Biomedical Engineering Reference
In-Depth Information
Fig. 7.14 Simulated temperature variation for a signal with peak spectral power limits of a -
41.3 dBm/MHz b -27.4 dBm/MHz c 0.9 dBm/MHz using bio heat equation d -27.4 dBm/MHz
without using bio heat equation, IEEE copyright [
39
]
It can be seen in Fig.
7.14
a, b that the temperature of the whole head is increased
from the initial temperature of 37-37.178 C. It is not possible to see a significant
temperature difference between the tissues at a close proximity to the antenna and
those that are at a considerable distance from the antenna. This can be explained as
follows. The temperature of the head as a whole increases up to 37.178 C due to
the metabolic activities in the tissues. The input powers to the antennas for cases
shown in Fig.
7.14
a, b are not large enough to cause a significant temperature
increase due to the power absorption by the tissues. The temperature increases
caused by the small radiated powers in these two cases are small enough to be
regulated by the blood perfusion inside the head. This explanation is further jus-
tified by the results shown in Fig.
7.14
c, d. The power delivered to the antenna for
the case in Fig.
7.14
c is higher than that of Fig.
7.14
a, b. The high delivered power
to the antenna generates a large enough electric field that causes high power
absorption in the tissues. As a result, this high power absorption causes a consid-
erable temperature increase in the tissues. It is clearly visible in Fig.
7.14
c that the
temperature of the tissues closer to the antenna are higher (a maximum of
37.316 C is recorded in the simulations) than the temperature increase due to the
metabolic activities in rest of the tissues (i.e. 37.178 C). The simulations resulted
in Fig.
7.14
d ignore the heat generation from the metabolic activities and it does not
regulate the temperature through blood perfusion. The power of the excitation pulse
is set to fall within the -27.4 dBm/MHz spectral mask, which is similar to that of
