耗电流低于200μA的低功耗4mA至20mA过程控制电流环路解决方案

AD5933和AD5934是一款高精度的阻抗转换器系统解决方案,集片内可编程频率发生器与12位、1MSPS(AD5933)或250kSPS(AD5934)的模数转换器(ADC)于一身。可调频率发生器产生已知频率来激励外部复阻抗。图1所示电路在低欧姆范围直至数百kΩ范围内产生精确的阻抗测量,同时还优化了AD5933/AD5934的整体精度。     

嵌入式电阻抗测量系统研究

为提高阻抗测量的便捷性及数字化应用,基于ARM架构的S3C2440处理器和Linux3.0.4内核,研发了一套嵌入式电阻抗测量系统。系统采用AD5933作为阻抗传感器,利用I2C通信协议实现AD5933与S3C2440处理器之间的数据通讯,开发QT用户界面实现测量结果的显示,通过操作触摸屏实现阻抗参数的采集、显示、保存及曲线绘制等功能。实验结果表明图像重建质量较好,信噪比达65.6dB,验证了系统软硬件设计的可靠性与稳定性。该研究有助于推动阻抗测量技术在数字化医疗及临床应用的发展。     

基于LoRa的活立木阻抗测量系统

活立木的阻抗可以反映出活立木的健康状态,针对林业物联网中的活立木阻抗测量成本高、不方便、实时性差的问题,设计了一种基于LoRa的活立木阻抗测量系统。系统利用STM32芯片,外设AD5933通过量程自动切换算法采集活立木的阻抗数据,使用LoRa通信将所采集数据通过SX1267芯片发送到接收端。上位机软件接收后,利用卡尔曼滤波算法对同一批数据进行滤波处理,得到最终的阻抗值,以方便监测活立木的健康状况。经过与市场主流测试仪进行测试对比表明:该系统的测量精度接近0.05%,可以准确测量出活立木的阻抗。研究结果为活立木健康监测中的活立木阻抗测量提供了一种低成本、易操作及时效性强的实施方案。     

基于AD5933的高精度生物阻抗测量方法

本文利用阻抗测量芯片AD5933,以单片机作为控制器,依据此芯片比例法测量原理、DFT解调原理结合软件校准和软件补偿的算法,实现了一种高精度生物阻抗测量方法.实验结果表明,此方法有效提高精度,测量阻抗幅值的相对误差小于0.5%,相位绝对误差小于0.7°.     

AD5933在电磁层析成像硬件系统中的应用

应用阻抗数字转换器AD5933,改进设计了电磁层析成像(EMT)系统的硬件电路.该设计不仅提高了硬件系统集成度,而且增强了EMT激励系统配置的灵活性和信号解调的实时性.     

基于ＳＴＭ３２的生物电阻抗测量系统的设计与应用

为了更好的了解患者的血凝病理状况,方便医生及时用药,该文基于STM32和AD5933设计了一种血凝电阻抗测量系统。使用该系统测量标准电阻、电容构成的RC并联网络,与TH2832LCR电桥仪对比,误差小于0.9%;进行标准电阻的扫频测量,误差小于0.5%。提出一种凝血因子反应时间R检测方法,对40组血样进行测量,并与实际R值对比,误差均小于4%;使用等浓度差的CaCl2溶液与多组枸橼酸钠抗凝血混合,发现随着CaCl2溶液浓度以0.025mol/L微量减小,R明显增大,符合生物学规律;在不同条件下对多组血样进行测量,误差均小于5%。结果表明该电阻抗测量系统可以用于凝血因子反应时间的检测且具有较高的精度、灵敏度和较好的重复性、重现性。     

基于DFT和虚参考矢量的混频阻抗动态信号测量方法

 为实现对生物阻抗信号在同一时刻,不同频率下的动态检测,本文对混频激励下阻抗信息的提取方法进行了研究,分析了DFT能量泄漏与栅栏效应对正弦信号测量结果的影响,提出了基于DFT和虚参考矢量的混频生物阻抗测量方法.通过仿真和实验,验证了虚参考矢量方法的补偿作用.实验表明,本方法可以通过测量不同频率下的人体阻抗,体现出呼吸、脉搏等信息在不同频率下的动态响应.     

基于AD5933的膀胱电阻抗测量系统

针对膀胱尿容量无损检测设备结构复杂、操作难度大和便携性差等问题,设计一种基于AD5933的膀胱电阻抗测量系统。该系统包括上位机和由数据通信模块、阻抗测量模块和测量电极构成的下位机,采用I2C串口通信,通过下位机输出特定频率的电流信号至人体下腹部,测量膀胱电阻抗。实验结果表明,该系统能实现持续测量人体膀胱电阻抗,膀胱电阻抗所呈现的变化趋势与尿动力学研究相吻合。该系统结构紧凑,操作简便,精度可满足膀胱尿容量评估要求,可通过上位机进行可视化操作和实时监测,对设计开发新型的便携式膀胱尿容量无损检测设备具有指导和借鉴作用。     

ADI发布阻抗数字转换器AD5933

美国模拟器件公司(ADI)日前发布高精度、完全集成的阻抗数字转换器(IDC)AD5933，从而解决了从电容到数字和从阻抗到数字直接转换的复杂而困难的信号处理难题。这款器件适合于各种高性能仪表和检测应用，包括从血压计和葡萄糖分析仪到用于汽车和工业腐蚀分析系统的位置传感器。AD5933结合了直接数字频率合成(DDS)、模数转换和数字信号处理技术，     

倒相音箱的设计

我们知道电动机空载转动时电流最小,阻抗最大。当我们给电动机加上负载后,电动机运转时电流会增大,阻抗会降低。所以我们可以通过测量电动机的阻抗来计算出电动机负载的大小。假如我们将扬声器看成是个直线电动机,可以通过测量扬声器的阻抗来判断扬声器负载的状态。     

Analysis of the impedance of a coaxial, large-bore copper-vaporlaser

The impedance of the laser head of a 100-W copper-vapor laser is investigated. The laser head is of a coaxial geometry, which is commonly used for longitudinally electrically excited, pulsed-gas lasers. The plasma conductivity is estimated using the available data on plasma parameters. The effect of radial gradient of the gas temperature and electron density is considered. The tube inductance and capacitance are estimated and the combined effect is demonstrated. The skin effect is considered. A method to calculate the exact influence of the skin effect on the tube impedance is presented. The full calculation procedure is demonstrated for the case of a 100-W, 8-cm-diameter, copper-vapor laser. The consequent impedance is used to calculate the laser current under given excitation conditions. Very good agreement exists between the calculated and measured laser current. The metal-sleeve diameter is found that is optimal for power matching     

Krylov subspace iterative techniques: on the detection of brain activity with electrical impedance tomography

In this paper, we review some numerical techniques based on the linear Krylov subspace iteration that can be used for the efficient calculation of the forward and the inverse electrical impedance tomography problems. Exploring their computational advantages in solving large-scale systems of equations, we specifically address their implementation in reconstructing localized impedance changes occurring within the human brain. If the conductivity of the head tissues is assumed to be real, the pre-conditioned conjugate gradients (PCGs) algorithm can be used to calculate efficiently the approximate forward solution to a given error tolerance. The performance and the regularizing properties of the PCG iteration for solving ill-conditioned systems of equations (PCGNs) is then explored, and a suitable preconditioning matrix is suggested in order to enhance its convergence rate. For image reconstruction, the nonlinear inverse problem is considered. Based on the Gauss-Newton method for solving nonlinear problems we have developed two algorithms that implement the PCGN iteration to calculate the linear step solution. Using an anatomically detailed model of the human head and a specific scalp electrode arrangement, images of a simulated impedance change inside brain's white matter have been reconstructed.     

Electronic module for the thermal monitoring of a Li-ion battery cell through the electrochemical impedance estimation

Electrochemical impedance is a not directly measurable parameter of the Li-ion cells that can be exploited to retrieve useful information about the state of the cell itself, such as the State of Charge or the internal temperature. This complex parameter depends on the frequency, which means that it's real and imaginary parts change in function of the frequency at which the cell is activated. Nowadays impedance is mainly measured using laboratory equipment as part of dedicated benchmarks, requiring expensive facilities and relatively long procedures. In this paper we propose a new solution to get the impedance value of a Li-ion cell by using both an efficient approach minimizing the test duration, and an innovative electronic solution suitable for automotive embedded needs. The electrochemical impedance is then analysed to deduce the cell's internal temperature with experimental results.     

An Approximate Dynamic Green's Function in Three Dimensions for Finite Length Microstripline

A spatial Green's function in 2-D for straight and infinite microstriplines has been shown to be accurate at frequencies that the dynamic effects cannot be neglected. It is reasonable, therefore, to expect that a similarly accurate spatial Green's function in 3-D can be constructed for finite and curved microstriplines. Based on the same image model of charges and currents as in 2-D, this paper constructs the 3-D Green's function. The Green's function is then applied, through Harrington's moment rnethod, to calculate the input impedance of a few microstriplines, viz., a matched microstripline, straight and hairpin open-ended stubs. The input impedance of a microstrip stub always has a small resistive component indicating the radiative loss. This resistive component agrees with that calculated from the Lewin's formula. Finally, as expected, the imaginary part of the input impedance agrees with that calculated from the TEM approach.     

Imaging electrical impedance from acoustic measurements by means of magnetoacoustic tomography with magnetic induction (MAT-MI)

We have conducted computer simulation and experimental studies on magnetoacoustic-tomography with magnetic induction (MAT-MI) for electrical impedance imaging. In MAT-MI, the object to be imaged is placed in a static magnetic field, while pulsed magnetic stimulation is applied in order to induce eddy current in the object. In the static magnetic field, the Lorentz force acts upon the eddy current and causes acoustic vibrations in the object. The propagated acoustic wave is then measured around the object to reconstruct the electrical impedance distribution. In the present simulation study, a two-layer spherical model is used. Parameters of the model such as sample size, conductivity values, strength of the static and pulsed magnetic field, are set to simulate features of biological tissue samples and feasible experimental constraints. In the forward simulation, the electrical potential and current density are solved using Poisson's equation, and the acoustic pressure is calculated as the forward solution. The electrical impedance distribution is then reconstructed from the simulated pressure distribution surrounding the sample. The present computer simulation results suggest that MAT-MI can reconstruct conductivity images of biological tissue with high spatial resolution and high contrast. The feasibility of MAT-MI in providing high spatial resolution images containing impedance-related information has also been demonstrated in a phantom experiment.     

Finite-difference time-domain implementation of surface impedanceboundary conditions

Surface impedance boundary conditions can be utilized to avoid using small cells, made necessary by shorter wavelengths in conducting media throughout the solution volume. The standard approach is to approximate the surface impedance over a very small bandwidth by its value at the center frequency, and then use that result in the boundary condition. In this paper, two implementations of the surface impedance boundary condition are presented. One implementation is a constant surface impedance boundary condition and the other is a dispersive surface impedance boundary condition that is applicable over a very large frequency bandwidth and over a large range of conductivities. Frequency domain results are presented in one dimension for two conductivity values and are compared with exact results. Scattering width results from an infinite square cylinder are presented as a two dimensional demonstration     

晶闸管的瞬态热阻抗及其结温温升的研究

系统地阐述了晶闸管的瞬态热阻抗 ,针对晶闸管承受不同的功率脉冲 ,利用不同的计算方法计算瞬态热阻抗值 ,从而确定结温温升 ,并比较了它们的原理、精度及其应用范围。特别是利用了一种新的瞬态热阻抗计算模型 ,当晶闸管承受持续时间极短且周期、占空比均变化的任意波形功率脉冲时 ,它能够比较精确地分析晶闸管的热特性 ,计算半导体结的最大温升     

一种新的微波频率下混合电解质水溶液复等效介电常数的计算方法

目前,大部分电解质水溶液的等效介电常数计算模型是针对静止频率下其实部进行的.而对于实部与虚部同时计算方法的报道中,都是通过大量实验测量,利用德拜参数拟合而得到相应结果的,且局限于少数几种溶液,例如盐水和海水等.本文中,通过实验得到了不同电解质水溶液的复等效介电常数,基于此实验结果,提出了一个新的计算模型,引入了不同离子的复影响因子的概念,用来计算微波频率下电解质水溶液的复等效介电常数.在915MHz和2450MHz下,比较了实验结果和计算结果,它们比较好地符合,从而证明了公式的有效性.这将为微波化学中微波加热稀溶液化学反应中的电磁场和温度分布计算提供基础,同时也将对地球物理、遥感以及水污染监测等相关领域研究有帮助.     

Solution of problems of electromagnetic wave scattering by bodies with an anisotropic impedance with the help of the pattern equation method

The pattern equation method is generalized to solution of problems of electromagnetic wave diffraction by bodies with an anisotropic impedance. A numerical algorithm of the method is developed for bodies of revolution. Techniques of simulation of artificially hard and soft surfaces with the help of an anisotropic impedance are indicated. The method is applied to calculate the scattering characteristics of bodies having a complex structure of conductivity lines on their surfaces.     

Impedance Calculation of Three Narrow Resonant Strips on the Transverse Plane of a Rectangular Waveguide (Short Paper)

A theoretical analysis has been developed to calculate the impedance of two inductive strips and one capacitive strip located on the transverse plane of a rectangular waveguide. The current ratios among the strips were determined by a variational method and then used for impedance calculations. The results can be applied to the impedance calculations of a single capacitive strip, two inductive strips, or three inductive ships as special cases.