Hello Oualid,

A bode plot is in general a good way to display the bandwidth of an amplifier, filter an oscilloscope, etc.  In the case of an amplifier a bode plot will show the width of the frequency range where there is a fairly flat response (that is the frequency range where there is fairly constant gain).  The wider that range the better an amplifier can accurately reproduce a signal, i.e. the better fidelity it will have.  If you have a signal with a fast rise or fall in intensity, and you want to capture that you will need an amplifier with a fairly wide bandwidth that goes into the high frequency range.  Typically what is used to define where that range ends is the -3 db point.

If you have an oscilloscope with a wider bandwidth the more likely it will reproduce the signal you are displaying with greater fidelity.

A bode plot is a good way of displaying the bandwidth of an instrument and its ability to work with signals that contain particular frequency components. 

Dear Oualid Dilmi,

As I am understand, you want to know what is the difference between Nyquist and Bode plot and what is the benefit of Bode plot comparing with Nyquist plot. General, both plots are used for graphical illustration of dependency of impedance (as a complex number) on frequency. Thus, both of them contain the same information because plots are based on the the same data. It is just different view of the same thing. Bode plot : |Z| and Phase shift against frequency and Niquist: Re against Im. Practically, for example Bode plot can help to interpret Niquist plot because the Phase shift is seen immediately while in Niquist plot is given by artan(Im/Re).

Normally I put both of them next to each other to better interpretation. Usually, Nyquist diagram is enough for me. But it depends on your application and what you want to show - want to highlight.

What John E. Hansen said is of course truth too. Impedance spectroscopy is general method provide information about a frequency response about any system (If can I generalyzed) including electrochemistry.

Hello. thank you Roman Fiala. for me, it is clear that impedance spectroscopy is a technique with a reponse according to the frequency. as we know the nyquist reprsentation (Im z vs. Re z) can give several informations about the electochemical system such as the electrolyte resistance. the charge transfer resistance. capacity of double layer....and it can give an aidea about the reactionel proceess (charge transfer, diffusion, adsorption ....) whears the bode presentation concerns the variation of impedance module or the phase according to the frequency. but i think that bode plot used to investigate a phenomena that we can not show by nyquist diagram.

Bod plot has the frequency explicit. It is helpful with the data at small impedances which can swamped by large impedances using Nyquist.

Another benefit of Bode plot is that it gives direct reading of resistance of the material under study at low frequencies. This is the intercept on the vertical axis in Log|Z| vs Log Freq. In this regard, it is very effective because sometimes Nyquist plot can have "bizarre" look due to transport mechanisms involved and makes it almost hard, with less precision, to read off resistance of the system.

We can extract from nyquist plot the informations about resistance, the phenomens .... etc. but with bode plot in addition to these informations. You can extract the shit angle, numbre of circeles ....etc.

You find attached some examples of bode and nyquist plots