On antennas for implantable RF medical devices

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Sähkötekniikan korkeakoulu | Master's thesis
Radio Science and Engineering
Degree programme
EST - Master’s Programme in Radio Science and Engineering
This thesis studied by simulations how the radiation efficiency of two implanted antennas depends on the antenna size and operation frequency. The studied antenna structures are a dipole and a loop made of perfect electric conductor. Antennas are placed inside a tissue model. It is found that at the higher frequency, the radiation efficiency is higher for the same size antenna. In this master’s thesis, a figure-of-merit (FoM) has been derived for implantable antennas. The FoM is proportional to the theoretical channel capacity achievable with the antenna and it is derived under assumptions that the orientation and alignment of the antenna is random and that receiver noise or allowed transmit power does not depend on the frequency. Frequency regulations are not taken into account. Using the FoM, two antenna types are studied by simulation. The studied antenna structures are a dipole and a loop. Further, it also studied what operating frequency maximizes the FoM when the physical size of the antenna is constrained. It is found that optimal operation frequency, which maximizes the FoM is inversely proportional to the antenna size. A small ultra-wideband antenna at 500 MHz is designed for wireless capsule endoscopy. The design process is facilitated with a parametric analysis on the antenna operation inside a lossy tissue. The antenna is a three-layered vertically stacked square spiral PIFA. The proposed antenna exhibits omnidirectional radiation with a maximum far-field gain of -29.67 dB and 0.08% radiation efficiency and -10 dB impedance bandwidth is 300 MHz inside the tissue.
Nikoskinen , Keijo
Thesis advisor
Viikari, Ville
biocompatibility, bio-telemetry, capsule endoscopy, implantable antennas, implantable medical devices (IMDs), miniaturization, multilayered square spiral antenna, optimal operation frequency.
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