Limits of WPT through the human body using Radio Frequency

Recently, the medical community has been developing new technologies to enhance medical treatments and diagnosis means, having in mind the patients' comfort and safety. Implantable medical devices are an example of such solutions. Nonetheless, these devices present some disadvantages, namely need of batteries. Hence, these implants have a limited lifetime, and require periodical surgical interventions to change or to recharge. In order to solve this problem, systems based on Radio Frequency (RF) has been developed to transfer energy inside the organism. However, transmitting power to inside the human body must be performed carefully, since high power levels might be prejudicial to the subject. In this context, the goal of this work is to study the performance of the Wireless Power Transfer (WPT) to inside the human body, while respecting the Specific Absorption Rate (SAR) limits. Therefore, the levels of absorbed power in different body parts were verified by simulation, in order to reach conclusions about the user's safety. More specifically, two biological models that represent the thigh and the arm were considered. The simulation results led us to conclude that it is possible to transmit approximately 140 mW on the limbs location, while respecting the SAR limits. In turn, it is possible to receive a power superior to 93 µW inside the human body. Additionally, real tests were also carried out in three subjects to verify the power attenuation related to each body structure.