Piezoelectric Energy Harvesting Devices for Low Frequency Vibration Applications

Abstract

Energy harvesting, a process of capturing ambient waste energy and converting it into usable electricity, has been attracting more and more researchers’ interest because of the limitations of traditional power sources, the increasing demands upon mobile devices such as wireless sensor networks, and the recent advent of the extremely low power electrical and mechanical devices such as microelectromechanical systems (MEMS). In this research, bulk- and wafer-scale of piezoelectric power generator prototypes were developed. The Lead Zirconate Titanate (PZT) bimorph cantilever in bulk scale with a big proof mass at the free end tip was studied to convert ambient vibration energy of 100 Hz and above 1g (1g = 9.81 m/s2) acceleration amplitudes. The optimal design was based on matching the resonant frequency of the device with the environmental exciting frequency, and balancing the power output and the fracture safety factor. The fabricated PZT power generator with an effective volume of 0.0564 cm3 and a safety factor of 10g can produce 6.21 Vpk, 257 µW, or 4558 µW/cm3 with an optimal resistive load of 75 k? from 1g acceleration at its resonant frequency of 97.6 Hz. To overcome the high fragility of PZT, substitute piezoelectric materials, Macro Fiber Composite (MFC) and polyvinylidene fluoride (PVDF), and alternative operational ambient for power generators were investigated for high vibration amplitude applications. Before fabricating piezoelectric power generators in wafer scale, interlayer effects on the properties of PZT thin film were surveyed. The fabricated device based on Si wafer, with a beam dimension about 4.800 mm × 0.400 mm × 0.036 mm and an integrated Si mass dimension about 1.360 mm × 0.940 mm × 0.456 mm produced 160 mVpk, 2.13 µW, or 3272 µW/cm3 with the optimal resistive load of 6 kO from 2g acceleration at its resonant frequency of 461.15 Hz. To precisely control the resonant frequency of the power generator, Si on insulator (SOI) wafer substitutes for Si wafer. The resonant frequency of the fabricated device is as low as about 184 Hz. The difference between the calculated and measured resonant frequency has been decreased to 4.25%.