what is the reason of opposite y coordinate direction?
why +y direction is not important on impedance plotting?
Dear Alireza,
If I have well understood you are asking why we start from zero in the vertical axis of Nyquist plot. The reason is that before zero you can have a signal related to inductance at high frequency. Inductive behavior in the high frequency range is fairly easily explained by instrumental artifacts, or by the inductance of the electrode, or the inductance of the connecting wires. So you don’t know if it is a real inductance.
Hello Alireza,
one very common plot for impedance spectroscopy is the plot in the complex plane z' against z'', it is often called Argand or Nyquist plot. Normally it is used in the form of z' against -z'', as you have written. I think this is done because a very common model, which is used to fit and/or describe impedance behavior, the RC equivalent circuit, gives a semicircle in the first quadrant of this plot.
Very good general information to this topic could be found in this book:
Book Impedance Spectroscopy: Theory, Experiment, and Applications
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