Abstract
In this paper we have shown that electrode polarization impedance (EPI) can be separated from measured tissue impedance as long as the characteristic frequencies of EPI and tissue are not too close, so that the EPI is largely displayed as a separate dispersion. In 2-electrode measurements the EPI and sample are physically connected in series, and commonly modelled by equivalent components in series. We have calculated the parallel equivalent elements and converted the series connected EPI and sample to a parallel admittance model. By curve fitting on the converted model we have shown that this provides a new method for estimating the EPI with enhanced accuracy compared to similar techniques used on the impedance model.
Highlights
By converting the impedance values from the series connected sample and electrode polarization impedance (EPI – commonly abbreviated by ZEP) to a parallel admittance model, we have introduced a new method for estimation of the EPI contribution in a set of measurement data
Both dispersions could be fitted to a Cole segment, and subtraction of a parasitic LF can be done with enhanced precision in this model compared to the same data plotted in the impedance model (Fig. 4)
Converting impedances connected in series to a parallel admittance model is an effective method for estimation of EPI or other LF properties by curve fitting in Wessel-plots
Summary
By converting the impedance values from the series connected sample and electrode polarization impedance (EPI – commonly abbreviated by ZEP) to a parallel admittance model, we have introduced a new method for estimation of the EPI contribution in a set of measurement data. In Kalvøy et al we even found influence from EPI above 100 kHz in measurements on sub-mm needle electrodes [6]. Together with the dependency of frequency and electrode properties like material [7], radius [2] and shape [13], the EPI has been shown to be dependent on the measured sample [2, 4, 7] and current density [2]. Due to the influence from this variety of factors the EPI is not separated from the sample properties in an impedance measurement
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