## Lumped RC element simulation

How to use openEMS. Discussion on examples, tutorials etc

Moderator: thorsten

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

### Lumped RC element simulation

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: 1477
Joined: Mon 27 Jun 2011, 12:26

### Re: Lumped RC element simulation

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

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
Contact:

### Re: Lumped RC element simulation

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.

br,
Sebastian

thorsten
Posts: 1477
Joined: Mon 27 Jun 2011, 12:26

### Re: Lumped RC element simulation

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
Posts: 114
Joined: Mon 27 Jun 2011, 12:36
Contact:

### Re: Lumped RC element simulation

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
Posts: 114
Joined: Mon 27 Jun 2011, 12:36
Contact:

### Re: Lumped RC element simulation

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.

hannesko
Posts: 9
Joined: Wed 03 Jun 2020, 10:36

### Re: Lumped RC element simulation

sebastian wrote:
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.
Hi Thorsten & Sebastian! A few years later ( ): I would be interested in implementing a lumped inductance! Reason: I am quite convinced that openEMS is a very suitable tool for simulating field-to-line coupling of lightning electromagnetic fields to power transmission lines. All kinds of lumped elements are important to have at hand in these scenarios. I would certainly need a crash course or at least some help, because I have no idea where I would have to start , but this "how to create an extension for the simulator core." sounds like what I would need. At least I am familiar with the book Taflove 3rd ed & some simple/basic FDTD coding. Anyone?