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

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Rosalinekavitha

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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?
 

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.
 

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
(coil length), bringing down your SRF and your Q.

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

- - - Updated - - -

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.
 

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

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