Current or Potential Are the Output Quantity

As I and U play a particular role in an electrochemical system, and both cem be considered to be either input or output quantities, according to the type of regulation of the polarization (potentiostat or galvanostat), I and U appear in either the input or the output vector columns. According to equation (14.16) 

Remember 14.2 The small-signal transfer function may be analyzed at different values of the static property space, which represents a linearized characterization of the system. The same information is obtained as would be obtained by analyzing the entire nonlinear electrochemical system using a large-amplitude perturbation technique such as cyclic voltammetry, but the analysis is simpler. 

Equations (14.17) and (14.18) are simultaneously satisfied therefore, by replacing U in equation (14.17) by its value given by equation (14.18), 

Therefore, the elementary transfer functions that give the response of current and potential to the perturbation of the m input quantity are related by the electrochemical impedance. For a given experiment, only one input quantity is sinusoidally modulated aroimd a mean value, and all others are maintained constant by different regulations. 

The notation such as the ratio Vjt/W n tneans that eiU input quantities W,- (with I m) are fixed. Then equation (14.21) can be written as 

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