Biomedical Engineering Reference
In-Depth Information
Fig.
7.14
b. There is an observed negligible temperature increase near the antenna
for this case. This proves that the reason for the absence of a visible temperature
increase for the simulations of Fig.
7.14
b is blood perfusion. As can be observed in
all four figures, the temperature in the glycerin insertion region of the antenna is
lower than the temperature of the surrounding tissue that is heated up by metabolic
activities. This is due to the fact that the initial temperature of glycerin is lower than
the body temperature for the simulations.
7.5 Conclusion
IR-UWB has gained research interest as a lucrative wireless technology for
wireless implant communication applications, such as WCE and neural recording
systems. However, use of high frequency and wideband IR-UWB signals causes
increased amount of electromagnetic power absorption by the human tissue. It is
important to analyze these electromagnetic effects in order to assess the feasibility
of using IR-UWB signals as a wireless implant communication technology. Unlike
narrowband signals, IR-UWB signals are high frequency signals with a large
bandwidth. Hence, characterizing the frequency dependent nature in the relative
permittivity of the human tissue plays an important role in obtaining realistic
results for electromagnetic effects caused by IR-UWB signals. This chapter
describes the electromagnetic exposure effects caused by two types of UWB
implanted devices used in wireless body area network applications: head implants
and WCE devices. For the WCE applications of IR-UWB, it was observed that the
SAR value determines the maximum IR-UWB transmit power that can be utilized
in a WCE device that uses IR-UWB signals with 1 GHz bandwidth and a center
frequency of 4 GHz. The maximum allowable total in-band power per pulse was
found to be 21.5 mW for the particular WCE device position investigated in this
chapter. The temperature increase caused by this transmit power level is discov-
ered to be well within the control of thermal regulatory mechanisms of the human
body.
For the head implant applications, the FCC regulations for the outdoor transmit
power for UWB communication determines the maximum allowable signal power
from an implanted IR-UWB based transmitter. It was observed for UWB based
head implant applications that the SAR and SA results for the maximum peak
power limit of -27.4 dBm/MHz falls within the ICNIRP regulated limits while
emitting a UWB signal that falls within the FCC spectral mask when it propagates
into the outdoor environment. The temperature increase due to the exposure of the
head tissues to the IR-UWB electromagnetic field at those peak power limits is
found to be well within the control of thermal regulatory mechanisms of the
human body. Simulations also showed that it is possible to excite the antenna with
a signal power higher than the outdoor allowable -41.3 dBm/MHz power limit. It
was found that a pulse with a peak power limit of 13.9 dB higher than the FCC
regulated peak power could be utilised for head implant applications of IR-UWB
