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On the consideration of operational deformation shapes in bi-stable energy harvesters

There has been considerable research on the design of vibration based energy harvesters in the last decade exploring the potential of autonomous power supply for miniaturized electronic systems. Nonlinear energy harvesting mechanisms are in general perceived as more robust than linear harvester designs owing to the broadband resonance dynamics which allow for efficient energy transduction over a diverse range of input vibrations. In particular, geometrically bi-stable composites with embedded piezoelectric elements have been investigated as a scalable and bio-compatible design with a strong potential for harvesting energy from the high-amplitude interwell oscillations encompassing both the statically stable states of the harvester. Significant research effort has been devoted to devise efficient strategies for shifting between the co-existing stable solution configurations of bi-stable harvesters, thus allowing to consistently maintain the high-amplitude inter-well oscillations favorable for energy harvesting. However, analysis of the compatibility of conventional linear mode shape based harvester designs to harness the complete potential for energy harvesting from nonlinear solution configurations of bistable harvesters has received lesser attention. This study presents an experimental analysis of the operational deformation shapes associated with the intra-well and inter-well response regimes of bi-stable energy harvesters. A qualitative comparison of the operational deformation shapes characterizing the nonlinear response of the harvester with the linear design mode shapes is presented. The results indicate that operational deformation shapes differing significantly from the linear mode shapes are active in the nonlinear response regime of the harvester. The aforementioned deformation shapes, while influencing the mechanical response of the harvester, may not result in any significant contribution to the harvested power as they are essentially excluded in the linear mode shape based harvester design envelop. The presented experimental results essentially highlight the need for considering the operational deformation shapes associated with the nonlinear response regime while designing for the dimensions and the position of the piezoelectric elements on bi-stable composites to ensure that the complete potential for energy conversion across all of the dynamical regimes is harnessed adequately.