Energy scavenging for sensor applications using structural strains

Resident sensors are envisioned for civil infrastructure applications, but providing long-term power for such devices remains a design challenge. An ideal solution would be to scavenge energy from structural strains and make the scavenging component a part of the sensor package. In principle, piezoelectric materials are suited to that role, and studies by others have demonstrated the feasibility of energy scavenging from flexible PZT devices operated at large strains and high strain rates. We have conducted experiments to collect electrical energy from PZT ceramics. We summarize the governing piezoelectric equations and outline the most convenient forms to use for the energy scavenging problem, illustrated by tracing one complete loading cycle. We review the material properties for the three PZT ceramics used in our experiments. We show experimental results recording voltage and charge in the cases of open-circuit, resistive loads, and capacitive loads, showing good agreement with analytical predictions. However, the greatest challenge is the approach to energy storage. In theory, capacitors can store energy but at varying voltage and with non-negligible leakage, whereas a battery can store energy at constant voltage with little leakage. We conducted experiments on both approaches, and we discuss our findings of the feasibility and efficiency of battery recharging at the scale of our devices, which have nominal dimensions of 10x10x1 mm.