Biomedical Engineering Reference
In-Depth Information
Fig. 7.11 a-b Directivity of the implanted antenna and c-d gain of the implanted antenna for (a,
c) Antenna radiating outwards of the brain for adult head (b, d) Antenna radiating towards the
brain for adult head
figure that the resulting maximum antennaAntenna gain is -13.9 dBi. This means
that if a pulse with a peak power limit of 13.9 dB higher than the FCC regulated
peak power limit of -41.3 dBm/MHz is used as the power from the implanted
antenna, the radiation in free space will lie at the FCC limit. This corresponds to an
input pulse with peak spectral limit of -27.4 dBm/MHz. In the third scenario, an
IR-UWB pulse that causes a maximum SAR of 2 W/kg is used: the latter value is
specified as the maximum allowable SAR limit by the ICNIRP regulations. The
Specific Absorption (SA) in previous three scenarios is also calculated for a pulse
width of 2 ns, in order to form a comparison with the ICNIRP special regulations
for pulse transmissions. The results depicted in Fig.
7.12
show that the SAR and
SA values obtained for the first and second scenario are well within the ICNIRP
regulation limit for a single pulse of 2 W/kg and 2 mJ/kg respectively. This is due
to the very small power contained in the signal (a total in-band accepted power of
0.0024 mW in scenario one and 0.0504 mW in scenario two considering a
bandwidth of 1 GHz). It should be noted that the color scale 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 SAR variation in scenario three
uses a signal which lies within a peak limit of 0.9 dBm/MHz for an amplitude
