Towards Dependable Self-Powered Things for the IoT

The IoT requires rethinking of traditional ways of providing power. The environment is a source of mechanical energy that could be converted into electrical energy via the direct piezoelectric effect. In order to have a reliable and sustainable energy supply for low power sensing systems in buildings, vibrational energy harvesting is being pursued. Lead based materials in a piezoelectric compliant mechanism energy harvester can provide up to 3.9 mWcm^-2g² (H.G. Yeo, 2016). However, lead has become an environmental concern. Thus, there is a need to develop lead-free alternatives for active layers in piezoelectric energy harvesters.

We choose to explore lead-free piezoelectric materials with high figure of merit (FoM), in particular BiFeO₃ and (K,Na)NbO₃. Films were grown by chemical solution deposition. The poster summarizes recent progress in film development optimization with corresponding piezoelectric properties. The e_31,eff coefficient relative to the direct piezoelectric effect for BiFeO₃ is -1.26 C/m², the corresponding FoM is equal to 0.015 C²/m⁴. The 0.5% Manganese doped KNN shows ferroelectric properties with the d₃₃ coefficient relative to the inverse piezoelectric effect equal to 20 pm/V. We will integrate these materials into a Compliant Mechanism Piezoelectric energy-harvesting device (H.G. Yeo, 2016).

This study responds to a need for powering interconnected devices for the IoT in a sustainable manner without using piezoelectric materials containing lead. One outcome is that the viability of vibrational energy harvesters using lead free piezoelectric thin films such as BiFeO₃ and (K,Na)NbO₃ will be assessed. The chemical solution deposition method chosen is cost effective in comparison to sputtering or pulsed laser deposition and is readily scaled to large areas.

The following textbook was published: Trolier-McKinstry and Newnham: Materials Engineering: Bonding, Structure, and Structure-Property Relationships, Cambridge University Press, 2018. So far, it has been adopted at three universities, with several more promised to utilize it in 2019.

References:

H.G. Yeo, 2016: H.G. Yeo et al, Efficient Piezoelectric Energy Harvesters Utilizing (001) Textured Bimorph PZT Films on Flexible Metal Foils, Adv Fun Mat, 2016