Design and development of mechanical amplifier structure for piezoelectric harvester in high force environment / Long Su Xian

Long , Su Xian (2022) Design and development of mechanical amplifier structure for piezoelectric harvester in high force environment / Long Su Xian. PhD thesis, Universiti Malaya.

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Abstract

In recent years, harvesting electrical energy from mechanical vibration by using piezoelectric material has become the main focus of many researchers in developing a sustainable energy harvester. This is useful for Wireless Sensor Network (WSN), where a replacement or replenishment of energy source, such as a battery is unpractical. From previous studies, the amount of energy generated by piezoelectric energy harvester (PEH) is very limited even in a high force environment. To solve this issue, a mechanical amplifier structure such as the Rectangular Cymbal structure is implemented to amplify the tensile loading force towards the piezoelectric. From the material strength perspective, this performance can be further enhanced by using a compressive-typed mechanical amplifier structure, as the compressive yield strength of piezoelectric material is 10 times higher than its tensile yield strength. In this study, a novel compressive Hull PEH is designed and developed. A coupled piezoelectric-circuit finite element model (CPC-FEM) is developed to evaluate the energy harvesting performance based on the power output and stress analysis. Parametric optimization has been carried out to further enhance the amplification effect and determine the relationship of each parameter on the power output. An improved FEA power output of 11.34 mW is obtained for the optimized Hull PEH under 1 kN of sinusoidal force at 2 Hz. It is 178% larger than the unoptimized Hull PEH and 308% larger than the benchmarking tensile-typed Rectangular Cymbal PEH. The developed Hull PEH has a volume power density of 1.817 kW/m3. An analytical force amplification factor of 9.72 is proven based on the kinematic theorem and the deformation of the frame. In the experiment, it exhibits at least 5 times larger voltage output than the benchmark case and at least 14 times greater than the standalone piezoelectric plate under impact force from a range of 10 N to 1 kN, with less than 5.2% of deviation to the FEA result. A maximum peak power output of 7.16 W is produced across a 50 kΩ of optimum load resistance. It is 37.68 times higher than that of the benchmark PEH under 1 kN of impact force. Meanwhile, 84.38% of energy conversion efficiency is achieved by the Hull PEH based on the average input and output energies. It shows a power output of 54 μW at 180 kΩ and 5.28 times higher voltage output than the Rectangular Cymbal structure under 10 N of sinusoidal force at 50 Hz. It has a slight deviation of 3.8% from the FEA result. Therefore, the reliability of the developed CPC-FEM has been proven. The Hull PEH is concluded to have better harvesting performance in both simulation and experiment despite the loading environment either in high or low force. Hence, a higher power output PEH with enhanced load capacity and amplification effect has been realized. It has a lower stress concentration and is more cost-effective than the benchmark case. The developed PEH holds great potential to act as a sustainable energy source for some microcontroller applications with an LTC-3588 energy harvesting circuit.

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