Electronic – How significant are hysteresis losses in iron wires with RF currents


I understand that iron isn't a great choice of conductor for RF currents, as a wire dipole antenna for example. I understand there are several reasons, but I'm wondering specifically about one: hysteresis losses. How significant are hysteresis losses when an iron wire is a conductor, not part of a magnetic circuit? Can they be calculated? Are there any empirical data?

Best Answer

I have doubts that hysterisis loss will count for much because most of the magnetic flux lines are around/outside the conductor and barely cutting through it. Yes, there is greater flux density up close to the wire but this is also the mechanism that makes skin conductivity (aka skin effect\$^1\$) so bad in iron at any appreciable frequency and, because current travels at the surface of the iron, the flux lines will probably never be totally contained within the iron meaning there is a significant air gap and B will be low hence hysterisis loss will also be low.

\$^1\$ Quote from wiki -

Skin depth also varies as the inverse square root of the permeability of the conductor. In the case of iron, its conductivity is about 1/7 that of copper. However being ferromagnetic its permeability is about 10,000 times greater. This reduces the skin depth for iron to about 1/38 that of copper, about 220 micrometres at 60 Hz. Iron wire is thus useless for A.C. power lines. The skin effect also reduces the effective thickness of laminations in power transformers, increasing their losses. Iron rods work well for direct-current (DC) welding but it is impossible to use them at frequencies much higher than 60 Hz. At a few kilohertz, the welding rod will glow red hot as current flows through the greatly increased A.C. resistance resulting from the skin effect, with relatively little power remaining for the arc itself. Only non-magnetic rods can be used for high-frequency welding.