硅薄膜沉积中等离子体辉光功率和阻抗的测试分析

采用改进的电压和电流测试方法对衬底电极外加不同电压V_s的射频等离子体中的阻抗和功率消耗进行了测试分析.结果表明：在射频电极施加恒定的电压V_el时，随衬底电极外加电压V_s的增加，辉光的电流在增加，结果导致阻抗在减小；另外，通过计算分析发现：仅有一小部分功率用于辉光，大部分功率消耗在匹配器和电缆上.通过对等离子体电学特性的综合测试分析也说明：在保证有足够多的硅烷时，衬底电极外加电压V关键词： 等离子体 辉光功率 阻抗 诊断     

A systems feedback representation of piezoelectric transducer operational impedance

An analysis of thickness-mode piezoelectric transducer impedance under a variety of mechanical load conditions is presented. A wideband, systems model is used to describe this impedance, which is representative of the electrical input impedance in the transmitting mode and the electrical output impedance for the receiving mode.For a fixed input voltage, the total current flowing through the transducer is considered as the vector sum of two current quantities. Firstly, an input current arising directly from the applied voltage source and secondly, a feedback current, which is generated by secondary piezoelectric action. By treating the problem in this manner, an extremely valuable insight into the nature of the electrical characteristics is provided. Complex variations in the impedance behaviour are readily explained and the physical processes that contribute to such deviations are clearly isolated.     

Inverse estimation of the acoustic impedance of a porous woven hose from measured transmission coefficients

A porous tube, comprised of a resin-coated woven fabric has recently been used as an effective component for use in intake systems of internal combustion engines to reduce the intake noise. For the prediction of the acoustic performance of an engine intake system with a porous woven hose, the acoustic wall impedance of the hose must be known. However, the accurate measurement of the wall impedance of a porous woven hose is not easy because of its peculiar acoustical and structural characteristics. A new measurement technique is proposed herein, that is valid over the low to mid frequency ranges. The acoustics impedance is inversely estimated from an overdetermined set of measured pressure transmission coefficients for specimens of different lengths and the reflection coefficient of end termination. The method involves only one measurement setup, and, as a result, it is very simple. A variation of the proposed method, an inverse estimation method using one of the four-pole parameters is also proposed. An error sensitivity analysis was performed to investigate the effect of measurement error on the accuracy of the final result. The measured TL for samples with arbitrary lengths and arbitrary porous frequency are in reasonably good agreement with values predicted from curve-fitted impedance data.     

A simplified model of mouth radiation impedance closed by mask cavity

Acoustic radiation impedance of the mouth is an important parameter when the vocal tract is modelled by the equivalent electrical circuit. If the vocal tract is closed by a cavity, as when the speaker wears some kind of mask, total impedance acoustically loading the vocal tract becomes serial connection of the mouth radiation impedance and the mask impedance. In that case the mouth radiation impedance has to be changed compared to free field conditions. This paper introduces a simplified approach to the modelling of that change by an appropriate reduction coefficient. The analysis based on an experiment preformed by measurement in the vocal tract physical model accompanied with analytical estimation has shown that the value of such reduction coefficient is 0.5. The results reveal that for a vocal tract closed with mask cavity the change in mouth radiation impedance introduced in an equivalent electrical circuit can be approximated by the value for free field radiation decreased by about 50%.     

基于电阻抗层析成像的高强度聚焦超声温度监测技术

作为一种对正常组织无损伤且不易引起癌细胞转移的非入侵肿瘤治疗手段,高强度聚焦超声(HIFU)治疗过程中焦域的温度监测是实现剂量精准控制的关键.本文基于生物组织的温度-电阻抗的关系,将电阻抗层析成像(EIT)和HIFU治疗相结合,提出了一种利用组织焦平面的表面电压实现电阻抗重构的检测技术.建立了HIFU治疗和EIT综合系统模型,在考虑组织的声吸收条件下,对三维Helmholtz方程在柱坐标下的声场计算进行了二维简化,并引入Pennes生物热传导方程来计算HIFU焦域的声压和温升分布特性;引入生物组织的温度-电阻抗关系,基于麦克斯韦电磁场理论,建立了具有温度分布HIFU焦域的电流和电压计算模型,利用恒流注入的边界条件实现电场计算,获得焦平面的表面电压分布.在数值计算中,利用实验聚焦换能器参数,模拟了在固定声功率下组织焦域的声场和温度场分布,以及中心和偏心聚焦条件下不同治疗时刻的电导率分布;然后通过对称电极的循环电流注入,计算了组织模型焦平面内的电流密度和电势分布,获得了焦平面圆周分布的表面电极电压;进一步采用修正的牛顿-拉夫逊算法,利用32×32的表面电极电压实现了焦平面内电导率分布的重建.结果表明,基于温度-电阻抗关系的EIT电导率重建技术不但能准确定位HIFU焦域中心,还能恢复HIFU治疗中焦域的温度分布,证明了EIT用于HIFU治疗中温度监测的可行性,为其疗效评估和剂量控制提供了一种无创电阻抗测量和成像新方法.     

单线法测量横向阻抗系统设计与模拟计算

 介绍了单线法测量横向阻抗的基本原理、系统设计和初步模拟计算结果。单线法横向阻抗测量系统由待测元件/参考元件、内置导线、导线偏移调节机构、阻抗匹配段和测量仪器构成。调节机构可以精确调整内置导线的横向位置以激励偶极模式。利用微波工作室软件模拟计算待测元件（2 856 MHz“凸型”腔）的偶极模。“凸型”腔横向阻抗的幅值和偶极模频率的计算结果与ABCI程序数值计算的结果基本相符，说明了单线法横向阻抗测量系统理论上的可行性。     

同轴线法在小孔径真空元件阻抗测量中的应用北大核心CSCD

粒子加速器中真空元件的阻抗是引起束流不稳定的重要原因。基于储存环的新一代同步辐射光源的设计发射度更小,相应地要求更小的真空盒孔径,进而带来阻抗的显著增加,这就要求在设计阶段对真空元件的阻抗进行准确的评估和优化。阻抗测量是验证阻抗模型准确性的重要手段,而同轴线法是常用的实验室测量方法。对小孔径真空元件同轴线法纵向阻抗测量进行了研究,针对窄带阻抗元件,使用pillbox腔开展了相关的阻抗测量,研究了不同的内导体尺寸对于测量结果的影响,同时基于尾场模拟、散射参数模拟以及本征模模拟对测量结果进行了验证,模拟和测量结果符合很好,并证明原有的内导体导致谐振峰频移的理论分析应用于小孔径元件时存在偏差。此外针对非窄带阻抗元件,对条带冲击磁铁结构进行了同轴线法阻抗测量,研究了内导体对结果的影响,验证了同轴线法测量的有效性。     

PEN薄膜阻抗转变规律研究

采用真空蒸发的方法制备了PEN材料薄膜，研究了不同外电路参数下薄膜的电双稳特性.发现薄膜从高阻向低阻转变过程所需时间随电流非线性下降，此期间薄膜阻抗也呈现非线性，并对非线性规律作了数据拟合.发现整个跃变过程中存在一种能量效应，即当外加电压超过某一阈值时，该跃迁所需的能量不变. 关键词： PEN薄膜 非线性阻抗 电双稳     

Method to measure acoustic impedance and reflection coefficient.

A frequency-domain based system for measuring acoustic impedance and reflection coefficient is described. The calibration procedure uses a least-mean-squares approximation to the Thevenin parameters describing the source and receiver characteristics in which the data measured on closed, cylindrical tubes are matched to a viscothermal tube model. The system is intended for use in acoustical measurement in human ear canals, in which the cross-sectional area of the ear canal at the point of insertion is imprecisely known. This area is acoustically estimated from the impedance data, and the reflection coefficient is calculated in terms of this area and the impedance data. Measurements on a variety of closed tubes show the method is accurate over the frequency range investigated (less than 10.7 kHz). The time-domain reflection function is evaluated by transforming the reflection coefficient from the frequency domain, but the finite bandwidth of the measured data limits the accuracy of time-domain response measurements. The method is well suited for frequency-domain measurements in human ear canals.     

Ultrasonic flow measurement and wall acoustic impedance effects

An examination of the influence of wall acoustic impedance effects on sound propagation in flowing liquids confined by cylindrical walls is presented. Special focus is given to the importance of the wall acoustic impedance value for ultrasonic flow meter performance. The mathematical model presented allows any radially-dependent axial flow profile to be examined in the linear flow acoustics regime where fluid flow speed is much smaller than the fluid sound speed everywhere in the fluid medium.     

基于生物阻抗谱成像的生物组织检测方法

基于电阻抗成像技术和生物阻抗谱技术,提出一种面向生物组织检测的生物阻抗谱成像方法.该方法将目标区域可视化并精准识别目标种类,可用于肺癌早期检测,协助临床医生对早期肺癌进行精准检测,提高早期肺癌的治愈率.本文通过数值仿真的方法验证生物阻抗谱成像方法在肺癌早期检测中的可行性和有效性,仿真结果表明:1)生物阻抗谱成像方法可以实现早期肺癌区域的可视化,并精确判别出早期肺癌种类; 2)生物阻抗谱成像方法中阻抗谱的最佳采集模式是4次循环采集,最佳分类器是Linear-SVM, 5折交叉验证的平均分类准确率可以达到99.9%.为了验证仿真结果,本文选取3种具有不同电学特性的生物组织模拟癌变区域进行了检测.实验结果表明该方法可以对生物组织区域可视化,并判别出生物组织的种类.该方法可以兼顾电阻抗成像和生物阻抗谱方法的优点,有望用于肺癌早期检测.     

交流阻抗及功率因数测量中偏差的修正

介绍了在交流阻抗及功率因数测量中由测量仪表引起的偏差的修正方法.主要讨论了一级修正和精确修正两种方法,导出了计算复阻抗和功率因数的修正式.给出了测量日光灯电路的阻抗及功率因数的实例.由计算结果可以看出,精确修正后的结果与不做修正的结果之间存在较大的差异,说明在要求较精确测量的情况下,应该对测量结果进行修正.     

合肥国家同步辐射实验室纵向阻抗测量平台的改进

 介绍了合肥国家同步辐射实验室在原有纵向耦合阻抗测量系统基础上根据国际流行的同轴线原理改进的新纵向耦合阻抗测量系统的基本原理、系统组成和初步测量结果。对“药丸形”腔的阻抗的实验测量结果和阻抗计算程序计算结果基本相符，验证了该系统的有效性。     

Empirical model of the acoustic impedance of a circular orifice in grazing mean flow

Although there are many analytical and empirical models for orifice impedance, the predicted acoustical performance when adopting any one of them sometimes shows a large discrepancy with the measured result in some cases. In order to obtain a new practical and precise empirical impedance model under grazing flow conditions, the acoustic impedance of circular orifices has been measured with a variation of the involved parameters under very carefully tested and controlled measurement conditions. The parameters involved in determining the acoustic impedance of an orifice are comprised of the orifice diameter, orifice thickness, perforation ratio, mean flow velocity, and frequency. The range of involved parameters is chosen to cover the practical data span of perforates in typical exhaust systems of internal combustion engines. The empirical impedance model is obtained by using nonlinear regression analysis of the various results of the parametric tests. The proposed empirical model of orifice impedance, with a very high correlation coefficient, is applied to the prediction of the transmission loss of concentric resonators, which have geometric configurations typical of acoustically short and long through-flow resonators. By comparing the measured and predicted results, in which the predictions are made by employing many previous orifice impedance models as well as the present model, it is confirmed that the proposed orifice impedance model yields the most accurate prediction among all other existing impedance models.     

Experimental measurement of the nonlinearities of electrodynamic microphones

This paper presents an experimental way of characterizing the nonlinearities of electrodynamic microphones used as acoustical sources. This functioning occurs for reciprocal calibration techniques. For this purpose, its electrical impedance is measured with a Wayne Kerr wedge which has an excellent precision. Moreover, it can be noted that the Thiele and Small model is used to characterize its electrical impedance. Furthermore, an experimental method based on Simplex algorithm allows us to construct polynomial laws which describe the dependence of the Thiele and Small parameters with the input voltage. The nonlinear variations obtained allow us to determine the nonlinear differential equation of the electrodynamic microphone. Then, this equation is solved numerically in order to confirm the accuracy of the polynomial laws obtained by the Simplex algorithm. The distortions are measured with a laser Doppler velocimeter and compared with the ones obtained by the numerical solving of the nonlinear differential equation. The experimental displacement spectrum is consistent with the theoretical one.     

欠匹配型磁绝缘感应电压叠加器次级阻抗优化方法

磁绝缘感应电压叠加器(MIVA)次级阻抗对脉冲功率驱动源和负载之间的功率耦合具有重要影响.基于稳态磁绝缘Creedon层流理论和鞘层电子流再俘获(re-trapping)理论,建立了负载欠匹配型MIVA电路分析方法,数值分析获得了MIVA输出参数(输出电压、阴/阳极电流和电功率)随负载欠匹配程度的变化规律.考虑阴极传导电流作为闪光X射线照相二极管的有效电流,建立了以MIVA末端X射线剂量率最大为目标的次级阻抗优化方法.获得了欠匹配型MIVA次级优化阻抗Z_(op)~*的变化规律:随着X射线剂量率对电压依赖程度提高,欠匹配型MIVA次级优化阻抗Z_(op)~*呈指数降低;负载阻抗越大,Z_(op)~*越大.     

An electro-acoustics impedance error criterion and its application to active noise control

Characteristics of radiation impedance and its inducing variation of electrical impedance for a controllable source have been investigated. An impedance-based error criterion has been proposed and its application to active noise control is demonstrated through a coil driven loudspeaker. A general formula of radiation impedance is derived for two control strategies, according to the criterion of total acoustic power output. The radiation impedances of some commonly used sound sources are calculated. We discuss in detail the relation between variation of the input electrical impedance and radiation impedance for the two control strategies. An AC-bridge circuit is designed to measure the weak variation of electrical impedance resulted from radiation impedance. The input electrical impedance of a loudspeaker was measured and the experimental result is consistent with that of theoretical analysis. An impedance-based error criterion is proposed since the AC-bridge relative output is unique for a certain control strategy. The implementation of this criterion applied to an active control system is analyzed by simulations. An analogue control system is set up and experiments are carried out in a semi-anechoic chamber to verify the new control approach.     

Recent approaches to the measurement of acoustic impedance and materials characterization

Three methods are discussed: an automated pulse tube system; a direct, point measurement technique; and the application of a parametric array for oblique angle measurement.The first of these extends the capability of a proven impedance measurement technique using a waterborne acoustic waveguide (pulse tube). Data obtained in a frequency range 3 to 100 kHz, determined from complex reflection coefficients, are presented, via a transfer function analyser interfacing with a computer and plotter, to produce impedance diagrams.A direct, point impedance technique based on sensing particle velocity, or displacement of a surface and associated acoustic pressure is next discussed. Use is made of laser interferometry to measure the vector quantity, while scalar values are determined from a pressure sensor. This data affords a direct measurement of point impedance and can be applied in obtaining complex response information from heterogeneous materials or structures.The last method employs a non-linear acoustic device to obtain a requisite acoustic beam-width allowing characterization of materials at oblique angles, with samples of limited size, at low ultrasonic frequencies.     

基于multisine激励与整周期采样的多频电阻抗成像系统设计

本文从周期信号的整周期采样无频谱泄露这一原理出发,提出基于multisine信号的整周期采样理论,从理论上推导出满足multisine整周期采样的采样率设置条件,构建了基于FPGA+数模转换器+模数转换器的整周期采样实现方法,研制了一种基于multisine激励和整周期采样的新型多频电阻抗成像(mfEIT)系统;设计了胡萝卜棒+黄瓜棒的双目标成像模型,并进行了多频时差成像和频差成像实验.实验表明,本mfEIT系统能够在一个基波周期(1 ms)内实现20个频率点(2—997 kHz)多目标组织边界的全频阻抗测量,成像结果可区分具有不同电特性生物组织的结构与位置.本文提出的基于multisine信号的整周期采样理论及其实现方法,只需一个multisine基波周期即可完成一次全频阻抗测量,为研制高速mfEIT系统奠定了理论和技术基础.     

采用系统函数分析换能器阻抗测量方法的性能

在分析传统三电压法测量阻抗优缺点的基础上,提出了一种发射换能器阻抗测量方法,以解决海上单模激发现场检修发射相控阵一致性的难题。该方法仍利用三电压法电路结构,但修改了测量参数。首先介绍了基于系统函数的换能器阻抗测量方法的原理,然后报道了当串联电阻选取不同数值时换能器阻抗测量的结果以及它们与高精度阻抗分析仪测量结果的比较,最后进行误差分析和测量曲线的等效电路参数拟合。通过对它的性能分析可以看到,在保证采样精度条件下,选择阻值相对换能器阻抗偏小的电阻值,其测量精度完全能达到高精度阻抗分析仪的精度。最后,通过对实验测量阻抗曲线的等效电路参数的最小二乘拟合表明,其拟合电参数准确,能应用到换能器匹配网络的设计。