Frequency Self-tuning Scheme for Broadband Vibration Energy Harvesting

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Abstract
The recent proliferation of microscale devices has raised the issue of energy harvesting for replacing batteries that present maintenance and recycling problems. Particularly, piezoelectric seismic microgenerators offer the advantages of easy maintenance and high power output, but are very sensitive to frequency drifts that can dramatically decrease their performance. The purpose of the present article is to expose a technique to ensure that the harvester resonance frequency matches the base motion frequency, without any external intervention. The principles of the proposed method rely on ultralow-cost frequency sensing combined with an energy-efficient stiffness tuning, through the use of an additional actuator. Experimental results carried out to validate the model show that such an approach permits increasing the effective bandwidth of the structure by a factor of 4 in terms of mechanical vibrations and having a 100% frequency band gain in terms of total power output of the device (i.e., taking into account the energy spent by the actuation). The total energy produced by the harvesting device, taking into account the actuation cost, is discussed as well.

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