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Re: RF biological hazards? (fwd)
---------- Forwarded message ----------
Date: Mon, 04 May 1998 18:58:21 -0700
From: Jim Lux <jimlux-at-earthlink-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: RF biological hazards? (fwd)
Tesla List wrote:
>
> ---------- Forwarded message ----------
> Date: Tue, 5 May 1998 10:11:49 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: RF biological hazards? (fwd)
>
> I too am inclined to think that skin effect plays little part in not
> feeling TC discharges. In fact, one can often feel the gap firing rate
> modulation and the shocks can be considerable in a powerful coil.
> Skin effect is heavily dependent on conductivity. The higher the
> conductivity, the closer the bulk of the current reside near the
> surface. I would imagine that humans do not stack up too well against
> copper in the conductivity stakes.
>
> Malcolm
Some interesting info from the Jan 1980 issue of the IEEE Proceedings
(issue devoted to biological effects of EM energy):
K.H.Mild, in "occupational exposure to RF EM fields", says that it takes
an E field of about 1000 V/m to light a fluorescent tube and that at
around 200 V/m, it stops glowing. He also makes the point, very
important for Tesla coils, that in the near field (which you most
certainly are with a wavelength of hundreds of meters), the magnetic
field contributes a significant fraction(if not the majority) of the
absorbed RF energy. I'm going to do some calculations, assuming the TC
is a "short" dipole (i.e. it is much less than a half wavelength long).
The ANSI standard (C95.1-1974) (for 10-300 MHz) is 200 V/meter and
0.5A/m (both RMS). In the far field 300 V/meter = 250 W/m^2 = 0.8 A/m.
Most of Mild's research was involved with wood welders, plastic
sealers and diathermy, all of which operate in the ISM bands at 13.56,
27.12, and 40.68 MHz. Mild reports that an induction furnace with 10-20
cm coils at 10.3 kHz connected to a 250 kVA transformer produced fields
of 25 milliTesla, which corresponds to 20 kA/m
Another article, by Grissett, "Biological effects of electric and
magnetic fields associated with ELF communications systems", which from
their frequency, may be more relevant to Tesla coiling, although they
are concerned more with chronic effects from fairly low fields: 0.02 mT
and 0.07 V/m.
Finally, there is a paper by Schwan and Foster, which has a whole raft
of dielectric constant (around 80, mostly because of the water) and
resistivity data for various kinds of tissue and frequencies. Specific
resistivities seem to be in the 200-600 ohm-cm range for the hundreds of
kHz range.