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RE: Interesting Skin Depth Data

Hi Dale,

At 04:17 PM 03/10/2000 -0800, "Dale Hall" <Dale.Hall-at-trw-dot-com> wrote:
>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.

This is, of course, a top terminal arc to a good ground.

>
>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.

If you know the terminal capacitance, you can figure out the current in the
discharge spike.  However, it is probably a damped high frequency (maybe
GHz) pulse so it gets messy.  In general, the top terminal may be charged
to a few joules of energy.  The question is, during and arc, where does
that energy get dissipated.  If all the energy is dissipated in the body
that is on thing.  If it gets dissipated elsewhere, that is another.  There
may be a number of variables.  Of course, we don't want three people to die
finding each one!!  Not a good area for "trial and error" study ;-))

DC currents of a few amps flowing through the body are obviously in the far
lethal area.  However, those currents typically kill by stopping the heart
and interfering with the nervous system.  Since RF currents do not
interfere with the nervous system in the same way, the same RMS current
levels don't instantly kill.  However, that is far from saying they are
safe.  We only have the reports from the practitioners of long term
exposure to go on, but their reports are not surprising.  They live to try
it another day but they are obviously getting a little "cooked" internally...

Of course people have been struck by relatively large Tesla coils.  They
get burns at the point of contact and often get "quite a jolt".  The burns
are obvious point contact resistance heat dissipation.  The shock is due to
the large net DC current from discharging the terminal capacitance often at
120 PBS until they get out of it.

Of course, the people with really high power coils have vast experience and
they also are darn sure not to get hit by the coil.  Hint, hint... ;-))

>
>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.

I was thinking more along the terms or the few folks who sit on their coils
while they are running.  In that case, they are just resistors in the
current path to the larger capacitance around them and the top of the coil.
 However, their bodies may have a fairly low resistance compared to the arc
so the power dissipation in "them" may be fairly limited.

Their reports of muscle aches, head aches, and other obvious indications of
internal current flow and it's effects is well known.  Apparently, after
even decades of exposure, these people have not reported any "long term"
bad health effects.  Good news for the rest of us standing 15 feet away
;-))  However, they also know when to stop...

Of course, there are a number of other obvious problems with getting too
close to Tesla coils like getting connected up with the primary circuit
which has killed two people...  There are a few unknown things that could
be studied regarding people interacting with Tesla coils.  However, there
are great risks involved in such "testing" that typically cannot be guarded
against in our amateur setups.  Ham and other large chunks of cooking meat
may be a suitable substitute for live humans.  It could also be
instrumented inside and out with relative ease.  Perhaps something as
simple as neon bulbs would be a good indicator.  A fun science fair type of
project to show how the RF currents flow inside of meat and then have a
picture of one of those people sitting on a coil in the background ;-)))
Better yet, cook the meat and then...

To sum it all up.  People that are not experts with Tesla coils should
never "play" with the output arcs because they don't know enough about it.
People that are experts should not play with arcs because they know too
much about it...

Cheers,

	Terry

>
>Regards, Dale
>