Ferro-electrets material in human body energy harvesting

Abstract

Using piezoelectric materials to harvest energy from human movement provides a potential power source to wearable devices and electronic textiles in everyday life. Two common comerical piezoelectric material: lead zirconate titante (PZT) and polyvinylidene fluoride (PVDF) are unsuitable for human body energy harvesting applications due to the high hardness and fragility of PZT and the low piezoelectric coefficients of PVDF. Ferroelectret is a thin polymer foam that can store electric charges in its internal voids, have strong piezoelectric properties and low elastic modulus which would make them very desirable for human body energy harvesting. The piezoelectricity of ferroelectrets originates from the combination of the internally stored charges and the cellular structures. However, the resulting pizoelectric properties of commercialized ferroelectrets are limited by the random individual void geometry and irregular overall cellular structure due to its existing fabrication processes.
This work develop a numerical model using finite element analysis (FEA) approach to design and optimize the structure of ferroelectret during fabrication. Based on the models, we used polydimethysiloxane (PDMS) materials to fabricate ferroelectrets with different internal structures. The fabrication is done by casting method with 3D-printed moulds and silicon moulds produced using MEMS processes. The piezoelectric properties of fabricated PDMS ferroelectret are investigated to further validate the accuracy of our proposed numerical model in the work. The designed PDMS ferroelectret presented a maximum piezoelectric coefficient d33 of 520 pC/N. It can provide the maximum output voltage of 13 V and average output of 2.73 μW when connected to a 65 MΩ resistive load under acompressive force of 800 N at human normal walking model. The optimization PDMS ferroelectret structure for human body energy harvesting is also evaluated. In addition, a method for further improving the PDMS ferroelectret piezoelectric stability is proposed.

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ORCID for Stephen Beeby: orcid.org/0000-0002-0800-1759

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