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Simulating a Planar Spiral in HFSS

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Catalyst

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free space loss hfss

Hello,

I am attempting to simulate a planar spiral made out of copper which has been etched on plastic substrate (no oxide) to help predict it's inductance and resistance but to also see the magnetic field around the structure if possible. I would like to know if anyone can help steer me in the right direction into how to go about this using HFSS.

The main features of the spiral are:

* Frequency = 30 MHz
* Number of Turns = 5
*Out spiral dimensions = 4cm by 4cm
* Track width = 1000 microns
* Space between turns = 500 microns
* Copper thickness = 10 microns
* Plastic substrate thickness = 100 microns


I need to know what are the main elements I would need to include in the simulation such as the type of excitation or source,, where to apply the source, radiation boundaries etc

Does anyone have an idea?

Kind Regards

Cat
 

rfmw

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I've done some planar spirals in HFSS. You'll probably have to use lumped port, as in the attached picture. Due to the very low frequency I would expect a huge rad boundary around your tiny antenna...

EDIT: use many dummy objects around the antenna to improve the mesh.
 

Catalyst

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Does the radiation box boundary have to be 1/4 wavelength away from the structure?

Do i assign a lumped port to both terminals, both set to 50 Ohm Impedance?
 

rfmw

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Yes, rad boundary should be placed 1/4 lambda away. However what is your application, because you have electrically very small antenna, therefore very low radiation resistance (efficiency).

Draw a rectangle between the spirals and attach a lumped port on it...
 

Catalyst

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But theres only one spiral ? :s
 

cuongtran

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A lot of simu has the excitation set-up likes the of rfmw, but I wonder why don't you choose the more real way, that means for example a stripline to connect the contact head with a waveport..
 

rfmw

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Oh, sorry Catalyst, I now realize you have a spiral as an inductor, not as a "spiral antenna", which I simulated. So you have one wire at the middle of spiral and the other one at the outer edge?

EDIT: a picture of your structure would be nice
 

Catalyst

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Oh Sorry, here is an example, just a plane inductor....

I know its the most basic design :) .... any ideas?
 

maxwellian

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What are you using for a dielectric constant for plastic?

Is there a backside metal on the plastic?

--Max
 

Catalyst

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Just using plastic, no metal on other side, am not sure about the dielectric constant yet, I'm working on it, just want the spiral set up properly first so i can have confidence in it.

Can anyone help me get started off with setting the excitations properly?
 

maxwellian

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I'm not trying to create a commercial here, but this example was really easy to simulate in Sonnet Lite.

Sonnet Lite needs about 14 MB of RAM to run, and finished in about 1 minute on my laptop. It reports that your spiral is expected to have an inductance of 1630 nH at 30 MHz, about 1535 nH at 1 MHz and about 2100 nH at around 60 MHz.

The software is free from Sonnet's web site, so it doesn't cost you anything.

I know you want to simulate this in HFSS, so maybe this gives you another value to compare your HFSS results to. If you want to try it in Sonnet, let me know your email address and I can send you the Sonnet Lite file to use it for yourself.

--Max
 

Catalyst

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do you have a guide on how to use sonnet light to model and extract inductance, resistance and self resonant frequency?

Regards
 

maxwellian

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Catalyst said:
do you have a guide on how to use sonnet light to model and extract inductance, resistance and self resonant frequency?

Regards
Yes, I saw one on Sonnet's User Forum. It looks like one of the Sonnet people put it up there. You can find it here:

http://www.sonnetlist.com/phpBB2/viewtopic.php?t=103

The Sonnet User Forum is here:

http://www.sonnetlist.com/phpBB2/viewforum.php?f=1

They have a Spiral Inductor Guide that shows how to make inductors and get outputs like inductance, Q, loss and so on.

Their guide shows how to build inductors over a ground plane. It's easier to make ports in this case. However, for your inductor, I did things just a little different. I brought a short line from the tap inside the spiral to the outside, and connected it to the outside turn tap to make a continuous connection. Then I sliced the metal trace at the outside, and put what Sonnet calls an ungrounded internal port on a break on the slice, putting it in series with the entire loop. That gave me a 1-port system.

I also put a big layer of air above and below the plastic (which I arbitrarily assigned a dielectric constant of 4; I don't know what your real value should be). Last, I set the top and bottom of the Sonnet Lite box to free space.

I can send you my project file if you want it; just give me your email address.

--Max
 

Catalyst

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That is a big help max, cheers.


I would still like to sort out a good HFSS simulation setup though, it is starting to bug me. Would be nice to compare results with Sonnet Lite.

Does anyone have more advice for a HFSS simulation of a planar spiral inductor (not antenna)?


Kind Regards

Cat
 

Catalyst

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I've been trying Sonnet light to simulate a few basic spiral antennas. I always obtain a resistance value which is around 0.2 Ohms more than it should be.

No matter what I change in my design it always seems to be 0.2 Ohms too high. Does anyone know what is going on and how I can rectify this? or is this a normal situation with Sonnet?

Cheers

Cat
 

Joe_User

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What is the nominal impedance? I guess if it is supposed to be 0.3 ohms, a 0.2 ohm error is pretty high. But if it is supposed to be 50 ohms, a 0.2 ohm error is pretty small, and I would be pretty happy with a 0.2 ohm error.

If you are working with verys small impedances, than a 0.2 ohm error could be pretty important. In that case, if it were me, I would probably send my file to the Sonnet guys and ask them for help. There is even a menu item that lets you do this. Select File -> Send to Sonnet from the project editor.

Joe
 

iceman13

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there is no usefull position if the lumped port paralel with project

ı think use sweep along line 0.035 mm suitable .make project 3D and turn lumped port 90 degree !
 

kamal14

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I've done some planar spirals in HFSS. You'll probably have to use lumped port, as in the attached picture. Due to the very low frequency I would expect a huge rad boundary around your tiny antenna...

EDIT: use many dummy objects around the antenna to improve the mesh.


I am new in HFSS. I need to design a planar spiral antenna. Can you pls help me how can I design it? My email address is kamal14_kuet@yahoo.com.
 

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