What is the significance of using U/2I in four point probe theory?

In summary: The Van der Pauw Method is a method used to measure the resistance of materials. It is named after the Dutch physicist Johannes van der Pauw. It is a two-point probe measurement technique, in which a current is passed through the material and the voltage between two points is measured.
  • #1
ScieneShines
2
0
Dear Ladys and Gentlemans,

I want to measure the sheet resistance R_square on a printed product.
My measuring equipment consists a SMU to supply and measure and a four point Probe by Jandel.
As output size I get the electrical resistance R (basically the measured Voltage U divided by the supply current I)
So I have to multiply the geometric factor and a correction factor (correction factor because the width is small)

The derivation for the geometric factor I have found on :
http://www.four-point-probes.com/four-point-probe-...

And the correction factor table is shown here, in my case its on page 54
https://www.iiserkol.ac.in/~ph324/StudyMaterials/G...

Funny but true, I get twice the value than in the reference measurement system (eddy current technology)
So may we can discuss why?
And the bigger Question: why is the resistance calculated in the derivation with U/2I.
In my opinion there is no superposition of currents because they have a different sign.
Thank you in advance,
ScieneShines
 
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  • #2
Well, since you didn't show any of your work, we would have no idea where any error lies.

Now my disclaimer. Not my area of expertise, so take anything I mention merely as a 'second pair of eyes.'

From doing a spot read/scan of the links you supplied, you may have mis-applied the geometry correction. See especially pgs 4 thru 7 of the PDF you referenced. That seems to answer your 'why the factor of two' question and also cover the 'factor of two' error you seem to be getting.

Hopefully the above is at least a place to start!

Cheers,
Tom
p.s. Since this is a schoolwork question, I have requested it be moved to the Homework forum.
 
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Likes Joshy
  • #3
First things first : Thank you for your answer and no this is definitivly not a Schoolwork, Homework or anything else... Did you do those things in school? Respect for that.

I'm 100% sure that i used the correct correction factor.
Symmetry condition are given.
 
  • #4
Welcome to the PF. :smile:
ScieneShines said:
I'm 100% sure that i used the correct correction factor.
I agree with @Tom.G that we need to see your work to be able to help you.
 
  • #5

1. What is the purpose of using U/2I in four point probe theory?

The U/2I term in four point probe theory is used to calculate the sheet resistance of a material. It takes into account the voltage (U) and current (I) measurements from the four point probe setup and allows for more accurate calculations of the sheet resistance.

2. How does U/2I affect the accuracy of four point probe measurements?

The use of U/2I in four point probe theory significantly improves the accuracy of sheet resistance calculations. Without this term, the calculated sheet resistance may be overestimated due to the effects of contact resistance and sample inhomogeneities.

3. Can U/2I be used for all types of materials in four point probe measurements?

Yes, U/2I can be used for all types of materials in four point probe measurements. It is a universal term that takes into account the properties of the material and the setup of the four point probe.

4. How is U/2I calculated in four point probe theory?

U/2I is calculated by taking the ratio of the voltage (U) and current (I) measurements from the four point probe setup. This calculation is typically done using a computer program or spreadsheet.

5. Are there any limitations to using U/2I in four point probe theory?

While U/2I greatly improves the accuracy of four point probe measurements, it does have some limitations. It assumes that the material being measured is uniform and has a constant sheet resistance. It may also be affected by variations in contact resistance and sample thickness.

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