Author 
Topic 

Annda
Albania
1 Posts 
Posted  Sep 19 2024 : 00:38:40

Okay, so I have this problem but first of all, I am not so sure I understand correctly how to use the dielectric. So I am trying this example where I have a coaxial cable and the space between the two cylindrical conductors of radii a and c is filled with two homogeneous dielectrics of #949;1 and #949;2. The interface between the two dielectrics is of radius b. I made three .qui file using Matlab and created three cylinders each with length 10m and with radii 2.5, 5m and 7.5m. The code I used in the .lst file is this: * C cylinder3.qui 1 0.000 0.000 0.000 D cylinder4.qui 2 1 0.000 0.000 0.000 0.000 0.000 0.000 C cylinder5.qui 1 0.000 0.000 0.000 To understand if I got this clear the second line shows that I am using a dielectric and the inner side has the permittivity 1 and the outer side of the dielectric has the permittivity 2. Then there are the coordinates in which the second cylinder is placed and the other part says that the point (0.0, 0.0, 0.0) is in the medium with the dielectric medium of 1. When I used the in the second line 1 before 2 I got a warning. This is how I understood the line. The result I get is C12=C21=0.5704nF. Using Gauss law doing this example I got the result C=0.6207nF. Now the problem I seem to have is that when I run this in FasterCap I get this result: Dimension 2 x 2 g1_1 8.07306e010 4.23448e010 g2_1 7.21873e010 1.17276e009. Which means that C12 is not the same as C21.
Anndaa 

Enrico
543 Posts 
Posted  Sep 20 2024 : 11:06:26

Hi Annda,
without the complete input files it is difficult to provide an answer.
For sure there are two points I can comment on:
1) I agree there's too much symmetry. Not sure however from where you get the C12=C21 as in the below matrix there is indeed the asymmetry. If this is coming from FastCap, and not FasterCap, please be careful as FastCap forces symmetry in the Maxwell matrix by averaging the entries and 570pF is almost equal to (432.4pF+721.8pF)/2
2) In your list file, the inner cylinder is specified as in contact with a dielectric with permittivity 1, instead I believe this should be 2
C cylinder3.qui 2 0.000 0.000 0.000 D cylinder4.qui 2 1 0.000 0.000 0.000 0.000 0.000 0.000 C cylinder5.qui 1 0.000 0.000 0.000
Best Regards, Enrico




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