Radio propagation models for in-body sensors

Radio technology has the potential to enable real-time collection and monitoring of physiological signals for better healthcare. Implantable biomedical sensors transmitting continuously physiological information to an external unit can facilitate the personalized treatment of chronic diseases. Other in-body medical devices like the wireless capsule endoscope have been proven extremely useful as a diagnostic tool for diseases in the gastrointestinal tract. Nevertheless, the design of efficient wireless communication systems to transmit reliably the information collected inside the body to an external receiver for display and analysis requires accurate radio propagation models. Because of the impossibility to conduct in-body measurements with human subjects, research in this field has made use of measurements in phantoms and intricate computer simulations. This paper surveys the different propagation models for implant communication that have been presented in the literature for narrowband and ultra wideband signals. Research challenges and perspectives for the improvement of the path loss models are discussed too.