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Unformatted text preview: Energy Harvesting for Human Wearable and Implantable Bio-Sensors Paul D. Mitcheson Abstract There are clear trade-offs between functionality, battery lifetime and battery volume for wearable and im- plantable wireless-biosensors which energy harvesting devices may be able to overcome. Reliable energy harvesting has now become a reality for machine condition monitoring and is finding applications in chemical process plants, refineries and water treatment works. However, practical miniature devices that can harvest sufficient energy from the human body to power a wireless bio-sensor are still in their infancy. This paper reviews the options for human energy harvesting in order to determine power availability for harvester-powered body sensor networks. The main competing technologies for energy harvesting from the human body are inertial kinetic energy harvesting devices and thermoelectric devices. These devices are advantageous to some other types as they can be hermetically sealed. In this paper the fundamental limit to the power output of these devices is compared as a function of generator volume when attached to a human whilst walking and running. It is shown that the kinetic energy devices have the highest fundamental power limits in both cases. However, when a comparison is made between the devices using device effectivenesses figures from previously demonstrated prototypes presented in the literature, the thermal device is competitive with the kinetic energy harvesting device when the subject is running and achieves the highest power density when the subject is walking. I. INTRODUCTION In order for any wireless bio-sensor device to be truly convenient for the wearer it should not require user interven- tion. As a consequence, the power supplies for such devices should be maintenance-free and able to supply power as required for an unlimited time period. Batteries are of course the most common supply for portable electrical devices but are exhaustable sources. Since the late 1990s there has been a significant research interest in miniature energy harvesting devices which turn ambient energy in the form or motion, thermal gradients, light or electromagnetic radiation into an electrical form in order to supply power to nodes in wireless sensor networks. There are now several companies selling motion-driven energy harvesters for use in industrial envi- ronments , . In these applications the energy harvester typically converts high frequency, low amplitude machine vibrations into electrical energy. Such devices are capable of harvesting tens of mW, depending on their size and the vibration characteristics of the source to which they are attached ....
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- Fall '08