Menu

Discussion Forum

New Discussion
Filtrer

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Surface impedance in v4.0

Posted 30 mars 2011, 22:42 UTC−4 RF & Microwave Engineering Version 4.3a 6 Replies

dnh37
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi,

In version 3.5a you could set a "surface impedance" in Ohms, this was found by going Physics > boundary settings > Boundary condition: Transition boundary condition > then set the surface impedance in Ohms.

On version 4.0a when I add a transition boundary condition, I have the option to set Electric conductivity. However this is in 1/(Ohm.m), when I want just a surface impedance in Ohms.. how do I achieve this?

Thanks,
6 Replies Last Post 6 nov. 2013, 21:17 UTC−5
dnh37
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 30 mars 2011, 22:57 UTC−4
Please note, I tried setting the following in v4.0a:

Electric conductivity = 6e-5/1e-9
Thickness (found right under "Electric Conductivity" setting) = 1e-9

i.e. I thought by dividing the reciprocal of the surface impedance (reciprocal of surface impedance is, for me, 6e-5 Ohm) by the thickness (some number plucked out of the air, here it is 1 nm) I should return to the correct units for conductivity. By which I mean, I imagined that to get surface impedance it'd multiply the Elec conductivity by the Thickness and take the reciprocal. So I tried to trick it by giving it what it might need in order that in the end, the surface impedance comes out to 1/6e-5.

However, this gives me a strange result and not the same (correct) result as I got in comsol v3.5 when setting Surface Impedance = 1/6e-5, so I presume this is incorrect.
Please note, I tried setting the following in v4.0a: Electric conductivity = 6e-5/1e-9 Thickness (found right under "Electric Conductivity" setting) = 1e-9 i.e. I thought by dividing the reciprocal of the surface impedance (reciprocal of surface impedance is, for me, 6e-5 Ohm) by the thickness (some number plucked out of the air, here it is 1 nm) I should return to the correct units for conductivity. By which I mean, I imagined that to get surface impedance it'd multiply the Elec conductivity by the Thickness and take the reciprocal. So I tried to trick it by giving it what it might need in order that in the end, the surface impedance comes out to 1/6e-5. However, this gives me a strange result and not the same (correct) result as I got in comsol v3.5 when setting Surface Impedance = 1/6e-5, so I presume this is incorrect.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 31 mars 2011, 09:58 UTC−4
Hi

mostly if you have problems to understand the units, check the 2D - 3D dimensions and say to yourself that it applys to the mesh element of infinitesimal size dx*dy*dz. In 2D dz is replaced by 1[m] hence a division by [1/m] of your variable

--
Good luck
Ivar
Hi mostly if you have problems to understand the units, check the 2D - 3D dimensions and say to yourself that it applys to the mesh element of infinitesimal size dx*dy*dz. In 2D dz is replaced by 1[m] hence a division by [1/m] of your variable -- Good luck Ivar
dnh37
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 11 avr. 2011, 17:21 UTC−4
Thanks Ivar. I thought about it a lot and contacted COMSOL. I appreciate your thoughts though.

Here is the correct answer, from COMSOL support email address:

============
The Transition Boundary Condition (TBC) in version 4 is not the same as in
version 3.5a. The TBC in 3.5a is valid for electrically thin layers, i.e.,
d << delta, for thickness d and skin depth delta. The TBC in version 4 is
extended to a more general form that holds also for layers that are not
electrically thin.

If you look at the equations for the TBC in the documentation, you see
that they reduce to the ones used in 3.5a when kd << 1. Unfortunately,
there is an error in the TBC which will not be fixed until version 4.2.
This error makes the TBC wrong for d << delta.

If you just want to use the same TBC as in 3.5a, you can add a surface
current feature on your layer boundary and define the surface current as Js
= 1/Z*tE, where Z is the surface impedance and tE is the tangential
electric field.

If you need more help correcting the TBC equations or setting up a surface
current boundary condition, please get back to me.
============
Thanks Ivar. I thought about it a lot and contacted COMSOL. I appreciate your thoughts though. Here is the correct answer, from COMSOL support email address: ============ The Transition Boundary Condition (TBC) in version 4 is not the same as in version 3.5a. The TBC in 3.5a is valid for electrically thin layers, i.e., d
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 11 avr. 2011, 18:39 UTC−4
Hi

thanks good to know, luckily v4.2 is supposed to be just "around the corner" ;)

--
Good luck
Ivar
Hi thanks good to know, luckily v4.2 is supposed to be just "around the corner" ;) -- Good luck Ivar
Maarten Cauwe
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 27 avr. 2011, 04:11 UTC−4
Is this limitation/bug also valid for the impedance boundary condition? I'm getting some strange results doing mode analysis on a microstrip using IBC, and this could explain what I'm seeing.

Could you ask Comsol support, as it is linked to your ongoing discussion with them?

Thanks,

Maarten.
Is this limitation/bug also valid for the impedance boundary condition? I'm getting some strange results doing mode analysis on a microstrip using IBC, and this could explain what I'm seeing. Could you ask Comsol support, as it is linked to your ongoing discussion with them? Thanks, Maarten.
Yu Sun
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 6 nov. 2013, 21:17 UTC−5
could you please show how to set surface impedance using surface current boundary in detail?
I tried to modify its equation, but failed.
my modified equation in 2D simulation is:

emw.Jsx=sig1*emw.tEx
emw.Jsy=sig1*emw.tEy
emw.Jsz=sig1*emw.Ez
emw.Js0x=0
emw.Js0y=0
emw.Js0z=0


quote:
" If you just want to use the same TBC as in 3.5a, you can add a surface
current feature on your layer boundary and define the surface current as Js
= 1/Z*tE, where Z is the surface impedance and tE is the tangential
electric field."
could you please show how to set surface impedance using surface current boundary in detail? I tried to modify its equation, but failed. my modified equation in 2D simulation is: emw.Jsx=sig1*emw.tEx emw.Jsy=sig1*emw.tEy emw.Jsz=sig1*emw.Ez emw.Js0x=0 emw.Js0y=0 emw.Js0z=0 quote: " If you just want to use the same TBC as in 3.5a, you can add a surface current feature on your layer boundary and define the surface current as Js = 1/Z*tE, where Z is the surface impedance and tE is the tangential electric field."

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content