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Re: Displacement Current Revisited



Tesla List wrote:

> Original Poster: Ed Phillips <evp-at-pacbell-dot-net>
>         This is a question for Richard Hull.  (This appears to be one of the
> reasons for his interest in electrometers.)  I have never done any
> instrumentation, but have often noticed the very significant residual
> charge left in the varnish over the secondary.  Also have noticed severe
> shocks when holding a metal object (screwdriver, etc.) in my hand and
> bring said object close enough to the secondary terminal that sparks
> occasionally jump to it.  I believe that this is a rectification-related
> phenomenon, but have done no measurements and haven't seen the results
> of any.
>

I haven't really followed this thread but I can add some hard facts to this
aspect.  You are correct that rectification is involved.  Most any oxide,
particularly aluminum oxide will rectify.

A few years ago I was hired by plaintiff's attorneys as an expert witness to
investigate something similar.  A urologist had been blinded by a defective
resectoscope (fiber-optic device used to do bladder and urinary tract surgery).
The device consisted of two major parts: the fiber optic telescope and the
resection unit.  The latter unit is simply a small stainless loop connected to
an electrosurgical ("electrosurg") unit.  A polyp is hooked by the loop and a
pedal pushed whereupon an RF current cuts the polyp.  The electrosurg unit is
remarkably like a small solid-state tesla coil, making about 600 watts of RF in
the low hundreds of kilohertz and at perhaps 5000 volts.  It provides either a
pure carrier (surgery) or 60 hz AM modulated (coagulation).

The company that made the scope made a louse resection unit and so they had a
(literally) basement machinist make an anodized aluminum adapter to fit their
scope to another brand of resector.  During surgery, this assembly, about the
size of a 1st grade pencil, is inserted through the penis (OUCH!) into the
bladder.  The bladder is  irrigated with saline.  The saline is returned
through
another tube in the scope.  The aluminum adapter was defective and allowed
irrigation solution to run down the shaft of the scope.  The surgeon was
cutting
a polyp from the top of the bladder and so was looking up through the scope.
Fluid trickled down the shaft and puddled in his eye.  When he keyed the
electrosurg unit, the RF flowed down the stream, into his eye,
skin-effect-followed the eyeball until it hit the optic nerve whereupon it blew
the nerve apart.  Instant blindness.

In the lawsuit, the blinded Dr testified that when the RF hit him he jumped and
stumbled backward, testimony confirmed by nurses.  The company's defense was
that A) RF won't shock (true) and b) the optic nerve has no feeling (true), c)
their electrosurg unit was free of DC (true) and thus there was no stimulation
to cause him to jump backward.  My job was to determine what made him jump.

I determined that when the irrigation fluid flowed across the anodized
aluminum,
it formed a poor aluminum oxide rectifier.  When the adapter in question was
placed in contact with a container of saline and RF applied, several hundred
volts of DC appeared.  I demonstrated this in court and was not challenged in
any serious manner by the defense's experts.  (Through amazingly massive
incompetence, including not cross-examining the other side's expert witness,
the
Doc's lawyers lost the case for him.)

So yes, rectification capable of generating enough DC to shock is certainly
possible in a strong RF field.  Surely enough to diddle with a compass needle
(I
believe that's what this is about, isn't it?)

Something possibly related is what I occasionally see in my shop when
bombarding
neon (passing high current from a pole pig through the newly made unit to heat
and outgas it).  If one electrode heats faster than the other, the one to get
red hot first can act like a diode tube filament.  The neon tube then acts like
a diode.  This is apparent from the 60hz flicker (as opposed to 120 hz) from
the
tube and the unhappy growl coming from the pig when its core gets saturated
from
DC.  I suppose this effect could be present in a static gap on a tesla coil
too.  Anyone observed it?

John

--
John De Armond
johngd-at-bellsouth-dot-net
Neon John's Custom Neon
"Bendin' Glass 'n Passin' Gas"