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RE: Interesting Skin Depth Data

Hi all,
The theory of using the resonator frequency may be perhaps 
flawed when doing skin affect analysis.

Based upon my oscilloscope observations the 
frequency of an arc event is in the MHz range.

The entire arc event is over in less that a microsecond (1MHz)
The arc risetimes I've measured are in the order of 
~25nS to ~100nS (~20MHz-5MHz) and some even higher freq.

The resonator serves to provide charge to the Csec.

The discharge of Csec generates the arc freq quite independent 
of the resonator ring up freq, for any one arc event.

At 10-20 MHz arc oscillation, the ~30 MHy of the secondary 
represents good XL isolation from the arc (like a series choke).

At 10-20Mhz the skin affect may well be more of a factor in the human case.

Regards, Dale

-----Original Message-----
From: Tesla List [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, March 09, 2000 6:46 AM
To: tesla-at-pupman-dot-com
Subject: Re: Interesting Skin Depth Data


Original Poster: "Bert Hickman" <bert.hickman-at-aquila-dot-com> 

Tesla List wrote:
> 
> Original Poster: "Ruud de Graaf" <rdegraaf-at-daxis.nl>
> 
> Hi Coilers,
> 
> Maybe this is old news for the real TC die hards, but I found some
interesting
> stuff about skin depth on
> <http://www.misty-dot-com/~don/skin.html>http://www.misty-dot-com/~don/skin.html.
Thank
> you Don Klipstein! I must still read his info carefully, so I can't
comment on
> it right now, but I'am really interested in the general opinion of the list
> members about this paper.
> 
> Ruud de Graaf
> Greetings from lovely and wet Holland

Ruud and all,

The main problem is there's an error in the assumption used in the skin
depth analysis on the website. The approximation used by the web page
author _only_ applies if the diameter of the conductor is much greater
than the skin depth of the conductor at the applied frequency. There's
another problem in that the conductivity of human flesh may be off by an
order of magnitude (probably closer to 400 ohm-cm). 

There may also be a problem with the assumed conductivity of human
flesh. Electrical conductivity various by the type of tissue, ranging
from about 2500 ohm-cm (for fat) down to about 140 ohm-cm (for blood).
The working "average" for human flesh is estimated to be about 400
ohm-cm (John Kraus, "Electromagnetics with Applications, 5th edition,
McGraw-Hill). So... if we compute the skin depth at 175 kHz using web
page value of 40 ohm-cm for human flesh, we find that the skin depth is
about 30 inches. However, using Kraus's figure of 400 ohm-cm, this
climbs to about 95". The point is that, in either case, skin depth is
much larger than the diameter of the tissue (unless you're VERY obese...
:^)), so that the Rac/Rdc approximation shown on the web site cannot be
applied. In reality, there's virtually no skin effect occuring within
your body. 

There's ample evidence that it's actually reduced nerve sensitivity
that's the root cause of reduced perception at higher frequencies. Quite
simply, nerve response IS significantly reduced at higher frequencies,
even at levels that can casue physiological damage with no sensation of
pain! An example of this can be seen in the "influence of Frequency"
section (3.3) of the CERN Safety Instruction web page at:
http://www.cern.ch/CERN/Divisions/TIS/safdoc/IS/is28/is28_en.html#2.4

This is the straight skinny: Inside your body, there's NO skin effect
for discharges from Tesla Coils!  :^)

-- Bert --