# Excel and electromagnetism

Joined Dec 29, 2004
83
Hi,
I would like to know if somebody has already done this kind of project:
Using EXCEL, compute the voltage (E field, surface density....) inside a capacitor using the cells of the spreadsheet. The way the voltage are found is by using the average of the 4 cells surrounding it.

For example , if you want to compute the voltage at the cell C3 , the equation should be:
=0.25*(B3+D3+C4+C2)

I want compute the capacitance per unit of length. I can give more detail about the delta between cells and the grid size N.
It is a project I am doing but I am lost.
Thank you
B

#### beenthere

Joined Apr 20, 2004
15,819
There are probably a few more conditions that apply to your calculation. Otherwise, simply use a newly-made capacitor that has no charge on the plates whatever, and all the voltages are therefore zero.

You formula for individual cell voltages is also a rule for the game of Life. Is there some size constraint to each cell? Make them infinitely small and there is only an infinitely small voltage difference, so the average is the same as the voltage on any cell.

Capacitance of what per unit of length? Telephone poles? Fibre optic cable?

Joined Dec 29, 2004
83
I tried to give some information on the attachment.

we are using the size of the cell but the distance between two nodes.

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#### beenthere

Joined Apr 20, 2004
15,819

Joined Dec 29, 2004
83
The top plate starts at A1 to J1 for example.
I go to the top of the capacitor,I first compute for the electric field, by computing =(B1-A1)/Delta. I go across through the end.

Then I compute D(flux) =E*epsilon then since the charge is equal to D, to find the capacitance ,I add all the "small" charges but I dont know what Voltage to use?
B

#### Dave

Joined Nov 17, 2003
6,969
There is a very common method for this type of problem using a node based approach, called Transmission Line Matrix.

It involves fragmenting the simulation space into nodal areas/volumes (known as Symettric Condensed Nodes, which represent an inductor/capacitor pair on a TM line) and solving for the voltage and current at this point on the TM line. There is no need to perform an averaging of the adjacent nodes and the solution is exact.

TLM has been successfully used by making equivalences with Maxwell's Equations and solving for E and H field components in 3-dimensional space, making it a very powerful EM simulation methodology.

This may be of little use to your project, but for the purposes of clarity I thought I would bring it to your attention.

Dave

#### Dave

Joined Nov 17, 2003
6,969
I tried to give some information on the attachment.

we are using the size of the cell but the distance between two nodes.
Can I also suggest that you (where possible) copy the contents of the Word document to a new post within this thread - many people are warey of opening MS Office documents from on-line forums due to security concerns. Either that or convert the Word document to PDF.

Dave