The radiofrequency portion of the electromagnetic spectrum
extends over a wide range of frequencies, from about 10 kHz
to 300 GHz. In the last two or three decades, the use of
devices that emit radiofrequency radiation (RFR) has
increased dramatically. Radiofrequency devices include, for
example, radio and television transmitters, military and
civilian radar systems, extensive communications systems
(including satellite communications systems and a wide
assortment of mobile radios), microwave ovens, industrial RF
heat sealers, and various medical devices.
The proliferation of RF devices has been accompanied by
increased concern about ensuring the safety of their use.
Throughout the world many organizations, both government and
nongovernment, have established RFR safety standards or
guidelines for exposure. Because of different criteria, the
USSR and some of the Eastern European countries have more
stringent safety standards than most Western countries. The
Soviet standards are based on centralnervous-system and
behavioral responses attributed to RFR exposure in animals.
In Western countries the standards are based primarily on
the calculated thermal burden that would be produced in
people exposed to RFR. In each case, better methods are
needed to properly extrapolate or relate effects observed in
animals to similar effects expected to be found in people.
(The development of new RFR safety guidelines is discussed
in Chapter 11.) Safety standards will be revised as more
knowledge is obtained about RFR effects on the human body.
An essential element of the research in biological effects
of RFR is dosimetry--the determination of energy absorbed by
an object exposed to the electromagnetic (EM) fields
composing RFR. Since the energy absorbed is directly related
to the internal EM fields (that is, the EM fields inside the
object, not the EM fields incident upon the object),
dosimetry is also interpreted to mean the determination of
internal EM fields. The internal and incident EM fields can
be quite different, depending on the size and shape of the
object, its electrical properties, its orientation with
respect to the incident EM fields, and the frequency of the
incident fields. Because any biological effects will be
related directly to the internal fields, any
cause-and-effect relationship must be formulated in terms of
these fields, not the incident fields.
However, direct measurement of the incident fields is easier
and more practical than of the internal fields, especially
in people, so we use dosimetry to relate the internal fields
(which cause the effect) to the incident fields (which are
more easily measured). As used here, the term "internal
fields" is to be broadly interpreted as fields that interact
directly with the biological system and include, for
example, the fields that, in perception of 60-Hz EM fields,
move hair on the skin as well as fields that act on nerves
well inside the body. In general, the presence of the body
causes the internal fields to be different from the incident
fields (the fields without the body present).
Dosimetry is important in experiments designed to discover
biological effects produced by RFR and in relating those
effects to RFR exposure of people. First, we need dosimetry
to determine which internal fields in animals cause a given
biological effect. Then we need dosimetry to determine which
incident fields would produce similar internal fields in
people, and therefore a similar biological effect. Dosimetry
is needed whether the effects are produced by low-level
internal fields or the higher level fields that cause body
temperature to rise.
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