Biomedical Engineering Reference
In-Depth Information
50
Total SAR= 0.0102 mW/kg
Total Mass= 4.766 kg
45
SAR %
40
35
Mass %
30
25
20
15
10
5
0
Tissue Type
Fig. 7.13 SAR percentages and mass variation of tissue considered in the simulation, IEEE
copyright [
39
]
scenario is 0.102 mW/kg, and the total mass of the head tissue is equal to
4.766 kg. It should be noted that the total SAR is calculated by dividing the total
absorbed power by the corresponding tissue masses, unlike the calculation of the
10 g averaged SAR where local averaging over a 10 g of tissue material is con-
sidered and the maximal value is retained.
As illustrated in Fig.
7.13
, brain, fat, skin and bone can be considered as tissue
types with considerably high SAR percentage values. The maximum SAR per-
centages are recorded for the brain tissue. This is due to the fact that most of the
radiated power from the antenna side lobe is directed towards the latter. The SAR
percentage for the skin is relatively high considering its lower mass percentage;
this is mainly due to the high water content in the former's tissue. The low water
content in the bone tissue causes a comparatively low SAR value despite its
comparatively high mass percentage.
7.4.4 Temperature Variation due to the Operation
of IR-UWB-Based Head Implants
Simulations using the same input power scenarios as shown in Fig.
7.12
a-c are
used to obtain the corresponding temperature variations. The bio heat equation
considers the variation of basal metabolic rate and blood perfusion. Because of the
short duration of the excitation pulse, the heat conduction that occurs through
sweating is assumed negligible. The temperature increase is obtained after the
steady state is achieved. The initial body temperature is considered to be 37 C.
Figure
7.14
depicts the obtained temperature variations.
