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

Many electrochemical systems can be studied using equivalent circuit models. One simple model is the Randles circuit, which consists of a resistance connected in series with a parallel combination of a capacitance and another resistance. This second resistance is called polarization resistance, and for many practical applications, it is very important to estimate its value. Using a special form of a pulsed excitation, we show that it is possible to estimate a value for the polarization resistance with a very simple calculation. A time-frequency analysis of the proposed pulsed excitation showed not only the zero frequency content of the signal but also the time when this zero frequency occurs. Using Laplace analysis, we show also that the transient current through the capacitance is zero, when the frequency contents of the pulse is zero. In this way it is possible to estimate the value of the resistive component of an electrochemical cell. Experimental results show an approximation error of less than 0.5%. We conclude this is an alternative technique to estimate the polarization resistance.