Time domain transmissometry

For low-frequency application (mHz to MHz), the classical approach using two or four electrodes interfaces are commonly used. The three electrodes interface is usually employed in conjunction with active electrical properties at surfaces, such as sensor surfaces. Because the behavior within the immediate vicinity of the working electrode overwhelms the measurement, the results are basically monopolar measurements. 

The front ends used in time domain transmissometry are similar to those employed in frequency domain measurements. However, extra care should be taken to ensure high linearity and stability against transient voltage or current changes. 

The voltage across the MUT (Vmut) is deformed with respect to the stimulus VappUed as a consequence of capacitance charging (e.g., cell membranes). In the simple case of a 

This is the typical result in TDS yielding the time constant x, and the relaxation strength A. In contrast to a three element circuit, more complicated objects yield several time constants over a wide frequency range. More sophisticated is the calculation of distributed time constant as it would be required for the Cole model. 

The current Imut is related to die elements of the equivalent circuit as follows  

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