Motion Extraction for Left- Ventricular Volume Measurement

Methods to automatically determine the boundary of left heart chambers from X-ray films (cineangiocardiograms) by computer are discussed. Several authors have considered entering a first approximation to the boundary manually by light-pen, and then letting the computer determine the exact boundary from successive frames automatically. A method to do the first step automatically as well is proposed in this paper, utilizing ventricle motion and contrast medium flow. Experiments indicate that brightness as a function of time varies much stronger inside the area of the left heart chamber than outside, due to heart, contraction and contrast medium fluctuation. Hence, using a suitable criterion for motion, it is possible to extract an approximate outline of the left ventricle by simple operations. This outline is then used as initial information for the subsequent frame-by-frame detection of the precise boundary of the heart chamber.     

Bladder Volume Sensing by Resistance Measurement

The resistance of the urinary bladder, as measured between two electrodes attached to the external bladder wall at frequencies above 100 kHz, is proportional to the bladder volume for properly placed electrodes. The feasibility of using an oscillator, the frequency of which is controlled by the bladder interelectrode resistance, to provide an electrical signal proportional to bladder volume for use in connection with an electronic bladder stimulator is presented. The implications of this result are discussed.     

离体血液阻抗谱测量系统的设计

血液阻抗的大小随着测量频率的变换而变化,同时不同的血液成份有着不同的导电性能.为了能准确地测量这些特性,血液阻抗测量系统要求两路同频严格正交信号源,且信号频率在要求范围内程控可调.由于DDS芯片AD9854内部使用了二个高速、高性能的积分D/A转换器,得到二路正交的信号输出.因此文章采用直接数字合成技术,以AD9854为核心设计了用于血液阻抗谱测量系统的恒流驱动信号源.实验结果表明:采用AD9854,电路设计简单,工作可靠,容易实现频率调整,频谱稳定度和精确度以及相位误差满足测量系统的要求.     

先进的阻抗与电容测量转换器

本次在线座谈主要介绍了ADI先进的阻抗与电容测量转换器的原理及应用。本文包括两部分内容：第一部分主要讨论阻抗转换器,第二部分主要讨论电容转换器。在这两部分中,我们先回顾电阻和电容测量方法的主要特点,然后介绍ADI针对这两种应用推出的先进的阻抗数字转换器及电容数字转化器。     

电动式扬声器阻抗曲线分析与测量

扬声器的相关性能指标包括频率响应与有效频率范围、额定频带的特性灵敏度级、谐波失真、额定噪声功率、额定阻抗、额定共振频率,其中额定阻抗、额定共振频率可以从阻抗曲线中得到.围绕扬声器的阻抗曲线,先介绍了扬声器的分类,再重点介绍电动式扬声器的工作原理与等效电路,最后分析了扬声器阻抗曲线以及利用PULSE电声分析系统测量扬声器的阻抗曲线.     

基于TDR技术的HDMI高速差分总线特性阻抗的测量

高清多媒体接口(HDMI)技术正在迅猛的增长,传输速率也越来越快,遇到的高速连接的挑战也越来越大。通过时域反射(TDR)技术对HDMI的高速差分总线进行特性阻抗测量,可以直接的测量和显示印刷电路板(PCB)走线以及连接器和线缆的阻抗连续性能,对于诊断和分析HDMI系统高速连接的可靠性和稳定性起到非常重要的作用。     

Bladder Volume Sensing by Local Distension Measurement

Restoration of volitional control of the micturition reflex requires the use of bladder volume sensors. A method of measuring bladder volume by monitoring local distension has been developed in the laboratory. Tests conducted in experimental animals yielded 15 percent accuracy with bladder volume at micturition reflex threshold.     

Junction Thermal Impedance Measurement of Superluminescent Diodes

A new method is presented for junction thermal impedance measurement of superluminescent diodes. A few derivatives of mean wavelength, optical power, and voltage over temperature and current are used for the calculation. Carrier effect is removed. High accuracy is obtained by data regression on variables separately. Both analytical formula and experimental results are provided     

柱形等离子体辐射体输入阻抗测量

通过研究等离子体作为电磁波传导媒质的基本物理原理,可知表面波激发的柱形等离子体在特定条件下,可以代替传统的金属用于构成最基本的辐射振子。针对此等离子体辐射体为有源天线的特点,结合传输线阻抗匹配的原理,设计实验对其输入阻抗进行测量,得到符合理论分析的初步结果。对等离子体作为辐射体传输电磁波的研究具有重要的参考价值。     

电阻抗成像激励测量方式和成像方法研究

本文描述了电阻抗成像基本原理以及国内外目前在电阻抗成像方面的技术进展情况,分析了在电极数量相同条件下三种激励测量方式的优劣,从成像目标、成像算法、成像质量、使用范围、检测系统要求等方面对动态和静态两种成像方式做了简单对比,对未来电阻抗成像技术作了展望.     

二同轴接头理论模型特性阻抗的计算

当今高速信号的传输越来越迫切地需要高性能的连接器与之匹配,故用于传输高速差分信号的多内导体同轴接头在民用机载和军用设备上得到广泛应用。基于计算机的数值计算的方法在分析这种结构复杂的连接器方面体现出了优越性。介绍了运用矩量法计算二同轴接头理论模型特性阻抗的基本原理,并将计算结果与HFSS仿真结果作比较,由对比可知此方法准确、快捷,是分析二同轴接头理论模型特性阻抗的一种有效方法。     

压电器件阻抗测试系统的研制

基于压电器件的等效电路模型,利用导纳圆理论图测量压电器件阻抗特性参数及过零检测相位差测量原理,构建了一套完整的压电器件性能参数阻抗测试系统。通过单片机控制信号产生幅值固定、频率可变的正弦信号,经功率放大后驱动压电器件产生超声高频振动,并采集压电器件两端的电压、电流及相位差信号,通过串口传给上位机。上位机采用基于Labview人机交互界面,实现压电器件阻抗特性参数计算和图形显示。实验结果表明,本测试系统能测量压电器件各主要相关参数,并动态显示阻抗特性曲线,可用于压电器件的参数测试与性能评估。     

压电器件阻抗测试系统的研制

基于压电器件的等效电路模型,利用导纳圆理论图测量压电器件阻抗特性参数及过零检测相位差测量原理,构建了一套完整的压电器件性能参数阻抗测试系统。通过单片机控制信号产生幅值固定、频率可变的正弦信号,经功率放大后驱动压电器件产生超声高频振动,并采集压电器件两端的电压、电流及相位差信号,通过串口传给上位机。上位机采用基于Labview人机交互界面,实现压电器件阻抗特性参数计算和图形显示。实验结果表明,本测试系统能测量压电器件各主要相关参数,并动态显示阻抗特性曲线,可用于压电器件的参数测试与性能评估。     

Evaluation of Die Stress in MEMS Packaging: Experimental and Theoretical Approaches

The device performance of microelectromechanical system (MEMS) inertial sensors such as accelerometers and gyroscopes is strongly influenced by the stress developed in the silicon die during packaging processes. This is due to the die warpage in the presence of the stress. It has previously been shown that most of the stress is generated during a die-attach process. In this study, we employ both experimental and theoretical approaches to gain a better understanding in a stress development induced during the packaging processes of a small silicon die (3.5times3.5 mm²). The former approach is accompanied with an optical profilometer while the latter part by a finite element analysis and an analytical model. A specific emphasis is given to the effects of structural parameters such as the die-attach adhesive thickness and material properties on the stress development. The results from all three approaches show good agreement, in that more compliant and thicker adhesives offer great relief in the stress development, as well as bend the die convex downward from its central location. A stress model proposed from this study not only provides a diagnostic tool for very small stress-sensitive devices, but it will also present a design tool for low-stress MEMS packaging systems     

Measurement and Modeling of the Apparent Characteristic Impedance of Microstrip

Voltage and current cannot be defined uniquely for microstrip except at zero frequency, and therefore microstrip has not been rigorously incorporated into circuit theory. However, in engineering practice, micro-strip exhibits an apparent characteristic impedance, denoted here by ZA, that can be measured. Three methods of measuring ZA were devised and used in measuring three impedance levels of microstrip. These methods are described and experimental results presented. The measurements of ZA were found to be consistent with the power-current characteristic impedance definition of the approximate longitudinal-section electric (LSE) model of nricrostrip. Simple approximate formulas for representing ZA are also discussed.     

低压电力线信道阻抗测量与匹配

为了测量电力线的阻抗,设计一个电力线载波通信信号发射系统,分析了电力线信道的阻抗特性,根据LC谐振原理,设计低压电力线阻抗测量方案并制作了实际电路在学校各个地方进行实际测量。根据实际测量结果,得出电力线电抗呈感性,包含电阻和感抗两部分,并且阻抗变化的主要因素是感抗的变化。对于实验室、宿舍、办公室这类用电器较多的环境,电力线的电感值较小;而对于教室、走廊、活动室这类用电器较少的环境,电力线的电感值较大。这一结论对电压电力线的阻抗匹配是非常有用的,最后提出一种简单实用的匹配电路设计。     

自动阻抗测量仪工作原理及阻抗测量方法

介绍了一种由微处理器控制的多频自动阻抗测量仪，其能快速、便捷、准确地测量元件的各项参数。主要叙述了该测量仪的内部结构、工作原理，以及阻抗参数的测量方法和实际工作应用。     

PNP型HBT基极接触阻抗的理论估算

给出了非合金接触情况下 ,PNP型 HBT基极比接触电阻和接触阻抗的解析计算方法和结果。讨论了接触阻抗随频率的变化规律 ,并给出了集总元件电路模型     

用于人体皮肤阻抗测量的激励源设计

皮肤阻抗测量中,系统对激励源的质量要求很高。设计了一种基于AD9851和STC89C52的交变电流模式激励源。该激励源输出电流的幅值和频率在一定范围内可调,动态范围大,能用于人体皮肤阻抗的测量。试验表明,此激励源输出信号幅度和频率稳定性好,且输出阻抗高。     

X波段带线波导缝隙天线阻抗的精确测量

本文用等效短路面代替短路活塞的方法,实现短路法测量两端口网络的S参数;用不等间距的有限数据点,通过计算机统计回归解处理数据,得到了两端口网络S参数的准确值,从而可消除同轴一带线波导转换接头的影响,在X波段精确地测量了带线波导缝隙天线的阻抗及其随结构的变化。这种方法同样适用于类似结构的微带天线的阻抗测量。