Re: Giving credit to Tesla (fwd)

To: tesla-at-pupman-dot-com
Subject: Re: Giving credit to Tesla (fwd)
From: Tesla List <mod1-at-pupman-dot-com>
Date: Fri, 24 Apr 1998 21:14:04 -0600 (MDT)
Approved: mod1-at-pupman-dot-com


---------- Forwarded message ----------
Date: Fri, 24 Apr 1998 14:22:25 -0700
From: Jim Lux <jimlux-at-earthlink-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Giving credit to Tesla (fwd)

> 
> The skin effect is painless because of the body's(nerve endings) slow
> response rate to the high frequency voltages from the Tesla Coil, what
> frequency is the upper limit to the responsiveness of the nerves?  Is it
> 700 Hz?

Not quite true.

The skin effect has nothing to do with your integumentary system (i.e. your
skin), but with the fact that ac currents tend not to propagate below the
surface of a conductor. The higher the conductivity, the higher the
permeability, and the higher the frequency, the less penetration into the
interior of the conductor. At RF frequencies, say above 100 kHz, the
pentration depth is quite small (thousandths of an inch in good
conductors). So, if you have an RF current flowing through your body, it is
mostly on the surface (the depth is a bit more, because you aren't all that
great a conductor, compared to copper or other metals, although, the more
you sweat, the better the surface conductivity is). The nerve endings are
below the surface, where the RF current isn't, so they don't get
stimulated.


As to the frequency response of nerves, it depends on the kind of nerve.
Your muscles can respond to nerve stimulations as short as a millisecond,
although you may not feel it, except from the actual muscle motion. I used
to do some testing where we would put a 5 mA or so pulse through the radial
nerve (in your arm) with surface electrodes. We would adjust the current to
the point where the thumb would just twitch.

You can see a very short flash of light or hear a very short sound impulse,
although that is partly due to the low pass filtering effect of the
transducer (your retina or the cochlea) stretching the impulse out.  

I would say, though, that a basic frequency response of 1 kHz is probably a
reasonable guess.

A final note: It is possible to get a nasty RF burn, even with the skin
effect. If you get the power density high enough, even in the surface
layer, it will get hot, and you will get burned. Also, if you get hit by a
spark, the heat from the ionized gas at 10,000 deg K (or there abouts) will
burn, as well. (and hurt like the dickens).