a. Experimental work indicates that the average power output of the microwave
the generator. Therefore, at present, the "dosage unit" is described in terms of watts
per square centimeter (W/cm2), referring to the average power density per unit cross-
sectional area of the radiation beam.
b. The biological effects associated with the propagation of microwave energy
are as follows.
(1) Thermal effects. The electromagnetic radiation of microwaves does not
possess sufficient energy to produce ionization; however, it can cause excitation of
atoms. Thus, when the radiation is absorbed in matter, there is a rise in temperature of
the object or organism. The depth of heating is frequency dependent. For example:
(a) Frequencies less than 1,000 MHz produce heat in deep tissues.
(b) Frequencies greater than 3,000 MHz heat superficial (skin) tissue.
(c) Between 1,000 and 3,000 MHz combinations of deep and superficial
heating occur. The critical organs affected thermally are the eye and the testicle. The
eye is susceptible to thermal damage, since it has an inefficient vascular system to
circulate blood and exchange heat to the surrounding tissues. The accumulation of
heat in the lens of the eye can result in the coagulation of lens protein and an
irreversible opacity can be formed. The threshold for this effect has not been
determined. It is for this reason that the eye is considered the most critical organ. The
testicle is extremely sensitive to heat because of its physical location relative to body
surfaces and its poor ability to dissipate heat by means of its vascular system. The
effects of whole body increase in temperature are the same as those experienced with a
naturally occurring fever. These whole body thermal effects are reversed by removing
the individual from the microwave field.
(2) Athermal effects. Various events can be demonstrated experimentally,
namely, pearl chain formations or lining up of particles of matter, inactivation of certain
enzymes, and change in root tips of garlic. However, to date none of these have clinical
application to man. Following are a few examples.
(a) Unexplained response of man to radar. Epigastric distress and/or
nausea may occasionally occur at levels as low as five to 10 mw/cm2 and are most
commonly associated with the frequency range from 8,000 to 12,000 MHz.
(b) Auditory response. Certain people can hear a buzz when exposed to
but the pulse repetition frequency.