DRAFT Recommended Practice for Measurements and ...

1/29/98 48 C95.3-1991 Revision — 2 nd Draft
10/98 Draft
this system. If three loop antennas are arranged with a common center, an isotropic
response is achieved [B9]. This type of probe is commercially available.
Fig 4.2 Schematic Representation of Three-Dimensional Isotropic E/H Probe
4.4.8 Personnel monitors.
Personal monitors are typically small, portable broadband detectors, suitable for
attachment to workers’ clothing, equipped with an alarm feature for alerting the subject to
the presence of high-level RF fields that may approach the MPE limits of various
exposure standards. Most personal monitors provide an alarm with a preset threshold of
RF exposure is exceeded [Tell, 1995]. In the region between 1 and 100 GHz, they use
resistive thermoelectric dipoles as sensors with a background of lossy material to reduce
the effect of scattering from the body. In the frequency range between 30 and 1000 MHz,
the sensor generally monitors the magnetic field to reduce the effects of scattering from
the body. Between 0.1 and 30 MHz, the monitors use surface charge detection as
sensors thus monitoring the radial fields which predominate near re-radiators in this
frequency range. These monitors may incorporate sensors for both electric and
magnetic fields and some contain frequency dependent sensors that automatically
weight the detected RF fields in accordance with frequency-dependent RF exposure
limits. This feature makes them especially useful in multiple frequency environments
such as broadcast and wireless telecommunications antenna sites.
Because personal monitors can only respond to RF fields at the position where the
monitor is located on the body, some care should be used in its placement and
interpreting exposure during an alarm condition. For example, wearing a belt mounted
personal monitor when the predominant exposure is at the eye may not provide sufficient
warning of excessive exposure. Conversely, when used in non-uniform RF field
environments such as VHF and UHF broadcast facilities, an alarm condition may be a
very conservative indication of potential excessive exposure since the MPE limits of
several exposure standards are based on spatial averages over the body dimensions.
Copyright © 1998 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft,
subject to change.