Time-Frequency Analysis of a Pulsed Excitation and Its Application in Randles Model

Many electrochemical systems can be studied usingequivalent circuit models. One simple model is the Randlescircuit, which consists of a resistance connected in series witha parallel combination of a capacitance and another resistance. This second resistance is called polarization resistance, and formany practical applications, it is very important to estimate itsvalue. Using a special form of a pulsed excitation, we show that it ispossible to estimate a value for the polarization resistance with avery simple calculation. A time-frequency analysis of the proposedpulsed excitation showed not only the zero frequency content ofthe signal but also the time when this zero frequency occurs. Using Laplace analysis, we show also that the transient currentthrough the capacitance is zero, when the frequency contents ofthe pulse is zero. In this way it is possible to estimate the valueof the resistive component of an electrochemical cell. Experimental results show an approximation error of lessthan 0.5%. We conclude this is an alternative technique toestimate the polarization resistance.

I. Introduction

Electrochemical systems can be found in many different aspects of our life. For example, corrosion process in oil pipes, transmission towers, and concrete bridges are described by electrochemical reactions. Batteries, and some biological systems can also be modeled as an electrochemical process. In these examples, electrical circuits have been used to model the electrochemical process, and from that model, it is possible to foresee instrumentation strategies.