Wireless channel model of ultra wideband radio signals for implantable biomedical devices

Abstract

Implantable biomedical devices that collect vital physiological data continuously and transmit them wirelessly seemed to be a sci-fi concept just a decade ago. Today, with advancements in microelectromechanical systems (MEMS), circuit fabrication technology and ultra wideband (UWB) radio technology, this concept no longer seems to be a farfetched dream. Still, there are many issues that need to be addressed to realize this dream. In this paper, we present results for wireless channel modeling of ultra wideband signals used in brain computer interface (BCI) technology. Such a channel model is an imperative part of designing wireless transmitters inside the human brain. Extensive literature survey shows that no such attempt has been made in the past to study the wireless channel inside the human brain as required for biomedical applications involving impantable sensors. In this paper, we conduct extensive experiments in an in-vitro setup. We have studied the effects of human tissue, fluids and blood (inside the human brain) on the electrocorticographic (EcoG) signals that are first sensed and then transmitted by implanted transmitters from inside the human brain to a receiver that is placed externally on the human head. Implantation depth has also been shown to have an impact on the received signal strength and quality. The received signal (at the external receiver) has been analyzed in significant detail and a channel model has been developed in this paper.