Towards an autonomous self-tuning vibration energy harvesting device for wireless sensornetwork applications

Abstract

Future deployment of wireless sensor networks will ultimately require a self-sustainablelocal power source for each sensor, and vibration energy harvesting is a promising approachfor such applications. A requirement for efficient vibration energy harvesting is to matchthe device and source frequencies. While techniques to tune the resonance frequency ofan energy harvesting device have recently been described, in many applicationsoptimization of such systems will require the energy harvesting device to be ableto autonomously tune its resonance frequency. In this work a vibration energyharvesting device with autonomous resonance frequency tunability utilizing amagnetic stiffness technique is presented. Here a piezoelectric cantilever beam array isemployed with magnets attached to the free ends of cantilever beams to enablemagnetic force resonance frequency tuning. The device is successfully tuned from − 27% to + 22% of its untuned resonance frequency while outputting a peak power of approximately 1 mW.Since the magnetic force tuning technique is semi-active, energy is only consumedduring the tuning process. The developed prototype consumed maximum energiesof 3.3 and 3.9 J to tune to the farthest source frequencies with respect to theuntuned resonance frequency of the device. The time necessary for this prototypedevice to harvest the energy expended during its most energy-intensive (largestresonant frequency adjustment) tuning operation is 88 min in a low amplitude0.1g vibration environment, which could be further optimized using higher efficiencypiezoelectric materials and system components.