Precise Impedance Measurement Research Articles

Accuracy improvement of impedance measurements by using the self-calibration

In this paper self-calibration measuring methods are introduced to improve the accuracy of impedance measurements according to the measuring system properties. Reference resistors are used for the self-calibration of different measuring systems. The measuring errors are self-corrected by special algorithms. The measuring conditions are optimised by the error analysis to minimise the measuring errors. These methods are applied to the impedance measurements of electrical elements and systems and to the characterisation of dielectric materials under high field intensities. Analysis and measurement results show an accuracy improvement compared with the measuring systems without self-calibration. Using the self-calibration methods precise impedance measurements are realisable in the measuring systems of lower accuracy and lower product cost.

High-frequency impedance spectroscopy of fast electrode reactions

A new technique of high-frequency impedance spectroscopy working in the frequency range between 1 kHz and 5 MHz has been developed. The method is characterized by a special electrochemical cell with two working electrodes, a newly designed dc control being completely ac-decoupled, a highly precise impedance measurement technique (ICEP = Impedance Conversion and Error Processing) and quantitative calculation of the electrodynamic field distribution in the cell. The accuracy of the measurements is better than 0.05%. The method was tested on the fast Ag/Ag + system. The results obtained are in quantitative agreement with a theoretical transfer function based on a 2-D inhomogeneous surface model.

The kinetics of the polycrystalline Ag/Ag+‐electrode studied by high‐frequency impedance spectroscopy

AbstractThe fast charge‐transfer reaction of the polycrystalline Ag/Ag+‐electrode was studied using a new technique of high‐impedance spectroscopy working in the frequency range between 1 kHz and 5 MHz. The method is characterized by a special electrochemical cell with two working electrodes, a new designed de‐control being completely ac‐decoupled, a highly precise impedance measurement technique (ICEP = Impedance Conversion and Error Processing) and the quantitative calculation of the electrodynamic field distribution. The accuracy of the measurements is better than 0.05%. The results obtained in the Ag/Ag+‐system are in a quantitative agreement with a theoretical transfer function based on a 2‐D inhomogeneous surface model. The exchange current densities were found to be about half an order of magnitude higher than the literature data.

Auditory brain stem responses and cortical auditory-evoked potentials in difficult-to-test children.

Brain-stem-evoked responses (BERs) and cortical auditory-evoked potentials (AEP) were recorded in 24 children showing severe behavioral disorders. BER testing always requires sedation if not general anesthesia. This allowed us to perform precise acoustic impedance measurements, and thus to find 3 glue ears. The electrophysiological tests revealed whether there was sensorineural deafness, which was cared for if necessary. Finally, when the BERs were normal, we evaluated the modifications in the cortical AEP, in relation to a clinical classification closely related to that of the DSM III of the American Academy of Psychiatry.

A field-theory of blood-pulse measurement by impedance plethysmography.

A field-theory model of blood-pulse measurement by four-electrode impedance plethysmography was developed and tested empirically. The model relates current distribution in the upper arm to the configuration of the drive electrodes. It predicts observed impedance change as a function of sense-electrode configuration and the increase in segmental volume associated with each blood pulse. The model was simulated on a digital computer for a number of critical cases. Corresponding measurements were taken on human subjects with an improved instrumentation system, which virtually eliminated the artifact caused by the skin-electrode interface. These measurements substantiated the major predictions of the model. It was concluded that precise impedance measurements were closely related to changes in segmental volume, and that any change in conductivity caused by the incoming arterial blood probably played a minor role. Insight was gained into the optimum placement of drive and sense electrodes at this measurement location.