Effect of porous auxetic structures on low-frequency piezoelectric energy harvesting systems: a finite element study

This work investigates the effect of porous auxetic structure on low-frequency piezoelectric energy harvesting (bimorph cantilever) systems. Two auxetic-based systems are proposed to apply transverse loads: full length auxetic (AS1) and patch auxetic (AS2) piezoelectric energy harvesting system. The objective is to achieve the optimum design solutions for auxetic systems that result in a higher output power than a conventional energy harvesting system (CD) when operated at low resonance frequencies (20-100 Hz). In the present work, Pb(ZrxTi1-x)O-3 (PZT-5H), 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3(BZT-BCT) and polyvinylidene fluoride (PVDF) piezoelectric materials are considered, while an auxetic sheet made up of brass is used as a substrate for energy harvesting. The results show that the PVDF is a suitable piezoelectric material for AS1 system to improve the power. The maximum power of 211 mu W is achieved at optimum auxetic sheet thickness. It is also observed that AS1 can improve power as high as two times compared to CD operating at particular sheet thicknesses. However, AS2 should be used for ceramic-based materials and enhance power by 30.8% and 24.3% at optimum sheet thicknesses when PZT-5H and BZT-BCT are used as piezoelectric material. It is recommended that instead of focusing solely on maximizing power, the maximum stress generated in the piezoelectric layers should be considered as well to look at its practical feasibility.