Implanted Wireless Sensors For Medical Applications: Exploring the Limits of Inductive Powering.

Wireless medical implant powering is an emerging sector for future healthcare applications. It enhances the healthcare safety level and the prospects of a better life. The main theme of this research is to design a wireless power budgeting for the medical implants. A proper link between an external source to the implant is established by an inductive coupling for a particular physiological parameter monitoring. A battery-free implant device requires sufficient power supply for active monitoring. The main target of this research is to develop a wearable and external antenna design for transferring sufficient power to the implant for its activation without violating the regulations of specific absorption rate limits. In addition, there is another goal of improving the implant depth. In this research, two different models (link model and SAR model) are used for the assessment in the virtual environment. Previously, a two-turns antenna is used for power transmission but in this research, several antenna structures are studied such as – the circular two-turns with a capacitor loaded loop, benzene shape, rectangular shape, octagonal shape, and circular spiral shape. Among these structures, circular spiral shape, with the combination of same and counter directions of spiral loops, shows satisfactory results. Through the proper optimization approach, the circular spiral antenna is capable of providing 25% more power at the implant with respect to the two-turns antenna. For 16 mm link distance, the circular spiral antenna can transmit 686 mW whereas a two-turns antenna is efficient up to 452 mW. Even the implant can be placed 2.5 mm more depth without interrupting the power transmission link between antennas. The circular spiral antenna is able to transfer significant power up to 9 mm skull thickness whereas 6.4 mm is the average width. Two experimental setups are developed for antenna performance analysis such as “air gap testing”, and “pigskin and air gap testing”. In the experiments, the effect of parasitic elements over the link power efficiency is identical to both the experiments. The results of “in vitro” testing of the newly developed wearable external antenna inspires for future implementation in the monitoring of intracranial pressure. From the performance analysis, in both the virtual environment and experimental setup, the circular spiral antenna has enough potentiality to use in inductive powering for further research and development