triangular patches. Numerical results are presented for transmission coefficients and transmission cross-section patterns for electrically small apertures.