Re: Contrary current flow within a radiator

Ian White GM3SEK wrote:
Jim Kelley wrote:
Dave wrote:
"Art Unwin" <ArthurUnwin@xxxxxxxxx> wrote in message news:e83c4e3a-8327-48df-b439-cb4bbc7d3f46@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>>..


( I am assuming that skin depthg is not limitless.)
of course it is limitless, it is an exponential function so it never goes to zero. the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, still a significant current.

The plots at the link Frank provided show current going rather abruptly to zero - even negative ("contrary"?) in some cases. I wouldn't presume to know whether it is modeled correctly.


Decrease of RF current with depth below the surface of a conductor is only a true exponential if the available conductor depth is infinite. In the modeled situations where there is 'competition' from a skin effect on the opposite side of the conductor, the solution is a Bessel function which does pass through zero and reverse direction at certain depths.

In other words, the model is behaving as expected.

Programs such as NEC and Maxwell are not released until they have gone through a very detailed process of checking and validation. The first step is to check against special cases that can be independently solved by analytical methods (in other words, pure math). The work isn't complete until all the results agree within close margins, and the reasons for any differences are fully understood.

By the time we amateurs come to hear about these programs, they have already been thoroughly validated by developers and professional users. That doesn't make them immune from further criticism... but only by people who have done the work to earn that right.

Hi Ian,

Please know that my comment was never intended as a slight of anyone's work. I simply don't presume to know anything about it other than to observe that the citation appears to contradict the assertion that skin depth is limitless and exponential in real conductors.

73, ac6xg
.

Relevant Pages

  • Re: Contrary current flow within a radiator
    ... it is an exponential function so it never goes to zero. ... the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, ... The plots at the link Frank provided show current going rather abruptly to zero - even negative in some cases. ... Decrease of RF current with depth below the surface of a conductor is only a true exponential if the available conductor depth is infinite. ...
    (rec.radio.amateur.antenna)
  • Re: Contrary current flow within a radiator
    ... goes to zero. ... Decrease of RF current with depth below the surface of a conductor is ... already been thoroughly validated by developers and professional users. ... Present thinking, I thought, suggest that the skin depth is quite thin ...
    (rec.radio.amateur.antenna)
  • Re: Contrary current flow within a radiator
    ... of course it is limitless, it is an exponential function so it never goes to zero. ... the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, ...
    (rec.radio.amateur.antenna)
  • Re: Contrary current flow within a radiator
    ... of course it is limitless, it is an exponential function so it never goes to zero. ... the so called 'skin depth' is only the point where the current has dropped to 1/e or about 37% of the surface value, ... The plots at the link Frank provided show current going rather abruptly to zero - even negative in some cases. ...
    (rec.radio.amateur.antenna)
  • Re: Zero Ohms = Mathematically Incorrect
    ... division by zero can usually be solved as a limit. ... Let's say, however, you measure the voltage across one half the conductor. ... The key to understanding this is that the zero ohms is not the entire circuit resistance ... ... Strictly speaking, current doesn't flow through it, charge does. ...
    (sci.electronics.basics)
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