Electrical impedance

About: Electrical impedance is a research topic. Over the lifetime, 36015 publications have been published within this topic receiving 371891 citations. The topic is also known as: electrical impedance & complex impedance.

Scheme for rapid adjustment of network impedance.

Abstract: A static controlled reactance device (10) is inserted in series with an AC electric power transmission line (6, 8) to adjust its transfer impedance. An inductor (X, 20)(reactor) is serially connected with two back-to-back connected thyristors (24, 26) which control the conduction period and hence the effective reactance of the inductor (21). Additional reactive elements are provided in parallel with the thyristor controlled reactor to filter harmonics and to obtain required range of variable reactance. Alternatively, the static controlled reactance device (10) discussed above may be connected to the secondary winding of a series transformer (12) having its primary winding connected in series to the transmission line. In a three phase transmission system, the controlled reactance device (10) may be connected in delta configuration on the secondary side of the series transformer (12) to eliminate triple harmonics. With series transformer (12), secondary windings to which the controlled reactances are connected could be arranged for six-pulse or twelve-pulse operation.

Characterisation and Modelling of a High Temperature PEM Fuel Cell Stack using Electrochemical Impedance Spectroscopy

Abstract: In designing and controlling fuel cell systems, it is advantageous to have models which predict fuel cell behaviour in steady-state as well as in dynamic operation. This work examines the use of electro-chemical impedance spectroscopy (EIS) for characterising and developing an impedance model for a high temperature PEM (HT-PEM) fuel cell stack. A Labview virtual instrument has been developed to perform the signal generation and data acquisition which is needed to perform EIS. The typical output of an EIS measurement on a fuel cell is a Nyquist plot, which shows the imaginary and real parts of the impedance of the measured system. The full stack impedance depends on the impedance of each of the single cells of the stack. Equivalent circuit models for each single cell can be used to predict the stack impedance at different temperature profiles of the stack. The information available in such models can be used to predict the fuel cell stack performance, e.g. in systems where different electronic components introduce current harmonics.

Electrical characterisation of high-frequency thickness-shear-mode resonators by impedance analysis

Abstract: Increasing the frequency of coated AT-cut quartz resonators should result in an increase of the measuring signal of these devices in the application as chemical sensors. A combined photolithographic/etching process allows a reliable fabrication of mechanically stable resonators with frequencies up to 75 MHz. The results of the electrical characterisation of the high-frequency resonators by means of impedance analysis are presented. The measured Q -values are about 5×10 4 , which is an excellent figure for high-frequency resonators. The separation of unwanted inharmonic from harmonic modes is improved by reducing the diameters of the deposited electrodes. The dependence of the equivalent circuit values on frequency and electrode diameters are investigated. The results reveal good agreement with theoretical values obtained from a one-dimensional transmission-line model for L and C 1 and quite poor agreement in R and C 0 . Investigations on the impedance behaviour under liquid load show an increase in damping for high-frequency resonators as expected. The possibility for operating the high-frequency resonators in an oscillator circuit under liquid load depends on various influence parameters. A general estimation is difficult to be made and should be tested experimentally for certain applications. However, the use of resonators with frequencies higher than 50 MHz in liquids seems not to be advisable.

Conrolled physical and subjective intensities of electric shock

Abstract: A series of investigations was conducted to determine which physical parameters must be controlled to deliver constant electrical stimulation and the effect of controlling these parameters on subjective estimates of shock intensity. Constant voltage and constant current stimulation were tested with eight waveforms and five electrode configurations, including a concentric disc electrode. Dry skin and treated skin techniques were tested in a comparative power experiment and with a method of magnitude estimation. Passing an electrical stimulus through an electrode-skin circuit produces a marked reduction in the impedance of that circuit. This drop in impedance is a local effect, rather than a centrally mediated response, causes differences in perceived magnitude, and occurs no matter whether voltage, current, or power is held constant and no matter what waveform, frequency or electrode configuration is used. The use of the concentric disc electrode and treatment of the skin with an electrolyte makes it possible to reduce impedance to a predetermined level, which when combined with constant voltage or constant current results in a constant physical stimulus and constant subjective estimates of the stimulus intensity.