The use of body motion for powering biomedical devices

Abstract

Powering electronic devices from environmental sources such as light and temperature gradients has been demonstrated with commercially viable products such as solarpowered calculators and thermal-powered wristwatches. A new electromagnetic generator approach presented here is found to have the potential to power miniature medical devices. The power output from harvesting environmental energy is proportional to the acceleration-squared-to-frequency (ASTF) and the quality (Q) factor of the system. Human-based activities exhibit large ASTF values and low Q factors while machines are typically associated with low ASTF values and high Q factors. This paper reviews the generation limits of energy harvesting, the possibilities of energy generation from body motion, and the development of a new oscillating generator. The device presented is composed of a rotor with a multipole permanent magnet (PM) ring with an eccentric weight and a stator with a radial gear-shaped planar coil. The oscillations of the rotor due to the eccentric mass when subject to body motion induce a voltage on the planar coil. As much as 2.35μW of power has been produced with a preliminary prototype placed laterally on the hip while walking. It is estimated that energy from human motion could generate as much power as 1mW/cm3with such a device. © 2009 Springer-Verlag.