Discussion Forum

Posted: 8 years ago Mar 1, 2017, 8:11 p.m. EST

1. I suggest you post a drawing of your geometry, preferably including labeling the parts, and showing it from multiple angles. Your geometry is not obvious from your description. A tiny line segment isolated in space (??) is unlikely to actually be of any interest to you. 2. The free-space RF wavelength at 3 GHz is about 10cm. This is five orders of magnitude larger than the length of your "10 micron long" wire. If your overall system is going to act like an antenna, you will need to model a lot more of it than just this one extremely tiny wire segment, since most of the radiation will be coming from the other parts. But if you want to know the contribution to the overall magnetic field near this wire, you can find that without using Comsol, using the law of Biot-Savart. See https://en.wikipedia.org/wiki/Biot%E2%80%93Savart_law . You see, that applies locally to your itty-bitty wire, since it is so very, very small compared to a wavelength, such that the magnetic field near it is nearly the same as from an equivalent DC current. 3. Regarding impedance, I can only assume that you intend to connect your "antenna" to some kind of transmission line. You are going to have to model more or less everything you connect to the end of the transmission line, if you want to compute the impedance correctly. Surely, that must include more than this extremely-tiny 10 micron long wire, right? Or... are you simply shorting out the end of a very thin (e.g., 10 micron wide) transmission line, and you are wondering how to compute any radiation from that shorted end?? By the way, to a first approximation, your extremely short wire has an impedance which is real-valued and equal to zero Ohms. (I presume you want to know more than just that, however.) 4. Finally, by "MW," you mean "microwave," right? MW (all capitals) is also used for "megawatt." You weren't planning on pumping a million watts into this tiny wire, were you?

Posted: 8 years ago Mar 2, 2017, 11:01 a.m. EST

Hello, I hope you are having a good day. I have included two images of the geometry I would like to simulate. I would like to know the field distribution inside the ring and as a function of z. I am worried about coupling between the input and exit ports of the structure. Also if I could get the impedance of the ring at 3 GHZ so I can make some compensating structures that would also be appreciated. Ultimately, I would like to simulate many structures and then optimize their parameters given certain conditions. Any help would be appreciated.

Attachments:

• render annotated 1.png
• render annotated 2.png

Posted: 8 years ago Mar 3, 2017, 10:23 a.m. EST

I suggest you analyze that structure using the AC/DC module, since it is small on an RF scale. You can do a sanity check on your results using analytic expressions for a simple current ring. See http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/curloo.html , among others.