Micropower Generation using Buckling Piezoelectric Elements
Counsell, Nathan Alan
In recent years, piezoelectric materials and structures have gained significant attention for energy harvesting purposes. This attention can be attributed to the enhancement of low-power electronics and the high energy density of piezoelectric materials compared to other forms of energy conversion and transduction. This work explores the recent contributions to the field of piezoelectric energy harvesting, contributing two novel methods that can be implemented to improve the power output and efficiency of a single piezoelectric element. The methods that have been investigated in this thesis are based on the buckling of piezoelectric material. The initial method examines a diaphragm preformed piezoelectric element, where numerical and simulation model has been carried out. This work has then been validated through experimentation, where empirical data has been collected verifying the COMSOL model and future optimising the manufacturing process of the diaphragm. This work contributes to a peer-reviewed paper “Powering lights with Piezoelectric energy-harvesting floors” published in the journal Energy Technology. This work shows that employed a diaphragm structure can increase both efficiency and power output with an increase of efficiency from 0.522% to 3.765%. The observed power output increase from 191.686µJ to 644.16µJ. The second method investigates a preloaded piezoelectric curved structure with elastic walls. The use of nonlinear materials is critical to the development of a buckling structure, allowing energy to be stored upon actuation while reducing input stresses. The result of this is a reduced buckling force, with an increased energy output and efficiency for the whole system. The findings of this work demonstrate that efficiency can be increase from 0.522% to 16.813% while achieving a greater power output from 191.686µJ to 208.577µJ. Furthermore, this work identifies that a monostable structure as opposed to a bi or multi-stable structure can significantly produce higher power outputs than conventional methods, whilst achieving long life within a small compact area. A COMSOL simulation of the mechanical behaviour coupled with the constitutive equations has been developed to enable future optimises to structure and design and validated using the empirical data. In additional, two equations have been developed using empirical data to aid in selection of buckling force and power output for an energy harvester. This is to enable developers of low-power electronics to select the optimised system for their application reducing the need for primary batteries within electrical devices.
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