In the study, a numeri-
cal human head model
was used. The anatomical
z
human head with two
143 mm
shoulders used in XFDTD
is composed of 27 types of
x
biological tissues, includ-
ing mainly the skin, bone,
x
brain, muscle, humor,
99.5
lens, and cornea (as shown
y mm
in Figure 15). The dielec-
tric constant and conduc-
tivity of the tissues are fre-
quency dependent. The
model can be considered
as an irregular, inhomoge-
Figure 15. A human head model and its orientation near a human head.
neous, and lossy dielectric
object.
In the FDTD simulations, the gap between the
antenna and the head varies from 2 mm to 4 mm, and
the mesh cell size of 1 mm × 1 mm × 1 mm with
0
respect to x, y, and z axes and time step of 1.926 ps are
used to meet the two main constraints for the highest
-10
frequency of 10.6 GHz in the UWB band. For the
achieved convergence, the impedance performance
-20
was calculated using a Gaussian monocycle of a 32-
time step pulse width using 3,000 time steps. The
sinusoidal source centered at 3 GHz, 7 GHz, and 10
-30
In Free Space
GHz was used to simulate the radiation patterns
With Head
using 2,000 time steps.
-40
Figure 16 compares the simulated return losses of
2
4
6
8
10
12
the antenna in free space and with the head. It is clear
Frequency (GHz)
that the presence of the head slightly affects the imped-
ance matching.
However, Figure 17 demonstrates the severe effect
of the human head on the radiation performance by
Figure 16. A comparison of return losses of the antenna in
calculating the gain along the x-axis and observing
free space and near the human head.
10
0
-10
-20
-30
In Free Space, φ= 0°, θ= 90°
-40
With Head, φ= 0°, θ= 90°
In Free Space, φ=180°, θ= 90°
-50
With Head, φ=180°, θ= 90°
-60
2
4
6
8
10
12
Frequency (GHz)
(a)
(b)
Figure 17. (a) A comparison of gain of the antenna in free space and near the human head. (b) The distribution of electric
fields in time domain (321 time steps).
December 2006
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