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Electromagnetic Fields in Biological Systems
values were far below the limits of the international guidelines set in EC (1999). The
highest exposure was found for immediate contact to a Wi-Fi notebook and equaled
about 1.2% of the limit. At more than 98% of all measurement points the limit consumption was below 0.1% of the limit. It was also shown that public exposure is dominated by
the mobile terminal and not by the access points.
Exposure to both Wi-Fi access points and mobile terminals (laptops) was also considered in a study by Foster at the University of Pennsylvania (Foster 2007). The study
considered 55 locations around the world and presented a total of 356 measurements.
By considering a distance of 1 m from laptops while uploading large files, the exposure
levels were found to be of the order of up to μW/m 2 . The median power density was a
factor of 10 higher than the exposure level. However, in all cases under consideration
the measured Wi-Fi signal levels were very far below the international exposure limits
(ICNIRP 1998; IEEE 2005) and in nearly all cases far below other RF signals present in
the same environment. Finally, Cortel-Carrasco et al. (2006) performed measurements
of the electric field near a Wi-Fi 802.11b router as well as numerical simulations of the
electric field surrounding a wireless laptop computer with two hands over the keyboard.
In their study, they assumed that wireless channel occupation could be theoretically
considered as a means of estimating the actual power emitted by the device.
Wi-Fi dosimetry for children has also been performed. Exposure of a 10-year-old sitting
child model to EM fields at the frequencies of 2500 and 5000 MHz (commonly used by Wi-Fi
devices) was studied in Findlay and Dimbylow (2010). In all situations considered, the SAR
values calculated were considerably below basic restrictions. Exposure to half-wavelength
dipoles showed that the highest localized SAR calculated was in the head for a 2400 MHz
dipole antenna at 3 cm distance and 100% duty factor. The SAR value for this scenario was
8.17 W/kg per W. However, under more realistic exposure conditions, with the antenna operating at 100 mW at 31 cm distance and 10% duty factor, the peak localized SAR was found
equal to 1.8 mW/kg. This value is considerably below the ICNIRP basic restriction of 2 W/
kg. Calculations were also performed for typical Wi-Fi exposure scenarios using inverted-F
antennas (IFAs) mounted on laptops, as shown in Figure 5.32. The SAR intensity plots for
the IFAs mounted on the bottom left (BL), top right (TR), and bottom center (BC) positions
at 2400 MHz are shown in Figure 5.33a, b, and c, respectively. Using an IFA operating at
100 mW with a duty factor of 10% and assuming that the human body is placed 34 cm away
from the antenna, the maximum peak localized SAR was found to be 3.99 mW/kg in the
torso region. Increasing the duty factor to 100%, while keeping the IFA operating at 100 mW
increased the highest localized SAR value in the head to 5.7 mW/kg. This value is less than 1%
of the SAR calculated in the head for a typical cellular phone exposure scenario (MartinezBurdalo et al. 2004). Furthermore, most of the energy was found to be absorbed in the hands
region. Moving the antenna to the top of the screen increased the SAR absorbed in the head,
as expected. Changing the laptop casing from plastic to a perfect conductor significantly
increased the SAR values. The localized SAR was highly dependent on antenna position and
frequency but typically was two to three times higher than that calculated for a plastic casing.
The World Health Organization’s (WHO) latest fact sheet on wireless networks says
that “Recent surveys have indicated that RF exposures from base stations and wireless
technologies in publicly accessible areas (including schools and hospitals) are normally
thousands of times below international standards” and concludes that “Considering the
Electromagnetic Fields in Biological Systems
values were far below the limits of the international guidelines set in EC (1999). The
highest exposure was found for immediate contact to a Wi-Fi notebook and equaled
about 1.2% of the limit. At more than 98% of all measurement points the limit consumption was below 0.1% of the limit. It was also shown that public exposure is dominated by
the mobile terminal and not by the access points.
Exposure to both Wi-Fi access points and mobile terminals (laptops) was also considered in a study by Foster at the University of Pennsylvania (Foster 2007). The study
considered 55 locations around the world and presented a total of 356 measurements.
By considering a distance of 1 m from laptops while uploading large files, the exposure
levels were found to be of the order of up to μW/m 2 . The median power density was a
factor of 10 higher than the exposure level. However, in all cases under consideration
the measured Wi-Fi signal levels were very far below the international exposure limits
(ICNIRP 1998; IEEE 2005) and in nearly all cases far below other RF signals present in
the same environment. Finally, Cortel-Carrasco et al. (2006) performed measurements
of the electric field near a Wi-Fi 802.11b router as well as numerical simulations of the
electric field surrounding a wireless laptop computer with two hands over the keyboard.
In their study, they assumed that wireless channel occupation could be theoretically
considered as a means of estimating the actual power emitted by the device.
Wi-Fi dosimetry for children has also been performed. Exposure of a 10-year-old sitting
child model to EM fields at the frequencies of 2500 and 5000 MHz (commonly used by Wi-Fi
devices) was studied in Findlay and Dimbylow (2010). In all situations considered, the SAR
values calculated were considerably below basic restrictions. Exposure to half-wavelength
dipoles showed that the highest localized SAR calculated was in the head for a 2400 MHz
dipole antenna at 3 cm distance and 100% duty factor. The SAR value for this scenario was
8.17 W/kg per W. However, under more realistic exposure conditions, with the antenna operating at 100 mW at 31 cm distance and 10% duty factor, the peak localized SAR was found
equal to 1.8 mW/kg. This value is considerably below the ICNIRP basic restriction of 2 W/
kg. Calculations were also performed for typical Wi-Fi exposure scenarios using inverted-F
antennas (IFAs) mounted on laptops, as shown in Figure 5.32. The SAR intensity plots for
the IFAs mounted on the bottom left (BL), top right (TR), and bottom center (BC) positions
at 2400 MHz are shown in Figure 5.33a, b, and c, respectively. Using an IFA operating at
100 mW with a duty factor of 10% and assuming that the human body is placed 34 cm away
from the antenna, the maximum peak localized SAR was found to be 3.99 mW/kg in the
torso region. Increasing the duty factor to 100%, while keeping the IFA operating at 100 mW
increased the highest localized SAR value in the head to 5.7 mW/kg. This value is less than 1%
of the SAR calculated in the head for a typical cellular phone exposure scenario (MartinezBurdalo et al. 2004). Furthermore, most of the energy was found to be absorbed in the hands
region. Moving the antenna to the top of the screen increased the SAR absorbed in the head,
as expected. Changing the laptop casing from plastic to a perfect conductor significantly
increased the SAR values. The localized SAR was highly dependent on antenna position and
frequency but typically was two to three times higher than that calculated for a plastic casing.
The World Health Organization’s (WHO) latest fact sheet on wireless networks says
that “Recent surveys have indicated that RF exposures from base stations and wireless
technologies in publicly accessible areas (including schools and hospitals) are normally
thousands of times below international standards” and concludes that “Considering the