# How to choose optimal wire width of spiral coil to attain high q factor?

1. ## How to choose optimal wire width of spiral coil to attain high q factor?

How to choose optimal wire width of spiral coil to attain high q factor? There are formula to calculate optimal turns n pitch. Is it by trail n error to choose wire width?

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2. ## Re: How to choose optimal wire width of spiral coil to attain high q factor?

Hi,

High Q means low loss.

What are the losses in a coil?
* core loss --> choose a core that is suitable for frequency and flux
* ohmic winding loss --> choose wires with high (overall) wire cross section, and short length if possible
* loss due to proximity effects --> chose useful layer stacking
* loss due to skin effect --> choose HF litz instead of one solid wire
* others?

For each of these effects there are numerous documents, tutorials, application notes, calculations ... in the internet.

Thus: No, it's no "trial and error".

But as with every development: it starts with your requirements.
Frequency, waveform, currents, size, cost, Q factor.....

Klaus

3. ## Re: How to choose optimal wire width of spiral coil to attain high q factor?

Originally Posted by KlausST
Hi,

High Q means low loss.

What are the losses in a coil?
* core loss --> choose a core that is suitable for frequency and flux
* ohmic winding loss --> choose wires with high (overall) wire cross section, and short length if possible
* loss due to proximity effects --> chose useful layer stacking
* loss due to skin effect --> choose HF litz instead of one solid wire
* others?

For each of these effects there are numerous documents, tutorials, application notes, calculations ... in the internet.

Thus: No, it's no "trial and error".

But as with every development: it starts with your requirements.
Frequency, waveform, currents, size, cost, Q factor.....

Klaus
Thanks for your valuable suggestion. Nice n informative.

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4. ## Re: How to choose optimal wire width of spiral coil to attain high q factor?

A problem with spiral inductors is that when you increase
W, looking for Q, you also force the L to grow somewhat
for the same core area. So you won't get the W2/W1
improvement in series R, that you might imagine. You
also increase the stray C (coil bottom area) and self-C

Some foundries have "inductor tool kits" for specific
processes. Absent this, cut and try and keep track.

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5. ## Re: How to choose optimal wire width of spiral coil to attain high q factor?

All major vendors of EM analysis tools - Integrand (EMX), Helic (VeloceRF), Lorentz (PeakView) - provide tools to synthesize an inductor layout to desired characteristics (L, Q, ...).

1 members found this post helpful.

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6. ## Re: How to choose optimal wire width of spiral coil to attain high q factor?

For various values of wire radius, pitch and internal radius (given that fixed outer diameter) have been simulated using HFSS. It shows that least value of Q is 8 n maximum is 467267. Is this maximum value permissible?

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For maximum Q, series resistance should be minimum. For the purpose of minimizing R, i have chosen mimimal wire radius of 0.12mm. But when i increased wire radius to 0.3mm(but decreased turns) i found increased value of Q.

7. ## Re: How to choose optimal wire width of spiral coil to attain high q factor?

This shows that your evaluation of Q is not what others discuss.

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