New methods for the measurement of cathode interface impedance

Two improved methods for the measurement of cathode interface impedance have been developed, and their limitations have been analyzed. One of these, the complementary network method, is an improvement of a technique disclosed at the IRE National Convention in 1952. The other, the shunt admittance bridge, has not been described previously. Both methods allow the measurement of impedance with both small resistance and short time constant, well below the limit, 50 ohms at 0.1 µsec, of most present equipments. With the development of improved cathode alloys, the measurement of interface impedances having short time constants and low resistances has become important to control this parameter in manufacture and to obtain further improvement. For the complementary-network bridge, the theoretical analysis has shown the extreme importance of minimizing stray inductance in the complementary network. When corrections are applied, the complementary-network bridge has good accuracy, with less than one-ohm error at 10 ohms and 0.05 µsec and lower relative errors for higher resistances. The shunt admittance bridge is most satisfactory when tubes with transconductances greater than 10,000 µmho are to be measured. An impedance transformation is used which allows much easier physical realization of the measurement network than in other interface measurement methods. For tubes with transconductances greater than 10,000 µmho, the shunt admittance bridge will provide accurate time constant and resistance data down to 0.02 µsec and 5 ohms.     

Comparison of impedance at the microelectrode-saline andmicroelectrode-culture medium interface

The impedance characteristics of gold-plated indium-tin-oxide microelectrodes immersed in culture medium (MEM) are described and compared with the impedance characteristics observed when those microelectrodes are immersed in isotonic saline. For microelectrode areas of approximately 100 microns2, applied voltage levels of 5, 50, and 100 mV, and for frequencies of from 100 Hz to 10 kHz the resistance, capacitance, capacitive reactance, and total impedance are given as a function of frequency both in culture medium and in saline. The results, which hold for current densities ranging from 0.45 to 700 pA/microns2, are compared. Also given are the alpha and K values determining the frequency characteristics of the interface resistance and capacitance in medium and in saline.     

Reducing power bus impedance at resonance with lossy components

Power bus structures in printed circuit boards with solid power and ground planes exhibit resonances. When the power bus is resonant, the power bus impedance can increase dramatically. This paper explores the effect of component equivalent series resistance (ESR) on power bus resonances. General guidelines for selecting an optimum ESR are provided and are supported by laboratory measurements and numerical simulations.     

Haptic display with an interface device capable of continuous-time impedance display within a sampling period

Stability of a haptic interface is an important issue in virtual reality because an operator directly touches haptic interface devices. Stability is influenced by the sampling period and the discrete-time property of the control system. For decreasing the sampling system influence, this paper proposes a haptic device with an analog circuit which is placed between the computer and the haptic device. The circuit functions as springs and dampers. The control system can specify stiffness, damping coefficients, and their equilibrium. Since the impedance generated by the electric spring and damper can work continuously within the sampling period, it is effective for making the system more stable. We also develop a control method for displaying a static virtual object with the proposed device. Further, we discuss the effects of the proposed approach analytically, using passivity analysis for a 1-degree-of-freedom display system. Finally, some experimental results in a two-dimensional virtual environment are presented.     

Differential amplifier input impedance and Blackman's impedance relation

Recently the input impedance of a differential amplifier was derived and discussed. This correspondence derives similar results using a different approach, namely, Blackman's impedance relation, and generalizes earlier observations. The results provide an alternative activeRCrealization of a bilinearRLimpedance. Various all-pass networks are also analyzed.     

电桥测量基础

电桥是精密测量电阻或其他模拟量的一种有效的方法。本文介绍了如何实现具有较大信号输出的硅应变计与模数转换器（ADC）的接口．特别是∑一△ADC。当使用硅应变计时．它是一种实现压力变送器的低成本方案。[编者按]     

Distinguishability in impedance imaging

Impedance imaging systems apply currents to the surface of a body, measure the induced voltages on the surface, and from this information, reconstruct an approximation to the electrical conductivity in the interior. This paper gives a detailed discussion of several ways to measure the ability of such a system to distinguish between two different conductivity distributions. The subtle differences between these related measures are discussed, and examples are provided to show that these different measures can give rise to different answers to various practical questions about system design.     

Origins of the impedance change in impedance cardiography by athree-dimensional finite element model

A three-dimensional finite-element model of the thorax and neck using eight-node trilinear hexahedron elements was constructed to investigate the impedance change associated with various physiological events during systole. A three-dimensional finite-element code was developed to solve the generalized Laplace equation with Dirichlet and homogeneous Neumann boundary conditions. The current in each element as well as potential at each node was calculated. The results suggest that an approximately linear relationship exists between the impedance change and blood volume change in the aorta. This is a promising result since the relationship helps explain the correlation between impedance cardiography and invasive techniques. Impedance changes due to blood volume changes in the aorta and ventricles, the lung-resistivity change, and the blood-resistivity change were calculated for standard impedance electrode configurations     

中介逻辑与中介公理集合论的综述

以中介逻辑演算系统和中介公理集合论为主要内容的中介数学系统是一种在数学基础意义上将精确性量性对象扩展到模糊量性对象的系统,它对数学的逻辑基础和集合论研究产生了重要影响。文中主要从下面3个方面论述：中介数学系统的研究背景;中介数学系统的基本内容及其与经典数学系统的关系,其中简要介绍了中介概念、中介原则、中介逻辑演算系统、中介公理集合论和中介数学系统的研究现状;有关中介逻辑的学术争论,特别围绕中介逻辑是不是一个新逻辑引用了正反双方的意见。此外,还展望了中介数学系统的应用前景。     

变阻抗TEM喇叭天线设计中末端端口阻抗问题的研究

恒阻抗TEM喇叭天线的上、下板之间的间距、板的宽度沿天线轴向呈线性渐变,且喇叭天线的驱动端口、末端端口的宽高比相同。与恒阻抗TEM喇叭天线不同,指数渐变型TEM喇叭天线上下极板之间的间距沿轴向呈指数渐变。研究发现,当指数渐变型TEM喇叭的极板宽度采用不同的渐变形式时,极板宽度线性变化型TEM喇叭天线的驻波比最佳,主射方向远场脉冲峰峰值最大。当天线轴向长度、末端端口高度一定时,天线主射方向远场脉冲峰峰值随着天线末端端口宽度的增大而增大;当末端端口宽度达到一定值时,脉冲峰峰值达到最大值,继续增大末端端口宽度,脉冲峰峰值减小;当天线主射方向远场脉冲峰峰值达到最大值时,天线末端端口阻抗值为215Ω。     

Bulk and interface imperfections in semiconductors

Charges trapped at imperfection centers can be detected by observing the slow time dependences of the high-frequency small-signal capacitance and the current of a space charge region which is depleted of carriers. Detection of as low as 10¹⁰ to 10¹¹ trapped electron charges per cm³ in a volume of 10⁻³ cm × 10⁻³ cm², or 10⁵ to 10 electron charges, can be achieved. This technique has been used to study the temperature, electric field and photon energy dependences of the thermal, optical and Auger-impact emission and capture rates of electrons and holes at impurity and defect centers in depleted bulk and surface space charge regions in semiconductors, as well as the generation, annealing and diffusion kinetics of these centers. It has also been used to monitor the silicon integrated circuit fabrication processes. The principle of this technique is described and experimental examples are given to illustrate the applications of the technique.     

Filtering noncorrelated noise in impedance cardiography

Impedance cardiography (ICG) may be altered by noises as respiration and movement artifacts, mainly during exercise. In this work, a scaled Fourier linear combiner (SFLC) event-related to the R-R interval of ECG is proposed. It estimates the deterministic component of the impedance cardiographic signal and removes the noises uncorrelated to this interval. The impedance cardiographic signal is modeled as Fourier series with the coefficients estimated by the least mean square (LMS) algorithm. Simulations have been carried out to evaluate the filter performance for different noise conditions. Moreover, the method capability to remove uncorrelated noises was also examined in physiological data obtained in rest and exercise, by synchronizing respiration and pedalling with a metronome. Analyzing the ICG power spectrum, it was concluded that the proposed filter could remove the noises that are not synchronized with heart rate     

阻抗问题的分析和改善

文章对PCB阻抗超差问题进行了分析,主要描述了该问题形成的要素和原因．并提出相对应的改善措施。     

Antenna impedance in a reentry environment

In-flight measurements of the impedance ofC- andS-band waveguides radiating into a reentry plasma are compared with computed data. The vehicle utilized for the experiment was the Trailblazer II. The measurements were made during the reentry portion of the flight and received byX-band telemetry. The computed data are obtained from the variational formulation for aperture admittance of waveguides radiating into an inhomogeneons plasma medium. The dominant TE10mode is assumed to exist over the aperture. The form employed here utilizes the piecewise solution of Riccatti equations which permits rapid evaluation of the resulting equation for the admittance.     

Analysis of interface states and series resistance of Ag/SiO2/n-Si MIS Schottky diode using current-voltage and impedance spectroscopy methods

The electrical characteristics and interface state density properties of Ag/SiO₂/n-Si metal-insulator-semiconductor diode have been analyzed by current-voltage and impedance spectroscopy techniques. The electronic parameters such as barrier height, ideality factor and average series resistance were determined and were found to be 0.62 eV, 1.91 and 975.8 Ω, respectively. The calculated ideality factor shows that Ag/SiO₂/n-Si structure obeys a metal-interfacial layer-semiconductor configuration rather than ideal Schottky barrier diode. The interface state density of the diode is of order of ∼10¹¹ eV⁻¹ cm⁻². The dielectrical relaxation mechanism of the diode is analyzed by Cole-Cole plots, indicating the presence of single relaxation mechanism. It is evaluated that the interfacial oxide layer modifies electrical parameters such as interface state density, series resistance and barrier height of Ag/SiO₂/n-Si diode.     

Generalized impedance boundary conditions in scattering

The authors present generalized surface impedance conditions that improve medium characterization. One of the most common conditions that is often used to simulate a dielectric coating is the standard impedance boundary condition, and the improved boundary condition discussed can be viewed as a generalization of this, distinguished by the presence of higher-order derivatives of the field. By virtue of the derivatives, the conditions are less local in character, and the additional degrees of freedom can be used to better simulate the material properties of a surface. Following a review of the standard impedance condition, the new conditions are introduced. Several forms are presented, each with coefficients which are functions of the geometry and material properties of the surface. The applications of these to a variety of scattering problems are then discussed     

CW and pulsed mode transfer impedance measurements in coaxialcables

Transfer impedance measurements have been performed both in frequency and time domains. CW measurements were performed using a matched triaxial system, a quintaxial system, and stripline injection. For nuclear electromagnetic pulse (NEMP) purposes, measurements up to a maximum frequency of 200 MHz are sufficient. For this frequency range the matched triaxial system was found to be the most convenient. Amplitude and phase measurements in different cables are discussed. Direct and indirect injection was employed in the time domain measurements. A delayed coupling is demonstrated when the diffusion term is dominant in the transfer impedance. In a magnetically shielded cable, hysteresis and saturation effects have been observed. At 5 kA the transfer impedance of the magnetically shielded cable increased by an order of magnitude due to saturation     

图像的中介滤波算法与图像中介保真度度量

 首先通过对图像噪声产生过程的分析,并根据随机性和模糊性的特征,提出新的图像噪声的定义;然后,以中介真值程度的数值化度量为基础,设计了新的图像去噪滤波算法.通过仿真实例,并采用经典的PSNR评价方法,与已有的典型算法处理结果比较表明,基于中介真值程度度量的图像去噪算法的去噪效果优越,因而更具有实用性和有效性.针对PNSR等经典评价方法的结果往往与人们主观视觉不一致的弱点,本文提出一种新的基于图像中介熵的图像保真度度量方法,对示例的评价结果表明,该方法符合人们的主观感受.