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Input impedance problem in a nanodipole

Posted Jan 16, 2012, 12:11 p.m. EST RF & Microwave Engineering Version 4.2, Version 4.2a 2 Replies

Gustavo Leite Silvano
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Hello everybody,
I'm trying to simulate a dipole with a voltage source in the middle of them. For that, I'm using a lumped port that is found in the middle of the dipoles, and it have the voltage that I want. But i'm having a very small input impedance. An I doing something wrong?
I found to a model tutorial simulate that use the lumped port, that is the "rf coil", and it's found in the rf module paste.
In the attachment is the geometry and where the lumped port is found, and my simulation too.
I'm using comsol 4.0a as my software.
Thanks
2 Replies Last Post Jan 17, 2012, 9:14 p.m. EST
Edgar Kaiser
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Posted: 1 decade ago Jan 17, 2012, 3:39 a.m. EST
Gustavo,

there are a couple of errors in your model.

- The lumped port must connect the branches of the dipole. You can model it as a rectangle on a workplane on the xy-axis.
- It must be a uniform port, not coaxial, because the dipole is symmetric.
- The dipole branches' boundaries must be set to perfect electrical conductor or an impedance boundary condition. This is a COMSOL restriction. Lumped ports don't work if they are connected to explicit materials.

I would also recommend to use a PML. It will reduce inaccuracies from reflections.

And everybody recommends upgrading to the latest version. 4.0 is said to be buggy.

Cheers
Edgar

Gustavo, there are a couple of errors in your model. - The lumped port must connect the branches of the dipole. You can model it as a rectangle on a workplane on the xy-axis. - It must be a uniform port, not coaxial, because the dipole is symmetric. - The dipole branches' boundaries must be set to perfect electrical conductor or an impedance boundary condition. This is a COMSOL restriction. Lumped ports don't work if they are connected to explicit materials. I would also recommend to use a PML. It will reduce inaccuracies from reflections. And everybody recommends upgrading to the latest version. 4.0 is said to be buggy. Cheers Edgar
Gustavo Leite Silvano
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Posted: 1 decade ago Jan 17, 2012, 9:14 p.m. EST
Thanks for the reply, it worked well in my simulation, but just in MHz. For THz it continues to give me a low port impedance, and is in THz that I have to make my simulation. I'm using a PML condition in my sphere, it finish the resolution, but it give me this warning:

Ill-conditioned preconditioner. Increase factor in error estimate to 2104.222454317748

If you can help me I'll be grateful.
Thanks for the reply, it worked well in my simulation, but just in MHz. For THz it continues to give me a low port impedance, and is in THz that I have to make my simulation. I'm using a PML condition in my sphere, it finish the resolution, but it give me this warning: Ill-conditioned preconditioner. Increase factor in error estimate to 2104.222454317748 If you can help me I'll be grateful.

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