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Electromagnetic Fields in Biological Systems
5.3.2 Measurement Devices and Equipment
The criteria for performing scientifically sound measurements in experimental dosimetry have been outlined in Kuster, Balzano, and Lin (1997a). The measurement procedure
should be comprehensible and evident to both experts and nonexperts and should provide reproducible results, independent of the phantom or the measurement devices and
equipment used. Furthermore, the measured dosimetric quantities should not underestimate the actual maximum exposure occurring in real-life situations.
Three methods are generally used to measure external electric and magnetic fields
emitted by mobile communication devices: portable RF measurement devices, spectrum analyzers, and personal exposure monitors. Portable RF measurement devices
include broadband instruments with RF field sensors. These provide a relatively simple
and convenient means for measuring electric and magnetic field strengths. On the contrary, spectrum analyzers are narrowband instruments. Finally, exposure estimates can
be made using body-worn personal exposure monitors, which are often used in epidemiological studies.
When selecting a measurement device to assess exposure to RF fields, a number
of key factors must be taken into account. For example, broadband portable RF measurement devices are relatively spectral insensitive and have a slow response time. To
overcome these limitations, narrowband measurements with spectrum analyzers are
sometimes preferred instead. Furthermore, the type of the personal exposure monitor
used in epidemiological studies highly depends on the environment in which subjects
are exposed. Workers on antenna sites could wear cheap, pocket-sized devices, whereas
more sensitive instruments have been developed to capture relatively low-level exposures of the general population over a range of frequency bands used in mobile communication systems. Other factors such as the peak power limitations of the sensor,
polarization aspects of the field, dynamic range, and capability to measure in near- and
far-fields depending on the circumstances of the field measurement, also determine the
choice of instrumentation.
Portable RF measurement devices consisting of field probes (sensors) are most commonly utilized for experimental dosimetry of the human body exposed to RF EM
fields emitted by mobile communication devices. In order to achieve a satisfactory
measurement precision, the probes must be optimized for each particular application with respect to sensitivity, isotropy, linearity, spatial resolution, field distortion
(boundary effects, etc.), and immunity (ELF fields, secondary modes of reception, etc.).
Furthermore, field probes must be calibrated at each frequency and inside the phantom
materials under interest. Various calibration systems for field probes have been developed (Jokela, Hyysalo, and Puranen 1998; Meier et al. 1996).
The dimensions of the field probe are typically on the order of 4–5 mm (Balzano,
Garay, and Manning 1995; Schmid, Egger, and Kuster 1996). Immersing such field
probes into the tissue-simulant material of the experimental phantom displaces a significant amount of liquid/gel. This displacement might influence the field distribution
that one is trying to measure, particularly at the higher frequencies. Field distortions in
the vicinity of the probe can result in large errors when the probe is close to the boundaries and field distortion inside the probe can significantly impair its spherical isotropy.
Electromagnetic Fields in Biological Systems
5.3.2 Measurement Devices and Equipment
The criteria for performing scientifically sound measurements in experimental dosimetry have been outlined in Kuster, Balzano, and Lin (1997a). The measurement procedure
should be comprehensible and evident to both experts and nonexperts and should provide reproducible results, independent of the phantom or the measurement devices and
equipment used. Furthermore, the measured dosimetric quantities should not underestimate the actual maximum exposure occurring in real-life situations.
Three methods are generally used to measure external electric and magnetic fields
emitted by mobile communication devices: portable RF measurement devices, spectrum analyzers, and personal exposure monitors. Portable RF measurement devices
include broadband instruments with RF field sensors. These provide a relatively simple
and convenient means for measuring electric and magnetic field strengths. On the contrary, spectrum analyzers are narrowband instruments. Finally, exposure estimates can
be made using body-worn personal exposure monitors, which are often used in epidemiological studies.
When selecting a measurement device to assess exposure to RF fields, a number
of key factors must be taken into account. For example, broadband portable RF measurement devices are relatively spectral insensitive and have a slow response time. To
overcome these limitations, narrowband measurements with spectrum analyzers are
sometimes preferred instead. Furthermore, the type of the personal exposure monitor
used in epidemiological studies highly depends on the environment in which subjects
are exposed. Workers on antenna sites could wear cheap, pocket-sized devices, whereas
more sensitive instruments have been developed to capture relatively low-level exposures of the general population over a range of frequency bands used in mobile communication systems. Other factors such as the peak power limitations of the sensor,
polarization aspects of the field, dynamic range, and capability to measure in near- and
far-fields depending on the circumstances of the field measurement, also determine the
choice of instrumentation.
Portable RF measurement devices consisting of field probes (sensors) are most commonly utilized for experimental dosimetry of the human body exposed to RF EM
fields emitted by mobile communication devices. In order to achieve a satisfactory
measurement precision, the probes must be optimized for each particular application with respect to sensitivity, isotropy, linearity, spatial resolution, field distortion
(boundary effects, etc.), and immunity (ELF fields, secondary modes of reception, etc.).
Furthermore, field probes must be calibrated at each frequency and inside the phantom
materials under interest. Various calibration systems for field probes have been developed (Jokela, Hyysalo, and Puranen 1998; Meier et al. 1996).
The dimensions of the field probe are typically on the order of 4–5 mm (Balzano,
Garay, and Manning 1995; Schmid, Egger, and Kuster 1996). Immersing such field
probes into the tissue-simulant material of the experimental phantom displaces a significant amount of liquid/gel. This displacement might influence the field distribution
that one is trying to measure, particularly at the higher frequencies. Field distortions in
the vicinity of the probe can result in large errors when the probe is close to the boundaries and field distortion inside the probe can significantly impair its spherical isotropy.