Topic
Output impedance
About: Output impedance is a research topic. Over the lifetime, 11185 publications have been published within this topic receiving 134949 citations.
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14 Mar 1999
TL;DR: In this article, an alternative forbidden region for Z/sub 0/Z/sub i/ is proposed, based on which individual impedance specification for each load is defined, and theoretical verification, accompanied with simulation results, shows that the proposed impedance specification is a sufficient condition for small signal system stability.
Abstract: This paper continues the effort to define load impedance specification for a stable DC distributed power system. To improve the existing load impedance specification, an alternative forbidden region for Z/sub 0//Z/sub i/ is proposed, based on which individual impedance specification for each load is defined. Theoretical verification, accompanied with simulation results, shows that the proposed impedance specification is a sufficient condition for small signal system stability. Finally, conservativeness in load impedance specification is discussed.
125 citations
Patent•
24 Dec 1993
TL;DR: In this article, a method for determining the state of charge of an electrochemical cell by comparing the impedance of the cell at two or more frequencies or by comparing a cell's impedance at a medium frequency with the impedance at high frequency is presented.
Abstract: A method for determining whether an electrochemical cell is substantially fully charged. The determination is made by ascertaining the rate of change of the impedance of the cell with changing frequency, at low frequency. A method for determining the state of charge of an electrochemical cell by comparing the impedance of the cell at two or more frequencies or by comparing the impedance of the cell, at a medium frequency, with the impedance at high frequency. Apparatus for generating output signals representative of the magnitude of resistive and reactive components of an impedance (30). The apparatus has a signal generator (70) for passing AC current through the impedance, and a synchronous demodulator circuit (88) for demodulating AC signal appearing across the impedance pursuant to passing the current through it. A phase shift circuit (130, 132, 136, 138, 140) selectively generates control signals in phase or 90° phase shifted relative to the AC current through the impedance to control the demodulator circuit to respectively produce the output signals representing resistive and reactive components.
123 citations
08 Jul 1994
TL;DR: In this article, a new method using internal current density data measured by NMR imaging technique was proposed to improve the accuracy of the impedance image reconstruction in electrical impedance tomography (EIT).
Abstract: We have proposed a new method of image reconstruction in EIT (electrical impedance tomography). In EIT, we usually use boundary current and voltage measurements to provide the information about the spatial distribution of electrical impedance or resistivity. One of the major problems in EIT has been the inaccessibility of internal voltage or current data in finding the internal impedance values. The new method uses internal current density data measured by NMR imaging technique. By knowing the internal current density, we can improve the accuracy of the impedance images.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
123 citations
TL;DR: Comparing the results from the two circuits suggests that there is little to choose between them in terms of a practical implementation, and both circuits were stable over the frequency ranges 1 kHz to 1 MHz.
Abstract: Multi-frequency electrical impedance tomography (EIT) systems require stable voltage controlled current generators that will work over a wide frequency range and with a large variation in load impedance. In this paper we compare the performance of two commonly used designs: the first is a modified Howland circuit whilst the second is based on a current mirror. The output current and the output impedance of both circuits were determined through PSPICE simulation and through measurement. Both circuits were stable over the frequency ranges 1 kHz to 1 MHz. The maximum variation of output current with frequency for the modified Howland circuit was 2.0% and for the circuit based on a current mirror 1.6%. The output impedance for both circuits was greater than 100 kohms for frequencies up to 100 kHz. However, neither circuit achieved this output impedance at 1 MHz. Comparing the results from the two circuits suggests that there is little to choose between them in terms of a practical implementation.
122 citations
01 Jan 1994
TL;DR: In this article, the authors proposed a new image reconstruction method using internal current density data measured by NMR, which obtained a two-dimensional current density distribution within a phantom by processing the real and imaginary MR images from a 47T NMR machine.
Abstract: In electrical impedance tomography (EIT), we use boundary current and voltage measurements to provide the information about the cross-sectional distribution of electrical impedance or resistivity One of the major problems in EIT has been the inaccessibility of internal voltage or current data in finding the internal impedance values We propose a new image reconstruction method using internal current density data measured by NMR We obtained a two-dimensional current density distribution within a phantom by processing the real and imaginary MR images from a 47T NMR machine We implemented a resistivity image reconstruction algorithm using the finite element method and sensitivity matrix We presented computer simulation results of the image reconstruction algorithm and furture direction of the research
121 citations