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Mobile Communication Fields in Biological Systems
to 0.25 cm. Such models for the phone-radiating element are very often used nowadays
also, since they represent a sort of canonical exposure source.
Recently, the need for more compact terminals and dual-band operation has given
rise to new antenna types, such as helical antennas (Koulouridis and Nikita 2004,
Figure 5.12b). However, regarding numerical dosimetry, helical antennas do not align
to the FDTD grid. As a result, only large structures have been studied employing a
pure FDTD scheme, in which the electric field components along the helix wires are
set to zero (Bernardi, Cavagnaro, and Pisa 1996; Caputa et al. 2000; Cavagnaro and
Pisa 1996; Christ et al. 2010; Troulis, Scanlon, and Evans 2003). For smaller structures,
published reports have either employed a stack of electric dipoles and magnetic loop
sources with relative weights obtained from analytical expressions for the helix far-field
(Rowley, Waterhouse, and Joyner 2002) or a hybrid MoM/FDTD technique (Dimbylow,
Khalid, and Mann 2003; Mangoud, Abd-Alhameed, and Excell 2000). Investigations
using FDTD, properly modified through the use of a graded mesh, are presented in the
studies of Bernardi et al. (2001) and Cerri et al. (1998).
Some special antenna designs, such as a magnetically shielded monopole on a ground
plane (Yildirim and El-Sharawy 1996; Figure 5.12c), vertical folded loop antenna
(Katsibas et al. 1998; Figure 5.12d), and N antenna (Pan, Bahrwas, and Wolff 1997;
Figure 5.12e) have also been analyzed. Furthermore, flush-mounted types of antennas
that blend into the handset such as side mounted, top-mounted, and back-mounted
antennas have been considered. Planar-inverted-F, bent-inverted-F, printed-folded-loop
antennas that can be efficiently and conveniently integrated with a handheld transceiver
unit are analyzed in Bernardi et al. (2000b), Katsibas et al. (1998), Li et al. (2000), and
Rowley and Waterhouse (1999).
Finally, in order to model the correct shape of cell phones, both CAD files provided
by cellular phone manufacturers (Gandhi et al. 1999) and topometric sensors (Schiavoni
et al. 2000) have been used. Recently, CAD files have also been used to model the internal structures (printed circuit board, battery, keypad, and buttons) of the phone. For
example, the development and validation of the numerical model of the Motorola T250
is described in detail in Chavannes et al. (2003; Figure 5.12f). An alternate approach
to a suitable numerical model of the cellular phone was proposed by Pisa et al. (2005).
It starts with a simplified model which includes only the main phone parts (antenna,
keyboard, internal box, and plastic coating) having “realistic” dimensions and electric
properties. These are subsequently tuned using an optimization procedure.
5.4.1.2 Phone Positioning
In cellular phone dosimetry studies, the transceiver has to be appropriately positioned
against the numerical head model utilized. For canonical modeling of the human head,
positioning of the cellular phone against the ear canal of the numerical head model is
straightforward. An example case is illustrated in Figure 5.13. Point E corresponds to
the projection of the ear canal on the dielectric front face of the handset.
Regarding anatomical head models, guidelines exist that describe the standardization of phone positioning. The EN 50361-2001 (CENELEC 2001) and IEEE 1528-2003
(IEEE 2003) standards recommend measurement techniques for determining the peak
spatial-average SAR in the human head from wireless communication devices, such as
Mobile Communication Fields in Biological Systems
to 0.25 cm. Such models for the phone-radiating element are very often used nowadays
also, since they represent a sort of canonical exposure source.
Recently, the need for more compact terminals and dual-band operation has given
rise to new antenna types, such as helical antennas (Koulouridis and Nikita 2004,
Figure 5.12b). However, regarding numerical dosimetry, helical antennas do not align
to the FDTD grid. As a result, only large structures have been studied employing a
pure FDTD scheme, in which the electric field components along the helix wires are
set to zero (Bernardi, Cavagnaro, and Pisa 1996; Caputa et al. 2000; Cavagnaro and
Pisa 1996; Christ et al. 2010; Troulis, Scanlon, and Evans 2003). For smaller structures,
published reports have either employed a stack of electric dipoles and magnetic loop
sources with relative weights obtained from analytical expressions for the helix far-field
(Rowley, Waterhouse, and Joyner 2002) or a hybrid MoM/FDTD technique (Dimbylow,
Khalid, and Mann 2003; Mangoud, Abd-Alhameed, and Excell 2000). Investigations
using FDTD, properly modified through the use of a graded mesh, are presented in the
studies of Bernardi et al. (2001) and Cerri et al. (1998).
Some special antenna designs, such as a magnetically shielded monopole on a ground
plane (Yildirim and El-Sharawy 1996; Figure 5.12c), vertical folded loop antenna
(Katsibas et al. 1998; Figure 5.12d), and N antenna (Pan, Bahrwas, and Wolff 1997;
Figure 5.12e) have also been analyzed. Furthermore, flush-mounted types of antennas
that blend into the handset such as side mounted, top-mounted, and back-mounted
antennas have been considered. Planar-inverted-F, bent-inverted-F, printed-folded-loop
antennas that can be efficiently and conveniently integrated with a handheld transceiver
unit are analyzed in Bernardi et al. (2000b), Katsibas et al. (1998), Li et al. (2000), and
Rowley and Waterhouse (1999).
Finally, in order to model the correct shape of cell phones, both CAD files provided
by cellular phone manufacturers (Gandhi et al. 1999) and topometric sensors (Schiavoni
et al. 2000) have been used. Recently, CAD files have also been used to model the internal structures (printed circuit board, battery, keypad, and buttons) of the phone. For
example, the development and validation of the numerical model of the Motorola T250
is described in detail in Chavannes et al. (2003; Figure 5.12f). An alternate approach
to a suitable numerical model of the cellular phone was proposed by Pisa et al. (2005).
It starts with a simplified model which includes only the main phone parts (antenna,
keyboard, internal box, and plastic coating) having “realistic” dimensions and electric
properties. These are subsequently tuned using an optimization procedure.
5.4.1.2 Phone Positioning
In cellular phone dosimetry studies, the transceiver has to be appropriately positioned
against the numerical head model utilized. For canonical modeling of the human head,
positioning of the cellular phone against the ear canal of the numerical head model is
straightforward. An example case is illustrated in Figure 5.13. Point E corresponds to
the projection of the ear canal on the dielectric front face of the handset.
Regarding anatomical head models, guidelines exist that describe the standardization of phone positioning. The EN 50361-2001 (CENELEC 2001) and IEEE 1528-2003
(IEEE 2003) standards recommend measurement techniques for determining the peak
spatial-average SAR in the human head from wireless communication devices, such as