Impedance study of non-stationary systems: four-dimensional analysis

The impedance study of non-stationary systems is of a great interest to electrochemistry concerning the investigation of real objects in low and infra low frequency ranges. The method described in this paper requires the measurement of a consecutive series of impedance diagrams during the time of the system evolution. The analysis of this four-dimensional data set is based on the hypothesis of a continuum of the state and parameter spaces. This approach allows the estimation of the non-stationary transfer function of the system presented by its instantaneous impedance projections. The method described is applied to simulated data and the validity of the non-stationary estimation is verified.