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27 March 2012Improved pen harvester for powering a pulse rate sensor
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 grms
and 3 Hz; and 0.13 mW at 1.14 grms 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.
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Anthony Marin, Patrick Heitzmann, Jens Twiefel, Shashank Priya, "Improved pen harvester for powering a pulse rate sensor," Proc. SPIE 8341, Active and Passive Smart Structures and Integrated Systems 2012, 83411D (27 March 2012); https://doi.org/10.1117/12.917013