Fundamentals of Electromagnetics - RF/Microwave Interaction with Biological Tissues - page 48

the electric field is mostly used as a reference. Standards then specify the value
of the electric field, for instance, which should not be exceeded in some place
or for some time. This creates a situation that should be well understood: The
reference level is a level that the reference, for instance the electric field,
should not exceed. This value is measured in the absence of the person. The
corresponding basic limitation then indicates the power absorbed by a person
that should be present in this electric field, measured in the absence of the
person.
Hence, correctly measuring the electric field or the associated EM power is
of prime importance. The basic theory has been exposed in the first sections
of this chapter. It should be stressed, however, that in most circumstances the
electric field can vary quite significantly from one place to another, not far
away from the first: The variability in space may be quite important. This may
happen, for instance, because of standing waves caused by steady obstacles. If
the obstacles are moving, for instance cars in a street, variability in time is
added. The difficulty of correctly evaluating a living system should not be
underestimated.
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