Modular FFT Impedance Spectroscope for Measuring Passive Circuits Dynamically

Abstract

This work presents the design and implementation of a Fast Fourier Transform (FFT) electrical impedance spectroscope using low-cost function generator, oscilloscope, personal computer and operational amplifiers. The electrical impedance measurement is carried out by sending several probe voltage signals with different frequencies, modulated in a single-one, by means of a function generator. The response is monitored using an oscilloscope and analyzed in a PC. The amplitude and phase of the electrical impedance at low frequencies (Hz to kHz) are obtained using the FFT. This is a quick method to obtain real-time measurements, useful to measure impedance of dynamical systems. To validate the system, it tested to measure an RC circuit and a thermistorcapacitor cell; the results were compared with theoretical calculations and measurements made by a commercial potentiostat. The system exhibited the ability to measure impedance spectra of circuits whose response evolve in time, sampling every 600 ms.