Lumped RC element simulation

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antpol
Posts: 9
Joined: Tue 13 Nov 2012, 14:11

Lumped RC element simulation

Post by antpol » Sun 02 Dec 2012, 02:00

Hi all again.
I try to understand results of LumpedElement.m simulation.
Could you Thorsten or Sebastian answer my questions?
1a. How did you deduce (calculate) a value of the inductance parasitic_L = 63e-9?
I set Lumped.R to 0, next I ran simulation and tried to calculate parasitic_L based on figure 2 (resistance vs. frequency), but I didn't get 63e-9 henries :?
1b. Why R{Z} blue curve is not equal to zero on whole frequency axis? Though Lumped.R=0.
1c. Why I{Z} red curve is < 0 while Lumped.C is short circuit by setting Lumped.R=0? Though only parasitic_L reactance should be there that have only positive values!?
2. What does it exactly mean that Lumped.R=1000 and Lumped.C=10e-12 ? At what frequency? Why simulation gives resistance about 117 ohms for 0MHz if Lumped.R is set to 1000?
3. Why did you set f_excite = 300e6? What determines this value? I wonder whether it depends on R*C = 10 ns or on lumped element size (8x8x8 mm^3).
4. Will be results of LumpedElement.m simulation still valid if I change Lumped.C to 10e-9 or much less 10e-6? Do I need to make any changes in the m.file?

If my questions are too basic, please bear with me.

thorsten
Posts: 1468
Joined: Mon 27 Jun 2011, 12:26

Re: Lumped RC element simulation

Post by thorsten » Sun 02 Dec 2012, 14:33

Hi,
1a. How did you deduce (calculate) a value of the inductance parasitic_L = 63e-9?
You need to set R and C to 0 and also parasitic_L = 0. Thereby you get the pure inductance of the feeding wire.
If you keep parasitic_L at 63nH you compensate the wire-inductance and should get nearly zero for L or C...
1b. Why R{Z} blue curve is not equal to zero on whole frequency axis? Though Lumped.R=0.
1c. Why I{Z} red curve is < 0 while Lumped.C is short circuit by setting Lumped.R=0? Though only parasitic_L reactance should be there that have only positive values!?
FDTD is a numerical method, you will always get small errors... the real part around +/-0.01 Ohms looks ok to me...

To 2-4:
The lumped element is kind of like a SMD capacitor with losses. That means it is a C with parallel R (or G).
Have a look at how I calculated the analytic Z.

A larger C should work, give it a try...

regards

antpol
Posts: 9
Joined: Tue 13 Nov 2012, 14:11

Re: Lumped RC element simulation

Post by antpol » Thu 06 Dec 2012, 00:07

Thanks. It helps me a lot.
Now I need the ideal inductance in my model, without any serial or parallel resistance.
Simulations, which I carried out, shows that OpenEMS allows only L | | R or C | | R. Am I right?
How do I get the ideal inductance? Using a very large R in the L | | R model is not a solution for me.

sebastian
Posts: 114
Joined: Mon 27 Jun 2011, 12:36
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Re: Lumped RC element simulation

Post by sebastian » Thu 06 Dec 2012, 20:42

If you run

Code: Select all

help AddLumpedElement
you'll see that this function accepts tho optional argumguments 'R', 'L' and 'C'. A "pure" inductance is therefor possible.
Be careful with the word ideal. An FDTD will never report ideal results, the truncation of the floating point numbers will limit the archivable dynamic of the simulation. Furthermore the theory neglects many physical effects, which are modeled by FDTD algorithm.

Was this your question?

br,
Sebastian

thorsten
Posts: 1468
Joined: Mon 27 Jun 2011, 12:26

Re: Lumped RC element simulation

Post by thorsten » Thu 06 Dec 2012, 21:20

Hi,
A "pure" inductance is therefor possible.
Unfortunately I have to say that an inductance is not yet implemented at all as a lumped element. Neither in series or in shunt. After all you can't buy a lumped inductance SMD chip as well... (I think?)
But that is something I may have to implement at some point. But it is not as easy and straight forward as a C or R.
So for now, only C or/and R is possible... Sorry...

regards
Thorsten

sebastian
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Re: Lumped RC element simulation

Post by sebastian » Thu 06 Dec 2012, 22:50

you certainly can: http://de.farnell.com/jsp/search/browse ... allpartial; choose from about 13000 components.

What to fix first: documentation or your code, Thorsten ;)

Sebastian

sebastian
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Re: Lumped RC element simulation

Post by sebastian » Thu 06 Dec 2012, 23:03

Taflove 3rd ed. page 711: we need one additional variable to hold the sum of the E-field (voltage in our implementation). Looks like the extension concept would be ideal for the implementation. Anyone?
Edit: this may also serve as a tutorial: how to create an extension for the simulator core.

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