I see a lot of comments around the web about the thickness of materials
used in making transmitting loop antennas. Many of them seem to
indicate the writer does not truly understand the impact the skin effect
has on resistance at RF frequencies. Here is an example.

"At 7 MHz, the skin depth is approximately 0.025 mm. 0.1mm-thick
flashing is only 4 skin depths thick, while usually 5 skin depths is
recommended for near perfect conduction."

This comment is correct in the sense that 5 skin depths will get you
close to the conduction you can achieve with a solid conductor of the
same diameter, but it seems to be missing the point that by adding skin
depths you are not fully utilizing the material conductivity.

Skin effect doesn't set a minimum thickness of the material to use. It
reduces the utility of added thickness. In all cases you will be better
off using less thick material and making the diameter larger until you
reach the point where the material is just not thick enough to support
itself.

At 0.1 mm thickness, the above writer may well be at the point where the
material is getting too thin to be self supporting. In the prior
paragraph he explains that 0.2 mm thick copper is too hard to work with
to roll into a tube. That is less than 32 gauge wire! 0.1 mm is 38
gauge wire. But at least his results won't be limited by the skin effect.

--

Rick

On 11/7/2015 10:20 AM, rickman wrote:
I see a lot of comments around the web about the thickness of materials
used in making transmitting loop antennas. Many of them seem to
indicate the writer does not truly understand the impact the skin effect
has on resistance at RF frequencies. Here is an example.

"At 7 MHz, the skin depth is approximately 0.025 mm. 0.1mm-thick
flashing is only 4 skin depths thick, while usually 5 skin depths is
recommended for near perfect conduction."

This comment is correct in the sense that 5 skin depths will get you
close to the conduction you can achieve with a solid conductor of the
same diameter, but it seems to be missing the point that by adding skin
depths you are not fully utilizing the material conductivity.

Skin effect doesn't set a minimum thickness of the material to use. It
reduces the utility of added thickness. In all cases you will be better
off using less thick material and making the diameter larger until you
reach the point where the material is just not thick enough to support
itself.

At 0.1 mm thickness, the above writer may well be at the point where the
material is getting too thin to be self supporting. In the prior
paragraph he explains that 0.2 mm thick copper is too hard to work with
to roll into a tube. That is less than 32 gauge wire! 0.1 mm is 38
gauge wire. But at least his results won't be limited by the skin effect.



http://owenduffy.net/calc/SkinDepth.htm