Sandwich piezoelectric energy harvester: Analytical modeling and experimental validation

Piezoelectric energy harvesting from ambient vibration sources has great potential for powering microelectronic devices and wireless sensors. Almost all the conventional piezoelectric energy harvesters (CPEHs) in the literature have been designed with a single metallic layer as substrate along with the piezoelectric material bonded over it. In this work, a novel sandwich structure is used as substrate for designing harvester. The substrate structure comprises of a soft-core material sandwiched between metallic layers. The proposed sandwich piezoelectric energy harvester (SPEH) has lower resonant frequency and generates higher voltage output than the CPEH with the same geometrical dimension. Furthermore, the SPEH offers high design flexibility in terms of tuning the resonant frequency through selection of materials and geometric parameters for the core and metal layers. The mathematical formulation of a generalized electromechanical model of the SPEH is developed using the Lagrange approach. The natural frequencies, displacement and voltage frequency response functions of the harvester are obtained analytically. A single-degree-of-freedom model for the SPEH is also derived. Subsequently, the analytical modeling is validated by finite element simulations and experimental results. When excited at 0.1 g, the SPEH generates 18.8% more voltage output at resonance as compared with a CPEH with the same geometrical dimension and tip mass accompanied by 24% reduction in resonant frequency. At 30 Hz resonance frequency, CPEH generates open-circuit voltage 17.6 V using 15 g of tip mass whereas SPEH uses only 8.2 g of tip mass to generate 16.6 V. SPEH generates 130.8 μW, 426.6 μW and 1158.0 μW at base accelerations 0.05 g, 0.1 g and 0.2 g with optimal resistance, respectively. Finally, the influence of geometric and material properties of core and metallic layers on the performance of SPEH are analyzed comprehensively. The proposed novel SPEH together with its analytical modeling is intended to serve as a basis for future sandwich harvester designs.