Fast Spectral Impedance Measurement Method Using a Structured Random Excitation

Abstract

The need for fast impedance measurement methods and instruments is necessary for accurate on-line characterization of many bio(electro)chemical systems in which most of the important processes occurs at low frequencies. However, the measurement by means of the traditional single-sine sweep signal is known to be a time consuming task particularly at ultra-low frequencies. In this work, we demonstrate the synthesis of a structured signal generated from a Gaussian white noise time series such that its power spectral magnitude is relatively flat over a wide bandwidth while maintaining a random phase. Such a signal allows the simultaneous measurement for multiple frequencies at once. When used to characterize a precision standard cell, the average deviation of the cell's spectral impedance from that measured using single-sine sweep on a research-grade BioLogic VSP-300 electrochemical station was about 1.03% over the frequency range 2 mHz to 200 kHz. Concurrently, the measurement time was reduced by a factor of 6.08 times compared to the reference instrument. The proposed methodology and processing can be readily adapted to other types of noises for fast impedance measurement.