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From: firstname.lastname@example.org (milne_v)
Subject: Re: Any ideas on measuring radiation in the home ?
Date: 5 Oct 2002 12:30:36 -0700
NNTP-Posting-Date: 5 Oct 2002 19:30:36 GMT
Mike Poulton wrote in message news:...
> On 03 Oct 2002, email@example.com (milne_v) said:
> > Radiated E-Field in volts/meter (or near field) is a verifiable and
> > measurable quantity. Why do linemwn wear those suits when they're
> > working near 400kv transmission lines?
> That has nothing to do with radiated EM, it is to prevent electrocution.
> They work hot, and capacitive coupling between their platform and the
> line causes significant current to flow when they touch it. Thus,
> without an equipotential suit, they would receive a severe (possibly
> lethal) shock.
> > There are also endless
> > guidelines for E-Field exposure limits both in residential, indistrial
> > and commercial environments posted by hydro companies for decades now.
> > What are the guidelines for? You get close enough to a large E-Field
> > and you'll get more than just thermal effects. Microwaves are also a
> > large source of directed E-Field which is from time to time envisioned
> > as a source for wireless power transmission, again more than thermal
> > effects. The power receiving apparatus is often called a rectenna.
> That seems rather irrelevant to the discussion at hand. Of course you
> can transmit power with EM radiation. That's how radio works! The
> issue is whether or not absorption of this radiation by humans causes
> anything but heating. I have yet to see a reliable study indicating
> otherwise. The only exception I know of is where the energy density is
> high enough to cause nearly instant vaporization of stuff and subsequent
> heating to very high temperatures, with enough of an E-field to then
> ionize the gases. This is still primarily thermal, but involves some
> magnetic and electrical interactions as well. At that power level, it
> really doesn't matter what's happening. This is what you see when you
> get a fireball in a microwave oven.
> > Try holding a pop can up in front of a powerfull radar horn while the
> > radar is operating. Use a long stick for the can. Must be something
> > blowing that can apart.
> Heat! Steam power!
> > High power broad band micowave sources using
> > sophisticated high power spark discharge devices such as marx
> > generators integrated into a tuned transmission line are being tested
> > for possible weaponization. Check out some of the US navel test ranges
> > or use a search engine for the term "transient electromagnetic
> > device".
> Again, they are thermal devices when used against people. When used for
> destroying electronics, they do so by being rectified by junctions
> therein and by producing thermal damage inside sensitive parts.
> > A number of home brew TED's are also on the net as well as
> > coin and can crushers. A similar technique is used in medicine to
> > produce powerfull, focused and directed acoustic shock waves, see
> > "lithotripter". All have one thing in common, they use a very
> > powerfull and high speed spark discharge. The first experiments in the
> > production of milli-meter wave radiation also used a spark discharge
> > system more than a hundred years ago.
> You are mixing three distinctly different technologies here. Can and
> coin crushers rely on the eddy currents created in metal loops due to
> rapidly changing magnetic fields. They do not use microwave or
> millimeter wave radiation and, in fact, do not use anything close to
> that frequency range. It is a single huge pulse of current. Any
> ringing that may occur after that pulse is simply coincidental, and
> would likely be in the low megahertz range. Most of these devices DO
> NOT use spark discharges. They use vacuum relays or simple shorting
> bars. I have seen one design that uses a triggered spark gap, but only
> a small fraction of the total energy is dissipated in the gap -- it just
> acts like a switch.
> Lithotripters are very different. They use a huge capacitor discharge
You mean like a spark discharge, except that the electrical energy is
stored in a capacitor and released with one shot as in mono-stable
mode whereas a resonant circuit (L-C) is producing a similar effect in
an astable fashion by charging C through L and then discharging C
through a load (ie: a spark gap).
This is debating minutia and has nothing to do with the theme of the
The spark discharge created the shock wave, huge capacitor
You're debating the "how" of the issue when I'm discussing the "what"
of the issue. BTW wireless transmision of electrical power using
microwave energy has nothing to do with thermal effects. Thermal
effects and destruction of semiconductor junctions via junction
rectification is a secondary effect to the induced E-Field. The
E-Field caused the thermal heating via junction rectification. The
E-Field is the first effect, not the thermal effects. The pop can, the
same. You pass enough electrical current through a conductor and you
get heat. You pass it through a gas and you get a shockwave due to
rapid heating of the gas. The E-Field is measureable using a variety
of methods, the effects of the E-Field are arbitrary and depend on
what it is that is being effected.
> underwater to create a mechanical shockwave that is focused to pulverize
> stones. Again, any ringing or EM radiation is coincidental and
> Spark gap transmitters are totally different from both of the
> aforementioned devices. They include a resonant circuit (L-C) to
> intentionally produce high frequency EM radiation.
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