SUMMARY

Hydraulic systems provide a unique opportunity to convert acoustic energy into electric energy due to the high intensity pressure ripple in the system. Hydraulic pressure energy harvesters (HPEHs) aim to provide a power source for powering or recharging wireless sensor networks on hydraulic systems through using an inherent byproduct of the pumps and actuators – the pressure ripple. HPEHs convert the pressure ripple into electricity by coupling the fluid fluctuations to a piezoelectric element, such as a stack or single crystal. Using a soft PZT stack within a HPEH device and a parallel resistive load, a HPEH can provide 12.8 mW of AC power for a 202 kPa dynamic pressure amplitude, which is sufficient to power sensors. There are three main parts of HPEH devices: (1) the mechanical coupling between the hydraulic fluid & piezoelectric element; (2) the piezoelectric material; and (3) an electrical circuit connected to the piezoelectric element. A Helmholtz resonator design is introduced and modeled for the coupling between a HPEH and the hydraulic system to provide pressure – and thus force – amplification to the piezoelectric element, resulting in a doubling of the normalized power response. For the piezoelectric material selection, a [011] cut PIN-PMN-PT single crystal that goes through a phase transformation between ferroelectric rhombohedral and ferroelectric orthorhombic is presented as a higher power efficiency per cycle solution for HPEH devices, resulting in power output levels 100 times greater than soft PZT stacks tested. For the electrical circuitry, this work provides a solution and model for power conditioning of low-voltage, low-frequency piezoelectric stack energy harvesting using an inductive load in parallel with a voltage multiplier (VM), or cascade circuit. This work introduces the HPEH devices, provides an electromechanical model, and investigates multiple methods to increase the power conversion efficiency and regulate the power output.