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Margo C.,ESPCI ParisTech | Katrib J.,National Center for Industrial Microwave Processing | Nadi M.,CNRS Jean Lamour Institute | Rouane A.,CNRS Jean Lamour Institute
2013 IEEE Faible Tension Faible Consommation, FTFC 2013 | Year: 2013

A new extension of the AD5933 impedance measurement chip is presented. It allows to use the chip in the four electrode configuration to reduce the artifact effects of interface impedance between the electrode and the sample to be measured. The measurement approach is validated on various test circuits, and the system has been able to measure small physiological samples (50 ul) in a four microelectrode configuration and with a low sensitivity to interface impedances. The system is a good candidate for any embedded bioimpedance measurement system which requires a low sensitivity to interface impedances. © 2013 IEEE. Source


Margo C.,ESPCI ParisTech | Katrib J.,National Center for Industrial Microwave Processing | Nadi M.,CNRS Jean Lamour Institute | Rouane A.,CNRS Jean Lamour Institute
Physiological Measurement | Year: 2013

This paper presents the design of a four electrode impedance measurement circuit dedicated to bioimpedance embedded applications. It extends the use of the AD5933 measurement chip to allow it to operate in a four electrode configuration in order to limit the effects of the parasitic impedances between the medium under test and the electrodes. The circuit has shown a good measurement accuracy on various test circuits. In association with a four microband electrode system it has been successfully used to characterize small physiological samples (50 μl) with conductivities ranging from 0.14 to 1.2 S m-1. It can be used as an alternative bioimpedance measurement approach for embedded applications operating in the four electrode configuration. © 2013 Institute of Physics and Engineering in Medicine. Source


El Harfi J.,National Center for Industrial Microwave Processing | El Harfi J.,University of Nottingham | Kingman S.W.,National Center for Industrial Microwave Processing | Dimitrakis G.,National Center for Industrial Microwave Processing | And 3 more authors.
Industrial and Engineering Chemistry Research | Year: 2012

Studies into the phenomena that explain the dielectric properties of azo initiators (AMBN and V70) at high temperatures are reported in this paper. Previous studies have successfully related the variation in dielectric properties of these species below 110 C to either phase changes or the thermal production of free radicals. In the latter case the marked increase in their response was attributed to the free radicals having more prominent dipoles than their initiator precursors. This study reports the results of experiments designed to explain their observed dielectric characteristics within the temperature range of 110-150 C. At these elevated temperatures, the decomposition half-life of the initiators studied should be of the order of few seconds. However, in both this and the previous reports, the dielectric response is found to remain at a significant level for several hours. The two prime explanations for the unexpected duration of the increased dielectric properties are (i) the presence of microwave induced protected radicals or (ii) the dielectric properties of the initiator decomposition products. The observations made in this study were subsequently used to define that the latter of these is the key to the observed phenomenon. © 2012 American Chemical Society. Source

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