Stretchable self-powered sensors through printable piezoelectrets

Stretchable Self-Powered Sensors through Printable Piezoelectrets Harvesting the body’s energy is a promising path towards creating sensors that can be worn over long periods, but achieving both comfort and useful power levels in the same system has remained difficult. This project is intended to usher in a new generation of long-lifetime self-powered wearable sensors by introducing mechanically responsive materials with responsiveness several times that of current piezoelectrics, and doing so in soft and low-cost polymers that can be readily 3D printed. Piezoelectrets, charged porous polymers with very high piezoelectric coefficients, are a promising path towards improved comfort, superior performance and reduced cost compared with current alternatives such as ceramic piezoelectrics. Using 3D printing allows direct control of both the internal pores and the overall structure to enable improved energy harvesting performance while incorporating softness and stretchability for comfort on the body by printing the piezoelectrets into serpentines and auxetic structures to match the mechanical performance of skin. The same approach also enables sensing regions to be incorporated into the same 3D printed piezoelectret by control of localized pore structure. The success of this project is intended to enable improved comfort and harvested energy in self-powered sensors across a range of domains, with long-term sensing is crucial in applications from preventing sudden infant death syndrome (SIDS) in newborns to concussions in professional football players. This project will also work toward training both graduate and undergraduate students in wearable energy harvesting, as well as in creating training modules for teaching adults in the community for workforce development. Piezoelectrets are porous polymers with quasi-permanent internal charge created through breakdown of internal pores during charging. The porous structure creates a high mechanical compliance, allowing piezoelectric coefficients several times higher than piezoelectric ceramics such as lead zirconate titanate, but current piezoelectrets are largely based on polymer foams with limited control of individual pore geometry and position limiting direct control of the responsivity. The objectives of this project are to improve the fundamental understanding and design of piezoelectrets through electromechanical modelling and 3D printed fabrication of pore geometries to enable both harvesting and strain sensing behaviors to be incorporated through control of the localized piezoelectric response, and to incorporate these ferroelectrets into highly stretchable auxetic structures for improved comfort on the body. Additive manufacturing enables physical control of both the local and overall part geometries, and stretchable electrodes can be readily incorporated into the resulting piezoelectrets through multi-material 3D printing. Due to their superior performance over the widely used piezoelectric class of materials, improving piezoelectret capability is of great scientific interest, and will enable transducers with better properties and performance along with superior self-powered wearable energy harvesters. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.