SUMMARY

Hydraulic pressure energy harvesters are devices designed to convert the acoustic pressure fluctuations common in hydraulic systems into low-power electricity that can be used for powering sensor nodes. Hydraulic systems inherently have a high energy intensity associated with the mean pressure and flow. Accompanying the mean pressure is dynamic pressure ripple, which is caused by the action of pumps and actuators. Pressure ripple is generally a deterministic source with a periodic time-domain behavior conducive to energy harvesting. Hydraulic pressure energy harvesters couple the acoustic pressure to piezoelectric stack(s), thereby exciting the stack well below its resonance frequency, which allows the conversion of the acoustic energy to electrical energy. Key research issues include: optimizing and modeling the device power output, including rectification; selection of piezoelectric material and modeling the hydraulic pressure energy harvester response under high static pressures (up to 35 MPa); and designing and modeling piezoelectric stack housings that amplify the pressure ripple and reduce the static pressure exposed to the stack. The power optimization is first accomplished by maximizing the AC power output, after which the rectified power can be analyzed and optimized for a given electromechanical system. The modeling of high pressure response includes selection of piezoelectric material, such as a [011] cut single crystal PIN-PMN-PT material that goes through a ferroelectric rhombohedral to ferroelectric orthorhombic phase transformation, causing a nonlinear response with higher power output potential. Finally, it is proposed to develop an Helmholtz resonator device to allow for amplification of the dominant frequency in the pressure ripple.