Stiffness compensation for piezoelectric energy harvesting

Improving the efficiency at low-frequency vibrations

Master thesis (2021)

Authors

E. van de Wetering Mechanical Engineering

Contributors

Thijs Blad Mechatronic Systems Design - Mechanical, Maritime and Materials Engineering (supervisor 1)
R.A.J. van Ostayen Mechatronic Systems Design - Mechanical, Maritime and Materials Engineering (supervisor 2)
A. Hunt Micro and Nano Engineering - Mechanical, Maritime and Materials Engineering (supervisor 2)
H. Polinder Transport Engineering and Logistics - Mechanical, Maritime and Materials Engineering (supervisor 2)
Faculty
Mechanical Engineering
Copyright: © 2021 Erik van de Wetering
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Published Date

26-01-2021

Language

English

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Faculty

Mechanical Engineering

Abstract

In the field of vibration energy harvesting, vibration energy is tranduced to electrical energy to power small, low powered devices. Many energy harvesters are produced in the form of a resonator, where resonant amplification enables efficient operation of the energy harvester. At low frequencies below 10 hz, input motions quickly increase for a constant input acceleration and resonant amplification results in energy harvesters that are too large to implement them. A solution is sought in creating a nonresonant energy harvester. The stiffness of a strongly coupled piezoelectric beam is compensated by adding negative stiffness to bring it to a near statically balanced state. This negative stiffness is embodied by attracting magnets. To model the dynamics and voltage output of the harvester, a modal analysis based distributed parameter model is used and further developed by including negative stiffness and force-displacement measurements of the stiffness compensated piezo. To investigate the mechanical behaviour of a compensated piezo, force-displacement measurements are carried out at different deformation speeds and load resistances. From these measurements, it has been observed that the stiffness of the compensated piezo strongly depends on the connected load resistance and the deformation speed. Furthermore, memory effects in piezoelectric hysteresis found in actuators such as curve alignment and wipeout have also been confirmed in force-displacement measurements. The performance of the harvester has been evaluated by exciting it on a linear air bearing stage. It has been found that for excitations between 2 and 6 hz, the error in RMS power between simulation and measurement remains below 10%. For its range of excitation, this harvester has been observed to be the most efficient with respect to prior art from literature. Therefore, stiffness compensation of a piezoelectric energy harvester can be considered as a successful method to improve the efficiency at low frequency excitation.