¿ªÔÆÌåÓý

ctrl + shift + ? for shortcuts
© 2025 Groups.io
  1. Loopantennas
  2. Topics

ADDRESSING SKIN DEPTH

 

Addressing skin depth:

For copper:

Conductivity:? ¦Ò = 6.30 E +7 S/m
Resistivity:? 1/¦Ò = 1.60 E -8 ¦¸m
Skin Depth: 2.47 E-5 m
Frequency of following analysis:? 7.000 MHz

For the above, refer to:?
? ??????????????????????? and
?
??

From the same reference the resistance due to skin depth can be calculated:?
? ? ?
For my 36-inch diameter loop made of 0.5-in copper tubing (and converting everything to the MKS system) the resistance due only to skin depth comes out to be:
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?? 0.0952 ohms

At 1 MHz, this will be "roughy" 0.1X of that value and at 100 MHz, this will be "roughly" 10X of that value.?? These are only roughly.? But it does indicate some frequency dependance.

However, in all cases from 1 MHz through 100 MHz, the added resistance is considerably greater than the DC or radiation resistance.? So, I'd conclude current in the loop should vary with frequency as a result of skin depth.? In addition, the variation between "DC" and 30 MHz should be only a factor of "roughly" 10.?

Interestingly this goes against the EZNEC analysis presented earlier.? It showed current pretty much constant even up to resonance.?

Guess someone needs to actually measure current as a function of frequency with a constant RF input level.??

I can short my 36-inch tuned loop to do that.? Anyone else want to contribute in this measurement????

Dave - W?LEV
 

The induced voltage in the loop rises proportional with the frequency. The inductive reactance rises also proportional with the frequency. Both compensate each other what, in shortcut mode, results in a constant current versus frequency. The ohmic resistance of the loop including the skin effect is rather small with relation to XL, that that it has little influence on the shortcut current. A loop connected to a real amplifier with Zin = >2 Ohms even more reduces the impact of the loop resistance on the loop current.
?
regards
Fred
 

On Tue, Oct 8, 2024 at 06:32 AM, Fred M wrote:
The ohmic resistance of the loop including the skin effect is rather small with relation to XL, that that it has little influence on the shortcut current.
Agreed.? In the context of a resistance calculation at frequency, skin effect cannot be ignored.? But, as you say, the inductive reactance still defines the overall loop impedance....at least for practical antenna sizes and materials.

1 - 3 of 3