Re: SSTC CW Coils and Hazards

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

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

For lowish frequencies, the current is more determined by the bulk
resistivity.  Turns out that wrists and ankles take the brunt of hit (lots
of bone, therefore high overall resistivity, and very little semiresistive
muscle, so current tends to flow along blood vessels).  For low frequencies,
eyes and thyroid aren't a big problem like they are for microwaves, where
the bulk absorbtion from radiated fields is the issue.  At low frequencies,
conducted currents are the real problem (i.e. you're standing on the ground
and touching something that acts like a monopole antenna, so you become the
antenna tuning network).

There's also a distance/power density thing... Most of the field for a TC is
right in close to the coil.  A couple meters away, and there's not much
field, and the power density is low.

For TC's a better model is to consider the victim (equipment or person) as
being a resistor in the middle of a capacitor in an LC circuit with
significant circulating power, rather than as an RF absorber in the antenna
far field.

Here's a sample back of the envelope.  Assume the person is a 30 cm diameter
cylinder standing 2 meters away.  To worst case it, assume that the
capacitor represented by topload and ground is a giant disk 6 meters in
diameter suspended over the person's head.  The area under the disk is about
30 square meters. The person has an area of 0.07 square meters, representing
about 0.2% of the total area in the cap.  Ignoring the high epsilon of a
person (they are mostly water after all), one would expect about 1/500th of
the total circulating power to flow through the person. If you had a 2kW CW
coil, that's about 4 watts.   In reality, the capacitor plates aren't that
big, there isn't that much power 2 meters out, etc....

Now compare to standing in the sunlight.  Last week, our incident solar
radiation here in Los Angeles was right around 1000 Watts/square meter,
peak, so that same person would receive about 70 Watts incident on their
head.

Here's where it gets dicey.. assume you're stupid enough to be only, say,
0.5 meters from that 2 kW coil.  And assume that, more realistically, the
field could be modeled as a 1 meter diameter disk capacitor... now you're
intercepting a LOT more of the circulating current.

As with all radiation dose things, distance is your friend.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, August 16, 2003 7:17 AM
Subject: Re: SSTC CW Coils and Hazards


 > Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<dhmccauley-at-spacecatlighting-dot-com>
 >
 >  >  > Low frequency RF emissions have been the subject of debate on this
 > group
 >  >  > for some time now.  It seems the few who have participated in this
 >  >  > discussion (See archives for past discussions) appear not to be too
 >  >  > concerned about the low frequency (100s khz) RF emissions, however I
 >  >  > myself am not convinced.
 >  >
 >  > About what are you not convinced? The analysis of the field strengths?
The
 >  > biological effects?
 >
 > The concerns regarding heating is how deep the heating effect is present
on
 > the human body and what long term effects it may have.
 > For example, if heating was simply localized to the outer layers of skin
is
 > one thing.  But if that same heating went deep within the body (head, eyes
 > in particular), thats
 > an entirely different thing altogether.
 >
 > Dan
 >
 >
 >  >   Although the primary concern for these
 >  >  > frequencies is I*R heating, there must be some hazard associated
with
 > it
 >  >  > especially considering the close proximity one is in when operating
 >  >  > these coils.
 >  >
 >  > Heating and burns ARE the hazard, in my opinion.  Unlike the usual
spark
 > gap
 >  > coil, CW coils (tube and SS) may also tend to make one get into
situations
 >  > where burns can occur. They're quieter and less "scary"
looking/sounding,
 >  > although the hazards are still there, so one might get closer without
 >  > realizing it.
 >  >
 >  >  >
 >  >  > I guess until concrete information regarding this is determined,
common
 >  >  > sense should dictate your actions around these coils.
 >  >
 >  > What concrete information are you looking for? RF measurements or
 >  > bioeffects?  The former is easy (relatively speaking).
 >  >
 >  >
 >  >
 >  >
 >  >
 >
 >