With the continued advancement in electronics the power requirement for micro-sensors has been decreasing opening the possibility for incorporating on-board energy harvesting devices to create self-powered sensors. The requirement for the energy harvesters are small size, light weight and the possibility of a low-budget mass production. In this study, we focus on developing an energy harvester for powering a pulse rate sensor. We propose to integrate an inductive energy harvester within a commonly available pen to harvest vibration energy from normal human motions like jogging and jumping. An existing prototype was reviewed which consists of a magnet wedged between two mechanical springs housed within a cylindrical shell. A single copper coil surrounds the cylindrical shell which harvests energy through Faraday's effect during magnet oscillation. This study reports a design change to the previous prototype providing a significant reduction in the device foot print without causing major losses in power generation. By breaking the single coil in the previous prototype into three separate coils an increase in power density was achieved. Several pulse rate sensors were evaluated to determine a target power requirement of 0.3 mW. To evaluate the prototype as a potential solution, the harvester was excited at various frequencies and accelerations typically produced through jogging and jumping motion. The improved prototype generated 0.043 mW at 0.56 g_rms and 3 Hz; and 0.13 mW at 1.14 g_rms at 5 Hz. The design change allowed reduction in total volume from 8.59 cm³ to 1.31 cm³ without significant losses in power generation.

Date Published: 27 March 2012
PDF: 10 pages
Proc. SPIE 8341, Active and Passive Smart Structures and Integrated Systems 2012, 83411D (27 March 2012); doi: 10.1117/12.917013

Published in SPIE Proceedings Vol. 8341:
Active and Passive Smart Structures and Integrated Systems 2012
Henry A. Sodano, Editor(s)