Re: skin effect...Re: Riding t-loads, and other dangerous stuff.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Jim,

I have noted that high voltage (a few kV) at 13.56 MHz tends to burn
straight inward (guess how I know this ;-))  You don't feel the electricity
at all since nerves don't react to RF (due to electrochemical reasons) but
you will feel the burn itself for a long time...

Electricity seems to go toward the least resistance which is inward toward
the juicy parts.  The outer skin is too resistive in comparison.  The field
theory behind the classic skin effect we apply to say gold plated copper,
does not seem to apply at all to the human body...

Cheers,

	Terry


At 07:44 AM 7/4/2001 -0700, you wrote:
> As a Tesla Coil
>> finale, they brought in a faculty member who sat on an insulated platform
>> (shown being erected:
>> http://sprott.physics.wisc.edu/photos/wop/2000/016.JPG) and performed the
>> "flaming fingertips" demo, as well as held a flourescent bulb,
>> etc(http://sprott.physics.wisc.edu/photos/wop/2000/017.JPG).  Recall that
>> this was for a crowd of 8-14y/o kids, primarily.  I don't recall if they
>> used the "skin effect" bulloney (bulogna) or not......
>
>Generally well respected authors have written about the "safety from skin
>effect" in peer reviewed journals.  They should know better, but obviously
>didn't actually do the calculations. Even worse, the reviewers and referees
>should have caught it, but, they didn't.
>
>As someone who works with designing and implementing RF systems on a daily
>basis, skin effect is something that I deal with pretty much continuously.
>However, I'm always working with good conductors, and pretty high
>frequencies (30 MHz on up), and the "skin" really is a "skin" and very thin.
>We agonize about surface oxide layers, how thin can the silver plating of
>carbon fiber waveguides be, the effects on 25 micron wide traces in thick
>film hybrids and PC boards, and stuff like that.  This is probably true of
>most other folks who do this professionally: there just isn't much work on
>hundred kHz signals in resistive media... and certainly true of the average
>academic, except for folks doing subsurface radar or ELF propagation, no
>research is being done on this area (for all intents and purposes, EM
>propagation can be modelled very very well with analytical and numerical
>models, and with low frequencies (long wavelengths), the simulation times
>are very reasonable). For an academic (taking some license.. it's really not
>this bad): No cutting edge research => no cutting edge publications => no
>tenure or academic fame.
>
>The result is that you (as an RF engineer) hear the words skin effect, and
>immediately think in terms of your own experience: current in a thin skin in
>a conductive thing, and never go and check to see if the assumptions are
>really valid.  Add to this a bit of empricism (I tried it and I didn't feel
>a shock (although, it wasn't skin effect, but the low pass nature of your
>nerves)), and the error is cast in concrete...
>
>Perhaps someone should write a peer reviewed journal paper (I don't know
>which journal... perhaps something aimed at Physics teachers...) or even an
>editorial column, about "The fallacy of "skin effect" and human skin"
>
>It just goes to show... even "experts" in a field may not be right... Check
>the math and be sure, especially if it is your own life on the line...
>
>I should point out that an interesting discussion on this came up in an RF
>safety class I took... Folks servicing aircraft on the deck of a carrier
>were getting strange aches and pains in their ankles and wrists...It turns
>out that they were providing a capacitively coupled path for RF (VHF
>frequencies) from the aircraft skin to the deck of the ship, and the wrist
>and ankle are high resistivity (lots of bone, not much water) compared to
>the rest of the body, so significant heating was occurring.  No shocks or
>tingle, etc.
>
>No skin effect there... and the frequency was >30 MHz...
>