UWB for low power, short range, in-body medical implants

Abstract

Medical implants are battery-powered, and have very stringent power consumption requirements. Devices like pacemakers consume few tens of microamps and last for well over 7-8 years. RF technologies are increasingly enabling communication and configuration of these medical implants. The Federal Communications Commission (FCC) has allocated a dedicated spectrum for operation of medical devices, the Medical Implant Communication System (MICS). This spectrum is in the range of 402-405 MHz and has suitable propagation characteristics through human tissues. Other narrow band low power standards (ZigBee) also exist and are used for on-body applications. The disadvantage of all these narrow-band standards is that their receivers require power hungry components like VCO, PLL and ADCs. Moreover, their power consumption does not scale down with data rates. Ultra wide band (UWB), in its simplest form, Impulse Radio (IR), is a promising low complexity standard. IR-UWB is the natural choice for low-power and low-data rate sensor nodes since for IR-UWB power scales down with low data rate. An UWB-IR transmitter is simple to design and power consumption and complexity are more on the receiver side. Hence, in applications like pacemakers and defibrillators, where the external base station has less stringent power requirements, UWB-IR becomes an option worth studying. Unfortunately, while UWB has been investigated for on-body medical implants no study has been done yet to show the feasibility of UWB for in-body medical implants. We look at the feasibility of UWB signals when they propagate inside human body. We present a MATLAB model for the path loss inside human body tissues for different distances and frequencies in the UWB range, starting with the theoretical background and going on to the complete model. Our results show that despite significant attenuation inside human tissue, UWB signals can be a promising low power.