Hi,
I'm trying to get the Nyquist plot of impedance I tested.
Because the analyzer can only get impedance-theta-frequency, so I manually change them to Z' (written as R1) and Z''(written as X1).
X1=abs(Z1.*sin(Theta1));
R1=abs(Z1.*cos(Theta1));
Considering the temperature change under the long-time test, I chose the log sweep option.
The Nyquist plot (C1.jpg) looks weird. Not only this one, I tried another test material and got a similar weird result (NyquistofCoil.jpg).
I just wonder how can I get a semicircle figure.
Hi Wang,
Can you please provide some more information like ;
What range of frequency are you testing? what kind of electrodes are you using? what type of sample and what is the thickness?
I tested with the frequency from 4kHz to 13MHz. For these 2 figures in my question, a core is under test, like this picture shows.
I am not really familiar with the materials you are testing, however, you should start from high frequency to low frequency i.e., from 13 MHz to 4 KHz.
Hi Wang
I am not familiar with your tested materials. In lithium-ion batteries, we often test the battery from 10kHz to 0.01Hz with a perturbation voltage, such as 5-10 mV, or a perturbation current, such as 1/20C. More details for battery EIS tests can be found in the attached material.
Thanks to Hosein and Haijun, I'll do further read, appreciate it.
And I solved this problem by changing theta angles into radians.
It's a stupid mistake, but I learned from it XD
Dear Wang,
another issue is the high Rs value, due to the poor electrical contacts on your coil.
Retry some better electrical contacts[1] to your coil, or even, much better, remake your contacts by soldering 4-electrical contacts[2,3] on your coil.
1. Contact resistance https://en.wikipedia.org/wiki/Contact_resistance
2. Two contacts for the current, only, plus, other, two contacts for the measurement of the Voltage.
3. Improving Cable Quality & Reliability https://www.camiresearch.com/Campaigns/Web-Articles/4-wire-testing.html
Thank you Samaras,
Actually, I'm using a 4-electrode contact, two for current and two for voltage. But I don't know why should I do that, so could you explain more about it?
And I don't think there is something wrong with the big resistance, the paper I'm following shows a similar result, but I'm going to check it again.
Dear Wang Jingyan,
a) I could explain more/better if you could send, please, a draft photo showing the 4-electrodes' contacts on your coil.
b) Also, show, please, some Bode plot(s) spectra[1] for the wire (0.6mm) of your actual coil either empty and/or with core.
1. Wide (maximum, possible) frequency regime (spectra).
In basic electrical terms, the sense electrodes can only detect accurate voltages when they are not also conducting current, hence the two other current electrodes. This is intuitive if you've ever tried to measure the open-circuit voltage of a battery that is in the process of charging/discharging.
In electrochemical terms, the sense electrodes give a reference to the potentiostat of the working or counter electrode's potential, since voltage itself is a relative quantity. For a good overview, try this paper:
Article Lifting the Lid on the Potentiostat: A Beginners Guide to Un...
Hi Loannis,
So sorry for the late response, a midterm week took me too long to work.
My set-up for this experiment is showing in this setup.png.
And here is bode plot in coilbode.jpg.
Dear Wang Jingyan ,
thank you, very much.
The outline (schema: setup.png) is fine.
However, what is the actual value of the Rs[1], e.g. the value of Zreal(5Hz), in mOhm ?
1. The Rs is shown in you draft 'core.png'.
Mr Wang, Its might be short circuiting/resistance limit. You may clean properly blocking electrode what you using for Impedance analysis............
Could you help me in resolving why my bare electrode impedance curve was up straight and also the shape of Nyquist plot didn't shown while doing Immunosensor Study
What is your cell (WE, RE, CE, electrolyte), dear Rajeswari Alagar Samy ?
Screen printed carbon electrode was used in 5mM K3Fe(CN)6 in 0.1M KCL as electrolyte solution. WE: Graphite, RE: Ag/AgCl
Dear Rajeswari Alagar Samy ,
side-effects (RE-aging[1]), due to the adsorbed potassium ferrous cyanides, mainly, to the RE surface, in your (both bare and Immunosensor) SPCEs cells, affect most of your Nyquist plots.
So, try to remeasure a set of sequential (a timeline set of) EIS-spectra, using a fresh (NEW) cell[1], in order to find (what is) the "expiration dates (the time), Texpir", for your (SPCE) cell(s).
Also, you might like to reduce the concentration (
Would try the way you suggested;Thank you Sir
@Ioannis Samaras.
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