Biomedical Engineering Reference
In-Depth Information
(b)
(c)
(a)
(f)
(d)
(e)
Max. SAR=
0.2002mW/kg
Max. SA=
0.4004 pJ/kg
Max. SAR
= 2 W/kg
Max. SA=
4 nJ/kg
Max. SAR
= 365 W/kg
Max. SA=
0.73
ยต
J/kg
Fig. 7.7 Side view (a-c) and top view (d-f) of the simulated 10 average SAR variations in the
human voxel model for IR-UWB pulses with peak spectral input power limits of (a-d) -
41.3 dBm/MHz (b-e) -1.82 dBm/MHz (c-f) 21.7 dBm/MHz and total in-band signal power of
(a-d) 0.0024 mW (b-e) 21.5 mW (c-f) 4.38 W
is set to reflect the maximum SAR in all the scenarios, and is logarithmically
marked to yield an acceptable resolution for low SAR values.
The results depicted in Fig.
7.7
show that the SAR variation for the third
scenario, where the input signal power is adjusted in order to obtain a signal with a
power level that lies within the FCC allowed spectral mask just outside the body
corresponds to an SAR variation that exceeds the ICNIRP allowed level of 2 W/
kg. In other words, it can be observed from the results that it is the ICNIRP
regulated SAR level of 2 W/kg that determines the maximum allowable signal
power radiated from the antenna. This corresponds to an IR-UWB pulse with a
total in-band signal power of 21.5 mW. The SAR variation shown in Fig.
7.7
ais
comparatively lower because of the small in-band power contained in the FCC
regulated IR-UWB input pulse.
7.3.3 Temperature Variation Caused by IR-UWB-Based
WCE Devices
The temperature variations for the same power level scenarios used for Fig.
7.7
a-b
are shown in Fig.
7.8
. The temperature increase is obtained after the steady state is
achieved. The initial body temperature is considered to be 37 C. It can be
observed from Fig.
7.8
a that the temperature of the whole body has increased to
37.173 C from the initial body temperature of 37 C. There is no significant
temperature increase in the tissues surrounding the WCE device compared to the
tissues that are far away from it. This can be explained as follows: the temperature
of the whole body has increased to 37.173C due to the metabolic activities of the
