Coplanar waveguides (for example picture look here) are often used in research to create a local in-plane magnetic field. Now if compared to a planar microcoil like this,

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driven by a AC voltage in the 1-5 GHz range, what would be the major limitations or differences when comparing those 2 techniques looking at the output/spectrum/power?

  • the cpw has probably the advantage to create a narrow band ac field with high q-factor and can be simply tuned by the GHz-Emitter over the whole 1-5 GHz range?
  • what will the AC magnetic field spectrum of the microcoil look like? Symmetrical/asymmetrical and broad around a peak at the driving frequency of the AC voltage source? But compared to CPW not temporally constant and underlying light resonance excitation? Is 1-5 GHz too high driving frequency to transport here energy at all to create a AC field?
  • what the difference in field strength (nT, mT, Tesla) that can be reached with those 2 techniques? Consider that both systems have a size in the the low micron meter range (below 100 micron lateral size)
  • the inductance of the microcoil will vary strongly over the 1-5 GHz range and due heating of the coil change additionally?

Where am I wrong/right. What did I miss?

  • \$\begingroup\$ To answer these questions you might have to simulate them in a 3D EM program like CST, COMSOL, HFSS, or Sonnet..... Sonnet is free \$\endgroup\$
    – hassan789
    Feb 25, 2013 at 14:31
  • \$\begingroup\$ @hassan789 shouldn't there be some general rule of thumbs at least for the spectrum, bandwidth, resonance? \$\endgroup\$
    – James Last
    Feb 26, 2013 at 13:49

1 Answer 1


You're going to see a lot of differences between a standard cpw and a planar microcoil. The bandwidth and Q will make tuning for your transmission frequency difficult, especially over 1 GHz to 5 GHz.

Field spectrum? Do you mean radiation pattern at different frequencies?

For higher power you'll probably need several in a phased array. If you gave us a better idea of what you are doing with it, we could help. You mention heat being a problem, is this an MRI application? But yes, inductance will vary strongly over frequency and heat.


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