Design and implementation of a wireless medical system prototype for implantable applications

Abstract

The design, implementation and testing of a wireless medical system (WMS) for continuous monitoring of biological parameters are presented in this paper. Special emphasis has been made on the implantable unit prototype. The proposed system consists of three main sections: implantable medical device (IMD), base station (BS) and graphical user interface. The IMD and BS communicate through an RF link that operates in both the industrial, scientific and medical (ISM, at 2.4---2.48 GHz) and the medical implantable communication service (MICS, at 402---405 MHz) bands. The IMD and BS are based on two commercially-available ultra-low power integrated circuits: a mixed-signal microcontroller and a medical implantable radio transceiver. A comprehensive explanation of the main design issues and implementation challenges is presented. The details regarding the analog front-end functionality, a low-power-oriented algorithm, an analysis of power consumption versus lifetime and a customized operating mode for power optimization are explained. The main considerations for link budget calculations in implantable applications are discussed. A test bench designed to emulate real conditions is used to verify the functionality of the WMS showing successful communication up to 2.1 m range with a data rate of 200 Kbps. The IMD works from a 3 V power supply with an average current consumption of 0.572 mA (including RF transmission) in continuous operation. This allows a 2 year IMD lifetime in periodic operation (for a 350 mAh battery), delivering 1 h of information per day.