EIS is foremost a measurement technique and not a modeling technique. A stimulus is applied and a response measured. Each response can be described with three variables, either CRn or LRn.
- Using a Gaussian equation fit parameters can be displayed as a line graph of multiple peaks in Bode form.
- As a separate exercise, values of the fit parameters are used to support a physical model of the system.
- The approach is applicable to both high and low impedance applications.
The Bode Plot below is a single Randles Equivalent Circuit Model, ECM, in series with an inductor. The right Log y-axis can be used for both capacitance and inductance (mirrored by using the absolute values). The left y-axis is the ratio of Zimag/Zreal (dashed line), emphasising impedance dominance along a current path rather than more obscure phase angle, ArcTan(Zimag/Zreal). Impedance curves are Zimag in blue, Zreal in red, Zmag is green. The different portions of the curve are identified by the annotations.
The y-axis of the Bode plot can also be changed to line graph ‘SpecView’ presentation using a Gaussian equation. This allows graphically overlaying multiple data sets. The Gaussian peak height can represent capacitance (left) or thickness, d =ee*A/C, (right) , peak position as either Fc (left) or Resistance (right), and peak width proportional to the power law parameter n. Below are shown results for high impedance anodic films on Zirconium; verses Log Freq (left) and Log R (right).
