Filter-embedded design and its applications to passive components

A design in which a filter is embedded in a fiber fixed on a substrate is proposed. It was successfully applied to the fabrication of low loss fiber optic components for a single-mode fiber transmission system. These components have a wide operational temperature range. The design is easily adapted to a multifilter or multifiber component. Filter embedding is achieved in two ways. One is to insert a thin filter chip in a slit which is machined into a fiber fixed on a substrate by a dicing saw (filter inserted type). The other is to evaporate a filter film directly on a fiber end face and butt this fiber to another fiber on a guide groove on a substrate (filter evaporated type)     

Some effects of localized stress on silicon planar transistors

When local compressive stress is applied to the emitter surface of a silicon planar transistor, increases in collector and base currents are observed. From the relationship between these currents and the base-to-emitter junction potential, it is inferred that changes in minority-carrier current occur in the stressed material. It is well known that the energy gap of a semiconductor is affected by mechanical stress, and the effects described here are consistent with a decrease in energy gap of a few tenths of an electron volt at compressive stresses of the order of 10¹¹dynes cm^-2. It is shown that the influence of stress on the current gain of a transistor depends on the strain distribution in the material. When the stress is applied over a relatively large area using a blunt stressing element, the increased minority-carrier current causes a rise in common-emitter current gain at low currents. In the case of the stress pattern produced by a sharper stressing element, a decrease in current gain is observed over a wide current range. It is proposed that this decrease results from a degradation in emitter efficiency caused by the stress concentration in the emitter region.     

Numerical simulation of GaAs MESFETs with a p-buffer layer on asemi-insulating substrate compensated by deep traps

A numerical analysis of GaAs MESFETs with a p-buffer layer on a semi-insulating substrate is performed in which impurity compensation by traps in the substrate is considered. It is shown that the use of a thick p-buffer layer results in a lower device current due to the formation of a steep barrier at the channel-substrate interface. It is also shown that with higher trap and acceptor densities in the substrate, the drain current is reduced due to the decrease in the substrate current. This decrease occurs because a negative-space-charge layer is formed in the substrate. It is demonstrated that when the p-buffer layer is fully depleted, its acceptors play the same electrical role as the acceptors within the space-charge region of the semi-insulating substrate. Thus, using a thick p-buffer layer has the same effect as using a substrate with a high density of traps, i.e. it minimizes the short-channel effects in GaAs MESFETs. Therefore, if the trap density in the substrate is low, the short-channel effects can be reduced by introducing a p-buffer layer or a buried p-layer     

GaAs dynamic memory design

Subthreshold leakage loss is a serious problem for GaAs dynamic memory. Since the leakage current in a MESFET is several orders of magnitude higher than that in a MOSFET, it is difficult to retain the charge at dynamic nodes resulting in data storage errors, In order to solve this problem, a novel DRAM architecture is proposed. The design is based on a cell consisting of a MESFET switch and a metal-insulator-metal (MIM) planar capacitor as the storage element. The leakage current is reduced by a level-shift technique and a self-biased transistor is used to maintain the dynamic charge during the sense period. A high performance sense amplifier is used to detect small bit line voltage changes and refresh the stored data. A 1 Kb prototype, fabricated in a 1 μm nonself-aligned GaAs MESFET technology, exhibited a total read/write access time of the order of 3 ns     

Analytical study on guided modes in vertical strip line embedded in NRD guide

Guided modes in a vertical strip line embedded in a non-radiative dielectric (NRD) guide were analysed based on the two-dimensional finite-element method. The dominant mode in this guiding structure is the TEM wave, and furthermore, it is evident that a quasi-LSM/sub 11/ odd mode occurs when a wide metal strip is used, whereas a quasi-LSE/sub 01/ even mode is generated when a narrow strip is employed.     

The relationship between the surface EMG and force transients in muscle: Simulation and experimental studies

The surface electromyogrmn (EMG) is an easily measured signal which when quantified by present techniques is a reliable measure of whether a muscle is active, a fairly reliable measure of steady state force and a rather unreliable measure of force transients in muscle. There is a real need for a reliable indicator of dynamic changes in muscle activity for the control of prosthetics, in diagnosis of neuromuscular diseases, in studies of the motor control system and in fundamental studies of muscle mechanics. This paper outlines the principles underlying the development of force and the EMG in muscle. The EMG is a poor estimate of muscle force since it is the result of the linear superposition of biphasic action potentials which result in an interference pattern. This in turn is dependent on the details of the firing intervals for each motor unit, whereas the force is quite insensitive to these details. Experimental results for the human biceps brachii are described in which it was not possible to obtain a consistent estimate of muscle active state from the EMG. An extensive computer simulation was used to explore the relationship between EMG and force under a variety of assumptions. The conclusion is that it is technically impossible to obtain consistent estimates of muscle force (or active state) unless a filter with a time constant of 300 ms is applied to the rectified EMG. This is inconsistent with the estimation of active state for voluntary contractions with observed rise time constants of 30-70 ms. It is susgested that the only solution is to repeat an experiment many times and average the rectified EMG. Unfortunately, in practice it is difficult to repeat certain aspects of voluntary muscular contractions.     

Determination of Test Intervals in Certain Repairable Standby Protective Systems

A System has associated with it a Safeguard such that whenever a failure in the Safeguard is detected, the System is shut down. The System is restarted as soon as the Safeguard is repaired. An example is a standby protective system attached to a nuclear power plant; as soon as failure is detected in the protective system the nuclear plant will be shut down until repair is completed. In order to insure that the Safeguard remains in the utmost state of readiness, the components of the Safeguard are periodically tested, and repaired if the test reveals a failure. In this paper we define a measure of readiness appropriate for the above systems and consider the problem of determining the testing frequency of the components of the Safeguard in such a way that an adequate level of readiness is maintained. As an illustration, the method is applied to a typical reactor-trip system.     

Reflection and transmission operators for strips or disks embeddedin homogenous and layered media

A notation is proposed to simplify the solution of scattering by strips and disks. Vector Fourier transforms are used and a double dot product for inner products in an uncountably infinite dimensional linear vector space is introduced. Scattering by a strip or a disk is characterized using a reflection operator and a transmission operator that relate the continuum of scattered waves to a continuum of incident waves. After the reflection operator for a single strip or disk is derived, it is shown how the reflection operator for a strip or disk in the presence of another reflecting medium, e.g. a layered medium, can be derived. The scattering by N strips or disks in a homogeneous medium is also discussed. The reflection operator for an embedded strip or disk in a layered medium is then derived. The method can be generalized to N strips or disks embedded in a layered medium and to a slot or aperture     

A dual planar reflectarray with synthesized phase and amplitude distribution

A quasi-planar reflector arrangement for generating an arbitrary phase and amplitude distribution in the antenna aperture and thus a wide range of far field patterns is presented. A parallel pair of reflectarrays is used. One is implemented as a standard reflectarray using rectangular patches on a microwave substrate with metallized backside. The other reflectarray is provided with a polarizing grid, which acts as a ground plane for one polarization and is transparent for the orthogonal polarization. An offset rectangular feed horn is embedded in the lower reflectarray to illuminate the upper reflector. A design procedure for a linear polarized antenna with a sector beam in the azimuth and a narrow beam width in the elevation is presented and is verified with measurement results.     

Optical pulse sequence transmission through single-mode fibers:interference signal analysis

The transmission of a pulse sequence through a single-mode fiber is considered under first- and second-order dispersion. An expression is given for the output power signal envelope in terms of the Fourier transform of a spectral function. The output envelope is composed of two terms: a linear one which is a distorted replica of the information sequence, and a nonlinear interference term. The latter is expressed in a more meaningful way and analyzed. The results allow a characterization and a classification of the interference pulses in terms of physically intuitive parameters     

Time domain analysis of patch antennas in a magnetized plasma bythe spatial network method

The near field of a patch antenna in a magnetized plasma is simulated by use of the spatial network method, which is a three-dimensional time domain simulation method. Two fundamental cases are examined in the radiated field: where the direction of the constant magnetic field is perpendicular to the patch plane, and where it is parallel. Results show that radiation characteristics of patch antennas in a magnetized plasma are different from those in free space. It was also confirmed that the Faraday effect is shown in the near field when a perpendicular constant magnetic field is applied to the antenna. In this analysis, the free boundary condition is approximated by terminating the volume with the free space characteristic impedance. A stricter model is necessary, if a reflectionless boundary is to be realized     

语音通信中的噪声抵消技术

讨论了一种语音通信中的有源噪声抵消技术,该技术可以提高移动语音通信的私密性。将人头等效成刚性球体,并将人嘴等效成活塞辐射,计算了人头散射声场和人嘴辐射声场,同时通过在人头周围放置控制声源控制人嘴辐射声场,声场分析计算和实验结果表明,该技术能有效控制人嘴向外辐射的声场能量,一定程度上提升了语音通话的私密性。     

Reduction of wave propagation loss by mesh in rectangular tunnels

The reduction of radio wave attenuation in rectangular tunnels is discussed. The attenuation of the dominant mode due to its field penetration into a lossy dielectric wall is reduced by means of the attachment of wire netting (mesh). First, a reflection coefficient from a mesh screen over a lossy surface is analytically evaluated. Then, based on a geometrical optical approach to the propagation model in tunnels, the attenuation of the dominant mode in a rectangular tunnel is derived using the reflection coefficient. The calculated attenuation constants are in good agreement with experimental ones obtained in a laboratory. Finally, the efficiency of attenuation reduction rate by the mesh shielding method is summarized as a function of spatial ratio of the mesh wire interval divided by the wavelength. It is shown that the efficiency of reduction rate by mesh is significant     

An initial growth of a small-signal two-dimensional domain in a bulk effect device

This paper presents a small-signal theory of a two-dimensional domain initiation in a bulk effect device, and discussions are focused on a transverse extension of the initial domain. It is introduced that the transverse extension velocity is not so fast as compared with the longitudinal propagation velocity in a stage of the domain initiation. This is because the longitudinal propagation velocity is much faster than the stable domain propagation velocity, although the transverse extension velocity is also faster than the mature domain velocity. It is necessary to estimate a marginal distance for an immature domain to travel in a domain growth time when a logic element utilizing the transverse extension of the high field domain is designed.     

Distributed power allocation algorithm in wireless networks under SNR constraints

In this work, the distributed power allocation problem in wireless networks is studied under signal-to-noise ratio (SNR) constraints. The sources of uncertainty are assumed to come from the quantization process and measurement noise in the feedback system. The power allocation is formulated as a reference tracking problem of a pre-defined signal to noise-interference ratio. First, the synthesis problem with SNR constraints is studied as a 2-norm minimization process, which is equivalent to a linear-quadratic-regulator (LQR) problem. The solution of the associated Riccati equation in the LQR formulation is completely characterized, resulting in a feedback law with a recurrent structure. This control law is re-written in a transfer function format, where a simple control strategy is obtained which is dependant on the round-trip delay in the feedback system. In addition, the corresponding 2-norm closed-loop performance is also studied. Thus, the selection of the weight in the LQR problem establishes a compromise between robustness to quantization errors and measurement noise, and tracking performance. A comprehensive simulation evaluation validates the analytical derivations described in the paper.     

Multimedia dictionary network application: design andimplementation

Proficiency in foreign languages is essential for professionals from countries in transition. A multimedia dictionary Internet application may offer needed help in everyday activities as well as in distance-learning systems. A multimedia dictionary is considered as both a conventional dictionary tool and a distance-learning network application. We analyze the architecture and implementation issues arising in the design and implementation of a multimedia dictionary network application. The application is considered multimedia since it is designed to support textual, visual, and audio information content. Practical implementation is shown to be feasible with current technology, but a lack of available multimedia standards has been recognized. This is why we have considered the existing standards as well as the standards in development. The application is developed in Java language, and may be run as either a standalone application or an applet. The latter entails accessibility in a ubiquitous manner to a large number of users. The application is intended for both non-native English users and professionals exposed to specific technical terminology     

基于ZEMAX的半导体激光准直镜设计方法研究

针对目前采用单个球面镜压缩激光时存在发散角效果差或者球面镜片数过多的问题,通过ABCD矩阵法从理论上对高斯光束经过单透镜时的传输特性进行了分析,得出了单透镜无法实现半导体激光光束理想准直的结论。提出了一种基于ZEMAX的半导体光源准直镜的设计方案,并给出了设计与优化方法。结合工程中常用的808nm半导体激光器,设计了双片型808nm半导体激光准直镜,并在ZEMAX中使用合适的优化函数和权重对像差进行了校正。通过采用非球面镜获得了较好的准直效果,发散角达到了0．032mrad。该设计使用的镜片数较少,结构简单。     

A decomposition technique for efficient generation of correlatedNakagami fading channels

Correlated Nakagami m-fading is commonly encountered in wireless communications. Its generation in a laboratory environment is therefore of theoretical and practical importance. However, no generic technique for this purpose is available in the literature. Correlated Rayleigh fading is easy to simulate since it has a simple relationship with a complex Gaussian process. Unfortunately, this is not the case for Nakagami fading. The difficulty lies in that the fading parameter can be a real number and there is no general theory linking a Nakagami vector to a finite set of correlated Gaussian vectors. In this paper, by introducing a direct-sum decomposition principle and determining the statistical mapping between the correlated Nakagami process and a set of Gaussian vectors for its generation, a simple general procedure is derived for the generation of correlated Nakagami channels with arbitrary parameters. A key parameter in the statistical mapping can be determined by using an iterative method. The validity of the new technique is examined through the generation of a correlated Nakagami sequence, as encountered in U.S. digital cellular, and a multibranch vector channel as encountered in diversity reception     

Fourier-transform analysis of electrostatic potential distributionthrough a thick slit

A potential distribution through a slit in a thick conducting plane is examined. The Fourier-transform is used to represent the potential in the spectral domain and the boundary conditions are enforced to represent a solution in closed form. The solution is in a rapidly converging series so that it is numerically efficient. The Fourier-transform approach is novel in that it allows one to obtain a simple series solution without recourse to the Schwarz-Christoffel transformation     

Analysis of a strip in a waveguide

An analysis and an experimental study of a strip in a transverse plane of a rectangular waveguide below cutoff are presented. This work is a preliminary step in analyzing a stripline-fed slot antenna array in which each stripline feed is enclosed in a rectangular waveguide below cutoff. A numerical method is developed to solve a “pseudo” mixed-potential integral equation for the current on the strip excited by a delta-gap source at some point along the strip. The Green's function for dipole sources in the rectangular waveguide is used in the spectral and spatial representations and Shanks' transform is employed to speed up the convergence of the doubly infinite series. Numerical and experimental results are presented for a monopole fed at one wall of a rectangular waveguide and for a bottom-fed and bottom-loaded strip in a rectangular waveguide