I have measured the impedance (EIS) of dielectric material experimentally. I can obtain the Nyquist plot from the built-in function of the spectrometer. I would like to plot the permittivity/ dielectric constant over the range of frequency (dielectric constant Vs frequency curve). I am wondering whether I will be able to calculate the permittivity/ dielectric constant and conductivity from impedance data.
Impedance spectroscopy is a powerful tool to extract the dielectric and electrical conductivity parameters.You should make the Cole-Cole plots and analyze them and fit the obtained plots with an appropriate equivalent circuit. and extract the capacitance and resistance. There are many papers in the literature which will provide the approach researchers have followed.
The impedance is obtained by Z* = U*/I*, and the equivalent parallel capacitance by Cp* = 1/jωZ*. The complex permittivity ε* = ε’ - jε’’ = Cp*/C0, where ε’ is the dielectric constant you want, C0 is the vacuum capacitance (or the geometric capacitance, i.e., the capacitance of the vacuum with the same geometry of your sample). The complex conductivity σ* = σ’ + jσ’’ = jωε0ε*, where ε0 is the dielectric constant of the vacuum and σ’ is the conductivity you want. To make the results of Z* of your sample more accurate, the influence of the edge capacitance and the stray capacitance from the measurement device should be eliminated.
This paper may be more helpful with the question, https://doi.org/10.1063/1.5081842.
Dear Prof. K. Sreenivas,
I appreciate, thank you for your suggestion.
Dear Mr. Men Guo,
I would like to request the answer if the capacitor electrodes (both) are not placed in parallel but on the surface of the dielectric. Is the calculation you mentioned above still applicable or do I have to follow another way of calculating 'complex permittivity and conductivity'?
Additionally, j=root(-1); what would be the value for j?
I thank you in advance.
Dear Tanzila,
My suggestions above are valid for samples with determined geometry. What kind of samples will you test? Are they liquids or solids? And can they be reshaped into cylinders? For an arbitrarily shaped dielectric, the capacitance is defined as dQ/dV, where Q and V are the charge and the voltage, respectively. However, it is tough to get the permittivity because the responsive volume is not easily known. I recommend you to refer to Section 3.2 in Dielectric relaxation in solids (A.K. Jonscher, 1st ed., Chelsea Dielectrics Press, London, 1983) for details.
These quantities (with *) in my last answer are complex numbers, so there is an imaginary number for each quantity.
Thank you for your questions.
Dear Men Guo,
I am dealing with porous concrete considering a certain moisture content within it. I can't even shape the concrete structure within the cylinders since it's solid and I want to measure the surface moisture of the concrete with certain electrode geometries (e.g., 10-15mm in diameter).
Anyway, thank you for your recommendation.
Many thanks for your answer.
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