The Effect of Mechanical Frequency on Piezoelectrochemical Energy Harvesters

Microenergy harvesters such as piezoelectro-chemical (PEC) devices allow the extraction of low-frequency mechanical energy, which might otherwise be lost. Recent literature on PEC harvesters has noted that the input mechanical frequency affects the device current outputs, but this effect is not well understood. Mechanical energy sources often have variable frequencies, so understanding PEC harvester performance as a function of frequency is vital for the optimization of these devices. Using a commercially available lithium ion pouch cell as a test system, this work finds that applying a square-wave frequency with the fastest strain rate and longest hold time maximizes PEC current output. There is a monotonic increase in peak power, maximum half-cycle energy, and energy conversion efficiency as the input mechanical frequency approaches zero. This indicates that PEC harvesters have more flexibility in operating frequency than piezoelectric harvesters, as PEC harvesters do not have resonance or antiresonance frequencies.