Mechanical Durability Assessment of an Energy-Harvesting Piezoelectric Inverted Flag

This paper presents results from a practical assessment of the endurance of an inverted flag energy harvester, tested over multiple days in a wind tunnel to provide first insights into flapping fatigue and failure. The inverted flag is a composite bimorph, composed of PVDF (polyvinylidene difluoride) strips combined with a passive metallic core to provide sufficient stiffness. The flag, derived from an earlier, more extensive study, flaps with a typical amplitude of ~120 degrees and a frequency of ~2 Hz, generating a constant power of ~0.09 mW in a wind velocity of 6 m/s. The flag was observed to complete ~5x10(5) cycles before failure, corresponding to ~70 h of operation. The energy generated over this lifespan is estimated to be sufficient to power a standard low-power temperature sensor for several months at a sampling rate of one sample/minute, which would be adequate for applications such as wildfire detection, environmental monitoring, and agriculture management. This study indicates that structural fatigue may present a practical obstacle to the wider development of this technology, particularly in the context of their usual justification as a 'deploy and forget' alternative to battery power. Further work is required to improve the fatigue resistance of the flag material.

Automated summary

This study presents an assessment of the endurance of an inverted flag energy harvester, indicating that structural fatigue poses a practical obstacle to its wider development. Further work is needed to improve the fatigue resistance of the flag material.