Electronic – Calculate resistance of coil/inductor made of PCB traces


This is to be a NFC coil/inductor of 1.1uH according do ST's eDesignSuite tool, with 7 turns.

enter image description here

The drawing above follows these parameters:

enter image description here

ST's tool give inductance value as 1.1uH, but also I need to know the resistance of entire track, in ohms.
I have measured the antenna total lenght on the layout software and it is 418 mm long.

So I have these parameters:

  • 0.25mm width
  • 418mm length
  • 0.5 oz (17.5 micrometers) copper thickness

Then I entered these value of this calculator: https://www.allaboutcircuits.com/tools/trace-resistance-calculator/

And the result given by the site is 1.66 Ohms. Can I trust this value? I need the know correct value of resistance to calculate the components of RF portion of NFC filter and matching circuits.

The board will have 0.5 oz copper thickness, I can guarantee this.

Help please. Regards.

Best Answer

Resistivity of Annealed copper: 1.72x10-8 Ωm

Resistivity is defined as:

\$ \rho = R\cdot \frac{A}{l}\$

therefore \$ R = \frac{\rho \cdot l}{A} \$

your length is 0.418m your area is \$0.25\,\mathrm{mm}\times 17.5\,\mu \mathrm{m}\$

therefore your resistance = \$ \frac{ 1.72\times10^{-8} \,\Omega \mathrm{m} \,\times\, 0.418\, \mathrm{m}}{ 0.25\,\mathrm{mm} \,\times\, 17.5\,\mu \mathrm{m}} = 1.64\,\Omega\$ at 20C

Related Topic