Feb 10 2018

Edward Tefft defends his MS thesis

Edward Tefft successfully defended his Masters of Science degree in Mechanical Engineering entitled “A Coupled Electromechanical Model of Piezoelectret Foam in a Multi-layer Stack Configuration” on February 9, 2018.  Congratulations Edward!


Piezoelectric polymers, such as the Emfit polypropylene piezoelectret foam investigated in this study, have distinct advantages over traditional piezoceramics. Although piezopolymers have a smaller piezoelectric coupling coefficient when compared to piezoceramics, they are well suited for in vivo applications, having a lead-free composition, for applications with curved or flexible surfaces, being flexible, or where weight or large shocks are factors, being light weight and resilient. Presented here is a 20-layer flexible electret stack harvester design with no adhesive between layers, but that incorporates the Emfit foam electret material, composite graphene sheets as the electrode material, and Kapton tape as the encapsulation material. Also presented is an electromechanical, fully coupled, single degree of freedom model of the multilayer piezoelectret foam stack’s mechanical and electrical vibration responses to harmonic base excitation, including a cubic stiffness nonlinear factor. The model parameters are tuned to fit the experimental data through an iterative error minimization process, with the final model accurately representing the stack’s frequency response for a range of electrical load resistances on the stack. Finally, the energy harvesting capabilities of the electret stack are demonstrated by charging a 100 µF capacitor to 1.041 V in 15 minutes and a 1000 µF capacitor to 1.025 V in an hour.