Characterisation of a flexible hybrid triboelectric-piezoelectric energy harvester (FHTPEH) performance based on the material and surface modification

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Mohammad Khairul Azwan Azhar
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Improvements of TEH is needed since it produces low output voltage, low power output and low power density of fewer than 1 W.m-2, compared to more conventional renewable energy sources such as solar, geothermal and wave. PEH’s flexibility and limited working frequency range should also be improved. Increasing the power output will extend its application to a much broader spectrum, applicable to many more industries. In order to overcome these challenges, there is a need to investigate the effect of triboelectric material, the effect triboelectric surface modification and the effect of natural rubber latex coating on Lead Zirconate Titanate (PZT) beam to the device’s performance. The objective of this work is to identify and test the effect of materials and surface modifications on the triboelectricity of the energy harvester; to investigate the effect of adding natural rubber layer on piezoelectricity of the energy harvester; and to evaluate the performance of the Flexible Hybrid Triboelectric Energy Harvester (FHTPEH) using the optimum parameters. The proposed design structure would allow the device to harvest using the triboelectricity as well as piezoelectricity transduction mechanical-electrical mechanism. FHTPEH comprises of TEH and PEH utilising the design of triple cantilever beam. The triple cantilever consists of top and bottom triboelectric energy harvester (TEH) and the middle section made up of piezoelectric energy harvester (PEH). The top and the bottom part is the Polytetrafluoroethylene (PTFE). The experiment for TEH consists of pairing the highest negative charged material, which is the PTFE with few other positively charged materials. The best pair was used for further experimenting by modifying the triboelectric surface to increase the power output. These two experiments yield the first prototype, namely HTPEH 1. At the frequency of 13 Hz and acceleration at 0.25, the ideal opened-circuit voltage, VOC produced for top TEH was 2.23 V and for the bottom, TEH was 2.24 V, while for the PEH was 9.27 V. HTPEH 1 produced an optimum power of 7.28 mW at a resistance of 9 kΩ, with a power density of 2.77 This experiment was continued by varying the thickness layer of two different types of natural rubber on the piezoelectric beam. The highest results will determine which type and what frequency do the optimum results come from. The second prototype, FHTPEH 2 was constructed without the surface modification on triboelectric and gives the total VOC of 17.25 V and peak power of 6.13 mW at the load of 10 kΩ with the power density of 2.32 Lastly, the evaluation of FHTPEH using optimum parameters yield the third prototype, FHTPEH 3 that comes with surface modification on the PTFE’s surface, and this gives out total VDC of 20.58 V at the frequency of 31 Hz. The ideal opened-circuit voltage, VOC produced for top TEH was 2.69 V, for the bottom TEH was 2.70 V, and the PEH was 21.38 V. Power output of 7.40 mW was generated at 8 kΩ with the power density of 2.79 Since only 0.10 mW is needed to operate a low power wireless sensor node, it is enough to power up approximately 74 low powered wireless sensor nodes with working frequency in the range of below 60 Hz. This work contributes to the application of condition monitoring in power plant and industries. HTPEH 1, FHTPEH 2 and FHTPEH 3 were further analysed in terms of spatial power density and spatial cost. Spatial power density achieved for HTPEH 1, FHTPEH 2 and FHTPEH 3 were 0.92, 0.77 0.93 respectively. Meanwhile, the spatial cost of HTPEH 1, FHTPEH 2 and FHTPEH 3 were 154.15 MYR.cm3.mW-1, 183.08 MYR.cm3.mW-1, 151.68 MYR.cm3.mW-1respectively.