how to find resistance and capacitance values from impedance measurements at different frequencies?

Hi, I'm a student approaching for the first time with Matlab. I need to test the conductivity of a particular material, so I measured the electrical impedance of my material, at different frequencies. The transfer function showed a first degree low pass filter behaviour. Moreover I need to estimate the resistance and capacitance parameters of this material, even with an iterative method, by starting from these experimental impedance measurements. Can anyone help me to solve this issue? Thanks a lot!

Answer 1

[Brandon Eidson]

Hello Consuelo, I understand that you have the electrical impedance (R + jX) measurements for various frequencies for a series resistor and capacitor.  If this is the case, you should be able to directly calculate the resistance and capacitance parameters (R will not change [much] with frequency and C = -1/(w*X), where "w" is frequency in radians/sec).  

Further, if you have the transfer function corresponding to your measurements, you can calculate the theorietical transfer function for a series R-C circuit with the output as the terminal voltage and in the input as the current.  Once again, you can calculate R and C.

If I have misunderstood you and the situation is more complex, I think you will benefit the System Design Optimization Toolbox. It includes the ability to estimate parameters from a system model and experimental measurements.  The following examples hows one way to do this.

https://www.mathworks.com/help/sldo/ug/estimate-model-parameter-values-gui.html