Ayala Garcia, Ivo
Autonomous operation of a tunable vibration based energy harvester.
University of Southampton, Faculty of Physical and Applied Sciences,
Vibration-based energy harvesters transduce kinetic energy into electrical energy, which is then utilized to power small electronic systems, like wireless sensor nodes. Vibration-based harvesters are designed with high Q-factor to maximize their power generation capability; however, this results in low bandwidth of operation. Different tuning mechanisms have been previously presented, but none is integrated as an autonomous system. The work described in this thesis outlines the development of a tunable vibration-based energy harvester that adjusts its resonant frequency to coincide with the base frequency and it is powered exclusively by the harvester.
This work builds upon an electromagnetic vibration-based energy harvester and a non-contact tuning mechanism previously developed in this research group. This thesis presents the integration of the different mechanical and electronic components required to operate the tuning mechanism with the lowest overhead power feasible; an optimal range of operation for the harvester, where the frequency bandwidth is maximized while the power used for tuning is minimized, is proposed. A closed loop frequency tuning system is presented that identifies when the base frequencies have changed and adjust the harvester resonant frequency in consequence, using the mathematical model of the harvester and the period difference between the harvester voltage and the base acceleration. Analysis of the operation of the harvester when exposed to a real application was performed. The system was modified to allow its operation under this condition.
The optimization of the power extraction and conversion was also evaluated. The flexibility of the tunable harvester to adjust its resonant frequency increases by increasing the power available to perform this adjustment. Passive extraction and conversion is preferred due to the reduced overhead power compared to active conversion.
The combined result of tuning and power extraction is a fully functional tunable energy harvester that operates autonomously. Its use as a power source for a wireless sensor node is demonstrated in this thesis.
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