Re: invfreqs and Warburg impedance

[Robert A. Macy]

I'm not familiar with the invfreqs program.  

For a simple 5 node system I used a "PSpice" approach.
 Using octave, set up the matrix, then solved for the
inverse matrix, then multiplied the voltage drive vector to
get the answers.  Many of the circuit values were known.
 Some were "curve" fit for best match.  

With this approach you can set the Capacitance Resistance
to functions of relationships to freq.  Do a best fit to
your data and predict the component values.  

                - Robert -


On Mon, 20 Dec 2004 09:22:57 -0600
 "Pascal A. Dupuis" <address@hidden>
wrote:
> 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
> 
> 
> 
>
-------------------------------------------------------------
> Octave is freely available under the terms of the GNU
> GPL.
> 
> Octave's home on the web:  http://www.octave.org
> How to fund new projects:
>  http://www.octave.org/funding.html
> Subscription information:
>  http://www.octave.org/archive.html
>
-------------------------------------------------------------
> 



-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
-------------------------------------------------------------