PhD Defense of Majdi BAHROUNI

Nowadays, there are various designs of miniature implantable antennas used to enable communication with implantable devices, depending on the area of use and implantation space. Due to their nature and purpose, these antennas are subject to numerous criteria, such as bandwidth, multi-band behaviour, radiation pattern, gain and specific absorption rate (SAR). This represents a challenge when it comes to achieving satisfactory results, without making major compromises on any of these parameters. In addition, many existing antenna structures do not follow a specific approach. Measuring the various parameters of these fabricated structures requires special conditions and environments mimicking the tissues in which they are intended to be placed. In this case, biological or synthetic phantoms are widely used.
In this manuscript, a design approach for miniature implantable antenna structures has been proposed based on known structures; Fractal curves have been particularly targeted due to their use for miniature and/or multi-band antenna design. Two bands were chosen to diversify the use of the antennas; the Medical Implant Communication System (MICS) band was chosen for telemetry, while the Industrial, Scientific, Medical (ISM) 2.4 GHz band was chosen for all the possible operations that the band allows, including Wireless Power Transfer (WPT).
A comparative study was carried out to test the reliability of two mixtures for creating phantoms that electrically mimic human skin: sodium chloride (NaCl)/sugar and Triton X-100/diethylene glycol butyl ether (DGBE). Two phantoms were then created from the latter for each of the MICS and ISM 2.4 GHz bands.
The second part is devoted to the design and manufacture of miniature dual-band implantable antenna structures. First, an antenna was designed based on the first iteration of the Koch fractal curve, using single-layer phantoms imitating human skin. The antenna structure is characterized by its reduced size, simplicity of design and agility in terms of resonant frequency. The prototype was built and measured in the characterized phantoms. To concretize the proposed approach, a second antenna structure was designed based on the first iteration of the Hilbert fractal structure, and simulated in single-layer and multilayer phantoms. Resonating at the same resonant frequencies, the antenna features a smaller size and simpler shape, while maintaining desirable performance.