RE: invfreqs and Warburg impedance - use LEVM

[Harbinson, Jeremy]

 Hi,
There is free fitting and simulation package for bioimpedance and other 
specialised impedance application. This has pre-built models for various CPEs 
such as Cole-Cole, Havriliak-Negami, Warburg etc. The package is a little bit 
awkward to use - you will need to read the manual carefully, but the package 
does work nicely once you have got to know it. You can download it from the 
Solartron web site

http://www.solartronanalytical.com/downloads/software.html

All the best,
Jeremy Harbinson

-----Original Message-----
From: Pascal A. Dupuis [mailto:address@hidden 
Sent: maandag 20 december 2004 16:23
To: address@hidden
Subject: invfreqs and Warburg impedance

Hello,

I'm trying to describe an Impedance measured over a few frequencies points as a 
combination of resistors/capacitors, using the invfreqs function. But the 
underlying system is comprised of a pair of electrodes, and some biological 
medium, so the impedance contains a so-called Warburg element, that is, a 
capacitor in parallel with a resistor, where the phase angle is constant (45 
°) and the product of R and C is equal to 1/f.

When I plot the impedance locus (real part, imaginary part), it is obvious that 
there is something going wrong with the approximation using constant R and C. 
Did someone already coped with this, coming to some iterative method permitting 
to extract the Warburg element and progressively come to a good approximation 
of the measured impedance.

TIA

Pascal Dupuis

--
Dr. ir. Pascal Dupuis
K. U. Leuven, ESAT/ELECTA (formerly ELEN):  http://www.esat.kuleuven.ac.be/ 
Kasteelpark Arenberg, 10; B-3001 Leuven-Heverlee, Belgium Tel. +32-16-32 10 21 
-- Fax +32-16-32 19 85



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