Welcome to PEDRA - Under Construction

PEDRA, as it was originally coined Parallel Electrical Dielectric Response Analysis, is used to fit Electrochemical Impedance Spectroscopy data using an Expandable Electrical Equivalent Circuit Model (EECM) rather than a fixed ECM. Rather than choosing an ECM based on physical perception, PEDRA seeks to find the number of dielectric responses in the spectrum.

Each dielectric response represents a current path.  Current along the path is limited by the resistance and blocked a capacitance or inductance. To account for non-ideal behavior a power law term is used. As the frequency changes one path is blocked and current finds another. Features are revealed by their impedance response as a function of sampled frequency. 

PEDRA 9.0, November 2025, offers: 1) a focussed approach, 2) a single screen user interface, 3) multiple data files, 4) user iterative curve fitting, 5) ability to exclude outliers, 6) flexible graphic presentation, 7) residuals, parameter error, response influence, 8) overlay report graphs to compare EIS results and more.

EIS is a powerful, macro-size technique (large ascribed surface area) that is extremely sensitive to micro/nano scale structural details. PEDRA offer a unique, fresh approach to EIS.

Services

PEDRA runs within

WaveMetrics IGOR PRO

A free 30-trial is available

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the PEDRA Approach.

Case Studies and Help Files

Frequently Asked Questions

How is PEDRA different?

PEDRA uses a different approach to fitting EIS data.

1) Instead of providing a electrical circuit model (ECM), PEDRA uses an Expandable Randles (cascading resistance) or Debye (parallel resistance) ECM.

2) The number of responses in the model is dependent on what the data can support.

3) Initial parameters are obtained directly from a plot of the data.

4) The type of response is identified by the parameters that describe it; either circuit (Resistance, Capacitance, power law term) or Physical (Resistance, dielectric thickness, fractal or factional distribution).

5) Displaying results using a 3-parameter Gaussian equation allows results to be presented as an overlay graph directly within PEDRA.

How are files imported into PEDRA?

PEDRA supports three methods of importing data: 1) legacy files, e.g. PARC, Solartron, Gamry, 2) delimiated files having using an interface to delete header information and choose data columns of frequency, real and imaginary impedance, 3) copy and paste spreadsheet from a spreadsheet.

What is the procedure for performing a fit to the data?

1) Import multiple data files into the experiment.

2) Estimate how many responses maybe in the spectra (this can be changed during the fit)

3) Set the parameter constraints (optional) using the Preferences menu. This helps in fit convergence.

4) Perform autofit. The process will return the last successful fit iteration.

5) Continue with user iterative fit process until convergence is achieved (i.e. hold and release parameters observing fit, fit residuals and parameter error).

6) Continue fitting data files. Any previously fitted data on the list can be overlayed on current file for comparison.

7) Once data files are fit, display results on an overlay plot with either the frequency (time constant) or resistance as the x-axis.

8) Use the extensive capability of IGOR PRO to create publication quality graphs.

9) Export fit results in spreadsheet form that includes experiment information, fit results and columar data/fit columns.

How is PEDRA's program interface different?

First, everything is on one screen using three panels.

1) The Main Graph panel contains a ribbon menu and a graph of fit results with options to choose axis, a) Ratio (Zimag/Zreal), SpecView (Gaussian line graph), b) Bode plot, either Zreal, Zimag or Zmag, Phase Angle.

2) The Information Panel contains all fitting controls and fit results (parameters, parameter error, response influence and time constant).

3) The Fit Control Panel contains all imported files each with fit and overlay check boxes.

PEDRA does not replace traditional model-choice impedance software, but operates in concert with other software. Fundamentally PEDRA identifies the number and types of responses present in a data. This information is often sufficient to correlate physical characteristics to in-service behavior. However, the information can also be used to assist in choosing  an appropriate electrical circuit model used in traditional EIS software.

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