Thirds Rule (FDTD Mesh Grid)

How to use openEMS. Discussion on examples, tutorials etc

Moderator: thorsten

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Joined: Fri 30 Nov 2018, 21:21

Re: Thirds Rule (FDTD Mesh Grid)

Post by FourierTransformer » Mon 14 Jan 2019, 21:43

thorsten wrote:
Mon 14 Jan 2019, 20:57
What I did mostly in those more complex cases I added mesh lines with the third rule while I was implementing the edges at the same time.
Thus I did not use (at all) the DetectEdges but did the meshing "manually". This way you have max. control (e.g. which edges are important and which are just internal) about the meshing too.
Sounds much easier than finding what is inside and what is outside a poly-line! :D

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Re: Thirds Rule (FDTD Mesh Grid)

Post by Hale_812 » Fri 18 Jan 2019, 01:00

AFAIK 1/3 rule has meaning generally in PCB simulations. Probably, ONLY in pcb simulations. So first, there should be an agreement about layers for a tool to work.
There is such tool:
(I didn't try it myself, because it still needs some compiling and installation)

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Re: Thirds Rule (FDTD Mesh Grid)

Post by PaulUK » Mon 28 Jan 2019, 20:49

Does anyone know if there is a disadvantage to use the thirds rule in addition to the mesh lines lying on the edges? Is the accuracy degraded if this is done?

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Re: Thirds Rule (FDTD Mesh Grid)

Post by thorsten » Mon 28 Jan 2019, 21:29

Hi Paul,

if you put a mesh line on the edge, the third-rule is negated and you just have a fine mesh on the edges. Which might be better than the coarse third rule would have been alone, but: Using again the same (dense) resolution for a third-rule only will again increase the accuracy without any disadvantages. Thus it is not a good idea. You need to decide which mesh resolution you want and use it ideally as a third-rule only.
Or in other words, the third rule helps to get away with a coarser mesh, if you put a line on the edge, you just use a dense mesh without that advantage...
I hope I was able to explain properly...


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Re: Thirds Rule (FDTD Mesh Grid)

Post by PaulUK » Mon 28 Jan 2019, 21:43

Thanks Thorsten,

Yes that makes sense. I'm working towards some coupled line couplers. The two varieties im considering are stepped line and the other is a continuously tapering line.

So based on your explaination I would use the thirds rule for the stepped line coupler, where the lines are rectangular. For the continuously tapering line I will have to use a dense mesh since the track will be an undulating curve. Many thanks.


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