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Mobile Communication Fields in Biological Systems
pregnancy stages, it was shown that significant increase of SAR and temperature elevation takes place at late pregnancy stage.
Finally, the possible changes the absorption could have when the phone is used in a
closed environment have been assessed in the literature. For example, when the cellular phone is used inside a car, metallic walls are present near the EM source that could
change its radiating properties and perhaps cause a higher absorption in the human
head (Dominguez, Raizer, and Carpes 2002).
5.4.1.4 Parametric Studies
Regarding cellular phone dosimetry, the dependence of the power absorbed by the human
head on the human subject (age and tissue dielectric properties), the phone-head distance, and the phone positioning has also been parametrically studied in the literature.
Kuster, Kastle, and Schmid (1997b) reported a distribution of slightly compressed ear
thickness ranging from 3 to 10 or more mm, with a mean value of about 5 mm in order
to show that the distance between the radiating source and the human head, as well
as the intermediate tissue and the ear thickness, are factors that strongly influence the
absorbed electromagnetic power. Furthermore, in the research of Hadjem et al. (2005),
exposure of several child head models to two cellular phones equipped with patch
antennas were studied and no significant difference in the power budget and the 10 g avg
SAR was found. Both uniform (CS) and nonuniform (CL) downscaling procedures were
adopted to derive the child head models of the study.
In the works of Koulouridis, Christopoulou, and Nikita (2005), a comparative dosimetric assessment for various head models (adult and child) and cellular phones operating at 1800 MHz was carried out. Variations in the size and anatomy of the human
head, the tissue dielectric properties, and the distance between the human head and the
cellular phone were taken into account. Helical antennas mounted on cellular phones
produced higher SAR values compared to linear ones due to the greater field concentration by the physically shorter helical antenna. Children and adults were found to absorb
similar levels of EM power and morphological changes in child head models did not
affect the radiation behavior of the system. On the other hand, the increase of the phonehead distance and the decrease of the dielectric properties significantly reduced the SAR
values. Quantitative results are depicted in Figures 5.18 and 5.19.
Finally, a recent study presented detailed parametric results for adult and children head models exposed to small helical antennas at 1710 MHz (Christopoulou,
Koulouridis, and Nikita 2009). The peak local and 1 g avg SAR values induced in realistic and spherical head models were found to exponentially decrease with the increase
in separation distance, while in spherical head models the 10 g avg SAR values were
linearly dependent on the separation distance. Furthermore, the results revealed that
comparable power levels (difference lower than 12%) were absorbed by adult and child
head models. The uniformly scaled down child head models led to higher 10 g avg SAR
(4%–37%) and power absorption (up to 9%) values for realistic exposure scenarios. These
trends were less emphasized (~12% and up to 2%, respectively) in canonical exposure
scenarios. Assessment of the peak SAR value dependence upon separation distance and
tissue dielectric properties concluded in a 60%–80% decrease for a 1 cm increase in distance and an up to 16% decrease for a 110% to 90% decrease in dielectric property values,
Mobile Communication Fields in Biological Systems
pregnancy stages, it was shown that significant increase of SAR and temperature elevation takes place at late pregnancy stage.
Finally, the possible changes the absorption could have when the phone is used in a
closed environment have been assessed in the literature. For example, when the cellular phone is used inside a car, metallic walls are present near the EM source that could
change its radiating properties and perhaps cause a higher absorption in the human
head (Dominguez, Raizer, and Carpes 2002).
5.4.1.4 Parametric Studies
Regarding cellular phone dosimetry, the dependence of the power absorbed by the human
head on the human subject (age and tissue dielectric properties), the phone-head distance, and the phone positioning has also been parametrically studied in the literature.
Kuster, Kastle, and Schmid (1997b) reported a distribution of slightly compressed ear
thickness ranging from 3 to 10 or more mm, with a mean value of about 5 mm in order
to show that the distance between the radiating source and the human head, as well
as the intermediate tissue and the ear thickness, are factors that strongly influence the
absorbed electromagnetic power. Furthermore, in the research of Hadjem et al. (2005),
exposure of several child head models to two cellular phones equipped with patch
antennas were studied and no significant difference in the power budget and the 10 g avg
SAR was found. Both uniform (CS) and nonuniform (CL) downscaling procedures were
adopted to derive the child head models of the study.
In the works of Koulouridis, Christopoulou, and Nikita (2005), a comparative dosimetric assessment for various head models (adult and child) and cellular phones operating at 1800 MHz was carried out. Variations in the size and anatomy of the human
head, the tissue dielectric properties, and the distance between the human head and the
cellular phone were taken into account. Helical antennas mounted on cellular phones
produced higher SAR values compared to linear ones due to the greater field concentration by the physically shorter helical antenna. Children and adults were found to absorb
similar levels of EM power and morphological changes in child head models did not
affect the radiation behavior of the system. On the other hand, the increase of the phonehead distance and the decrease of the dielectric properties significantly reduced the SAR
values. Quantitative results are depicted in Figures 5.18 and 5.19.
Finally, a recent study presented detailed parametric results for adult and children head models exposed to small helical antennas at 1710 MHz (Christopoulou,
Koulouridis, and Nikita 2009). The peak local and 1 g avg SAR values induced in realistic and spherical head models were found to exponentially decrease with the increase
in separation distance, while in spherical head models the 10 g avg SAR values were
linearly dependent on the separation distance. Furthermore, the results revealed that
comparable power levels (difference lower than 12%) were absorbed by adult and child
head models. The uniformly scaled down child head models led to higher 10 g avg SAR
(4%–37%) and power absorption (up to 9%) values for realistic exposure scenarios. These
trends were less emphasized (~12% and up to 2%, respectively) in canonical exposure
scenarios. Assessment of the peak SAR value dependence upon separation distance and
tissue dielectric properties concluded in a 60%–80% decrease for a 1 cm increase in distance and an up to 16% decrease for a 110% to 90% decrease in dielectric property values,