Ellen Skow

Energy harvesting from hydraulic pressure fluctuations

State-of-the-art hydraulic hose and piping systems employ integral sensor nodes for structural health monitoring to avoid catastrophic failures. Energy harvesting in hydraulic systems could enable self-powered wireless sensor nodes for applications such as energy-autonomous structural health monitoring and prognosis. Hydraulic systems inherently have a high energy intensity associated with the mean pressure and flow. Accompanying the mean pressure is the dynamic pressure ripple, which is caused by the action of pumps and actuators. Pressure ripple is a deterministic source with a periodic time-domain behavior conducive to energy harvesting. An energy harvester prototype was designed for generating low-power electricity from pressure ripples. The prototype employed an axially-poled off-the-shelf piezoelectric stack. A housing isolated the stack from the hydraulic fluid while maintaining a mechanical coupling allowing for dynamic-pressure-induced deflection of the stack. The prototype exhibited an off-resonance energy harvesting problem since the fundamental resonance of the piezoelectric stack was much higher than the frequency content of the pressure ripple. The prototype was designed to provide a suitable power output for powering sensors with a maximum output of 1.2 mW. This work also presents electromechanical model simulations and experimental characterization of the piezoelectric power output from the pressure ripple in terms of the force transmitted into the harvester. (Some figures may appear in colour only in the online journal)

Power performance improvements for high pressure ripple energy harvesting

A hydraulic pressure energy harvester (HPEH) device, which utilizes a housing in order to isolate a piezoelectric stack from the hydraulic fluid via a mechanical interface, generates power by converting the dynamic pressure within the system into electricity. Energy harvester prototypes were designed for generating low-power electricity from pressure ripples. These devices generate low-power electricity from off-resonance dynamic pressure excitation. The power produced per volume of piezoelectric material is analyzed to increase the power density; this is accomplished through evaluating piezoelectric stack characteristics, adding an inductor to the system circuit, and solving for optimal loading in order to achieve maximum power output. The prototype device utilizes a piezoelectric stack with high overall capacitance, which allows for inductance matching without using an active circuit. This work presents an electromechanical model and the experimental results of the HPEH devices using a parallel connection of inductive and resistive loads as the energy harvesting circuit. A non-ideal inductive load case is also considered and successfully modeled by accounting for the parasitic resistance of the inductive load. Various HPEH prototypes are fabricated, modeled, and compared in terms of their normalized power density levels, and milli-Watt level average power generation is demonstrated. The highest power density is reported for the single-crystal HPEH prototype.

Design and performance enhancement of hydraulic pressure energy harvesting systems

Hydraulic pressure ripple energy harvesters generate low-power electricity from off-resonance dynamic pressure excitation of piezoelectric elements. Improvements were made to hydraulic pressure ripple energy harvester prototype performance. 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. An energy harvester prototype was designed for generating low-power electricity from pressure ripples. These devices generate low-power electricity from off-resonance dynamic pressure excitation. The power produced per volume of device was increased through decreasing the device size and adding an inductor to the system circuit. The prototype device utilizes a piezoelectric stack with high overall capacitance allowing for inductance matching without using a switching circuit. Initial testing with addition of an inductor produced over 2.1 mW, an increase of 78% as compared to the device without the inductor. Two power output model simulations of a resistive-inductive circuit are analyzed: (1) ideal circuit case and (2) non-ideal circuit case with inductor internal resistance included.

Power Density Performance Improvements for High Pressure Ripple Energy Harvesting

A hydraulic pressure energy harvester (HPEH) device, which utilizes a housing in order to isolate a piezoelectric stack from the hydraulic fluid via a mechanical interface, generates power by converting the dynamic pressure within the system into electricity. Energy harvester prototypes were designed for generating low-power electricity from pressure ripples. These devices generate low-power electricity from off-resonance dynamic pressure excitation. The power produced per volume of piezoelectric material is analyzed to increase the power density; this is accomplished through evaluating piezoelectric stack characteristics, adding an inductor to the system circuit, and solving for optimal loading in order to achieve maximum power output. The prototype device utilizes a piezoelectric stack with high overall capacitance, which allows for inductance matching without using an active circuit. This work presents an electromechanical model and the experimental results of the HPEH devices using a parallel connection of inductive and resistive loads as the energy harvesting circuit. A non-ideal inductive load case is also considered and successfully modeled by accounting for the parasitic resistance of the inductive load. Various HPEH prototypes are fabricated, modeled, and compared in terms of their normalized power density levels, and milli-Watt level average power generation is demonstrated. The highest power density is reported for the single-crystal HPEH prototype.

Transduction as energy conversion: Harvesting of acoustic energy in hydraulic systems

Energy harvesting from acoustic energy sources is a form of transduction. While energy densities in typical airborne acoustic noise fields are extremely low, those in hydraulic systems may be orders of magnitude greater and represent an opportunity for direct energy conversion from piezoelectric materials for powering sensor and communication nodes. Hydraulic systems are challenging from a design perspective in that the device must be capable of withstanding static pressures up to and exceeding 35 MPa, while being simultaneously exposed to dynamic pressures on the order of 3.5 MPa. Hydraulic pressure energy harvester devices have been developed to exploit the high energy densities of dynamic pressures in hydraulic systems. There is an immediate application for this technology in that state-of-the-art hydraulic hose and piping systems employ integral sensor nodes for structural health monitoring for early detection of incipient failures. This paper presents the acoustic and electromechanical modeling of th...

Power conditioning for low-voltage piezoelectric stack energy harvesters

Low-power vibration and acoustic energy harvesting scenarios typically require a storage component to be charged to enable wireless sensor networks, which necessitates power conditioning of the AC output. Piezoelectric beam-type bending mode energy harvesters or other devices that operate using a piezoelectric element at resonance produce high voltage levels, for which AC-DC converters and step-down DC-DC converters have been previously investigated. However, for piezoelectric stack energy harvesters operating off-resonance and producing low voltage outputs, a step-up circuit is required for power conditioning, such as seen in electromagnetic vibration energy scavengers, RF communications, and MEMS harvesters. This paper theoretically and experimentally investigates power conditioning of a low-voltage piezoelectric stack energy harvester.

Design and Modeling of Hydraulic Pressure Energy Harvesters for Low Dynamic Pressure Environments

Hydraulic Pressure Energy Harvesters (HPEHs) use the direct piezoelectric effect to extract electrical power from the dynamic pressure ripple present in hydraulic systems. As with other energy harvesters, an HPEH is intended to be an enabling technology for powering sensor nodes. To date, HPEH devices have been developed for high-pressure, high-dynamic pressure ripple systems. High-pressure applications are common in industrial hydraulics, where static pressures may be up to 35 MPa. Other fluid systems, such as cross-country pipelines as well as water distribution networks operate at much lower pressures, e.g., from around 1 to 4 MPa, with proportionally lower dynamic pressures. Single-crystal piezoelectric materials are incorporated into the HPEH design, along with means to increase the load transfer into the piezoelectric material as well as increased output harvester circuits, so as to increase the power output of these devices. The load transfer from the pressurized fluid into the piezoelectric material is through an interface, where the interface area may be designed such that the area exposed to the fluid is greater than the cross-sectional area of the piezoelectric, yielding higher stress in the material than the pressure in the fluid. Furthermore, given the relatively large capacitance of the piezoelectric elements used in HPEH devices, inductive-tuned resonant harvester circuits implemented with passive elements are feasible. HPEH devices integrating these features are shown to produce viable power outputs from low dynamic pressure systems.Copyright

Coupling efficiency analysis of hydraulic pressure energy harvesters

The acoustic pressure within hydraulic systems, referred to as pressure ripple, is a high intensity energy source that can be utilized for powering sensor networks. A section of such a system can be modeled as a one dimensional waveguide, where the intensity can reach up to 1000 mW/cm2 from a 300 kPa pressure ripple (peak-to-peak acoustic pressure) within a hydraulic system. Hydraulic pressure energy harvesters (HPEH) are devices designed to convert the pressure ripple into electrical energy, thereby enabling wireless sensor nodes. HPEH couple the dynamic fluid pressure to a piezoelectric stack, which is connected to a harvester circuit to optimize power output. A key aspect of the HPEH design is the fluid-mechanical coupling of the pressure ripple to the stack for maximizing the energy extracted. The efficiency of HPEH device and harvester circuit potential power output can be determined using the volume velocity of the pressure ripple, the coupling efficiency of the HPEH, and the conversion efficiency o...

Energy Harvesting From Hydraulic Pressure Fluctuations

State-of-the-art hydraulic hose and piping systems employ integral sensor nodes for structural health monitoring in order to avoid catastrophic failures. These systems lend themselves to energy harvesting for powering sensor nodes. The foremost reason is that the power intensity of hydraulic systems is orders of magnitude higher than typical energy harvesting sources considered to date, such as wind turbulence, water flow, or vibrations of civil structures. Hydraulic systems inherently have a high energy intensity associated with the mean pressure and flow. Accompanying the mean pressure is what is termed dynamic pressure ripple caused by the action of pumps and actuators. Pressure ripple is conducive to energy harvesting as it is a deterministic source with an almost periodic time domain behavior. Pressure ripple generally increases in magnitude with the mean pressure of the system, which in turn increases the power that can be harvested. The harvested energy in hydraulic systems could enable self-powered wireless sensor nodes for applications such as energy-autonomous structural health monitoring and prognosis. An energy harvester prototype was designed for generating low-power electricity from dynamic pressure ripples. The prototype employed an axially-poled off-the-shelf piezoelectric stack. A housing isolated the stack from the hydraulic fluid while maintaining mechanical coupling to the system to allow for dynamic pressure induced deflection of the stack. The system exhibits an attractive off-resonance energy harvesting problem since the fundamental resonance of the piezoelectric stack is much higher than the frequency content of ripple. Although the energy harvester is not excited at resonance, the high energy intensity of the ripple results in significant electrical power output. The prototype provided a maximum output of 1.2 mW at 120Ω. With these results, it is clear that the energy harvester provides non-negligible power output suitable for powering sensors and other low power components. This work also presents electromechanical model simulations for predicting the piezoelectric power output in terms of the force transmitted from the pressure ripple as well as experimental characterization of the power output as a function of the force from the ripple.Copyright

Multifunctional self-powered hydraulic system sensor node

The current technology push to connect everyday objects via the “internet of things” has fueled significant advances in low-power processing and communication devices. One aspect of these connected products that still needs attention is the means by which they are powered. An attractive and feasible option is the use of energy harvesting from acoustic fields. Previous work developing a piezoelectric energy harvesting device has generated 2.6 mW of power from a hydraulic test rig. This paper presents an implementation of an energy harvesting device connected to a communications system that allows it to store energy and communicate sensor readings via Bluetooth Low Energy.