Abstract
Cellular polypropylene (PP) has been recently used in energy harvesting applications. In this work, we investigate its viability and long-term stability under various operating conditions. Specifically, the effect of constant stress and stress cycling on output power and long-term stability of ferroelectret energy harvesters is analyzed. Our findings show that after 112 days constant stress significantly increases the piezoelectric charge constant and output power from 0.51 μW for a stress-free harvester to 2.71 μW. It also increases the harvester center frequency from 450 to 700 Hz and decreases its optimal resistance from 7 to 5.5 M.
Highlights
Energy harvesting applications have seen significant interest over recent decades [1] as they have become a viable power source for mobile electronics
The piezoelectric charge constants of the CS and SF films were measured after 112 days of energy harvesting
We found that the charge constant was almost insensitive to voltage variation but significantly different for the two loading conditions with d33 = 155.8 ± 4.17 pC/N for the SF film and d33 =
Summary
Energy harvesting applications have seen significant interest over recent decades [1] as they have become a viable power source for mobile electronics. High piezoelectric constant and low stiffness are required to increase the efficiency of power transduction. Current piezoelectric materials with high charge constant, such as lead zirconate titanate (PZT), are stiff, which limits the harvester displacement [4,5]. Developed ferroelectrets, such as cellular polypropylene (PP) [5,6] and laminated fluoropolymers, are attractive alternatives to piezoelectrics They combine a high piezoelectric charge constant with material flexibility, making them better option for energy harvesting applications. Mellinger et al [12] studied the thermal and temporal stability of PP films under elevated temperature and static pressure conditions They found that at room temperature, the piezoelectric charge constant d33 of PP drops significantly in the first ten days before stabilizing to a long-term value.
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