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)     

The capacity region of a multiple-access discrete memoryless channel can increase with feedback (Corresp.)

The capacity of a single-input single-output discrete memoryless channel is not increased by the use of a noiseless feedback link. It is shown, by example, that this is not the case for a multiple-access discrete memoryless channel. That is, it is shown that the capacity region for such a channel is enlarged if a noiseless feedback link is utilized.     

A two wave theory of traveling-wave tubes and backward-wave oscillations

Starting from Pierce's small-signal TWT equations, a two-wave theory for complicated TWT's and BWO's is developed. Explicit gain expressions for TWT's with severs and velocity tapers are given. A detailed treatment is given of a BWA structure with a single-step velocity taper in the center. The BWO start oscillation current is calculated as a function of the taper strength. The effciency of a step velocity taper as a remedy for backward-wave oscillations in the higher passbands of a TWT is then analyzed. It is shown that a suitable taper can increase the start oscillation current by more than a factor of 10 without adverse effects on the TWT performance if the backward waye coupling impedance is low. A tube with a weak linear taper is analyzed by a perturbation technique and it is found that there is no significant difference between the start oscillation currents for tubes with weak linear or abrupt tapers of comparable strengths.     

High-Chip-Count UWB Biphase Coding for Multiuser UWB-Over-Fiber System

In this paper, we propose and demonstrate a novel technique to optically generate high-chip-count, phase-coded direct-sequence (DS) ultrawideband (UWB) signals for multiple-access UWB communications. In the proposed system, a lightwave from a laser source is phase-modulated by a Gaussian pulse train. The phase-modulated lightwave is then sent to a polarization modulator, to modulate the polarization state of the lightwave by a code pattern. The polarization-coded optical signal is then converted into a biphase-coded DS-UWB signal by a polarization-dependent frequency discriminator. The key device in the proposed system is the frequency discriminator, which is implemented using a length of polarization maintaining fiber (PMF) and a polarizer. A 127-chip, biphase-coding DS-UWB that has a data rate of 26.46 Mb/s and a chip rate of 3.36 Gb/s is experimentally generated. A multiuser UWB-over-fiber system is then proposed and a two-user system is demonstrated, in which the encoding is performed experimentally and the decoding is performed by numerically calculating the correlation between the coded UWB signal and the signature sequence. The signal of each user is well recognized. An effective two-user UWB-over-fiber system based on the DS-UWB technology is thus demonstrated.      

Temperature control for food in pots on cooking hobs

A control system for the temperature of food in a cooking pot is introduced. The cooking pot is heated on a consumer cooking hob. The temperature of the pot side is used as input for the controller. It is measured by an infrared detector. The infrared detector is a thermopile. The sensor signal is evaluated by a rule-based control algorithm. The system is simple, reliable, and very user friendly. An exact temperature settlement in a consumer hob is available for the first time. The system is used for automatic cooking     

Partial internal model control

Internal model control (IMC) is a well-known and effective control scheme. However, when unstable processes are concerned, the original IMC structure cannot be directly used for control system implementation. In this paper, a new scheme called partial internal model control (PIMC) is proposed, which is capable of controlling both stable and unstable processes. In PIMC, a process model is expressed as the sum of the stable and antistable parts and only the stable part of the process model is used as the internal model. The process stable part is canceled by the internal model and the remaining antistable part is stabilized and controlled with a primary controller, which is usually a PID-type regulator when the antistable part is of a low order. Various properties of a PIMC system such as internal stability and robust stability are analyzed. The design of PIMC is discussed in detail. Various simulation examples are included for illustration and a real-time implementation on a motor system is presented     

Firewalls fend off invasions from the Net

Whether a computer is in a corporation, government agency, university, small business, or at home, if it is linked to a network, hackers are a risk. The first line of defense against them is a firewall, provided it is set up correctly. Firewall technology is a set of mechanisms that collectively enforce a security policy on communication traffic entering or leaving a guarded network domain. The security policy is the overall plan for protecting the domain. Embodied in hardware, software, or both, a firewall guards and isolates the domain. Broadly, firewalls attempt to maintain privacy and ensure the authenticity of data communications that pass through their domain's boundaries. Whether data is entering or leaving a domain, it is protected from eavesdropping (passive wiretapping) and change (active wiretapping). But only communication traffic entering or leaving a domain comes under the influence of firewall technology     

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     

A Study on Straight-Line Tracking and Posture Control in Electric Bicycle

The development of automatic control for driving a bicycle is a challenging theme and is expected to be a human assist system. Previously, an acceleration-based method for stabilizing bicycle posture was proposed by the authors. In the experiments with this controller, the posture of the bicycle might be stabilized, but it is impossible to run on the desired trajectory, because there is no consideration with respect to a trajectory control. For the sake of expanding this system into more sophisticated equipment, a realization of the trajectory control for the bicycle is important. From the viewpoint of an assist system for human motion, a unified control of posture and trajectory brings a sophisticated function to a bicycle, and a high-performance bicycle is expected to be a convenient vehicle, similar to a small car. This paper proposes two strategies to stabilize bicycle posture and trajectory control that realizes a straight-line tracking: one is a lateral velocity controller, and the other is a steering function controller. The validity of the proposed approaches is evaluated by simulations and experiments.     

Maximizing sets and fuzzy Markoff algorithms

A fuzzy algorithm is an ordered set of fuzzy instructions that upon execution yield an approximate solution to a given problem. Two unrelated aspects of fuzzy algorithms are considered in this paper. The first is concerned with the problem of maximization of a reward function. It is argued that the conventional notion of a maximizing value for a function is not sufficiently informative and that a more useful notion is that of a maximizing set. Essentially, a maximizing set serves to provide information not only concerning the point or points at which a function is maximized, but also about the extent to which the values of the reward function approximate to its supremum at other points in its range. The second is concerned with the formalization of the notion of a fuzzy algorithm. In this connection, the notion of a fuzzy Markoff algorithm is introduced and illustrated by an example. It is shown that the generation of strings by a fuzzy algorithm bears a resemblance to a birth-and-death process and that the execution of the algorithm terminates when no more “live” strings are left     

Time-varying matched filters

We examine a generalized matched-filter problem in which the interference is a nonstationary process generated by passing white noise through a general linear time-varying filter. First a matched filter is constructed by transforming the problem into an equivalent formulation involving stationary interference and a time-varying propagation channel. Whereas the response of a time-invariant matched filter is sampled at its peak, the response of this time-varying matched filter is normalized before sampling to account for variations in the signal power. Next a matched filter is constructed using a spectral characterization of the nonstationary interference. This construction is then used to formulate a simplified solution for the case where the rate of variation in the nonstationary interference is sufficiently small. The different solutions are illustrated by a numerical example.     

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.     

激光诱导放电毛化技术中放电坑的表面形貌研究

利用高重频YAG激光作用在固体表面所产生的等离子体使工件和电极之间在电压远低于击穿阈值的条件下产生放电。实验结果显示 ,放电坑基本上呈火山坑形 ,既有单坑结构 ,也有多坑结构 ,其形貌受到放电波形、电源极性、放电介质等因素的影响。放电坑表面形貌的规律是 :①除了涂油时的阳极放电坑是单坑结构以外 ,其他条件下的放电坑都是复合多坑结构 ;②单坑结构呈火山坑形 ,坑底为圆弧形 ,熔凝物堆积在坑的边缘 ,多坑结构则是一个大的放电坑中有多个凸起尖峰     

Modeling of a nonpinchoff depletion mode MOSFET

A depletion-mode MOSFET is typically formed with a thin channel of opposite conductivity type to the substrate. When a large gate voltage is applied to deplete this channel, an inversion layer is induced. As strong inversion occurs, the depletion layer depth reaches a maximum and cannot be further increased. If this depth is less than the thickness of the channel, the channel cannot be pinched off unless a reverse bias is applied to the substrate. Such a depletion-mode MOSFET is modeled as a MOSFET connected in parallel with a JFET which shares a portion of the channel. The MOSFET has zero background bias so long as the JFET is not pinched off. When the substrate bias V/SUB SS/ is larger than V/SUB p/ to pinch off the JFET, the MOSFET channel depth is reduced, equivalent to applying a background bias to the MOSFET. This background bias V/SUB B/ is shown to be a square root function of V/SUB SS/ and V/SUB p/.     

Theoretical Aspects of Microstrip Waveguides

The Microstrip is a modification of the wire-above-ground system of transmission - the wire is replaced by a narrow strip printed on a dielectric sheet which is backed by a conductor. An exact theory for such a structure is difficult because the cross section is not homogeneous and has a geometry which does not lead to separation of variables. Furthermore it is an "open" structure where the energy is not confined to a finite region as it would be in conventional or "closed" waveguides.     

A novel strategy for microcomputer-based control of a single-phaseoutput cycloconverter

A novel control algorithm using a time process chart that is capable of accurate control of cycloconverters is developed. This algorithm is obtained by making a straight-line approximation in a newly contrived phase plane. In spite of its rather simple procedures, this algorithm is capable of highly accurate control that is comparable to that of the conventional analog scheme. A six-pulse noncirculating current-type cycloconverter is controlled with a small-scale interface and a high-speed control program. Experimental results confirm the validity and usefulness of the proposed method. As far as the processing time is concerned, this method could be used to control a system with a larger pulse number, such as a 12 or 24-pulse system     

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.     

On the Capacity of Randomly Used Shared Channels

The channel capacity of a communication channel made available to a user on a shared basis with other users is here considered. An overall system bandwidth B is divided into segments and parceled out to subscribers in an overlapping manner. Viewing emissions by the sharing user as Gaussian noise, the channel capacity is treated as a random variable, and its probability function, mean, and variance are studied. For a fixed power to each user, it is found that the average capacity of a user is maximum when the number of multiple assignments of a frequency band is approximately the inverse of the probability of use. The increase in channel capacity over exclusive assignment is also determined. The probability function of the capacity is worked out for some specific case to show its dependence on the frequency assignment policy, and a general procedure for determining the probability function is given.     

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.     

Wide-Range Precision Speed Measurement with Adaptive Optimization Using a Microcomputer

A new speed measurement method using a microcomputer is presented. In the initial part of the measurement, a definite small fraction of time for one revolution is counted using a software technique. A definite bit-size of the count is maintained by continuing counting over an optimum multiple of the initially measured time interval in case the bit-size of the initial count is less than a preset value. The multiple of the initial time period is measured with the help of an external counter, without any break in the continuity of counting. The speed is computed from the time count and displayed. For this measurement, only a standard digital speed transducer, a counter, and a microcomputer kit are required. The method has a small data acquisition and processing time, and gives a high accuracy that is programmable over a wide range of speed. The method is also quite economical.