Subject: EMF versus EMR (fwd)
Date: Mon, 8 Dec 1997 200011 -0600 (CST)
From: "Roy L. Beavers" <rbeavers@mail.llion.org>
To: emfguru@hotmail.com
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---------- Forwarded message ----------
Date: Mon, 8 Dec 1997 16:56:17 -0600
From: "Marjorie A. Lundquist"
To: rbeavers@mail.llion.org
Subject: EMF versus EMR
The use of the phrase "electromagnetic fields" instead of "electromagnetic
radiation" has provoked some discussion. Here is my opinion, for what it
is worth.
I consider that the most general term is "electromagnetic field". What
this implies is that there are both an electric and a magnetic field pres-
ent in the region of space under discussion, and that these two fields are
related to each other in the manner prescribed by Maxwell's equations of
electromagnetism. (There is no other implication.)
The term "electromagnetic radiation" refers to a special type of electro-
magnetic field: one that is travelling through space in such a manner that
it is transmitting energy and momentum from one spatial location to another
--from its source to wherever there may be a material medium capable of ab-
sorbing some of the energy and momentum of this EMR. EMR usually consists
of one or more "electromagnetic waves"; these may be plane waves, but they
need not be. (The use of the phrase "electromagnetic wave" connotes a spe-
cific frequency, whereas the use of EMR leaves the frequency indefinite and
may even connote a mix of frequencies.)
The RF field around an efficient antenna has different components. One of
these is called "the radiation field". The other components of the RF field
around an efficient antenna do NOT transport energy or momentum steadily
away from the radiation source; instead, they "slosh it around" in the vi-
cinity of the antenna.
The component called the "radiation field" is properly called EMR; it can
be hazardous, and its hazard is proportional to its intensity (to the mag-
netic field strength and the electic field strength). EMR transports ener-
gy and momentum steadily in a non-reversing direction.
The components that "slosh it around" can also be hazardous, but other
factors besides field strength and frequency control the degree of hazard
to health that these components pose.
I am satisfied that the most hazardous region of space around an efficient
RF antenna, though, is the region where the radiation field and the other
components contribute equally to the total EMF. This region lies at a spe-
cific distance from the radiation source (the antenna). [If I do put on a
course, I'll cover this in some detail, because it is not at all intuitive-
ly obvious that this should be the case.]
I'll halt the discussion here, and will just point out that the hazard to
health posed by EMR is pretty well characterized by field strength measure-
ments alone (together with knowledge of the frequency), while the hazard to
health posed by EMF in general is NOT adequately characterized by field
strength measurements alone (together with knowlege of the frequency).
So I consider that there is indeed a distinction between EMF and EMR, and
I urge people to be careful in the language they choose to use. - Marjorie
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Marjorie Lundquist, Ph.D., C.I.H.
Bioelectromagnetic Hygienist
P. O. Box 11831 Milwaukee, WI 53211-0831 USA
e-mail: marjorie@omnifest.uwm.edu
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Archive provided courtesy of WaveGuide, http://www.wave-guide.org
Reprinted with permission of Roy Beavers, http://www.feb.se/EMF-L/EMF-L.html