Piezoelectret foam-based vibration energy harvesting

The use of energy harvesting to provide power to low-power electronic devices has the potential to create autonomous, self-powered electronics. This article presents the investigation of a novel material for vibration-based energy harvesting. Piezoelectret foam, a lead-free, polymer-based electret material exhibiting piezoelectric-like properties, is investigated for low-power energy generation. An overview of the fabrication and operation of piezoelectret foams is first given. Mechanical testing is then performed, where anisotropy in the principal length directions is found along with Young's moduli between 0.5 and 1 GPa and tensile strengths from 35 to 70 MPa. Dynamic electromechanical characterization is performed in order to measure the piezoelectric d(33) coefficient of the foam over a wide frequency range. The d33 coefficient is found to be relatively constant at around 175 pC/N from 10 Hz to 1 kHz. Finally, the foam is evaluated as an energy harvesting material by first developing an electromechanical model to predict the voltage response during excitation, then performing dynamic experimentation to measure the voltage frequency response with comparisons to modeling predictions for a set of electrical loads, and finally conducting energy harvesting experimentation in which the foam is used to charge a capacitor. Harmonic excitation of a pre-tensioned 15.2 cm x 15.2 cm sample at 60 Hz and displacement of +/- 73 mu m yields an average power of 6.0 mu W delivered to a 1 mF storage capacitor. The capacitor is charged to 4.67 V in 30 min, proving the ability of piezoelectret foam to supply power to small electronic components.