Two questions about Kramers-Kronig transformations (EIS Kramers-Kronig) – Battery – Application Note 15Latest updated: August 31, 2021
In this application note, the questions “what can we do with truncated impedance” and “what can we do with an unstable system under galvanostatic control” are addressed. To answer these questions, analytical techniques such as ZFit and transforming YKK to ZKK are demonstrated on KK transforms.
Using the Kramers-Kronig (KK) transforms, the real part of a transfer function can be calculated for a causal, stable, linear time-invariant and finite system when and, when the change in its imaginary part, as a function of the frequency, is known. Alternatively, the imaginary part of a transfer function can be calculated when the evolution of its real part is known [1-4]. When the impedance of an electrode reaction is measured, it is possible to calculate the imaginary part using experimental values for the real part and calculate the real part using experimental values for the imaginary part. Comparing calculated impedance with the experimental impedance is a useful tool to check the validity of the impedance measurement with respect to the conditions of applicability of KK transforms.
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